Walsh, RN.,and Rk Cummim The open-field test A critical review. P s v c h o l o e i c a l Bulletin
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The Open-Field Test: A Critical Review
Robert A. Cummins
Roger N. Walsh
Department of Psych+
and ~ e b a o k r a ~ Department of Physiology, Llnioersify .c$
S&nces, Stanford Unioersity
Queensland, Brisbane. Australia
Over the w t 4 0 years Lhc open field bar ~ o l v e da a commonly used tool
for the rnmumcnt of animal behavior. Thh m i e w taka a dtical look at
with regard to the development of a
the we of I& instrument, u&y
standard form for iu w. The variou procedura and .their sbortcomingr are
'dkmued, - w i t h partimlar rcfupacc to the seemingly incooseguential detdk
which have b.& showb to ioduhte open-field prformancc per w. Depndent
paramrerr are considered both vith regard to their reliability and their validity for the measurement of such undul,ing mnstrucb as emotionality.
diversified enormously, yet in the literature,
sweeping generalimtions and conflicting interpretations continue to he made on the basis
of univariate studies. This paper aims at detailing the many variables involved in testing
and their influences on dependent parameters, as well as methods of analysis and
interpretation of results. We thereby hope to
gain an overview o i this area of study! to
point out shortcomings of some present work,
and LO derive implications for future research.
The originator of the open field was Calvin
Hall (Hall 1 9 3 4 ; Hall & Ballechey 1932),
who used d e f a t i o n in the open field as an
index of timidity. However, time bas seen a
proliieration of other dependent variables.
Some 30 have been used at one stage or another:. and the number of underlying constructs they supposedly measure bas multiplied accordingly. I n niany cases, however.
proof of construct validity has been a d l y
lacking.
IV'hat then is the open field and what, in
general terms: does it really measure? I n
essence, the test consists of the measurement
p i behaviors elicited by placing the subject
In a novel open space from which escape is
prevented by a surrounding wall.
We would like to exDrps our ~ratitudcto Otto
T h e elicitation of these behaviors is deBudlz-Olsen, Bun ~icdelman,TO& Horvalh, and pendent upon the interaction of the animal
Alice LH for their encouragement, advice, and with a variety of test factors such
criticism. Our uperimeotal work and prepration of -stimulation z a result of removal from(a)a
be manulc,jpt were supporkd
from
Australian Rwarch Grants Committee and t h e familnr home environment; ( b ) stimulation
Foundatton Fund for Rcvarch in Psychiatry.
involved in transferring the animal to the
Rcqursu for reprints should be x n t to Robert A.
Open
field; !c) m ~ o s u r eto the test environcumrnins,
D~~~~~~~~~
of Psycholow,Univerrlt,. of
\Vutero .4ustralia, Nedlands, Perth 6039, ~ust~alia.ment, consisting of both the open field itself
Since its introduction some 4 0 years ago.
the open-field test bas attained the status of
one of the most widely used instruments in
animal psychology. Its popularity probably
stems in large part' from the simplicity of the
apparatus, tbe-easy &d rapid meaurement
o f dearly defined behaviors, and a generally
accepted interpretation of these behaviors. I n .
addition, certain ol tbe measured behaviors
are sensitive to a a i d e range of genetic! experiential, physiological, and pharmacological
manipulations and are sufficiently reliable
under standardized conditions t'o give repeatable measures on an enormous range of independent variables. Simplicity, ease of quan:
tification, and a i d e applicability are therefore
probably the prime determinants of its
popularily.
However, in spite of its'sbtus as one of the
most widely used tests of animal behavior,
the open-field test bas survived for 40 years
uilh only one major review (Archer, 1973),
and this was limited to a consideration of its
usefulness for slimatinn emotionalitr in rodents. Apparatus, techniques, subjects, parameters, analyses, and interpretations .have
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4S3
OPEN-FIELD TEST
and its surroundings; and ( d ) aU prior eiperience of the t e t situation. In e&
e,ct'
tbis
last factor means that one is measuring,.
among other things, habituationand learning
in response to the test environment. Where
several test s q i o n i are employed, further
factors to be' considered indude previous
stimulalion involved in removing the animal
from. the. testing situation, transfer and reexposure !o the home environment a t the
completion of prior sesions, and modification
of h o m e a g e pehavior .and interaction- with
other home environment animals.
The magnitude of any particular behavior
elicited will therefore be a function of the
multiway interaction oi these factors. .4s yet
their relative importance is almost completely
unknown,.but thereis evidence to suggest that
each factor exerts a differential elfect on
animals oi varying genetic and experiential
backgrounds, and this is examined later.
Effectively 3nv behavioral experimentmeasures responses to the above fattors. However, in many-studies, such as maze learning;.
one hope3 that the subject will habituateto,
and hence be minimally influenced by, aspects
. of thetes: siruation other than the specific
stimulus c~lmponentbeing u s e d % the independent variable. In -the open-field test, on
the other hand, the whole test situation
(rather than any one specific stimulus component) is the independent variable, and.by
its very nature this independent variable must
be multifactorial. These factors are now considered under the headings of Techniques and
Apparatcs Characteristics, Testing Environment, and Procedural Details:
~ o o k i & a t the range of techniques employed. one finds'tbat for the apparatus, its
size, shape, color,. subdivision, wall height,
Boor texture, odor, nature and locauon.of the
starting arm, and presence or absence and
nature o i additional inherent stimuli have all
been varied; while for the surroundings the
nature, intensity and position of light, sound
andodor sources, and the visibility and position of the observer have- suffered similarly.
In fact it is hard to think of any facet which
has not been modified. This .diMculty of
standardization b compounded by the ex1rerre:rarity of reports which cite details of
more than a smdl proportion .of relevant
procedural variables.
Ph?sical .Characteristics o j the Apparatus
The most common shape of the open field
has been circular, but square and rectangular
designs are also prevalent. The wide range of
shapes leads eventually to the quejtion. \i:hen
is an open field not an open field? The extreme of the rectangular design is usually
termed a straightaway or a rur&a.v, yet the
behaviors measured may be akin to those
employed in the open. fidd (e.g., Poley &
Royce, 1970; Zimhardo & Ilontgomer).,
1 9 5 7 ) . Perhaps in view of the paucity of eiidence on the comparability of behavior observed in these devices and in the open field,
they are best regarded separately. As ,yet
there would seem to be no data available on
the effect o i open-field shape on behavior, hut
in view oi the evidence on strain difierences
in thigmota<s (or "wall hugging," Valle,
19i0) and the tendency of some animals to
remain in corners, standardization would
seem a sensible precaution.
Difierent s ~ e c i e jhave naturdlv been allocated appropriately sized open fields, such
The difficulty of finding comparable techa whole room for human infants (fieinniques in the use o f the open field has been gold, 1969) and a .5-m square field f o r mice
mentioned previously. Almost every physical (hlanosevitz. 1970). More importantly, howcharacteristic of the apparatus; i t i surround- ever, open-field size has -commonly been
in&, a n d every
s!ep have been varied for intraspedes studies, and the efiects
widely varied, so that although standardin- of such dimensional changes have been shown
Lion may have been established aithin in- to exert a significant &ect on some aspects
dividual laboratories, there is a disturbing oi behavior. .4s a ~ e n e r a lrule. ambulation
lack oi conformity in procedure and resulu urould seem to be more susceptible to change
in apparatus a n d environment than would
within theliterature as a whole.
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ROGER K . WALSH ASD ROBERT A. COMbfINS
defecation: Thus, while defecation is largely
unaflected by arena size in rats (Broadhurst,
1957, 1958a, 1958b), gerbils (Oldham &
Morlock; 1970), but not male WH mice
(Nagy & For&, 1970), ambulation increases
with increasing field size in rats (Broadhurst.
1957; Montgomery, 1951), mice (Blizard;
1971 ; Krsiak & J d u , 1971 ; Nagy & Forest,
1970); and gerbils (Oldham .& Morlock;
1970). Large field size has been reported to
produce a , disproportionately large increae
in ambulation under conditions of low illumination (Blizard, 1971):
An .example of the daculties .of comparison where different apparatuses are used is
afIorded by ~ l a r i ,Gorman, and Vernadakk
(1970), wbo tested ambulation of the offspribg of mothers injected with impbetamine
or chlorpromazine. Treatment effects were
found on Days 13-21 but not on Days 46,
and 60, and the results were interpreted ar
being due to differential maturation rat& (an
Age x Treatment' interaction hypothesis).
However, since two different field k w e r e
used for the infant and adolescent animals,
a n interaction between treatment and field
size was also possible.
Color bas ranged through white (Oldham
&'3Torlock, 1970) to black (Delbarre, Durn=,
& duionniere, 1970), and the material composing the field, particularly the Boor, has
included wood, metal, cqncrete, rubber, and
even glass (Satinder, 1968). There is almost
no evidence as yet on the eEect of these variables on behavior, but in view of the evidence
for the effects of similarity of test envimnment lo rearing environment on exploratory
behavior (Nielson, 1970; Wells, Lowe, Sheldon, & .Williams, 1969), some of these variables may be of particular relevance when
testing animals with differential rearing
histories.
Klost commonly, the open field has been
bare but occasionally experimenters have
added objects, usually with the aim of obtaining a measure of interaction with these additional stimuli. The number of these objects
has ranped from 2 (Ehrlich & Burns, 1958)
to 15 (Furchtgott, Wechkin, & Dees. 1961)
a n d t h e y have usually been small solid ob-''
jec&, such as nuts and balk, door stops, and
mirrors. However, the more exotic have included caged rats, f l d i n g ' l i g h t s and loudspeakers (Ehrlich & Bums, 1958; Fox &
Spencer, 1969), food pellets (Jarrard 9.
Brunnel, 1968), designs painted on the floor
and walls (Wimer & Sterns, 1964); and
Rheingold's (1969) study of human infants
induded toys and the .subject's mother or
another person(basicaUy a social facilitation
study). The relevant dependant paramiters
are most commonly the number of approaches
and time spent invejtigating the objects, and
sometimes preference scores for particular
objects.
THETESTING
EX~ONMENT
Characteristics not o n l y of the open field
itself but also of its surroundings infringe
upon the subjects and modify behavior.
The level of illumination has been the
variable most closely examined; but in spite
of repeatedly demonstrated eElects, . f&er
than one third of the articles mention the
test lighting used. With the exception of
Candland and Nag?r (1969), who reported
Lhe reverse, i t bas consistently been found
tbat high levels of illumination are associated
a i t h diminished locomotor. behavior. Valle
(1970) found that ambulation, rearing, and
thigmotaxis were all less under higher
illumination.
A number of interactions of illumination
level a i t h other independent variables bare
been reported. Thus, L i v w y and Egger
(1970) found tbat ambulation was less under
an illuminance of 9.3 lx than 0.005 lx in rats
a t 47 or 115 days of age but not at 18 or
24 days. Testing C57 BL/6J mice, Nagy and
Glaser (1970) found no main effect for illumination (9.3 k versus 0.09 k ) but found
si~nificant interactions between level of
illumination, age of subjects, and day of testing. Under high illumination, there were no
reliable activity differences due lo age, while
under low levels, IO&day-old subjects were
more active than 5&day+lds. T h e subjects
were less active under high than under low
illumination on Days 1 and 2 of testing but
not thereafter, suggesting that for the C57
BL/6J strain, illumination effects are largely
transitory. Interactions with strain have been
reported by McClearn (1960) and by Dixon
483
OPES-FIELD TEST
and Defries (1968b), who also found albinos
to he more photosensitive than pigmented
rats. Interaction witb. prior visual rearing
environment (dark, alternating light-dark, or
light in black, white, or patterned cages) was
noted by Sachett (1967).
Another commonly studied dependent pa;
rameter of. illumination has been defecation,
and Rith. some exceptions (Blizard, 1971);
no significant main.e8ect has been reported
(Kagy & Forest, 1970; Nagy & Glaser, 1970;
Nag) 8: Holm, 1970). The result seems unexpected in terms of much current thinking
which considers high illumination as "stressful" and defecation as the prime index of
emotionality.
A dijadvantage of the available studies of
illumination is that they include only two, or
a t the-most three levels, so that the precise
relationship with the magnitude01 the observed behavior is quite unlmoivn.
Less study has been made of ambient noise
and few papers refer to it. Presumably. Lherefore, in most cases it comprises merely the'
background noise oi the test room, but white
noise, most commonly of about SO dB (e.g.,
Eysenck & Broadhurst, 1964; Ivinskis, 196S),
has sometimes been superimposed. Its addition h s usually reduced locomotion (e.g.,
Bindra & Spinner, :l9jS), but L i v e ) , i n d
Egger (1970)' reported that white noise of
90 dB increased both ambulation and defecation. Certainly any abrupt loud noise can
markedly inhibit locomotion a n d even induce
prolonged immobility in a variety of species
(Hofer, 1970; Cummins, Walsh: & BudtzOlsen, Kote 1).
Environmental odors have largely been ignored. although several experimenters have
washed their apparatus. with a vaiiety of
agents in order to obviate possible biasing
efiects of odor trials left by previous subjects.
\\%ittier and McReynolds (1965) found this
to be asigni&ant effect for the test behavior
of mice. However, Satinder (1969) found
that the time spent by a rat on the side of
the open field which had been occupied by
its predecessor was significant only for males
preceded hy females. Interestingly; urination
or defecation by the,predeceswr was without
effect.
McCall (1969) has demonstrated tbe importance of odor for what he termed the
"caretaker efiect." I t was found that rats
tended to spend more time on the side of the
field nearest to the caretaker, who had reared
them, than on the side opposite where there
waj another experimenter, who had no previous experience with them. This effect was.
shown to b e dependent on olfactory rather
than %%ual cues, The visibility and behavior
01 the experimenter during testing have rarely
been mentioned. Presumably, therefore, in
most test situations he is visible to the subject except where obsenration is frombehind
a screen (e.g., Nielson, 1970) or a one-way
mirror (e.g., Fox 8: Spencer, 1969). This
hiding would seem a wise precaution, since
although no precise studies of the effects n i
experimenter visibility are available, it i i
quite obvious that any visible abrupt movement may cause inhibition of ongoin.=;..ac:
~ i v i t yand in some u s e s prolonged immobtl~ty
(Cummins et a]., Note I ) .
PkioCEDurw~ DETAILS
As is obvious from the foregoing discussion,
careful measurement can detect changesin
behabior due to very small changes in the
apparatus. I t is therefore regrettable that
there has beenalmost no study of the efiects
of variation in testing procedure. Testing
normally consists of removing the animal from
its home environment, carrying it to the test
area, and placing it in the open field. The
carrying can be done either by hand or via a
start box. Testing itself may vary on a num.ber of temporal factors, such as the duration
of exposure. to the open field and t h e intertrial interval. I t would be surprising if
changes in these procedures did not measurably aRect open-field behavior.
Details o i the animal's removal from the
home cage and transfer to the open field are
seldom reported, so that presumably they are
usually transported by hand. However, some
workers aiming to reduce handling stress have
employed transport compartments, such as a
box (Nielson: 1971: Tighe, 1965), tube
( D i ~ o n& Defries, 1968a), or transparent cup
(Hofer. 1970): In some a e s , the subjects
have been habituated to a transport compart'
456
ROGER
x. \VALSH
AKD ROBERT A: C U ~ ~ ~ I I X S
I.'B&>~o;
k Whole m mnjor body mmcmorl
1. Type of movement
a. Distance covered per unit time
b. Time spent in ambulntioo
c. Wesring frequency
d: Escape attempts
e. Laleocy (uwdlytime taken lo l a v e start area)
i. Time spentaithout movement
2. Loc1tions
a. Field area viGtnl (inner or peripheral a r m .
mmm, elr.)
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4. .AMliation (distance from p n n e r subject)
c. Stimulusintetxtion (e.g., dirtan& irom stimulus
abject)
B. Par1 body nromnmr
a. \lanipulatius of objects
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b. S S m g
c. Smtchinc
d: Digging
e. Teeth chattering
I. Grooming
g. vocalimtion
h. Visual erplomtion
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Autonomic nervnus %stem
'a. Defecation
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b. Digestive transit time
c. Urination.
d. Hurt tale a d rhythm
-e. X s p i r s t ~ r ?rstc
1U. Adrend activity
a, Adrenal ascokbic s d d
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b. Serum
corticosteroidr
W. E 3 m ~ 0 p b y s i o l o ~
3.
Hippocampal theta utivity
b. Elccvomyogmm activie
ment and carrying procedure prior to testing
(e.g., Nielson, 1970). Such familiarization
may increase the levels of ambulation a t the
start o f an open.-field trial (Abel, 1971).
Once ' traEported, the animals may be
placed either in the center of the open field
(e.g., Clark et al., 1970) or against the retaining wall (6ing, 1970). I n this context i t
is interesting 1o'note.Satinder's (1969) find'ing that rats tehd to remain on that side of
the field on which they are originalls placed.
Jndividual trial durations are usually short
(Krsiak & Janku,-19il), but trials of 1 hour
have been employed by Block and Essman
(1965). Many workers measure only total
behavior lor e3cb trial (intratrial time unit
equals trial length), thus relinquishing any
possibility of studying intratrial temporal
patterns of behavior. Some go a staee further,
mesuring only total behavior over all trials.
These practices sacrifice a considerable
amount of available information, and their
disadvanta,nes are detailed i n the d i s m ' o n
on temporal analysis of behavior.. Many aperimenters employ only one trial: a procedure of doubtful value in view of the difficulties of interpretation indicated by Wlinibey and Denenberg (1967), who found a
chanye in factor loading of ambulation from
Day 1 to Day Z..3.fultiple trials avoid this
criticism and afford greater reliability and
the opportunity of temporal analysis. Those
who give several trials seldom use more than
4, but up to 6 0 h a v e been used (Bronstein,
1972). \\'here multiple trials. are given, the
question of the optimal intertrial internal
arises; but most commonly, 24 hours has
been chosen, partly from convenience hut a h
since this obviates complications of diurnal
rhythm.
Almost no study seems to have been perlornied on .theefiects of variing these temporal factors. However, Battig (1969) found
that patterns of activity were undected by
exposure to the apparatus 2 hours previous
to the experiment, but that intertrial intervals
o i 3 and 12 minules produced a mild inhibition of ambulation on subsequent testing.
DEPENDEXT
'PARA~~RS
The number of dependent variables used
to aswy open-field behavior has grown substantially since the early work of Hall (1934).
until now over 50 are listed. This list (see
Table ' 1 ) is mostly compiised of behavioral
measures, although recently some physiolog'ical parameters, such as heart and respiration
rates! electrom~ogramrecordings, and plasma
steroid levels,. have also been included.
.kcan be seen from Table 1 most parameters have been varieties of motor behavior,
and of these, measures of ambulation have
been most favored. This is presumably because of the ease of quantification and the
evident face validity for interpretive con-
0PES.FIELD TEST
strucb of exploration and arousal. Amount
of ambulation has usually been scored spatially by the number of subdivisions entered,
but has also been estimated temporally by the
proportion of time spent inambulation. I t has
also been quantified according to cbaracteristics 01 its apparent aim, locality, and latency.
Thus, ambulatiob directed toward escape has
been measured by Ehrlich and Burns (195S),
who scored an escape attempt if the subject
got its head and forefeet over the wall 01 the
field.
Ambulation has also been scored according
to its locality, the most frequently .used
regional divisions being either inner or peripheral areas of the apparatus (Ebrlich & Burns,
1953; Ivinskis, 196s). Occupancy of the
peripheral a r m , either in corners ( h l o r r k n
8. Thatcher, 1969) or near walls (Valle,
1970);has been used as ai index of timidity.
Locality of ambulation has also been used
as a measure of interaction with either inanimate objects or other subjects. Fox and
Spencer (1969) measured object interaction
by the frequency and duration of activity
occurring within the same square as the object. In addition to these measures, McCall,
Lester, and Dolan, (1969) noted any qualitative difierences in the animals' responses to
the objects. The-w included the approach behavior t o the object and the exploration oi
the object itieli. Where conspecifics have
been used instead of inanimate objech, measures of "affiliation" (Latank, Cappell, &
Joy, 1970) hare been obtained by scoring the
average distance between the animals and the
time spent in direct contact with one another.
Activity can also be scored by it; absence.
Here the two major parameters are idenrified
by.the terms latency and freezing. Laten? is
measured by the time taken from the start of
a trial to the occurrence of a certain tvoe
of
<.
behavior. Theoretially, h e latency of an
arbitrary amount of any dependent parameter might be used, but open-field studies
have mercifull!, confined themselves to a relatively m a l l number, usually involving ambulation. Most commonly, latency to leave
the start area has been used (I~insb-is,1363;
Poley & Royce, 1970). However, laten? to
reach the center from a peripheral starting
487
position (King, 1970) and laten? to reach
the periphery from the center (Tobach, 1966)
have also been measured.
The other open-field parameter measuring
the absence of activity is freezing, defined as
the absence.of movement. This is a widely
used parameter usually taken as indicative of
a high-stres state. Certainly it is a behavioral
response which occurs across the phylogenetic
scale in the iace of perceived danger; elements
such as abrupt change,. environmental dislocation, physical restraint, and presence of
predators are patticularly potent eliciting factors. In the open field? freezing in response to
stimuli such as the above shows a marked
species specificity and has been recorded as
sometimes lasting for over 1 hour. I t has also
been found to be associated with marked
tachpnoea, bradycardia, and vagotonic
cardiac arrhytbrnis (Hofer, 1970).
Another cause of prolonged immobility is
of course sleep, and the not infrequent occurrence of apparent sleep has been noted b y
Fox and Spencer (1969) and Cummins et al.
(Note I ) . Fox and Spencer observed that
dogs liable to apparent sleep were extremely
inactive and that they would often defecate.
urinate,. and shiver when placed in the start
box. Once apparently asleep they were easily
roused by a sudden-noise but rrould then appear to promptly fall as!eep again, and the
authors suggested that this might possibly
represent displacement sleep as a result of
intense arousal. Similar apparent sleep has
been noted i n r a t s by Cummins et al. (No:e
I ) , sometimes associated withapparent shivering, which might actually be a result of the
marked tacbypnoea.observed in subjects during immobility (Hoier, 1970). Against the
suggestion of this apparent sleep being the
direct result of h>perarousal is the fact that
i t s frequency increases with increasing time
elapsed within and between trials. This time
course is more in accordance with that o f
habituation, and in point of fact, it has frequently been observed that habituation of an
arousal reaction may be accompanied by the
rapid onset of drowsinw and sleep (see Lynn,
1966, for a review). Paradoxically, a generalized orientation reaction may be easily
elicited during this drowsy phase. Subjectively? it seems possible to differentiate the
immobility followingsudden threat from that
as the
abruptness of onset, wide-open eyes, and
muscular rigidity in the former case, as opposed .to the gradual development, closed
eyes, and relaxed posture accompanying a p
pareni sleep. Perhaps the two behaviors
representexamples of the startle reaction and
habituation of the arousal reaction, respectively.
One test of this hypothesis might be the use
of electroencephalograph (EEG) recordiog?
since the orientation reaction is accompanied
by bippocampal theta rhythms,. whereas hippocampal desynchronization accompanies the
startle reaction-an
interesting example of
electroph~siological data differentiating two
behaCiorally similar responses. I n summary
then, immobility i n . the open field has been
regarded as indicative of high stress hut may
actually confound two distinct behaviors.
Another widely used measure of activity
has been rearing and bas proved a reliable
(Itinskis, 1968) and valuable measure. Combined with ambulation it has proved to reflect
a stab!e individual trait, "nonspecific excitability level," which has been significantly
correlated with hippocampal slow. wave activity. a well as with a wriety of other behaviors. This.measure.aljo displays systematic
variations with individual differences in;somatic functions such .as growth rate, body
temperature, caloric intake per surface area,
qualitative food preference, and endocrine
functions ( L i t - & Gollov6-Hemon. 1969;
Martinek & Lit, 1969). However, attempts
other than. the above to. systematically link
rearing a i t h other variables have been rare,
and it is most frequently taken at face value
as an index of activity.
.4s -rriight be predicted, sitling has been
found to be more frequent during conditions
associated with low levels of activity and to
be negatively correlated with ambulation,
rearing, and sniffing (Prescott, 1970). A surnmary of the influences exerted by different esperimental-procedures on whole body movement and defecation a n be seen in Table 2.
:With the exception of defecation, parameters other than whole body movement have
been less closely studied and i n many cases
have been cited in very few reports. These
of apparent sleep by such features
include scratching, digging, teeth ,chattering,
respiration, electromyograph (E3,lG); digestive tra&t time, cardiac rhythm, and EEG
measures. Of these part body movement measures, snihing has been relatively common
and bas generally been taken as an index of
exploration. It has akw proved a . useful coindex for nonspecific excitability, although a
less adequate one than either ambulation or
rearing. The terms scratching and digging
probably refer' to wentially the same behavior evinced under conditions 01 hard a n d
loose flwring material, respectively. Prescott
(1970) found that greater amounts of digging
in the sawdust floor of the open field were
associaled a i t h other evidence of highactivity. states. Teeth grinding was used by
Hughes (1969) as a possible indicator of
anxiety on the rationale that i t mayrepresent
a' '"tooth sharpening defenske behavior."
Respiration and E M C were used by Hofer
(1970) in her studies of prolonged immobility and have been mentioned previously.
Grooming and wushing are terms describing
tbe.same be5avior and have been found to be
of relatively low reliability (.Ivin!kis? ,1968)
and to be negatively related to indexes of
high-activity states (Prescott, 1970). Vocalizo!ion bas been taken as another indicttion
of distress, and the vocalization emitted on
placing an animal in the open field has sometimes been termed distress calling (e.g., Candland & Kagy. 1969). Canaland and Kagy
have suggested distress calling a s the major
index of emotionality in species for whom
the normal indexes of defecation and ambulation are not reliable, such as he cat and
domestic fowl, although alartinek and L i t
(1965) found hat it was not a reliable measure in dogs.
F'osihle p2ramete:s o f autononic nenrous
svstem function aie legion, but in practice
they have been limited to the more easily
measurable ones oi excretory and cardiac
iunction. Defecation, the parameter for which
the oppn field was designed, remains as one.
if not the most widely used, measure and
remains as the prime index of emotionality, a
role whose validity has been confirmed by
factor-analytic studies (\\limbe? & Denenberg, 1967). A related, but uncommon, measure is digestive transit time, defined as the
OPEN-FIELD 'TEST
timeinterval between consumption and first
appearance of a fecal staining ageni such as
chromic acid. hrot surprisingly, digestive
transit time and amount of defecation would
appear to be negatively correlated. These two
parameters have been used by Tobach (1966)
to demonstrate that open-field testing elicits
a significantly greater effect than the manipu'lative procedures involved prior to actual
testing. The third excretory measure, urinition, has been scored by frequency, presence
or absence, or amount and has occasionally
been combined with defecation to yield a
composite elimination -score (Tobach, 1966),
but in any form has failed to yield reliable
resullr in a variety of species (Ivinskis. 1968;
hlanosevitz, 1970; Martinek 8: Lat, 1969).
Cardiac measures have been used litge eycept by Hofer (1970), whose study has previously been mentioned, and by Candland
and N a p (1969) in an atttempt to validate
the use of the two most commonly used
indexes of emotionality, irAbulationand defe-'
cation. The C F E strain of rats were exposed
to the open field for 21 minutes for 30 days
and compared with home caged animals.
Cardiac rare and defecation were greater in
the open field, but whereas defecation declined over trials, there was no similar adaptation of cardiac rate, although the rate did
fall within irials. Furthermore, there was no
significant correlation between heart rate and
defecation, so that although both changed in
stable fashions and were both considered as
indexes of emotionality, they changed' in
largely independent ways.
Recent years have b e y n to see the application of physiological techniques to the open
field, a'movement which would seem to have
immense potential for expanding the =ope of
studies of reactions to novel environments,
for behavioral-physiological correlation! and
for validity testing of parameters and behav;
ioral constructs. The examples of respiration
and cardiac rate have prevjously been discussed, which leaves biochemical and electrophysiological parameters.
of
The number of biochemi~al.~arameters
potential interest is boundless, but studies'
have a s yet been largely restricted to assays
of adrenal function. This interest stems from
the long-held view of theinterrelatedness of
489
adrenal gland function and emotional behavior. However, studies have shown little relationship between open-field behavior and
adrenal weight or stemid output, and as yet
adrenalectomy bas yielded inconsistent or
negative effects in t h e r a t , mouse, and hamster (Fuller, Chambers, & Fuller, 1956; .
Moyer, 1958; Paul 8: Ravlena, 1962). Pare
and Cullen (1965) were unable to detect
consistent relationships between adrenal ascorbic acid levels and open-held behavior, and
similar negative finding5 were reported by
Ader (1969) for plasma and adrenal corticosterone in hooded and albino rats. Furthermore, although there was a significant effect.
across trials for mbulation, defecation, and
latency, there was no such change in plasma
corticosterone levels smplpd 1 5 ininutes alter
each test. Ader concluded that Lhe d a t a p r o ~ i d e dno evidence lor a relationship between
open-field behavior and adrenal function.
In contradistinctinn to this is the report by
Levine, Haltmeyer, liaras, and Denenberg
(1067) of greater plasma corticosteroid levels
in nonhandled than-in handled.subjec& I5
minutes after testing. There was no change.
however, in these corticosteroid levels across
the 4 days of testing, and the immediate postt e t steroid' levels did not differentiate Lhe
two treatment p u p s . This difierence in ability of the steroid levels to.differentiate the
handled and nonhandled subjects at 0 and 15
minutes after testing can probably be explained in terms of the differences which
Levine has consistently noted in the time
course of adrenal response in these two
poups. However, plasma corticosteroid levels
also failed to differentiate between enriched
and isolated C57BL/6J mice or to correlate
w i t h defecation or adrenal weight changes in
a study by Denenberg, Wehmer, Werhoff,
and f i r r o w (1969). I t would therefore seem
that plasmasteroid estimates represent a potentially useful tool but that their relationship to other open-field measures is as yet
unsettled. Future studies will probably require = temporal analysis of the adrenal'
response after testing, rather than the simpler
but less informative method of sampling only
immediate or maximum (appmldmately 15
minutes after testing) levels.
lndclendrnl
rarlsblc
Increased npenficld size
Increared
illumination
Environment noise
\\'bite noirc
hl,rupt noiw
Odor
Study
Broadburst (1957, 195Sa, 1958b)
Oldham 8; hlorlock (1970)
hlontgomcry (1951)
Elmadhunt (3957)
h'ao 8; F o r a t (19i0)
Ulizord (1971)
R ~ i a k8- Janku (1971)
Oldham 8; hlcrlork (19i0)
Naby & Forest (19i0)
Nagy & G l m r (1970)
h'ngy & Holm (19i0)
Rlimrd (1971)
Vnlle (1970)
Livrsey 8: Eggcr (1YiO)
hlcClearn (IYW)
Diran 8; Eldries (1968b)
Cnndland 8: Nagy (1969)
NOW 8: Clarer (1970)
Rnt
Gerbil
Rat
tlelecation
Defeatinn
hmbulation
>louse
hmbulation
Ilindm (I. Spinner (10%)
Livesev 8: Emcr (1970)
. .
Hofcr 119i0)Cumrnins, \Val&, & Budtr4lsen (Sote I)
\\Inittier & >lcReynoldr (1965)
Rnt
3louse
!%tinder ( 1 x 0 )
Rot
'
0
0
1
i
i
7
Gerbil
hlouse
:tmbulitinn
Defecation
Rot
Ambulation
>louSe
An~bulatian
i
f
0
0
0
1
1
1 only alter 24 days 01 age
I albiios more than pigmented
1 albinos more Lban pignlcnted
I
1 only on
'
Rnt
(freezing)
h s t i o n of
ambulstion
-
i
Dnys 1 and 2 in 1W- but not jOdny+lds
f ambulatiun in n r w in which prior subjects had b m ~ u lnlrd
:k s b v e i u t ~ignificant only lor m a l n preceded by
femnles
"Caretaker ellec1"-time
spcnl on side of o l r n field
nearest to P familiar caretaker
?
u1
Invatrial tmparil
nnalgsis
'
Broadhunt B; Eywnck (1964)
C u m i n s , \\:a&, & Budk-Olsen (Sate 2)
\Vwds, Ruck&haur, & Bowliog (19fLI)
Oldhnm gi hlorlock (19iO)
Cmdland B; Nagy (1969)
Rat
Collins (1966)
Nogy b- C l w r (1970)
Branstein (1972)
Broadburst (1969)
Cummi-, Wnlsh, & Budk-Olsen (Note I)
Furchtgou, \Vcchkin, & Dees (1961)
Ader (1969)
Ehrlicb & Burns (i953)
hlanoscuitz (1YiO)
h R a r t a & \Y&e (1971)
Diron 8; Defries (1%)
Nngy & Holm (1970)
h'agy & Clarer (19i0)
Adcr (19C9)
Brmdhunt & Eysendt (1964)
Cumnlinr. \Val&. & Budtr-Olwn &ole I)
nlouse
Ellecf
P~r~melcr
Subjc~t
'
r\mbulntion
Gerbil
Cst
Def-lion
I - q u a d n l i c !rend
I ~ u a d r n t i ctrend
I-liner trend
!-linear Vend
0 change--nmbulnlion described as nancxplaratory
padng
f a c m sir trials, in\.ertd U over 10 days
I
Rat
1
I
I
1 from nu). I to Dny 2
Pcrret
hjourc
but then f
I
Ambulnlion
1 across triall
I ~ C T O I S trials
!across trials
1 a c r e s trials'
1 across trids
I linmr trend
I q u a h t i c trend
1 quadratic trend
0
! Lath studies shot\. reliable
! individually specific mler
Cat
Domestic fowl
0
1
af d c c r u r e across trials
-
.
492
.
.
'
ROGER X. \ V U H LVD ROBERT A. C U l n f N S
-
odd-even correlation. Scores were summed
across Days 1 and 3 and across Days 2 and 4
and correlated for both strains separately.
Coefficients lor ambulation with both deiecation and rearing scores were .68 or above
for both strains, wbile frequency and duration of wahing .were reliable for albino but
not for hooded subjects. All other variables
failed to display acceptable reliability.
Somewhat similar findings bave been reR E r r m n l r v OP OPEN-FIELDVARIABLES
ported by Martin& and Ut (1969) in their
As yet there have been veq'few
study of the long-term stability of individual
of the reliability of the many variables in differences in evloratory and other behabior
use. This represen& a very disturbing state d,
Lhe rate of habituation in dogs. nesub.
of affairs, since unless a parameter can be j&
,
were given
of
,,,inUte.' durashorn to possess a satisfactory degree of reli- tiqn each spread over days and
then
ability and hence to be a stable characteristic retested in a smiliar manner approldmately
of individual subjects or situations, its use- . 300 days later, ~
~
b
~ satisfacl
~
fubess is almost nil. Fortunately, the most torily smb]e, a i t h the
of ambuwidely u . 4 variables, ambulation m d deleca- lation, raing, and snifhng gi\ing the
tion, have been found to poacceptable reliability even though snifing alone proved
reliability in several species. However, ambureliable, Vdimtion,
del&lation yields a complex pattern of test-retest
tion, urination, and body
(smding,
correlations because it is a factorially complex slthng,
. . lying) all proved inadequate. Furtherparameter, loading on both exploration and more, the rate of habituation of the combina.
emotionalit?, yet changing the direction of tion of ambulation, reuing, and miffing,gi\.en
its loading on-emotionality from positive on Gther by the regresion coefident
by
Day 1 to. negative thereafter (.\\'himbey 6: relative
between
and last
Denenberg, 1967). \Vhile correlationsof Day 1 on a day, was also found to be
hi^
ambulation 6 t h scores of subsequent days - studyof the
of habituation has been
-are satisfactoq' (about . j ) , they are lower further expanded by it and Gollo\+-Hemon
than the intercorrelations between other days. ( 1969), who reported that habituation cumes
Ivinskij (1968) studied a, variety of vari- Show dear intrinsic oscillations
whose size
able5 m w u r e d in several ways. Albino n d
a stable individual characteristic..
hooded rats were tested ove'r four daily tnals, The sum of these oscillations has been
and albinos were reteste'd in the same way a lobilily rcorc and a correla"on coeficient
63 and 217 days thereafter. I n mamining
, 7 7 (!\, = 20) was found when retesting
test-retest reliability of variables for the
performed after months in a dinlerent
albino group, scores were averaged over 4 situation,
days, and it was found that ambulation and
for
~h,,~, there would seem to be
the frequency of both defecation and washing the
not only oi the total magnilude
yield& product-moment correlations greater but in son,e
also for the rate and inIhan .4 ($ < .O1) Over the 217 days.
trinsic o ~ i l l a "of~ habituation
~ ~
of certain
frequent). of rearing, latenc?l to leave the . beha\iors. ~ ~ b ~ lrearing,
~ t iand~ deieca~ ,
center d r d e when initially placed there, and tion would seem to
adequak
duration of washing all yielded coefficients while urination, snihg, body position, and
of .34 (p < .Oj) or above. This left all three .
measures of urination (frequency, presence or ~ n n e r circle ambulation would seem to be
absence, and amount in ,,,illigrams),,duration definitely inadequate; and a number of
01 rearing,and inner circle ambu~a~ioo
nith . others, such as washing and latency to leave
very low and quiie nonsignjti-t
correla- the central circle where initially placed, must
tions. A further test dFas provided by an be viewed as only marginally reliable. H o a Possibly el~troencephalographic measures
represent some of the most uselul and fascinating parameters of the future. .As yet they
a r e a novelty, but the succes of the CzechoslovaL5an workers L i t and Gollovi-Hemon
(1969) in relating bippocampal theta activity
to behavioral open-Aeld measures augurs well
for this and other electroencephalography.
were
.
.
'
,,,
,
I
~
i
~
~
OPES-FIECLD TEST
ever, these few variables represent less than
a Lhird of those reviewed in this paper, so
-.
,.
1
that i t is obvious that most of the remainder
must ar y e t also be viewed with suspicion.
I t is interesting to note the apparent strain
differences in the reliability of the washing
measures. (I\inskis, 1968) ;which suggest that
due care must he exercised in extrapolating
the reported reliabilities to subjects of other
genelic and experimental backgrounds. Also
interesting is Itinskis' finding that different
m w u r e s of the same bebavior.gave comparable coefficients. I t is disturbing to note the
unacceptably low reliabilities of many of the
parameters which have been tested and to
reflect on the probable unacceptability of the
reports employing them. These low reliabilities may partially account for the plethora 01
inconsistent findings which fill the literature.
T E ~ O I UANALYSIS
L
OF OPEN-FIELD
B~mt~on
.
P
I t was mentioned in the discusion on techniques that testing may consist of more than
one trial and that these trials may be subdibjded into intervals, thus alloving temparal
analysis and effectively adding another dimension to the behavioral study. Many
workers measure only total behavior per trial
or even total behavior over all testing. This
failure to perfom1 temporal analyses within
and between trials efiectiuely coll3pses results
across two dimeasionsand hence the worker
tends to view behavior as static rather than
as constantly changing, as an event rather
than as a process, and partially ignores tbe
efiect of prior exposure to the apparatus. 1n
so doing, the analyses must result in a diminished sensitivity, since the subjeclrc may
difier in their behavior only at certain phases
of testing. The failure to periorm temporal
analyses also results in the dijcarding of an
immense amount oi information includine the
possibility of studying the na:ure, rate, and
lability of habituation-characteristics aha%
individual stability and imporlance hare been
clearly demonstrated ( L i t 8. Gollovi-Hemon:
1969; 3Iartineli gi f i t , 1969j. Occasionally
where an experiment calls for the manipulation of multiple independent 1.ariables: the
diiwrding of temporal analy~esmay wnier
493
some advantage in obviating the difiiculties
of interpreting higher order interactions, but
against this must be weighed the disadvaot a g s listed above.
Intratrial temporal analyses have b e e n l w
frequent h n those across trials and have
largely been..limited to ambulation. The general pattern for a variety of species seems
to be a decreasing frequency of ambulation
across i n t e n d s mithin trials. This decreased
rate may either remain approximately steady
(linear trend) or diminish exponentially from
an initially relatively high value (quadratic.
trend). The latter trend has been reported in
both male and female r a h of the hIaudsley
Reactive and Nonreactive strains by Broadh u n t and Eysenck (1964) and in young
\\'bite Legborn (GoUus domeslicrr~). The
former linear trend has been noted by
Oldham and Xforlock (1970) in Mongolian
eerbils and in Sprague-Dawley rats (Woods,
Ruckelshaus, 8. Bowling, 19.60).
Studying \ c u l i u t i o n in the cat, Candland
and Nagy (1969) found differences in intra-,
trial trends to be a function of age. Kittens
showed a marked intraswional decline over
10 minutes'but did not reach the considerably lower levels of the adult cats,. whose
vocalization diminished only slightly. In v i e t ~
of the absence of defecation and the apparently none.~loraton. nature of ambulation
(subjects paced backwards and forwards
near .the unit door without any apparent
exploratory intent), the authors suaested
that vocalization might yield a better index
of emotionality in this species than the
traditional measures.
S t u d i e ~across trials hatre been more extensive than those witbin trials. The varieties of
satistical analysis are of course limited by
the number o i triali. The simplest and most
common analysis has been determination of
the sienificance level of intertrial diiferences.
.9 more inlormative metbod is trend analysis,
and'where several trials are used, i t is
possible to examine not only the general
trend but also the nature. magnitude, and
periodicity of trend Euctuations.
Once again ambulation has most often been
studied and a variety oi patterns has been
noted. Consistency has been greatest in the
-, . .
,'
>
.
.
-
.
.
49.1
ROGER
N.
WALSH AXm ROBERT
mouse where the majority of workers have
reported decreasing ambulation across trials.
This has. been reported as a significant, efiect
for subjects reared under enriched and standard colony conditions (Manosevitz: 1970),
in small or large litters .(LaBarba &! iV%ite,
1 9 i l ) , and for B.ALB/c.J and CS7BL/6.J
inbred mice and their reciprocal F 1 hyhrids
a t sevcral aTes (Dixon & Deiries, 1968a).
Ambulation decreased across 4 days in
handled and unhandled C3H .mice tested
under high or low illumination a t 50, 70, or
100 days of age ( N a p & Holm, 1970). This
report furnishes an example o i the added
sensitivity and information afforded by intertrial analysis, since although the main effect
for handling was not significant,. a number of
its interactions with trials were. Thus, 50day-handled subjects were more active than
controls.on the first day, but their ambulation decreased more rapidly such that i t was
less than Lhe controlj on Daxs 3 and 4, and
this pattern was different a t the three ages.
Similar examples are available in the study
of Nag? and Claser. ( 1 9 i 0 ) , who demonstrated a significant (apparently asymptotic)
decline across 10 days in C57BL/6.J mice.
Less consistent results have been obtained
with the rat, although a decrease across days
. has been most often reported. This has sometimes been linear (Ader, 1969) or apparently
quadratic (Broadhurst 8: Eysenck, 1964)
where a decrease was reported f r o m D a y I
to 2 which was partially recouped on Days
3 and 4. Broadhurst $nd Eysenck 'hypothesized that inhibition may account for the
initial intertrial reduction as well as the intra. trial decline already discussed, while reduction of fear m a i account for the i n c r m e
in ambulation across Days 3 and 4. The rate
of decrexse washeightened by prior rearing
in a complex environment, a finding attrihuted to a more rapid habituation of the
arousal response to novel stimuli (\\'alsh 6Cummins, in press; Cummins et a]., Note
1). Barrett and Ray (1970) and VaUe
(1971) found that young r a t s become more
active across trials, but other workers have
found no significant intertrial chanze (e.g.,
Furchtgott e t al., 1961 ). Thus, every possi-
A.
CUMMISS
ble change--increase, decrease, or none-has
been reported.
Other s p m e s have been l e s closely studied.
I n the dog! Nartinek and Lit's (1969) find-ins of individually reliable d e c r e a in ambulation across trials has already. been discussed, but Fox and Spencer (1969) found
that exposure to the field some weeks previously resulted in modest increases. Xeither
kittens nor adult cats displayed any significant change across 10 days, while. the
domestic iowl showed a dramatic i n c r w e in
spiie of consistent decre&
within trials
(Candland &! N a p , 1969).
Latency to leave the starting .unit wass
found to increase across 3 days in rats of
various ages (Furchtgott e t al., 1961). A
more complex picture aas noted by Ader
(1969) when latency fell markedly from
Day I t o 2 but then increased slightly over
the' next ? days. Latency declined-across
5 test days in ferrets (Ehrlich k Burns:
1958) and there was a similar trend for both
rearing and scratching, while vocalization declined over 6 days in i d u l t cats but not in
kittens (Candland 9. Kagy? 1969). On the
other band, snifing by rats increased across
3 days, Lhough this was dependent on the age
of the subject (Furchtgott e t al., 1961).
Cross-trial studies of defecation have been
almost entirely limited to the mouse and the
rat, and once again only three or four trials
has been the norm. However, within these
limitations there would seem to be consistent
evidence of species difference3 in trend, i o r
n,hile the rat shows a l e w n i n g in deiecation
across days (a pattern that has beenaccepted
as the norm and the basis for hyptheses
building both within and betueen species),
the mouse displays the opposite trend. This
decrease in the rat has been widely reported,.
thought not without exceptions (Ader, 1969),
and has been confirmed over as many as 60
trials (Bronslein? 1972). Furthermore, this
decrease has been s h o r n by Broadhurst
(1969) to have a d e a r genetic-component
with a high average level of dominance, with
the s u ~ e s t i o nthat natural selection will tend
to favor low-scoring strains resistant to
change across trials.
OPEX-FIELD TEST
.
1
For the mouse on the other hand (practically. the only other species for which evidence is available: indicating the reliability
of the defecation measure), there has been a
high degee of consistency btween reports
on intertrial trends. Thus, defecation has been
found to increase across as many as six trials
(e.g., Collins, 1966). These studies afford an
interesting example oi the oversimplification
which may result from taking a relatively
small number of levels of any factor under
investigation, for when the number of trials
KU increased to. 10 (Kagy S. Glaser, 1970),
i t was found that the trend could now be
identified as an inverted U with the number
of boluses increasing through to Day 6 followtd by a decrease over the remaining 4
days. The marked consistency existing between studies of intertrial changes in defecation has recently become explicable in light
of a quantitative genetic analysis of openfield behavior in mice by Deiries, HeLpan,
Ross, and Howard (1969). I t was found that
change in defecation displayed as high a degree of heritability as did the daily and total
scores:In spite of a similarly hish consistency
between reports on change in mouse ambulation, genetic influence on change in this measure was found to be considerably less than
for eith-r daily or t o h l scores or ior any of
the defecation scores.
Interpretations of temporal changes in openfield behavior have varied with the paiameter
under study and the meaning attached to it
by the experimenter.. Thus, for example, the
cro%-trial' decrease in ambulation and deiea t i o n in the rat has been taken as indicating
a diminution in emotionality, anxiety, fear,
w p e attempts, and territorial marking, or
at !he more general level: of the development
of inhibition or habitualion. However, in
conjunction with an!, interpretation must b:
an awareness that the placement of a subiect
in an originally novel environment must elicit
an orientation reaction which subsequently
hnl~ituates.One might conceive of this reaction as a high+rder factor in a psychophysiological construct hierarchy, modulating multidetermined lower order constructs such as
fear, anxiety. territoriality, and the like.
a,hicl~would in turn modulate the even more
495
overdelemined spedric behaviors observed in
the open field. The precise nature and maggitude of the changes in these bzhaviors will
of course be determined by the geneticexperiential background of the individual, but
any attempt to esplain temporal behavioral
changes must certainly incorporate the concepts of orienhtion reaction and habituation.
I t has long been known that many dependent variables in the open field correlate
significantly with one another. This is all the
more to be noted since some positively correlated behaviors are mutually e~clusi\.e
(ambulation and rearing) and hence their
.degree of relatedness is presumably underestimated by simple correlation.
A basic deduction from these correlation
studiff has been that many parameters tend
to measure t h e same psychophysiological
-state and as such have provided several useful
implications. First, such correlations allow
for validity testing, since the patterns oi
behatior serving as a s u y s for altered psychological states should be predictable under diverse conditions. Second, they may afiord an
increased sensitivity and reliability of measurement. At the same time, they may also
allow an economy of measurement because
where parzmeters are highly correlated, one
may well dispense with some of them. Thus,
L i t and Cmllovi-Hemon (1969) were able to
dispense with measures of snifing and deaning in the knowledge thzt a weighted sum of
3mbulxion and rearing would still yield an
adequate correlation a i t h hippocampal them
activity.
Not surprisingly the correlation between
ambulation and defecation scores has most
often been studied. Since Hall's (1936) report there has been a high degree of consistency in the literature affirming a negative
relationship between these measures in the
rat. In the mouse a similar trend has most
often been noted! and this in spite of the
previously mentioned increase in defecation
across davs. More detailed s t u d i s in this.
species, however, have begun to reveal some
of the complexity of the relationship, and
.
496
ROGER N.WALSH .Ah73 ROBERT A. CUMhfISS
,
in a diallel study, Bruell (1967) found a
positive significant correlation (r = ,124) in
males, a i t h a negative and equally significant
correlation ( r = -.I 59) in femal6.s.
The relationship has been less frequently
studied in other species ,and .has almost always yielded nonsignificant correlations, espedally for $ecies in which defecation bas been
found to be an unreliable measure (e.g.,
Candland & S a g y , 1969).
I n the vast majority of cases, correlation
has been performed between scores totaled
over aU trials. However, considerably more
light h a been afforded by recent studies
which have examined the relationships between scores obtained on individual trials.
Nagy and Glaser !1970) divided C576L/6.J
mice into high and low ambulators and
studied the cross-trial patterns o i defecation
under a variety of ages and illuminations.
High and lorn ambulators did not differ in
defecation on Day 1, but thereafter the low
subjects defecated significantly more; and
their defecation continued to rise until declining from Day 6, whereas high ambulators
defecated man'mally on n a y 2. Meanwhile,
ambulation decreased steadily in both groups,
suggesting that the correlation is not asimple
one and afiordina another example of the
1 0 s of information contingent on failure to
perform temporal analyses.
As might be anticipated, the various measures of motor activity tend to be positively
correlated, even in cases in which the behaviors tend to be mutually exclusive, ris with
amhulation and rearing. These two parameters have been found to be highly (up to
3 1 ) correlated in a variety of rat strains
(e.g., lvinskis, 1968; Ray Fc Hxkhauser,
1969), although Delbarre et al..(1970) have
noted a dose;dependent, pharmacologically
induced dissociation between ambulation and
rearing.
Since the definition oi latency usually involves the ahsence of ambulation, i t is not
surprising that these two measures have been
found to be negatively correlated. This has
been widely reported for both the rat andmouse, and both parameten have been found
to load on common factors hut in opposite
directions--namely, exploratory behavior in
the rat (Denenberg & Wlimbey, 1968) and
on a factor which was unnamed and uninterpreted by the authors in the mouse, but by
analogy with studies on the rat would seem to
represent a factor of emotionality (Poley 8.
Royce, 1970).
Correlational studies of ambulation with
oLher variables have been less frequent.
Ader's (1969) use of corticosteroids has already been mentioned. A negative correlation
with urination, just significant a t t h e .O5
level, was reported b y Satinder (196S), a
doubtful finding in view of the demonstrated
l o r reliability of urination measures; Similarly, ambulation displayed a sipificant positive correlation with inner circle actitity in
spite of the latter's demonstrated unreliability (Ivinskis, 196s). Finally, ambulation and
vocalization showed a positive nonsignificant
trend in dogs (Fox & Spencer, 1969) and the
reverse in human infants (Rheingold, 1969).
.As the most widely studied parameter,
defecation has frequently been used as a co;relate. The negative correlation a i l h ambulation has already been detailed. I n view of
the ncative correlation of ambulation and
latency, i t might be anticipated that defecation and latency would he positively related,
but in the main 'only nonsi~nificant trend<
have been found (e.g.. Ader. 1969: Porter
Fc Wehmer, 1969). The lack of correlation
uith changes in heart rate (Candland &
N ~ F , 1968) has already. been mentioned:
while Satinder (1968) reported a n q a h v e
correlation Kith grooniin~over four trials.
.A logical extension of intercorrelating openfield variables is the study of their relationship to measures obtained on other behavioral
tests. Such correlations may afford the advantages previously mentioned of increased
sensitivity. reliability, and economy a? well
as providing valuable information on the
apparatus specificity of aqv apparent relationships. Perhaps the best example o i this
specificity is afforded by ambulation. Thus,
although some workers report good correlations between ambulation scores obtained in
different apparatuses (e.g., ambulation in the
open field, endosed maze: and an exploratory
box [Stretch, 1960, cited by Broadhurst &
Eysendt, 1964]), most have not been so en-
OPES-FLELD TEST
thusiastic. Particularly common have been
studiff of ambulation a s measured by activity wheel and open field. These studies have
yielded consistent reports of significant but
not particularly high correlations (Manosexitz, 1970; Weasner, Finger, PI. Read,
1960; correbtion coefficient of .41). Considerahly lower correlations have been found
where motor activity is measured by cage
tilting or stabilimetn.. Here i t is obvious that
the highly coordinated motor wheel activity
may be only slightly similar to the multitude
of part and whole body movements registered on the stabilimeter. I t should be noted
that even simultaneous measurement of motor
activity may yield relatively low correlations.
Thus, simultaneous mex?urement of total
open-field activity over 30 minutes gave coefficients of .65, .65, and .49 for cage tilting- beam interruption, cage tilting- flwr
contact, and heam interruption- floor contact,
respectively (Sparks 8: Lodiard, 1966). Openfield ncliuiry is sometimes used synonynously
with ambuhtion, but in \iew of the term's
varying usage by different workers and the
relatively low correlations above, it is best
avoided in this contest.
Ambulation h3s also been found to be correlated .+th m w u r e s whose ambulatory nature is less obvious. \Voods, Ruckelshaus,
and Bowling (1960) found significant correlations of the Hebb-\Villiams' maze error
scores ~ 4 t hambulation in rats reared under
free or restricted eovironments. They therefore suggested that the often reported finding
of lower error scores on maze and discrimination tasks in animals reared under conditions
of increased environmental complexity might
be due to a reduction in conflicting exploratory tendencies rather than to an increase in
learning ability per se. This sugests an a
yet apparently untried u u g e of the open
field, that is, the use of one or more of its
parameters as covariate adjusters in cases in
which related behaviors are believed to be
confounding variables. Thus, in the above
study the u s e o f ambulation as a covariate
oi error scores might yield a clearer pictuk
of the origin of the error score difference.
Satinder (196S), using measures of ambulation, defecation, urination! grooming, and
497
rearing, found little relation to conditioned
escape avoidance behavior in the rat except for positive correlations of avoidances
and intertrial crossings m'th ambuktion
and a negative relationship between intertrial
crolsings and defecation.
L i t and Collola-Hemon- (1969) have described the relationship of their previously described open-fieldderived m w u r e s (nonspecific excitability level, inhibition, and lability)
to both behavioral and physiological measures.
Thus, a n analysis of individualdifierences in
learning a double-T maze revealed h t these
three factors accounted for a major portion,
of variance on measures of learning, running
time between starting box and first r u n m y ,
and decision time on choice points. Furthermore, nonspecific excitability level was found
to van. systematically with indiridual diiferences in such diverse physiological m a ures as growth rate, body temperature, caloric
intake, qualitative food preference, and endocrine functions; a a i d e range to be sure and
an interesting example of what will hopefully be one of many demonstrations of physiological substrates of open-field behavior.
In view o i its multiple intercorrelated raria b l s , mosi of &em oi doubtful meaning and
their correlations with variables obtained in
other tests, the open held would seem to lend
itself ideally t o factor-analytic studies. Indeed, such an approach mould seem to aflord
an optimal method of interpretation and de-'
termination o f the factorial structure of openfield behavior, yet such itudies remain a
rarity. Since it furnishes an excellent example
of the potential of this method? the study by
\\?himbey and Denenberg (1467) is described
in some detail.
IVistar rats were assigned to one of 1G
treatment combinations that resulted irom
completely crossing four independent e.xperiential conditions, each at two levels, yielding
a 2 :< 2 X 2 :< 2 iactorid design: The four
variables a c r e handling oi the subject's
mother during the latter's infancy, handling of
the subject during infancy, housing o i molher
and young betureen birth and weaning, and,
finally, housing ior the first 21 days after
weaning. Commencing a t 220 days of age,
scores were obtained on a numhzr of widely
-
i
.
... . . . ...
. , -.
..-. . .
. . . - 4. 9 s .
.
. .,
'
.
-
..
.
..
.
.
.
.
:*.L
..
.
. .
.. - ..
.
.
-
.
.
.
.
_-'
:-..- : :. .
. ..
;.,
.
.
. ..
.
.
ROGER S . \ V . U , S H ASD:ROBERT ,A. CL;M>iISS
used :measures of exploration, emotionality,
avoidance learning, consummatory behavior,
and- the. Like, yielding a tntal of 3.7 scores including open-field ambulation and defecation
on Dags I-4-and a f i e i a n intervening period
of testing on several other apparatuses, on
Day 14. Outstanding feature of theanalysis
were the relatively l o x correlations of the
first day's ambulation score with those o i
.other da-s and the positive coirdation di
Day I ambulation w i t h a l l defecation scores
-in-cnmpsrison to the negative currelations of
ambulation on other days. The two orthogonal factorsacco'unting for most' o f . t b e variance of Lhese variables were interpreted as
cmotional reaclivily and cxpforation. Defecation loaded only on emoliond reacliaily.
whereas ambulation proved factorially complex, :loading positively on . czplorution but
changing i t s loading on emotional reactkit?
from.positive on Day 1 to negatirre for other
days. I n addition, defecation was found Lo
load on a Lhird factor wGch was named consummation+limination (Denenberg, 1969b).
T h e factorial complexity-of the ambulation
score Frovidcs, for the firs: time, an explana.
tion f o r w m e of the lar'gedumber of contrad i c t o ~ f i n d i n g sand interpretations of .this
-parameter. Ambulation: has f o r . many y a r s
been the traditional memr-e of rat exploration, while others h u e used il (sometimes
in conjunction with defecationbut sometimes
not) as an index of emotionality, fear, or
escape behavior. It can. now be seen that it
may-well he indicative of esploration as well
as .either high or low emotionality but that
intekpretation i s next to impossible where
only one trial is e'ven and the information
from deiecation scores is not taken into account. I n view of the similarity of the withinto the between-trizls decline in z m h u l a t i ~ n
in the rat, i t i s interesting,to speculate as to
whether there might be a similar reversal of
loading on emotionality within trials, especially for Trial' 1 . T h e advantage conferred
by the finding.that the two major parameters
of the open field' load well o n these two
important dimensions of animal behavior is
immense, but i t -must be noted that the generality of this finding for other species and
strains, for different experiential backgrounds,
'
-
and for different .test conditions remains unproved. One has only to remember the inc r k n g defecation across. trials iound in
the mouse, as compared w i t h t h e decrease
o f . the 'rat, to realize the relevance of these.
qualifications.
\\%at then are the iactors determining t h e
qualitative and quantitative nature of be:
llavior erjnced by a subject in the "pen field?
Basically, & is true: of any behavioral test,
this behavior represents the interaction of
the suhject with the experimental situation.
This concept of operationalism, that is, t h e
interaction between that which is measuring
and that which is being measured &d the
inseparability of the properlies and efiectj of
one irom the other, might well be extended
from physics to the behavioral science. Furthermore, each o i these factors influencing bebavior may be divided into interacting subcomponents which of course may he iurther
subdivided ad infiniturn. Division will mainly
be carried only to the first stage in this study:
since it is a t this level o i behavioral de:ermination which most open-field studies are concerned with and because of the incresing
complexity a n d diminishing returm trhich
iurther subdi\ision brings.
Sutject,variables are perhaps best clavified
under genetic, developmental, and experien.tial headings. Genetic c o m p n e n b of species,
'strain, and sex are most often discussed.
Developmental features usually refer t o the
physiological maturation procwes, but o n e
might subsume biological rhythms under this
beading. .E.xperiential variables have been
c l s i f i e d by a variety o i criteria,. most commonly by the nature of the stimulus and the
development phase a t xrhich it was given. For
the purpose of the present discussion, the
most u x i u l classification is into experience
p i n e d prior to testing, manipulation of the
subject involved in bringing it to the expe~imental situation, and e.rperience of the experimental situation up to the instant a t
which hehavior is beine-. measured.
Some idea o i the interactional tornplexity
of behavioral determination may be gained
OPEN-FIELD TEST
499
from looking at studies which have simul- mental situation, stimulation afforded by the
taneously examined the effects of several vari- experimental apparatus, stimulation afforded
ables from just one of the above divisions. by the test environment, e . ~ r i e n c eof the
Denenberg and his co-workers (Denenberg, test situation up to the inrtant of measureKaras, Rosenberg, 8i Schell, 196s; Denenberg ment, and method o f measurement. The imSr Rosenberg, 1963; Denenberg.& Whimbey, plications of this. for open-field studies are
1969) manipulated the handling of the-sub- discussed below but may also be generalized
jects, their pretieaning.and postweanins en- to other areas of behavioral research.
This interactional n a t u r e o i the behavior
vironments, using both male a n d female
Wistar rats and found. a significant four-way places severe limitations on the extent to
interaction among all variables o n open-field which generalizations czin be made from the
results of any individual esperiment. I t also
.
ambulation.
Coming now to the test situation side of increases the potential importance of changes
the equation, Lhis may be divided i n t o the in any one factor 01 the interaction equatest environment and measurement procedure. tion, so that apparently Lribial alterations of
T h e test environment. has previously bcen any one stage of the chain reaction may reconsidered in some detail under the headings sult in totally unexprcled changes in hebavTechniques and Apparatus Characteristics, ior. The importance of this for coniparisons
T h e Testing Environment, and Procedural between treatment groups rests on the differDetails. The nonequality of results,obtained ential efiects of any 'changes. hleier (1963):
by difierent methods of measurement of sup- in discussing the conditions which modify
posedly the same behavior has a h previously behavioral development, has stated:
been mentioned? and interactions between
Thc rondilions that have been drrcribed (c.8..
treatmqnt and measurement techniques are handling, Litler sire, malcroal w a i n and prepartal
well known in the literature. Such an inter- cxperirncc, cage sire and complexity. lo name a
action was remrtrd bv IVeasner et al. (19601. f r w ] . wcrr ~ r e v i o u s l y releqatrd to the groccles
demonstrated that' photoelectrically reg. limbo a: m i n t e n a n t e routines .which s e r e inirerecorded 2nd codihed, and even then ior
istered home-cage ambulation and revolving- quentty
only limited or local conrumplion. Now we rcaliur
wheel counts yielded different results for that
variablrs are
in their poteoo.
equivalent treatments. In comparing such t o cffrrt behavior change that is drmonlrable for
measures of behaxior obtained by-difierent prrio& often a t e n d i n g far into adulthood. \Ye
tffhniques, there are several
factors to be canno: help hut wonder how many of the nowc k i c controrersie in the behavior sciences could
considered. First, there is the question of
.,,be
rewired were detiled information availtibether the behaviors being measured by able on the maintenance routines employed by L ~
each method a r e in fact thesame. Presum- protaaonisls in thore controversies. (P. :7)
ably they can never be identical; the study
4 note of despair. has been c a t by
of S p a r k and Lockard (1966) using cage
Henderson
(1970), who stated "for the time
tilt, beam interruption, and floor contact
being
investigators
must be aware of the posm w u r e s of activity afiords a gross e m p l r
sibilities
that
early
environmental
interactions
of this. Second, there is the queslion of difnith
cenotype
may
limit
the
validity
of their
ferential sensitivities of techniques,. as regards
OUT unique laboratory situaFindings
to
their
bolh ~hresholdand sensitivity to increments
of behavior. And third, turning full circle: ' t i o d ' (p. 509). This statement stems from
there is the matter of interaction b e t ~ e e n the author's work on effects of genetic and
early environmental interactions on a number
the subject and the measurement apparatus.
of subsequent behaviors (Henderson, 1963,
The concept of operationalism fits well here. 1969); including open-field defecation, in
In summary then, any behavior represents which it was obvious that there tias no single
the determinant o i the interaction of genetic relationship between prior treatment and
badground, maturation, biological rhythms, subsequent defecation across difierent mouse
experience prior to testing, stimulation in- strains. >foreover, this is only one of the
volved in bringing the subject into the experi- posible 72 one-way, let alone multiaay,.inter'
P
widespread ignorance of the ethologid significance of much behavior studied in laboratory
situations (Henderson, 1968). .
The construct of emotionality bas been the
major one for open-field work. Although
rarely defined except in circular operational
t e r n (Denenberg, 1969b), i t can be thought
of as an entity underlying the nonspecific
affective components of behavior. We say
nonspecific components because. an. adequate
stimulus and appropriate goal-oriented behavior cannot be identified, although anthmpomorphic. analysisor experimental manipulation suggests the presence of a n aiiective state
(Ader. 1969). ii'hile initially b a e d on anthropomorphic interpretation, the construct
has been factoridly validated (Zi'himbey 8:
Denenberg. 1467). .%lLhough Ridely ajsumed
to underlie a large number of behaviors, factorial loadings have as yet been demonstrated
only for defecation and.ambulation. Ilinskis
(1970) attempted to test the validity of deiecation, an~bulation,latency, rearing, aashing,
inner drcle activity, and urination as indexes
ol emotionality in rats..His criteria of validity were, first, intertrial decrease of scores
acrosr, 4 days; second, efiects 01. prior openfield testing to reduce scores; and third, eifects of alterations in anibient auditory and
tisual stimulation. The adequan. of these
criteria would seem to be debatable, and in
iact Ivinskis concluded that ol the three, only
stimulus variation was satisfactory. Using
this criterion, of the seven parameters tested,
be
only t w d e i e c a t i o n .and latency-ould
considered valid indexes of emotionality. The
necesit).. for interpretive caution when using
the o~en-fieldtest is even more aDDarent
in
.
light
of
this
study,
especially
when
i
t
is
reINTERPRETATION OF OPEN-FIELDMEASZTRES
membered that of these two m w r e s only
Ihat t h e n does t h e open field measure? defecation has been found to be .acceptably
Interpretation may be in terms of under- reliable (Ivin~lris,1968).
lying constructs or on the basis of the behav:
Another widely referred to aflective conior's presumed purposi\-e or adaptive nature. struct, which would seem to be ven. d o s e t o
Underlying constructs may be suggested by the emotionality, is that of fear. It does not
face validity or anthropomorphic interpretation of a particular behavior, by resemblance seem certain to u h a t exent the behavioral
to a natural behavior pattern or to other andphysiulogical components of fear can be
constructs, or by factor analysis. I n t ~ i t i \ ~ edifierentiated from those of emotionality, and
or face validity interpretations have been the the two t e r n often seem to be used synony'norm until verv recentlv:
,, the diificulties and mously. Since measures of emotionality have
dangers of which are compounded by the most often been obtained in situations wbicb
actions derivable from the nine major independent variables listed earlier! As early as
1958, King listed variables likely to be of
importance in determining subsequent behavior and pointed to the lack of concern by
investigators for control oi variables other
than t h e o n e in which they themselves were
interested. Today, little has changed except
for the enormous r o w t h of the list .of variables known to be important. I t is small
wonder then that contradictions and failures
of replication abound in open-field and much
other behavioral research.
-What then cyl be done short of abandoning a nomothetic for an ideographic approach.
First, experimenters must bccome a m r e of
the nonsdditive nature of behabioral determination. With this in mind: one can see that
studies which examine only one factor in
imlation are of considerably lesj value than
those which permit consideration of a variable in light of the effects oi others. To this
end Henderwn (1969) recommended the use
of considerably more elaborate multifactorisl
multivariate desi.ps than have previously
been customary and felt that drawbacks o i
size and multiway interactions are a necessary price to be paid if this area is to advance
beyond its present limitations. .\ further
. need
.
which will enlarge such designs even more
i s the .need for large numbers of factorial
levels in view of the nonlinearity of response
to su many variables. Furthengore, those relevant variables not included in the design
must be ~ r u p u l o u s l y controlled, and' the
leveln a t wbich t h e were controlled must
be reported.
.
CLD TEST
anthropomorphically would seem likely to induce fear, one wonders if there is a n advantage to be gained at this stage by trying to
difierentiate them except denotatively in terms
of the specific experimental stimulus situation.
Specific.affective behaviors and constructs
have naturally been rare in view of the absence of adequate stimuli in most open-field
testing. However, with two subjects in the
field 'simultaneously; the construct of gregariousness has been used to explain differences
in average distance between and time spent
in contact by the subjects (Latan6 et al.,
1970).
Exploration has been a much used construct whose prime measure has been ambulation. While this assumption has been validated by factor analysis, its limitations have
been pointed out by hIcCall et al. '(1969).
Once again, many other parameters are
thought to be indicative of exploration (sniffing, rearing, etc.), but factor-analytic validation is still awaited. At the psychophysiological level, arousal-habituation has proved
extremely useful, especially in the work of
U t and Gollova-Hemon with their derived
constructs o f nonspwihc excitability level,
inhibition, and lability.
One of the' most pressing needs in the
formulation of open-field constructs is an
increased reporting of validity studies.
'501
have been enumerated already. but their
inclusion in a concluding section seems
more than warranted in view of the danger
of "the growing body of literature in this
area suffocating under its own weight" and in
the hope of helping to "convert the current
paper explosion in this area into a knowledge
explosion" ( H e n d e w n , 1969, p. 867).
First, with regard to procedural matters,
there is a need for a more precise specificstion.of subjects including their genetic background, prior treatment, apparatus, testing
conditions, measurement techniques, and temporal factors. Where replication or compari-'
son is the aim, all possible factors other
than the one under manipulation must be
suupulously controlled.
' h regards experimental design, tbere is a
need for the recognition of the essentially
nonadditive nature of behabioral determination. \Vith this in mind experiments which
manipulate only one independent variable
would be better replacd by multiway iactorial designs, which because of their economy andnonassumption of additivity yield
vastly more information and whose limitations regarding generality of conclusions can
be a r s e w d in light of interaction terms.
Similarly, there is a need for increased numbers of levels i n factors under investigation.
Testing subjects under. light and.-dark tells
The erlablishiog of validity u always tenuous, for nothing about the precise relationship bein the long rua validit!: b determined by whether tween behavior and level of illumination
the %ajority oi inrrsti~alars,or at least t h c most unless demonstrably untenable mumptions of
outspoken, believes the external criterion to hare linearity are made. Similarly, comparing two
been adequak. (Candland k Nagy. 1969, p. 841)
species or strains tells nothing of the genetic
Such has largely been tlie case in the open basis of behavioral differences: whereas an
field, but this consensual validity must now approach such as the diallel cross, which afrest on the b g i s of further criterion and fords a large number of precisely quantifiable
construct validity testing, for which, in addi- genetic levels, allows very detailed psychotion to the correlational studies which form genetic analysis. Failure to perform temporal
the basis of most convergent validity testing analyses of behavior discards large amounts
(h'unnally, 1967), factor analysis would seem of information and may result in diminished
sensitivity.
particularly suited.
For dependent parameters, there is a great
need for reliability and validity testing for a
I t is obvious in reviewing this area that wide range of conditions and subjects. >.Ian?
many of the all-too-numerous discrepancies, papers base far-reachinr assumptions and
failures of replications, and contradictions conclusions on parameters whose reliability
stem from preventable methodological and and validity remain unproven. The wider use
experimental design causes. Many o i these of physiological variables, particularly bio-
so?
.
.
.-
ROGER X. WALSH k
\KJ ROBERT A. C U J 1 M ~ ' S
chemical and electropbysiologicaI, .and the
determination of their relationship to behavioral
would seem to hold consider;
able prom&.
,As regards interpretation of behaviors, there
is a need for mnstruct validation' for which
factor analpis and ethologiul data would
seem to be particularly relevant. The former
tendency to regard variable and construct as
almost equivalent and constant across subjkts and treatments must be abandoned except where construct validation indicates that
it is permissible. Individual dependent parameters shouldnot be considered in isolation but
in light of changes in other parameters. This
has been demonstrated particularly ior arnbulation. Finally, the dangers' oi unqualified
generalization acmss genetic, experimental,
and testing backgrounds must be appreciated.
REFEKESCE S O T E
1. Cumminr. R. A,, Vialsh, R. N.. & B u d u - O k n ,
0.E. EnvironmenuUy induced cbango in opcnfield beha\,ior. Paw< prc-tcd
a t Lhe 44th annual
meeting oi Lhc Australian and K e n Z e a l a n d ASOciation ior the .Aduancement of Science, Sydncy,
August 19i2.
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Ader, R. Adrenocortical function and the measuremen1 of emotiooality. .4snolr of !he n'cw Ymk
Acodrm? 01 S d m c t , 1969. 159. 791-S95.
Archer, J . Tests for emotionalit? in rots azd mice:
A revira. Animal Bthocior, lFi3, 2 1 , 20'135.
Barrett, R. J., 8 Ray, 0. S. Behavior in Lhe openfield. Lashley I l l m ; r e , l u t t l e box, and Sidman
avoidance as a function of m a i n , sex and age.
Dcorlopmcnfal Psychology, 19i0, 3, i3-ii.
Battig. K. Drug r6erts on caploration of a combincd
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the X t w l'ork .4rodtmy o! Sdcnce, 1969, 159,
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Bindra, D., & Spinner, N. Raponse to dinerent
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Broadhunt. P. L. Psychogenetits of emolionalily in
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Broadhunt, P. L., k Eysenck, H. J. lnterprctationr
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Bruell. J . H. Brhasioral hetcrasb. In J . Hirwh
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Candland. D. K..'9: S ~ F , Z. h1. Thr Open-Field:
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Clark, C.. Gorman, D.,& Vrrnadlkir, A. EBects o!
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iO, , 2:5-2j5,
Collins. R . L. What clw does thc defecation score
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Dcfries. J. C. H e w n , J. @.,Ross, D., b- Howard
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