CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
EFFECT OF SIZE AND CONTOUR
II
ON SLANT PERCEPTION
A thesis submitted in partial satisfaction of the
requirements for the degree of Master of Arts in
Psychology
by
John Edward Queen
May, 1975
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The thesis of John Edward Queen is approved:
California State University, Northridge
May, 1975
ii
ACKNOhTLEDGMENTS
To the members of my Graduate Committee for their
constructive guidance, a warm thank you.
To Dunlap
and Associates, Inc., a most appreciative thanks for
allowing me the use of the equipment and facilities
that made this research possible.
I am especially
grateful to Dr. Joseph W. Wulfeck for his suggestions
and assistance throughout this project.
----- --~-----
iii
.
··--·-·-· --· ................ ....................
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TABLE OF CONTENTS
Page
ACKNOWLEDGMENT
iii
ABSTRACT
vii
INTRODUCTION
1
METHOD
9
Experimental Design
9
Subjects
9
Stimuli
10
Apparatus
10
Procedure
16
RESULTS
20
DISCUSSION
27
CONCLUSIONS
37
SUGGESTED RESEARCH
38
REFERENCES
39
APPENDIX
41
Instructions
42
Equipment Schematic
46
Equipment Parts List
47
Raw Data
48
iv
LIST OF TABLES
Table
Page
Stimulus Dimensions and Visual Angles
for the Small Size Contours
11
Stimulus Dimensions and Visual Angles
for the Large Size Contours
12
Mean Error Scores and Standard Deviations in Judging Horizontal Plane
21
4
Summary of Analysis of Variance
24
5
Summary of the Tukey's Test (a=.05)
Between Pairs of Means
1
2
3
v
i
'
l,
25
...... ---· ----·--···;--····- -·---------·--·---·-
···~--------··
......... --·····-.--------·-·-···
--------·--···--·---·------~-~---~-·-··------------------·---»·-·-·--·.
------------- -"i
.
I
!
LIST OF FIGURES
Figure
:f
Page
1
Visual angles to near and far edge
3
2a
Slant referenced to frontal-parallel
plane with axis of tilt rotated about
the horizontal
6
Slant referenced to frontal-parallel
plane rotated around a vertical axis
6
Slant referenced to horizontal plane
rotated around the horizontal axis
6
2b
2c
3
Relative stimulus size and contour
13
4a
Simplified diagram of tilting box
14
4b
Block diagram of recording system
14
5
Judged horizontal plane as a function
of contour and size
22
vi
ABSTRACT
EFFECT OF SIZE AND CONTOUR
ON SLANT PERCEPTION
by
John Edward Queen
Master of Arts in Psychology
May, 1975
Six male and six female observers judged the point at
which slowly moving contours appeared to be level with the
horizontal plane under complete reduction conditions.
different contours were judged at two size levels.
Seven
Four of;
the contours were converging trapezoids while two contours
were diverging trapezoids.
straight line.
The seventh contour was a
Judgments for the seven contours were
ficantly different,
signi~
(p < .001), as was the interaction
between size and contour (p
<
.05).
The converging and
diverging contours were found to be judged differently
(p
<
•
01) .
No differences due to size or sex v1ere found.
Contour was concluded to be the dominant cue for slant perception in the horizontal plane.
The possible existence of'
a visual receptor system that responds to orientation of
contours in the horizontal plane is discussed.
vii
INTRODUCTION
The theoretical explanations of slant perception have
been in controversy over the years.
pretations have been widely explored.
Two differing interOne of these theories
has become known as texture gradient theory and its chief
proponent is Flock (1964a, 1964b, 1964c, 1965).
Flock
emphasizes complex stimulus variables including texture
gradients and motion parallax.
Flock (1964b) states that
slant perception can be determined from the angular motion
ratio in light reflected to the eye from a slanted and
moving surface.
A different explanation has been argued by
Freeman (1965, 1966a, 196Gb, 1966c, 1966d, 1970).
Accord-
ing to Freeman, contour perspective is the primary cue for
slant perception.
Freeman (1966d) claims perspective theory
will predict the outcome of experiments involving texture
gradients.
While perceived slant will correlate with
texture-element size and regularity of texture, the eye
will not be more sensitive to texture perspective than to
contour perspective.
Contour perspective has been defined differently by
various authors, however, Braunstein and Payne (1969) statei
'
that three of the frequently used definitions are actually
mathematically equivalent.
Freeman (1966d) defines con-
tour perspective as "the difference angle in the projection
of the near edge and far edge" (p. 366).
Contour perspec-
tive varies not only with the slant of a surface, but also
1
1
2
--
·--~·-~~
-·--··-- --
---
--~-~----·--·-·-·-
with its height, width, and distance.
-·-·-
--
- ------ --·-
--~-~-
··--------~----------
_.,
.....
...
--~--~---~ ~-,
Figure 1 shows the
/
I
geometrical relationships for this difference angle defini-
1
tion of contour perspective.
1
I
Freeman (1966c, 1966d) pre-
sents various trigonometric equations for calculating per-
I
I
!
spective values.
The fundamental assumption of contour perspective
theory is that as contour perspective increases, perceived
slant increases.
Clark, Smith, and Rabe (1955) found, in
the absence of other cues, that retinal gradient of outline!
I
induced perception of slant.
When the opposite edges of the
stimuli converged, slant was perceived.
convergence increased judged slant.
Increasing the
Smith (1959, 1964,
1967) consistently found that the greatest variations in
slant judgments were associated with changes in contour
perspective.
The effect was demonstrated for both monocular
and binocular viewing of slanted rectangles (Smith, 1967).
The effect of increasing contour perspective resulting in
greater estimated slant was also confirmed by Dunn and
Thomas (1966) for two trapezoids of differing end ratios,
but constant length.
In a study testing the effectiveness of texture gradient theory in slant estimation, Braunstein (1968) coneluded that accurate discriminations proposed by gradient
theory were not possible.
Instead Braunstein offered the
hypothesis "that perspective is the principal source of
information used by Ss to judge slant ••. " (p. 253}.
3
Figure 1.
Visual angles to near and far edge.
Perspective angle is the angular
difference between the near and far
visual angles, a - 8 •
4
Similarly, Willey and Gyr (1969) found that the "higher
order" Gibsonian variables such as motion parallax, background texture, and binocular disparity had little effect
on monocular slant judgments.
However, the authors caution
that their data did not offer a simple choice between the
theories of Flock and Freeman.
While the basic assumption of contour theory has had
considerable support, other assumed variables have not.
Contrary to the prediction of contour theory that width of
the rectangle should effect slant judgment, Winnick and
Rogoff (1965) found no effect.
They varied the width of
four rectangles viewed binocularly under restricted and
full viewing conditions.
No differences between judged
slants existed.
The effect of size on slant perception is also in
dispute.
Stavrianos (1945) found that observers tended to
overestimate the slant of the larger of two rectangles.
Freeman (1966b) also reported that when the stimulus rectangles are large enough, the larger of a comparison pair
would be more overestimated in slant.
According to Freeman,
size per se is not the important stimulus, but contour
perspective.
Results for the effect of size will be reli-
able· ·only when the stimulus rectangles are large· enough to
present discriminable cues for perspective.
Smith (1967)
found that contour perspective could account for the
apparent size effect reported by Stavrianos because her
5
smaller stimulus pairs were less tall than wide and the
larger pair were less wide than tall.
Smith states that
stimulus height was a relatively ineffective cue and contrary to Freeman's (1966b) findings, there was no association of increase in stimulus height with decrease in judgedj
slant.
The converse effect seemed to be occurring.
The experiments of the various researchers on slant
-'
i
a horizontal axis.
For either case, the range of slants
i
used generated tilt as reference from the frontal-parallel
plane as shown in Figure 2a and 2b.
A recent study by
Wulfeck, Queen and Kitz (1974), investigating the influence
of contour on aircraft carrier landing lights, referenced
slant estimation to the horizontal plane.
This plane is
perpendicular to the frontal-parallel and is diagramed in
Figure 2c.
Wulfeck et al.
(1974) determined slant thresh-
olds for a rectangle and a trapezoid rotated about the
horizontal axis through the horizontal plane.
A slant
threshold of less than one degree was obtained which was
considerably less than Freeman's (1966a) value of 3.55 degrees for the frontal-parallel plane.
The authors suggest
further research on slant perception in the horizontal-plane
is needed to determine if it differs from the frontalparallel plane. _
6
~
Figure 2a.
Frontal-Parallel Plane
Slant referenced to frontal-parallel
plane with axis of tilt rotated about
the horizontal.
Frontal-Parallel Plane
~
Figure 2b.
Slant referenced to frontal-parallel
plane rotated around a vertical axis.
Figure 2c.
Slant referenced to horizontal plane
rotated around the horizontal axis.
7
.. -·
·-·- ........
. .. .
.. . . .... . ... .... ... .... .. .... . . . ..
... . ...........................- .......... ·············--·······1
Another serious methodological problem has been the
1
type of slant stimulus used and its shape relation to the
l
comparison stimulus.
Flock (1965) notes that if the stand- j
dard and comparison are similar in shape, a judgment could
be made on the basis of projective similarity.
i
1
i!
The observer
could then make a seemingly accurate response without per-
I
ii
!
ceiving either object as slanted.
Willey and Gyr (1969)
tested to determine if projective matching could be a confounding variable.
While they found a strong trend for
projective matching, it was not the sole determiner of
observer judgments.
Smith (1967) reports evidence to
criticize Freeman's experiments for allowing the possibility
of projective matching.
Smith claims to avoid this problem;
by using a rod as the comparison stimulus.
The rod has no
projective shape and would thus be an accurate indicator
of judged slant.
However, Freeman (1966b) argues that the
incorrect choice of comparison stimuli may account for part!
of the poor correspondence found in the literature between
judged slant and shape.
Contour perspective theory as an explanation of slant
perception is thus beset with at least three problems.
First, do the predictions of contour perspective apply to
the horizontal plane?
Secondly, what is the effect of
stimulus size on slant perception?
Thirdly, how does pro-
jective matching affect judgments of slant?
It is the purpose of this study to investigate directly
the first stated problem.
Within the context of determining
8
slant threshold
in~-ihe
horizontal plane, ·the. -se-concf·a:ncf________
third problems will also be investigated.
Specifically,
two experimental variables will be explored; contour and
size.
The effects of various levels of contour and size
on judged slant from the horizontal plane will be analyzed
with respect to predictions from contour perspective theory
The problem of projective matching will be eliminated by
-'\
the use of a method which does not require a comparison
stimulus.
The two predictions of contour perspective theory for
effect of contour are:
1.
the greater the convergence angle between
opposite ends of the figure, the greater
the perceived slant.
2.
if the perceived convergence angle is reversed
so that it is perceived as a diverging angle,
the perceived slant in the plane will also
reverse.
For the effects of size, contour perspective theory
predicts that if size increases so that the contour perspective of the shape increases, the perceived slant will
also increase.
i
I
~-·-·····-------·-----------------------··--------··-------1
METHOD
Experimental Design
The subjects were required to judge, using binocular
vision, the point at which slowly moving trapezoidal contours were level (not slanted) with the horizontal plane.
Subjects made eight judgments on each of seven contours at
two sizes.
Therefore subjects viewed 14 stimuli and made
112 judgments.
The procedure was a modification of the
psychophysical method of average error, in which judgments
were made about a single stimulus.
Use of a comparison
stimulus was not required.
The seven contours consisted of four converging trapezoids (normal perspective) , two diverging trapezoids
(reverse perspective) , and a straight line (lack of
spective) .
per~
The two sizes were such that the large size
was twice the dimensions of the small size.
The dependent variable was the angular error from the
horizontal plane of each judgment.
Subjects
The subjects were six male and six female paid volunteers.
Their ages ranged from 19-31 years old.
The mean
age for males was 24.5 years and for females was 24.0 years
All subjects had normal or corrected to normal vision and
those that wore corrective lens did so during the experiment. ·upon completion of testing, each subject was paid
$7.50.
9
10
r·······"~-·-····-"'··-····-·-·-·---··~··--····'-"···~··--·····-·-···----~···~·,·---··--· ---~-·------~---·-····-----~--~---"--""~·--~-------------~
I
!stimuli
II
The 12 contour outlines were trapezoidal shapes whose
I:
I
!edges were defined by point sources of light.
I
-
The contours :
I
!thus
appeared similar to airport runway lights.
I
Each length
!edge consisted of 16 equally spaced point sources and each
I
ridth edge was seven equally spaced point sources.
Tables
11 and 2 list the stimulus dimensions, contour ratios, and
!
.
!
!corresponding visual angles.
Figure 3 illustrates the rela~
tive shapes at both sizes for the four converging trapezoids (CT1-CT4).
1
~hich
I
Also disp_layed is the straight line (SL) ,
was a column of 16 point sources.
I
I
The two reverse
!trapezoids (diverging contours) were obtained by turning
I
!stimuli CT2 and CT4 end for end.
The former is referred to
as RTl and the latter as RT2.
The stimuli were constructed of 20 mil. opaque, black
\plastic.
The point sources were made by drilling 2.1 mm
!holes. through the plastic.
The stimuli were illuminated
lby being placed on a light box.
,Apparatus
The apparatus used in this experiment was the same
used by Wulfeck et al.
(1974) and is diagramed in Figure 4a
A tilting light box, which measured 3.66m x 0.46m x 0.23m,
lwas constructed of 0.48cm sheet aluminum.
The top was
0.64cm plexiglass with its bottom side sandblasted to form
a diffusing screen.
I
Inside the box were two equally spaced :
i
!columns of three 40 watt fluorescent lamps (GE #F40/DW/RS). '
L---···------···-----------~~------k------------------------- ------·-------~--~----------------------------·-·-J
.
Table 1
Stimulus Dimensions and Visual Angles for the Small Size Contours
Height
Visual Angle
At Level
Perspective
Angle
At Level
Contour
Near Edge
Far Edge
Length
End
Ratio
CTl
16.03cm
16.03cm
156.97cm
1.00
1.04°
.390
CT2
16.03cm
8.56cm
156.97cm
.54
1.04°
1.01°
CT3
16.03cm
4.29cm
156.97cm
.27
1.040
1.37°
CT4
16.03cm
2.24cm
156.97cm
.14
1.04°
1.540
RTl
8.56cm
16.03cm
156.97cm
1.87
1.040
-
RT2
2.24cm
16.03cm
156.97cm
7.16
1.040
-1.09°
156.97cm
--
1.040
SL
--
--
1.
Eye height above level stimulus
2.
Viewing distance
=
=
.41°
42.16cm
609.6 em
!-'
!-'
Table 2
Stimulus Dimensions and Visual Angles for the Large Size Contours
Height
Visual Angle
At Level
Perspective
Angle
At Level
Contour
Near Edge
Far Edge
Length
End
Ratio
CTl
32.08cm
32.08cm
313.94cm
1.00
2.2°
1.64°
CT2
32.08cm
17.15cm
313.94cm
.54
2.20
2.76°
CT3
32.08cm
8.57cm
313.94cm
.27
2.20
3.400
CT4
32.08cm
4.45cm
313.94cm
.14
2.20
3.70°
RTl
17.15cm
32.08cm
313.94cm
1.87
2.2°
-
RT2
4.45cm
32.08cm
313.94cm
7.16
2.20
-1.82°
313.94cm
--
2.2°
SL
--
--
1.
Eye height above level stimulus = 42.16cm
2.
Viewing distance from center of stimulus
.24°
= 609.6cm
·-····--· .....,.
----~-~-. -~-··------~-
·--·------..
- ·--- ---···--·-
··~-·-·· -~~--------------····-~--....!
1-'
N
13
rc-- --------- ,. _____.. _____, --·--------· --------
------------·-------~---
------------------·----------------·---------------..-------------
-~----
-------------1
I
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i
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f
!
Small Size Contours
CTl
CT2
CT3
'
CT4
SL
RT2
RTl
Large Size Contours
CTl
CT2
RTl
Figure 3.
CT3
CT4
SL
RT2
Relative stimulus size and contour.
NOTE: Hole diameters are shown oversized
and because of this some holes have been
omitted from the convergent ends of small
sized stimuli CT3 and CT4.
14
Figure 4a.
Simplified diagram of tilting light box.
Illustrated with lighted trapezoid having
an end ratio of one.
DVM
Posi+100 VDC
-100
~on
VDC ~~
~
v'lO=~'>------..;
Continuous
Display of
Position
DVM
~ Subject's Error
Jj
Mechanically Coupled
Sample-Hold
r------l'--1---,
Reversible
Motor
Programming
System
±3.5,3.0,2.5°
Photo Transistors
Figure 4b.
ON
Subject's
Response
Switch
OFF
Lights
Block diagram of recording system.
(Adapted from Wulfeck et al., 1974)
15
At the longitudinal center of the box was a steel axle.
The light box was mounted to an aluminum supporting frame
by passing the axle through ball bearing pillow blocks.
A
reversible, variable-speed electric motor was mounted below
the box on the supporting frame.
The box was tilted by a
drive chain connected to both ends of the box and coupled
to the motor by a sprocket.
The motor was adjusted so the
angular velocity of the box was 0.5 degree/second.
When a
plastic stimulus sheet was placed on top, the box was lighttight except for the point sources.
The control of the light box was fully automated by
the use of solid state logic gates, opto-electronics, and
relays (see Appendix for complete diagrams).
The control
circuitry provided six sets of eight ascending and descending presentations which were appropriately assigned to begin
at one of three angular offsets from the horizontal plane;
3.5, 3.0 or 2.5 degrees.
Assignment was random except for
the constraints that there be an equal number of ascending
and descending trials and that the 3.0 degree offset occur
twice for each series.
A 2000 Hz tone of one second
tion alerted that a trial would begin.
dura~
The time between
tone and stimulus presentation varied between 2.0, 2.5, or
3.0 seconds depending on which of the three angular offsets
was selected.
The recording system is block diagr.amed in Figure 4b.
A precision (0.1 percent linearity) multi-turn potentiometer with a center-tap was coupled directly to the electric
16
motor drive shaft.
computer supplied a stable ±100 VDC (±0.01 percent) reference to the potentiometer inputs and scaled the output so
that 10.00 VDC was equal to one degree of slant from the
horizontal plane.
A positive voltage indicated the near
end of the stimulus was above the horizontal, whereas a
negative voltage meant the near end was below.
When the
subject pressed the response switch, a digital voltmeter
(DVM) displayed and held the angular error until the switch
was pressed again.
A second DVM gave a continuous reading
of stimulus position.
±0.1 percent.
Both DVM's had an accuracy of
A precision plate level (Geier and Bluhm
Model 4-2012) accurate to ±0.02 degree was used to calibrate the zero position of the potentiometer.
The relia-
bility of the recording system, based upon 50 calibration
trials, was ±0.1 percent.
The intensity of the point sources or light was
300 ft. C measured on-axis by a Spectra Pritchard Photometer
(Model 1980).
The AC line voltage to the fluorescent
lamps was monitored during the experiment and was found to
range ±1.5 percent of 120 VAC.
According to the lamp
speci~
ficationsr intensity could also have varied ±1.5 percent.
Procedure
Assignment of stimulus conditions to subjects was done:
in the following manner.
For each group of males and
females, half the subjects were randomly assigned to receive
17
the small sized stimuli first.
the large size first.
The other half would view
The order of the contour stimuli
presentations was randomly assigned across sizes and
subjects.
The subject made a series of eight judgments on a
given stimulus.
Within the series an equal number of
ascending'and descending trials occurred in a randomized
order.
The trials were randomized orderings of the follow-
ing starting positions from level; 3.5, 3.0, and
2.5 degrees.
At the beginning of the experimental session, the
subject was given a set of instructions to read which
included the following scenario:
"You are going to be a subject in an experiment
to determine young women's and men's ability to
judge when an aircraft carrier deck is horizontal
under different conditions at night. The results
of the experiment will help reduce the number of
night carrier landing accidents and will also help
civilian pilots who may land on small airfields at
night."
A condensed version of the remainder of the instructions is
stated below.
"We'll make eight trials in a run viewing a deck.
shape. When a trial starts, you'll hear a little
"beep" signal. A second or so after the "beep"
the deck lights will come on and they'll be moving
slowly toward the horizontal from either a bow up
or bow down position. Push the switch in your hand
when the deck seems to you to have moved to exactly
horizontal.
"Now a last ~vord about the decision itself. You
have a pretty good idea of what's horizontal in the
world around you and you move around in it with a
18
lot of horizontal references all the time. In
this situation, there won't be any references.
All you'll have to work with will be the deck
lights and your own sense of where the horizontal
is. Once you've developed a judgment scheme, do
your best tci stick to it all the time."
Following the instructions, the subject was shown the
tilting light box and viewed its operation.
Any questions
the subject had concerning the task were answered at this
time.
The subject was then seated in a chair fitted with an
optical head holder.
The holder was adjusted so the subject
was 6.096m from longitudinal mid-point of the stimuli and
the eye height above the level stimuli was set to 42.164cm.
The eye to center of stimulus distance was therefore
6.lllm.
The lights in the laboratory were then turned off and
after one minute, the first stimulus was shown to the subject in a stationary position.
The subject was cautioned
not to assume the stimulus was at level.
the stimulus was turned off.
After 15 seconds
The subject again sat in
total darkness for one minute before the eight judgment
trials began.
Following the trials, a low level red light,
shielded from direct view by subject, was turned on to
allow the 'experimenter to change stimuli.
imately 2.5 minutes.
This took approx-:
The red light was extinguished and
after one minute, the subject viewed the next stimulus in a
stationary position.
Then after one minute in darkness,
the next eight judgments began.
This same procedure was
19
"" ""-"
""
-"" '"
c
""
-
-
""-- "'"
--~-"-"'
"'
""" __________"
-,--
"
-------
- - '""
c-
''" "----- -'"·-·------,---------"
followed for all seven stimuli at a given size.
_ _ _ _ _ ,,_,,,,
The
subject was given a 10 minute rest between viewing the set
of stimuli of the other size.
level red illumination was on.
During this rest the low
The remaining stimuli were
then presented with the same procedure as before.
experimental session lasted for about two hours.
The
l
~-y·-~·-,.-·-•-v<<'"''~~~~·•--"-~·,m•~
~·•·•·--·--~-·-~-~·~-·-••--,.,~-----~·----~~~
!
RESULTS
i
The mean of the eight judgments the subject made on a
I
stimulus was used as the error score in the data analysis.
Table 3 shows the means and standard deviations of error
judgments classified according to sex, size, and contour.
Figure 5 is a graph of the combined error means for
:
'I .
!
'
males and females plotted for every contour as a function
of size.
Examination of the graph reveals that the error
scores have clustered according to the three contour classiJ
fications.
The converging trapezoids (CT1-CT4) were judged
i
more accurately than the reverse trapezoids (RTl and RT2)
or the straight line (SL) •
The graph also reveals an inter-
action between size and contour.
The converging trapezoids
decreased in error as size increased, whereas the reversed
trapezoids increased in error.
As expected, size had no
simple main effect on judgments of the straight line.
The ordering of the contours at each size does not
fully support contour theory, especially at the larger
size.
At the small size, the converging contours were
ordered:
CTl > CT2
= CT3
>
CT4.
CT2 should have been
greater than CT3 for perfect agreement to theory.
order for the large size was CT2
>
was not expected by contour theory.
were ordered RTl
>
CT4
>
CTl
>
The
CT3 which
The reversed contours
RT2 for both the small and large size
which is the opposite of what was predicted.
20
21
Table 3
Mean Error Scores and Standard Deviations in
Judging Horizontal Plane
Small Size Contours
CTl
CT2
CT3
CT4
RTl
RT2
SL
-X
1.14
.99
.94
1.00
1.19
.94
1.31
(J
1.15
.81
.92
1.05
.93
1.08
.95
-X
.15
.26
.31
.12
.55
.65
.79
(J
.97
.94
.85
1.31
1.27
1.24
1.21
x
.65
.62
.62
.56
.87
.80
1.05
o
1.22
.98
.98
1.32
1.21
1.22
1.17
RTl
RT2
*Male
*Female
** Male
+
Female
Large Size Contours
CTl
CT2
CT3
CT4
SL
-X
.51
1.07
.56
.85
1.38
1.49
1.24
(J
.74
.86
.66
.57
.62
.73
.85
X
.28
.09
-.23
.12
1.08
.95
.82
(J
.77
1.00
.97
1.21
1.15
1.12
1.11
-X
.40
.58
.17
.49
1.23
1.22
1.03
(J
.80
1.10
.96
1.06
.98
1.02
1.05
*Male
*Female
**Male
+
Female
Positive values of means indicate near end of stimulus
above level
Negative values indicate near end below level
CT1-Cf4 are converging contours
RTl, RT2 are diverging contours
SL is the straight line
*Mean
**
is based on 48 responses
Mean is based on 96 responses
22
Positive indicates near end
of stimulus was above the
horizontal plane.
+1.2
+1.1
+1.0
+0.9
SL
RTl
til
Q)
Q)
+0.8
$-1
RT2
0'1
Q)
Q
+0.7
~
·r-1
$-1
0
+0.6
$-1
$-1
~
$-1
CTl
CT2
CT3
CT4
CT2
+0.5
Ctl
r-1
::1
tJl
~
+0.4
~
+0.3
+0.2
CT3
+0.1
0
Small
Large
Size
Figure 5.
Judged horizontal plane as a
function of contour and size.
23
~
.
~
-
----~
-·"·-
-
• •
••>-•~-••
~ ••··~r~~-
A five-way analysis of variance was conducted on the
error means.
The main effects tested were Sex x Order x
Size x Contour x Subjects.
Subjects were nested in Sex
and Order, with Size and Contour serving as within-subject
variables.
The results of this analysis are summarized in
Table 4.
The only significant main effect was for Contour,
F (6,60)
=
8.58, p
<
.001.
F (6,60) = 2.62, p
<
.05, was the only one to reach to
statistical significance.
The Size x Contour interaction
1
Referring to Figure 5, it appearJ
i
that the interaction between the normal contour trapezoids
and the reversed contour may account for the lack of main
=
effect for Size, F (1,10)
.005, p
>
.05.
A Tukey's Test of all pairs of means resulted in two
pairs that differed significantly (p < .05).
Both were at
the large size and were CT3 - RTl, and CT3 - RT2.
All other
pai_rs were not significantly different as summarized in
Table 5.
It appears that, within a contour classification,
neither size nor amount of contour convergence were effective variables.
To determine whether, as a group, the converging contours were judged more accurately than the diverging contours a Scheffe's Test was used to compare the grouped
means.
The 0.99 confidence interval was computed to be
0.231
<
T1 - T2
<
1.175
24
......
·-·--~·--~-.~ --~- ~
~~~·-"----.-.-
,.,.._.,. --
-.--~----~"--~-·~~---~-~~-~·---~~-·--·--~----" ---~
..
-~--·- --~-7-.
··~-~ --·-~----
..
-~------->•···-
·--~~·---~·---- -~-----....
Table 4
Summary of Analysis of Variance
Source
df
MS
Error
Term
F
Sex (A)
1
16.08
S(AxB)
1. 38
Order (B)
1
23.79
S (AxB)
2.04
Size (C)
1
0.002
CxS(AxB)
0.005
Contour (D)
6
1.97
DxS(AxB)
7.53
AxB
1
12.71
S(AxB)
1.09
Axe
1
0.09
CxS(AxB)
0.16
BxC
1
0.03
CxS(AxB)
0.05
AxD
6
0.18
DxS{AxB)
0.70
BxD
6
0.05
DxS(Axb)
0.17
CxD
6
0.59
CxDxS(AxB) 2.42
Subjects (S (AxB) )
8
11.68
AxBxC
1
0.96
CxS(AxB)
1.60
AxBxD
6
0.15
DxS(AxB)
0.60
AxCxD
6
0.20
CxDxS(AxB) 0.82
BxCxD
6
0.07
CxDxS(AxB) 0.29
.CxS (AxB)
8
0.60
DxS(AxB)
48
0.26
6
0.24
48
0.24
AxBxCxD
CxDxS(AxB)
CxDxS(AxB) 0.98
p
< 0. 001
<0.05
·Table 5
Summary of the Tukey's Test (a=.05) Between Pairs of Means
Contourl
Mean
LCT3
.17
LCTl
.40
LCT4
.49
CT4
.56
LCT2
.58
CT2
.62
CT3
.62
CTl
.65
RT2
.80
RTl
.87
LSL
1. 03
SL
1.05
LRT2
1.22
LRTl
1.23
LCT3
LCTl
LCT4
CT4
LCT2
CT2
CT3
CTl
RT2
RTl
LSL
LRT2
LRTl
.17
.40
.49
.56
.58
.62
.62
.65
.80
.87
1.03 1.05 1.22
1.23
0
• 23
.32
.39
.41
.45
.45
.48
.63
.70
.86
.88 1.05* 1.06*!
0
.09
.16
.18
.22
.22
.25
.40
.47
.63
.65
.82
.83
0
.07
.09
.13
.13
.16
.31
.38
. 54
.56
.73
.74
0
.02
.06
.06
.09
.24
.31
.47
.49
.66
.67
0
.04
.04
.07
.22
.29
.45
.47
.64
.65
0
0
.03
.18
.25
.41
.43
.60
.61
0
.03
.18
.25
.41
.43
.60
.61
0
.15
.22
.38
.40
.57
.58
0
.07
.23
.25
.42
.43
0
.16
.18
.36
.37
0
.02
.19
.20
0
.17
.18
0
.01
SL
0
1 "L" in front of contour code indicates large size contour
*
Significant difference
~·---.- . . . . . . . .
_ _ _ _,,.
>
~.96
• • • • • • • • • ~ .. · · · · · · - - - - - .. - . -• • •
·--· ....... -
...
~-----···"
._........
~~·-·······~
·-···
...........
N
U1
"'
26
Thus, at the a
=
.01 level, the eight converging contours
considered as a group produced less error than the four
reversed contours.
A Scheffe comparison between the grouped means of the
small size converging contours and the small size reversed
contours yielded a 0.95 confidence interval of
-0. 221 < TC - TR <
0. 657
Since this interval includes zero, the hypothesis of equal
judgments between the small sized contours was not rejected.
DISCUSSION
The purpose of this experiment was to determine if
three of the basic predictions of contour perspective
theory generalize from the frontal-parallel plane to the
horizontal plane.
The results offer only partial support
for the predictions of contour perspective theory.
The
basic prediction that greater perspective angles would
result in greater perceived slant was not fully supported.
The prediction that increased size would cause increased
judged slant was also equivocal.
The significant finding
of this experiment was the difference in slant perception
between the converging and diverging (reversed) contours.
This result is interpreted as supporting contour perspective theory.
The lack of effect for increasing perspective angle
was unexpected due to the strong support reported in studies
of slant perception referenced to the frontal-parallel
plane and also from one study (Wulfeck et al.,
erenced to the horizontal plane.
1974) ref-
Wulfeck et al. found
that a trapezoid shape was judged more slanted than a
rectangle shape of equal length.
The effect was ·found over
three sizes of stimuli; the largest size being equal to the
small size of the present study.
Contours CTl and CT2
correspond to the rectangle and trapezoid used by Wulfeck
et al.
The judged errors and standard deviations for these
contours in the present study were 0.65±1.22 degree and
27
28
-··"-- ..
-·~---
..
-·~---··
-~---
-~_.
.. '""" ··-- ...
~~---- ~-
.--
~---
--~--
-- _____
,__, __
---- .. -
0.62±0.99 degree, respectitely.
~-
••""
... --···· -----·
--
. - '""
~-
-· ---.-- .......
.
... -
--~~-
-~
,---·· ----------- --- ..
Those for Wulfeck et al.
were 0.65±0.43 degree and 0.38±0.46 degree.
However, the
subjects used by Wulfeck were all highly screened ROTC
college students, while the subjects in the present study
were not.
This difference in subject populations may
account for the increased variability in slant judgments
between the two studies.
The effectiveness of contour in
producing a difference in perceived slant in the horizontal
plane may interact with the specific population tested.
Another possible explanation for lack of effect for
increasing contour perspective is that the effectiveness of
contour convergence may be lessened by outline distortion
or the internal dynamics of the figure (Smith, 1959).
The
outlines of the figures in the present experiment were
formed by point sources of light and because of this, an
intensity gradient was present.
The intensity of this
gradient varied as a cosine function of slant from the
horizontal plane.
Thus the effect of contour on perceived
slant may have been reduced by competing slant information
present in the intensity gradient.
The effectiveness of
such gradients have been minimal as compared to the effect
of contour on perceived slant from the frontal-parallel
plane, but may be more effective in the horizontal plane.
It should be noted however, that the problem of luminance
gradients is not peculiar to point sources.
Freeman (1966b)
points out that a gradient in luminance will occur if a
29
stimulus is large and slanted more than 40 degrees fr;~~-th;;--j
frontal-parallel plane.
This gradient results from differ-
i
ential reflectance from the surface of the figure and varies
with angle of incidence.
The fact that the contours in the present study were
formed by discrete points and not a continuous edge boundary should not have influenced the effect of contour.
Smith (1959} had subjects judge the slant of rectangles and
i
trapezoids with three degrees of impoverished outlines.
!
i
The conditions included a continuous edge; four corners
without sides; four sides without corners; and only the
two longitudinal sides.
The results showed that the closure
of the figure was not directly related to accuracy in
judging slant.
The predominant influence on judged slant
was contours.
The most likely hypothesis for not obtaining the predieted contour effect is related to the shape-slant invariance problem.
Beck and Gibson (1955) note that Koffka
(1935} postulated-that slant and shape perception were psychologically linked together so that if one changes the
other also changes.
An impression of shape is never
obtained without an impression of slant.
Thus, the ration-
ale in contour perspective theory for why increased contour,
is perceived as more slanted is that the observer thinks the
contour is the result of viewing a slanted reference shape.
For example, an unslanted trapezoid is judged to be a
30
"'····-··- ··-- ...... -··---·-··
--- ·-- ....... --··· .. ----- ---····--· -- ----------·· -------------·-------------- -·-··-·
- ----·-----'----------· ----------··---··--·----------------·l
slanted rectangle, if the observer is told he is viewing a
slanted rectangle (reference shape).
i
In the present study,
observers were instructed they would be viewing shapes
that were trapezoids.
The implicit task was therefore to
ignore shape or convergence cues and set the figure to
vertical horizontal.
The observer's knowledge of the shape!
he was viewing may have worked against the retinal contour
image.
While the retinal image for the most convergent
shape should have caused the greatest perceived slant, the
observer may have compensated his judged slant because he
knew the contour convergence was primarily due to shape,
not slant.
Such a compensatory tendency is hypothesized
by Winnick and Rogoff (1965, p. 562) as "an effect additional to the shape-slant relationship and sometimes
opposing it."
The likelihood of this compensatory process
to have been operating in the current experiment seems very
high.
The strongest support the present study gives for the
effect of increasing levels of contour convergence is
evident when the effects for size are interpreted as due
to perspective angle.
Tables 1 and 2 indicate that per-
spective angle increases for the converging contours as
size increases.
Referring to Figure 5, the trend of
decreasing error from small to large size is taken as
supporting contour theory.
The theory implies that the
larger size be perceived as more slanted and therefore
31
be set level in a different plane than the smaller.
For
i
example, if a small converging contour had been adjusted to'
I
the observer's satisfaction that it was level and then the
/
corresponding larger contour was presented in a parallel
plane to the smaller, the larger would appear more slanted.
This analogy would predict an opposite effect on perceived
slant for the diverging contours, as seen in the graph and
reflected in the significant interaction between size and
shape in the analysis of variance.
The significance of the main effect of contour was
found to be between the converging and diverging contours.
When these contours are considered at each size, only the
'
means for the large size differ significantly between these !
two groups.
However, the grouping of the contours at small
'
i
size indicates that there is a trend for a contour effect at
the small size, which probably would have been reflected ini
i
,.
;
the differences between means if a larger sample had been
used.
It is likely that a larger sample would also have
classified the judgments of the straight line as being sig- ;
nificantly different from the two types of contour.
In light of the previous discussions of possible
effects of an intensity gradient or compensatory behavior,
the difference between the converging and reversed contours
demonstrates the influence of contour on slant perception
in the horizontal plane.
The interaction between these
two contour groups is predicted from contour perspective
theory, while intensity gradient or compensation should
32
...
·····--- ..
---"
- -- - . ----· -- ----have nulled out this interaction if either were the dominant
..... ,
--~--
.
""
cues in the experiment.
------··------------~······
~--··
--~
--~
-~-
The intensity gradient would allow
slant judgments independent of contour as purposed by
texture-gradient theory.
Compensation bias would require
the observer not to respond to retinal image only, but to
use his knowledge of.the contour and therefore not be
"misled" by the convergence or divergence of the image.
The results show that judgments were strongly influenced
by contour.
Between the possible cues for slant perception
operating in this experiment, contour perspective is the
dominant cue.
Contour perspective theory maintains that slant perception is basically determined by the geometrical properties of retinal images.
Freeman {1970) proposed that
physical size and distance, shape and slant of objects in
space are all specified in terms of visual angle subtense.
He states that "the eye responds solely to visual-angle
differences projected by the contours of objects at different distances" {p. 75) •
In the present experimental situa- l
tion two different visual-angles were available as cues.
l
;
The first is the perspective angle formed by the convergence
or divergence of the near and far ends of the figure.
The
second is the angle formed by the projected height of the
length of the figure.
The straight line stimuli were a
test of slant judgments in the absence of contour.
The
data show that the error judgments for the straight line
33
were not different from those for the contour shapes.
Freeman's hypothesis that the eye is only responsive to
contours is not supported by these findings.
Apparently
accurate slant judgments can be made on moving stimuli in
the horizontal plane that have no contour.
Freeman (1970) does maintain that slant perception is
a complex function of bo'th contour and height visual angle.
However, for the straight lines, height visual-angle cannot
explain the obtained results either.
The height visual~
angles at error settings for the small and large straight
lines were 0.77 and 1.63 degrees, respectively, yet the
mean angular errors for the two sizes were virtually the
same, 1.05 degrees for the small and 1.03 degrees for the
larger.
Thus two apparently different visual angles yielded
the same angular error.
The absolute value of visual-angle
height cannot be the cue to the slant of the straight line.
Similarly, it is doubtful that the intensity gradient
from the point sources of light could have been the cue
used to judge both sizes level at the same angle.
The near
point sources on the larger size were 20 percent closer than
the small ones and correspondingly the far ones were 20 percent farther away than the small.
The value of the inten-
sity gradient would be different for the two sizes when set
to the same angle.
Also, the angular relation between
individual point sources and the observer's eye are not the
same for the two sizes.
This is so because the near end
34
•••"'••->
••-•
co.-•---
-~·--.•-
••••~-"'·"-
•-•••
··-·••·•-•••••••·~---·••-•--
would be higher and the far end lower on the larger size
than the respective ends on the smaller size when set at
the error means.
The possible information offered by the
light sources is different for the two sizes when at the
same angle from the horizontal plane and would not be a
likely explanation of the obtained equality of judgment.
The results for the straight lines and the small effect
for increasing angles of contour suggest that angular subtenses are not the only cue to judgment of the horizontal
plane.
The mean error across all contours and sizes was
0.74 degree.
The accuracy with which slant threshold from
the horizontal was determined in this experiment and the
study by Wulfeck et al. indicate the pOssible existence of
a specific detector system sensitive to orientation in the
horizontal plane.
It is hypothesized that such a system
would be sensitive to the relative motion of the ends of
a stimulus.
The stimuli in the present research were
rotated about their longitudinal midpoint.
Therefore, as
the near end was ascending, the far end was descending and
vice versa.
The rate of change of this motion, either for
the ends considered separately or as a difference between
the ends, would be the probable stimulus dimension.
The hypothesized horizontal plane detector system would
be a complex integration of various types of detector cells .
of th visual cortex.
Sekuler (1974) points out that a
single detector cell cannot uniquely specify any property
35
to which it responds differentially.
Complex receptive
fields can be identified that are the integration of many
types of detectors.
However, Sekuler notes that the spe-
cific neural mechanisms of such integrations are in controversy and are under much current investigation.
Sekuler
concludes "information from cells of all types, simple,
complex, etc., is available to whatever centers are interested in such information" (p. 201) .
Braunstein (1968) also concludes velocity gradients
affect slant judgments.
Using computer generated velocity
and texture gradients he found that with no motion, slant
judgments varied with displayed texture.
When a uniform
velocity gradient was displayed, judged slant dropped to
zero, regardless of texture.
Braunstein states "this
demonstrates the inappropriateness of the line of reasoning ·
holding that depth perception requires special sources of
information (cues) and that flatness is perceived when
information from these sources is lacking.
Instead, infor-,
mation in the retinal image, such as a velocity gradient,
may indicate either extent in depth (slant) or flatness.
When information from a given source is eliminated, judgments are made on the basis of other available information"
(p. 252). In terms of the present study, the straight line
is the condition where sources of information have been
eliminated, leaving a velocity or motion gradient to indicate slant in the absence of contour.
36
.--··---~·
... -
-~·-
____ ., __ -·-.
-
,_ ......
'"-~----
.. ... . . ---·--·
,---~ ·---·~·
-· -·····
··---~-
,_,. ____ -·--···-· -· --- -··-··----····----·-·--··----
--~-~--~-· ---~----·---·-" --~··------· ----~~-----··------
•'"*"---,
Finally, the results of this research seem to indicatei
j
that the phenomenal world is slanted away from and down
I
from the frontal and horizontal planes.
I
Freeman (1966a)
found that slant threshold from the frontal-parallel was
3.55 degrees slanted away from the observer.
The current
research has shown that the average judged horizontal plane
was actually slanted 0.74 degrees down from the true horizontal plane.
Taken together, these data imply the per-
ceived world is rotated slightly towards the perceiver, or
conversely, the perceiver is slanted forward.
--- .
------------·CONCLUSIONS
---~-----
------·------·-~---~----.
----_____.__ -·····-----·---------···--·----------'"--!
:
j
1.
Contour is the dominant cue for slant perception
in the horizontal plane.
2.
The judged horizontal plane is slanted down from
the true horizontal plane.
3.
Converging contours appear to be more slanted
down than diverging contours and consequently the converging contours are judged to be nearer to true level
than the diverging contours.
4.
The effect of size on slant perception is related
to contour shape.
5.
The effect of increasing values of contour on
slant perception in the horizontal plane is equivocal.
6.
Motion gradients are hypothesized to be a possible
cue to slant perception in the horizontal plane.
37
1
SUGGESTED RESEARCH
Further research is required to isolate the sources of
slant information available in a moving straight line.
It
is suggested that the rate of motion be varied at both constant rates and
vari~ble
rates.
It is also suggested that
the intensity gradient from one end of the line to the
other end be varied.
For example, make the far end the
brightest or the middle the brightest.
The effects of nonlinear contours on slant perception
might be investigated.
This would be done by using curves,
such as concave or convex, for the contour sides.
38
1.
Beck, J., & Gibson, J.J. The relation of apparent
shape to apparent size. Journal of Experimental
Psychology, 1955, 50, 125-133.
2.
Braunstein, M.L. Motion and texture as sources of
slant information. Journal of Experimental
Psychology, 1968, 78, 247-253.
3.
Braunstein, M.L., & Payne, J. Perspective and form
ratio as determinants of relative slant judgments.
Journal of Experimental Psychology, 1969, 78,
247-253.
--
4.
Clark, W.C., Smith, A.H., & Rabe, A. Retinal gradient
of outline as a stimulus for slant. Canadian
Journal of Psychology, 1955, ~' 247-253.
5.
Dunn, B.E., & Thomas, S.W. Relative height and relative size as monocular depth cues in the trapezoid.
Perceptual and Motor Skills, 1966, 22, 275-281.
6.
Flock, H.R. A possible optical basis for monocular
slant perception. Psychological Review, 1964,
71, 380-391.
(a)
7.
Flock, H.R.
Some conditions sufficient for accurate
monocular perceptions of moving surface slants.
Journal of Experimental Psychology, 1964, 67,
560-572.
(b)
-
8.
Flock, H.R. Three theoretical views of slant perception. Psychological Bulletin, 1964, 62, 110. 121.
(c)
9.
Flock, H.R. Optical texture and linear perspective
as stimuli for slant perception. Psychological
Review, 1965, 72, 505-514.
10.
Freeman, R.B., Jr. Ecological optics and visual
slant. Psychological Review, 1965, 72, 501-504.
11.
Freeman, R.B., Jr. Absolute threshold for visual
slant: The effect of stimulus size and retinal
perspective. Journal of Experimental Psychology,
1966, 71, 170-176.
(a)
12.
Freeman, R.B., Jr. Effect of size on visual slant.
Journal of Experimental Psychology, 1966, 71,
96-103.
(b)
39
40
13.
Freeman, R.B., Jr. Function of cues in the perceptual
learning of visual slant: An experimental and
theoretical analysis. Psychological Monographs,
1966, 80 (Whole No. 610).
(c)
14.
Freeman, R.B., Jr. Optical texture versus retinal
perspective: A reply to Flock. Psychological
Review, 1966, 73, 365-371.
(d)
15.
Freeman, R.B., Jr. A psychophysical metric for
visual space perception. Ergonomics, 1970,
13 (1), 73-82;
16.
Koffka, K. Principles of Gestalt psychology.
Routledge and Kegan-Paul, 1935.
17.
Sekuler, R. Spatial vision. In M. Rosenzweig &
L. Porter (Eds.), Annual review of psychology. Palo
Alto, CA, Annual Reviews, Inc., 1974.
18.
Smith, A.H. Outline convergence versus closure in
the perception of slant. Perceptual and Motor
Skills, 1959, 1, 259-266.
19.
Smith, A.H. Judgment of slant with constant outline
convergence and variable surface texture gradient.
Perceptual and Motor Skills, 1964, 18, 869-875.
20.
Smith, A.H. Perceived slant as a function of stimulus
contour and vertical dimension. Perceptual and
Motor Skills, 1967, 24, 167-173.
London:
21.
Stavrianos, B.K. The relation of shape perception to
explicit judgments of inclination. Archives of
Psychology, 1945, No. 296.
22.
Willey, R., & Gyr, J.W. Motion parallax and projective similarity as factors in slant perception.
Journal of Experimental Psychology, 1969, 79,
525-532.
23.
Winnick, w., & Rogoff, I. Role of apparent slant in
shape judgments. Journal of Experimental Psychology, 1965, 69, 554-563.
24.
Wulfeck, J.W., Queen, J.E., & Kitz, W.M. The effect
of lighted deck shape on night carrier landing.
Inglewood, CA: Dunlap and Associates, Inc.,
October 1974.
i
-,!
APPENDIX
41
INSTRUCTIONS
You are going to be a subject in an experiment to
determine young women's and men's ability to judge when an
aircraft carrier deck is horizontal under different conditions at night.
The results of the experiment will help
reduce the number of night carrier landing accidents and
will also help civilian pilots who may land on small airfields at night.
You will be asked to judge when seven different landing
light outlines are horizontal when you see them from two
different sizes or apparent distances from you.
First, we will show you the apparatus you'll be using,
including the deck moving equipment and your eye-positioning
set up.
Note that the deck can start moving from either a
bow down or a bow up position toward and through the
horizontal.
Next, we'll turn out the lights and show you the first:
deck shape.
Finally, we'll start the experiment.
Once everything
is set-up and your eyes are positioned properly, you'll be
working in the dark with only the deck lights visible during
experimental trials and a pickle switch in your hand for
you to press to record your judgments.
We'll make eight trials in a run viewing a deck light
shape.
When a trial starts, you'll hear a little
42
11
beep 11
43
• . '•• *'>•0
·~··••••"•"•' o•
-··
••··-
-·•'-
-
·•·••
'
••'
~-
- · · · - · - - - • ~--~------·~--~·-•••M'
signal and the deck will start to move in the dark.
A
second or so after the "beep" the deck lights will come on
.and they'll be moving slowly toward the horizontal from
either the bow up or the bow .down position.
Pickle the
switch in your hand when the deck seems to you to have
moved to exactly horizontal.
The different trials will start from the different
down or up positions and from different distances from the
horizontal:
sometimes you'll have only a second or two to
make your decision, other times you'll have five or six
seconds.
So, when you hear the "beep," pull yourself
together and get as alert as you can.
As soon as the deck
lights come on, try to get even more alert.
Pay close
attention to the moving deck and be ready to make your
decision quickly if you have to.
You're going to have to
make very tough decisions ... that's why there are night
landing accidents .•. so it's going to take all your attention to make good ones.
You know a pilot is paying close
attention because his and his passenger's lives depend on
'it.
Try to put yourself in the same position.
A dim light will come on after each run of eight
trials, about every three minutes, and you'll get a brief
rest.
Try to relax as best you can to get ready for the
next run, but stay at your station.
When the light goes
out, another run is about to begin.
After viewing seven
shapes, or about every thirty minutes, you'll get a ten
44
minute break.
Get up and stretch.
Smoke if you wish or
ask for refreshments, but DO NOT turn on any lights and
don't go down to the lighted end of the lab.
If you have
to go to the "John," tell the experimenter and he'll show
you where it is, but DO NOT turn on the lights in' the
"John."
The whole experiment will last about two hours but
you'll get plenty of rest and you ought to be able to stay
in good shape.
Remember, pilots may fly six to eight hours
and then have to make only one decision like you'll be
making •.. and each one could be the most important in their
lives.
Do the very best you can to stay sharp and be "up"
for each decision!
Now, a last word about the decision, itself.
You have
a pretty good idea of what's horizontal in the world around·
you and you move around in it with a lot of horizontal
references all the time.
any references.
In this situation, there aren't
All you'll have to work with will be the
deck lights and your own sense of where the horizontal is.
Use them both the best you can.
In the early trials you
may find yourself using different schemes for making your
decision, like looking at one end of the deck or the other,
looking at the center of the deck, or scanning the deck
pattern.
Once you've developed a scheme that seems to work
for you, do your best to stick to it and use it all the
time under all the different conditions.
45
The last run will be a repeat of.the first one so we'll
know whether you got bored or tired, or stayed sharp or
got sharper as you went along.
We'll let you know roughly
how you did when you're all through.
Re-read these instructions if you wish.
tions you like.
Ask any ques-
Be sure you've got the whole thing before
we begin!
Thanks very much for your time and best effort.
.check will be mailed to you.
Your
EQUIPMENT SCHEMATIC
Fluorescent Lamps
S3
CX2
0
FF2
FFSl
0
,j:::.
"'
Trigger
OS3
·-- -,
I
I
I SRl1
f
I
L-
CXl
OSl
FFl
_..J
OS2
""··--····~-~----~--
., ___ ,..._
---------~-
--------~-~-
..
EQUIPMENT PARTS LIST
Al - A4
=
And Gates (BRS AG-11)
CXl, CX2
=
Input Control Units (BRS CX-10)
Dl, D2
=
Relay Drivers (BRS RD-312)
FFl, FF2
=
FFSl
=
Flip Flop Shift Register (BRS FF-12)
Il - I6
=
Inverters (BRS INV-10)
01
=
Or Gate (BRS OG-10)
OSl - OS3
=
One Shots (BRS OS-10)
Pl, P2
=
Photo Transistors (Fairchild PT2-1000)
Sl, S2
=
SPST Micro-Lever Switch
S3
=
SPST Momentary Contact Switch
SRl
=
28 VDC, 4P25T Reversing Stepper
Relay
SSl
=
Solid State AC Switch (Monsanto
MSR 101)
,Flip Flops (BRS FF-10)
47
~---
___ _._______ ........ --···--··- ...
-··········--·-------~- -~---··-···-
---·- ................ -. ·-----------------··--
·--·------···---·-~----"-"1
l
RAW DATA
Note 1:
The data for each subject is recorded
in the order collected.
Note 2:
A minus sign in front of a number indicates the near end of the stimulus was
below the horizontal plane.
Note 3:
All scores are in degrees.
Key:
M
=
F
= Female
Male
CTl, CT2, CT3, CT4
RTl, RT2
SL
=
= Converging
Diverging Contours
= Straight
48
Line
Contours
49
r·~-----~-----~- -~---~--~-~------~----·-- --~--
. -· · .
--~-
~------- ---·~---~------~ --"~~~----"·------~--~---.,....-·---~--~-·--·~---·----~~q~- ---------~-~----~-,.__.~-~----
..
.....
~-
---~------,
i
Ml
'
Large Size Contours
CT2
CTl
SL
CT3
RT2
RTl
CT4
1
0.74
-1.75
0.05
-0.88
1.40
1.15
0.63
2
-0.39
1.41
-0.83
0.72
1.58
1.58
1.50
3
4
-1.03
-1.39
-2.02
-0.74
-1.44
0.06
-0.81
0.56
0.11
0.56
-2.84
0.84
-1.90
-2.15
5
-1.17
-2.44
1.24
-0.05
-0.25
-1.19
-1.37
6
-0.71
0.53
-1.28
1.78
-0.27
0.32
7
-1.28
0.55
-0.78
0.78
-2.40
-0.89
0.85
0.30
8
-1.17
-1.65
-0.28
-1.36
-1.25
0.90
-1.22
-
-
-
- X
.556
0
.748
• 579
1.303
.418
.972
-
.846
.221
.148
1. 245
1.246
1.134
1.146
CTl
CT2
.350
Small Size Contours
CT3
SL
RTl
CT4
RT2
1
-2.00
0.92
1.14
-1.64
-1.21
0.35
-1.76
2
-1.16
-0.91
-1.47
-0.80
-0.47
0.26
0.24
3
4
-1.01
-0.26
-2.60
1.42
0.48
-0.97
-0.95
0.50
-0.45
0.33
-1.20
-1.75
-2.82
0.65
5
-1.71
-0.08
1.55
0.37
-2.56
-1.68
-2.77
6
-0.22
-0.97
-0.02
-1.13
-2.13
-0.73
7
0.86
-1.45
-0.82
0.18
-0.25
8
-1.79
-1.69
0.00
0.90
1.34
0.90
-1.59
0.03
-1.53
-2.07
-X
-
-
-
0
.816
1.012
.43
.730
-
.203
.674
1.384
.985
-
.929
1.072
.921
1.003
.553
1.441
50
·-~-·~-·••~•··~••
•• ·~- -· •- --~-·---·-•- ••'-••••~~-• •- • ~~---•••.-~ -• ·-•• ~ "''•~-·~···•·-'~---·••'"''"'~·•••--~- ·-a~~--~~ -•-••-. ·~·~·•o"h -«----~-"~'--•>•-•
-.> -~~~.-· - - •••··-~-·•·•'"'·~--~--· •-•• - · • · -
•••>>•~
'
I
M2
Small Size Contours
CT2
CTl
CT4
1
2
1.73
1.34
0.12
1.77
0.92
3
0.60
4
SL
CT3
RT2
RTl
-0.31
1.92
0.69
0.43
0.40
0.44
1.22
0.92
0.26
1.50
0.35
0.98
0.93
0.75
0.28
0.57
1.59
0.08
0.47
0.44
0.69
0.96
5
6
1.38
1. 05
0.21
1.22
1.46
0.77
1.40
0.73
0.64
-0.21
0.99
0.95
0.96
1.03
7
8
0.47
0.66
0.39
0.78
-0.62
0.63
1.00
-1.15
-0.15
0.19
0.81
1.81
0.53
0.86
-X
1.141
.961
.044
.739
.936
.621
.699
(J
.468
.465
.587
.586
.538
.393
.301
Large Size Contours
CTl
CT2
RTl
CT4
RT2
CT3
1
1.06
0.57
0.65
1.14
1.70
0.28
3.01
2
0.43
0.41
1.23
0.34
1.19
-0.44
0.48
3
0.45
1.07
1.27
0.66
1.41
1.05
1.36
4
0.60
1.49
1.63
1.02
1.05
0.85
0.71
5
0.59
1.49
1.15
-0.26
1.17
0.44
1.51
6
1.85
0.45
0.99
1.30
0.74
1.35
1.02
7
0.13
1.46
0.87
1.02
1.01
1.54
-0.15
1.61
0.38
8
0.30
0.71
1.07
1.91
1.80
SL
-X
.831
.811
1.273
.708
1.144
.623
1.376
(J
.559
.449
.340
.638
.284
.536
.748
i
51
r····------~------- ·-·-··~------------------------- ------------------------·--·----·--------·----·····----------------·------·~---~
I
M3
'
Large Size Contours
CT3
CTl
CT4
RT2
RTl
SL
CT2
1
2.90
-0.29
-0.96
2.40
1.15
3.39
2.42
2
-0.59
2.39
2.75
3.28
3.32
1.76
3.12
3
4
-1.20
2.82
3.69
1.96
1.59
0.85
2.58
2.17
-0.87
0.36
1.98
2.51
-0.24
2.37
5
2.90
2.14
-1.35
1. 29
1.10
0.36
2.26
6
-0.47
-0.32
-0.72
3.41
3.02
3.28
1.17
7
-1.39
3.64
3.07
3.32
1.59
-0.19
2.67
8
2.99
0.77
2.15
1.88
3.12
2.37
2.06
-X
.91
1.285
1.124
2.44
2.175
1.446
2.331
1.86
1.574
1.888
.75
.86
1.376
.529
(J
Small Size Contours
CTl
SL
CT3
RTl
CT4
CT2
RT2
1
1.07
3.58
2.91
2.69
2.41
1.07
2.16
2
3.43
2.37
1.54
3.22
2.25
2.85
2.93
3
2.32
2.85
1.71
3.23
2.01
1.74
2.77
4
2.50
3.20
2.31
2.13
2.10
1.38
2.29
5
1.95
1.98
3.18
2.39
2.69
1.44
2.19
6
3.08
1.22
1.14
2.36
3.45
3.00
2.86
7
3.12
1.78
3.86
3.52
2.98
2.45
2.90
8
2.91
3.19
1. 42
2.33
1.42
1.99
2.44
-X
2.548
2.521
2.259
2.734
2.414
1.99
2.568
(J
.717
.766
.909
.486
.586
.667
.310
52
r,.,.___ --·
·-··-·---·-~--.-~--·;;-"""""'"'"-"'• ··-·-···--~ ·--~-
......._ _, __ ~~---~----------.-~--··-·-··---~-~--»~···-
i
..
-.-~~~~-----···~-
..
. .
a-----a----~-~-~·--~~-----~ ·~-
-~~-~~----~~-~~~--~
M4
Small Size Contours
i
RT2
CT3
CT4
1
0.39
1.12
1.30
2
-0.17
0.97
3
-1.19
4
SL
CTl
CT2
RTl
0.90
2.37
1.19
1.19
1.98
1.52
1.94
1.78
0.98
1.61
1. 75
1.80
2.57
1.44
1.88
-0.78
0.22
1.27
0.58
3.50
1.03
1.44
5
1.76
0.35
1.23
1.60
1.74
1.12
1. 71
6
0.26
1.41
1.27
1.05
1.92
1.42
3.22
7
8
1.23
1.18
1.35
2.61
2.08
1.98
2.65
2.82
1.02
0.87
2.21
2.82
1.68
1.79
-X
.54
.985
1.378
1.534
2.368
1.455
1.858
a
1.25
.450
.318
.636
.546
.315
.698
Large Size Contours
CTl
CT4
RTl
CT2
CT3
RT2
1
0.00
1.90
0.78
1.92
0.63
1.52
2.29
2
-1.23
1.90
1.19
0.95
-0.33
1.70
2.36
3
0.86
1.93
2.21
1.35
-0.96
2.36
1.73
4
-1.70
0.88
0.23
0.88
1.98
1.28
3.36
5
0.39
0.01
1.18
1.08
2.46
1.51
0.72
6
-1.50
1.16
2.04
2.48
1.52
2.30
2.86
7
-1.22
1.46
2.91
0.77
-0.37
3.18
2.53
8
0.85
-0.02
0.96
1.82
0.27
3.05
3.64
2.113
2.436
.679
.863
-
X
a
-
.444
1.153
1.438
1.406
1.011
.756
.820
.569
.65
1.148
SL
53
M5
Small Size Contours
CT2
CTl
CT4
RTl
SL
CT3
RT2
1
0.89
-1.26
2.96
2.26
0.04
-0.56
2.67
2
1.20
2.33
0.47
0.26
2.25
1.93
1.01
3
4
0.25
-0.01
-0.08
0.46
2.83
0.72
2.02
-0.74
2.08
2.09
1.02
0.26
2.32
2.38
0.00
1.87
2.38
0.41
-0.18
1.92
-0.00
5
6
-0.92
1.51
0.18
2.10
1.37
2.28
-0.51
7
2.59
2.38
-0.92
-0.10
2.31
1.82
-0.12
8
-1.09
0.12
1.58
2.70
1.13
0.63
2.62
1.25
1.48
-
X
.535
a
1.308
.828
1.19
.983
1.34
1.123
.923
.818
1.613
.915
1.081
Large Size Contours
CTl
CT2
RT2
SL
CT3
RTl
CT4
1
-0.96
2.40
3.42
2.01
2.32
-0.09
-0.69
2
2.37
2.86
0.52
1.39
0.67
1.73
1.59
3
2.34
-0.32
1. 85
0.42
0.35
1.87
2.36
4
0.90
-0.21
0.81
1. 56
1.03
2.25
0.80
5
2.20
-0.38
2.01
2.02
2.04
1.23
6
2.03
2.12
2.64
1.18
7
-0.19
2.28
0.42
1.34
0.79
0.40
2.00
0.56
2.33
2.20
8
0.16
1.46
2.70
1.59
2.27
2.22
1.80
X
1.136
1.245
1.796
1.439
1.234
1.609
1.345
a
1.254
1.253
1.043
.477
.785
.831
.901
-
1. 47
54
-. ·--
·-'-··--~·---,"·•
----- ·--"
---~-·~--~·---
--·-
~--~ ~··
.,
~~-
--·---·· ----
-~--- -~·--
-- ,,, ·- ....
~~- ~~-· -~~-·- ~---
--·-
~-~~-~~
---
~-=--- ---~··-~~
..
"-~'
-- _,._- "----·
-~---
M6
Large Size Contours
SL
CT3
CTl
RT2
CT4
RTl
CT2
1
2
.0.36
0.72
2.26
2.06
0.12
1.71
0.92
1.17
0.63
1.29
1.97
1.54
1.56
3
0.67
1.08
0.25
,0.01
0.79
2.25
2.01
2.22
4
1.66
0. 47.
1.85
0.96
0.19
1.84
0.54
5
1.25
0.30
1.45
1.32
1.46
1.09
-0.29
6
1.75
-0.19
1.51
-0.58
0.55
0.74
0.15
2.74
2.30
7
0.42
1.61
2.38
0.70
1.91
8
0.87
1.13
1. 75
2.21
0.08
0.41
1.88
-X
1.155
.795
.850
1.240
1.120
1.660
1.180
.46
.831
1.022
.573
1.038
.611
.799
(J
Small Size Contours
RTl
CTl
SL
CT3
CT4
CT2
RT2
1
-1.28
2.26
2.01
1.44
1.99
0.66
0.47
2
1.53
0.46
1.83
2.25
1.83
1.77
1.77
3
0.33
0.00
2.08
2.03
2.46
0.07
1.00
4
1.16
1.76
1.63
1.11
1.58
1.34
0.73
5
0.50
1.34
1.81
1.73
2.18
1.96
1.29
6
1.50
0.08
2.35
0.31
1.83
1.92
2.15
7
1.56
0.33
2.19
2.68
1.78
0.92
1.93
8
0.88
2.09
2.38
0.00
1.19
2.15
0.68
-X
.773
1.040
2.035
1.444
1.855
1.349
1.252
(J
.892
.869
.250
.872
.356
.690
.593
55
Small Size Contours
---------------------------CTl
i
CT2
CT4
RT2
CT3
RTl
SL
1
0.59
-0.05
2.60
0.67
1.35
0.87
0.99
2
3
4
-0.48
-0.41
-0.96
1.43
-0.32
1.11
0.09
-0.71
1.34
5
6
-0.51
0.01
0.62
1.59
1.31
1.55
7
8
0.53
-0.14
1.41
0.65
0.41
2.27
1.99
1.38
0.98
0.59
1.98
1.79
1.56
1.89
0.20
1.96
1.61
1.37
1.40
2.01
1.58
1.71
1.76
2.08
1.72
2.10
1.63
1.76
2.26
4.11
3.34
3.06
1. 83
3.95
-X
-
a
.171
.805
1.101
1.368
1.474
1.681
2.663
.499
.663
1.043
.527
.544
.356
1.050
Large Size Contours
1
2
3
4
5
6
7
8
-
CT2
CT4
RTl
CT3
SL
2.40
1.72
1.32
0.76
2.67
1.42
0.98
1.29
-0.01
0.02
1.30
2.42
0.27
0.08
1.21
-1.23
0.72
2.11
0.72
0.44
1.47
-0.11
1.91
1.49
-0.26
1.34
0.89
0.48
1. 34
2.09
0.47
-0.39
1.79
1.57
1.37
1.54
2.15
1.96
0.87
1.27
CTl
0.44
1.22
1.27
1.23
RT2
-1.00
0.66
1.18
0.70
2.23
1.02
1.03
0.69
0.90
0.94
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0.990
1.659
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Large Size Contours
CTl
CT3
RTl
CT2
RT2
CT4
SL
2.09
1
0.90
-1.93
1.28
1.57
-0.25
2
2.57
2.25
2.89
-0.13
2.35
3
-2.03
-2.22
-0.69
2.42
2.17
-0.95
2.72
2.96
2.49
1.14
4
2.02
-0.01
1.36
1.07
1.22
0.88
0.60
5
1.98
1.43
1.97
1.28
2.24
-1.17
0.86
6
-1.52
-0.28
1.95
-0.33
1.36
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-1.24
3.17
3.04
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3.44
2.01
2.87
2.46
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2.94
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2.36
1.73
1.28
2.08
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.104
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2.128
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1.795
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1.441
1.945
1.651
.595
.990
1.063
1.779
1.204
CT4
RT2
Small Size Contours
CT2
RTl
CT3
SL
CTl
1
-2.39
3.04
2.43
-2.20
-1.40
1.08
-1.62
2
2.40
-1.14
-1.23
1.63
2.43
2.11
2.79
3
4
-0.50
-0.47
-2.57
2.23
3.43
-0.92
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1.48
2.09
1.77
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2.13
2.56
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2.20
5
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1.42
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6
1.73
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2.22
1.98
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0.15
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2.77
1.90
2.59
2.69
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1.94
2.64
2.19
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2.26
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1.525
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CTl
CT3
RT1
CT2
1
2
3
1.99
0.95
0.40
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2.15
2.38
1.47
2.53
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1.21
1.55
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5
2.62
3.28
0.07
1.61
1.37
2.45
2.51
2.93
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0.56
1.09
3.26
0.67
2.63
1.36
1.98
2.50
2.09
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1.769
1.334
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1.104
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CT4
RT2
2.15
2.95
2.67
2.10
2.62
2.91
2.32
2.86
2.91
1.71
2.31
0.45
0.51
2.98
1.77
2.13
2.16
0.76
2.17
1.82
2.24
3.17
2.97
2.15
3.41
2.82
3.41
2.169
1.844
2.038
2.381
2.893
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.384
.414
2.61
SL
Large Size Contours
CT2
RTl
SL
CTl
CT4
RT2
CT3
1
-0.19
3.33
2.08
1.27
1.31
1.95
1.04
2
1.76
1.34
1.63
1.59
2.35
2.02
0.89
0.62
1.03
1.08
2.64
2.91
1.02
1. 25
0.96
0.72
1.69
2.32
3.37
2.06
2.27
0.78
1.33
1.43
2.44
2.86
2.41
0.76
1.25
0.56
0.50
1.25
3
4
5
6
7
8
0.15
1.79
2.15
1.21
2.02
1.25
2.51
3.15
1.95
2.87
3.71
0.68
3.06
2.56
2.74
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1.164
2.165
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CT2
CT3
CT4
SL
RT2
RTl
1
2.75
-1.16
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0.08
1.52
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2
-0.93
0.57
-0.90
1.78
0.06
-2.16
3
4
5
1.30
2.12
-1.17
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0.82
0.15
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0.06
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0.97
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-0.66
-1.69
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0.60
0.15
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-0.97
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2.25
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0.62
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-1.01
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0.29
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0.72
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1.424
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0.14
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1.497
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Small Size Contours
SL
CT2
RT2
CTl
CT3
CT4
RTl
1
-0.98
-1.25
-0.53
-1.50
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0.41
-1.37
2
-0.19
-1.33
0.39
-1.11
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3
4
-0.19
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0.94
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0.00
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0.81
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8
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RTl
RT2
2.25
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2.84
1.74
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1.69
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1.31
3.10
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1.18
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4
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2.60
2.01
2.26
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1.76
1.45
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1.39
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1.26
0.94
1.19
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2.09
2.01
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1.91
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2.20
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1.98
0.87
1.18
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1.89
0.67
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0.88
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1.825
1.951
1.917
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1.454
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0.52
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2.001
1.467
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Large Size Contours
CT4
CT2
SL
RTl
CTl
RT2
CT3
1
0.09
-0.68
0.52
2.61
1.45
1.74
-2.04
2
-0.29
0.58
-0.81
1.78
0.22
1.02
0.59
3
4
-0.19
-1.44
0.46
0.47
-1.11
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0.32
0.44
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1.37
1.42
2.17
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-0.57
0.15
0.63
1.88
1.44
0.96
1.94
6
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0.66
1.49
1.11
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1.10
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0.69
1.41
0.21
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1.76
0.08
0.46
0.61
1.94
0.44
1.19
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RTl
SL
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CT3
CT4
CT2
CTl
1
-1.59
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2
-0.06
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3
0.70
0.47
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4
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0.08
1.25
0.96
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6
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8
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0.52
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0.03
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cr
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Small Size Contours
CTl
RT2
CT4
CT2
1
2
-2.80
-2.55
-1.00
-2.99
-0.47
-1.07
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3
4
-0.36
-2.81
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5
CT3
RT2
SL
0.65
-0.74
0.30
0.77
-0.80
-1.45
0.96
-2.36
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0.99
-1.93
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0.75
0.48
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0.37
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0.75
6
-1.50
-2.51
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0.76
-1.07
-1.37
0.55
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8
-1.32
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0.07
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0.49
1.32
-1.57
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0.00
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0.53
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-1.294
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-1.618
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cr
1.083
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1.236
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.604
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