S. S. STEVENS (1906-1973): LIFE AND SCIENCE
Joseph C. Stevens
The John B Pierce Laboratory and Yale University
[email protected]
Abstract
In commemoration of the 100th anniversary of S.S. Stevens’ birth, a short overall account is
presented here of his life and contributions to science. Especially noteworthy are his
psychophysical power law, his classification of scales of measurement, his elucidation of
sensory processes in every modality, and his prodigious promotion of the science of
psychoacoustics.
Fig. 1. S.S. Stevens, Professor of Psychophysics, Harvard University
Some of my psychophysical colleagues suggested my name to open the session on the life and
career of S.S. Stevens. For this honor I am most grateful. To those who don’t know me S.S.
Stevens and I were not related. He came from English stock, I, from Dutch stock.
Nevertheless, because of our common surname and close association we were frequently
assumed to be related. We were once amused when the famed French psychophysicist Henri
Piéron in a somewhat sarcastic review came down on the work of “S.S. Stevens et son fils
J.C. Stevens.“ Early in my career Smitty, as his friends and colleagues called him, advised me
to change my name, but family pride prevented me from doing then what I later came
somewhat to regret. There was just too much confusion about who did what.
I knew Smitty Stevens for twenty years, the first thirteen of them at Harvard. He was
my teacher and PhD mentor from 1953 to 1957, then my colleague and collaborator for nine
years from 1957 to 1966. In 1966 I left Cambridge for New Haven to build a program of
psychophysics at the John B Pierce Laboratory (with big help from Lawrence Marks). For
another seven years until Smitty’s death in 1973 we continued, at a distance, to advise,
critique, and sometimes argue with each other,
I give here an overall account of Smitty’s life, with emphasis on his accomplishments
as scientist and educator. For some of you the territory covered will be pretty familiar. Others
may know him only as the man who claimed to knock down Fechner’s logarithmic “law” and
replace it with his own power “law.” This was certainly his last great enterprise, but there
were noteworthy others that came earlier.
I have tried to make my account of Smitty’s life and science reasonably objective, but
I couldn’t entirely resist the temptation to personalize, especially the 13 years of his life
beginning in 1953 when he published his first version of the power law for loudness and
brightness, and I became his student. Also I must acknowledge early on that for much of the
information about his early life, I have had to rely on his short autobiography titled “Notes for
a Life Story” (Stevens. S.S, 1974).
Early life
Smitty was born in 1906 to a Mormon family, in Ogden, Utah. By the time he was only 17
years old he had lost both parents, graduated from high school, and was sent out on a threeyear stint as a Mormon missionary in Belgium and Switzerland. There he learned to preach in
fluent if broken French. So far as I could tell, his rearing in the Mormon faith seems to have
left little lasting influence on belief or practice thereafter.
On completion of his term as missionary he studied for two years at the
University of Utah, then another two years at Stanford, where he received the bachelor’s
degree in 1931. His college years were marked by attraction to what he later called the
“windy” subjects of philosophy, sociology, history, and political science. However he earned
enough credits in science courses to begin a shift toward the harder sciences and to gain
acceptance by the Harvard Medical School.
Toward the end of his senior year at Stanford he married Maxine Leonard. He
described her as a beautiful young woman. Others of his contemporaries have told me that she
was indeed both beautiful and of lovely manner. Five years later shortly after the birth of their
son, Peter, Maxine succumbed to a severe post-partum psychosis, which in Smitty’s words
“overwhelmed Maxine and devastated our lives.” Maxine returned to her parents’ home in
Utah where she died a couple of decades later.
Harvard Graduate School
After Smitty’s graduation from college he embarked for Harvard. However he gave up his
berth in the medical school and instead insinuated himself, via the School of Education, into
the Psychology Department. There he came under the mentorship of the distinguished
historian of experimental psychology, E.G. Boring. Although these two clashed hard from
time to time, notably over Smitty’s neglect of his duties as teaching assistant, Boring came to
be his chief supporter. He once said of him “Of all the graduate students who have worked
with me, he is the one of whose ultimate success I had the most certain belief…”
Smitty said that his career as scientist began when “I startled Boring by asking if I
could work on some problem of his. Well, yes, perhaps. He had heard that when you mix red
and green on a color wheel it looks gray only if you stand at the right distance. That seemed
interesting, and up in the attic of [Emerson Hall] under the rafters I found a place where I
could try it out. It worked all right, but so what? I tried various arrangements and noted that if
I looked slightly away from the color wheel the gray turned greenish. Finally I got around to
mixing a black and white to provide a gray that could be compared with the gray produced
with red and green.
Then late one afternoon my scientific career began. There occurred that surge of
elation, the eureka! that drives the investigator. I suddenly sensed that there was a law to be
worked out. Your could mix some green with the black and white and you could vary the
amount in a way that would just cancel the effect of a change of distance. A function could be
measured!” The results were published in 1934 in the American Journal of Psychology with
the title “The relation of saturation to the size of the retinal image,” Smitty’s first major
publication.
I recount this study because it illustrates his insights into the nature of a psychological
variable (in this case the gray mixture). It outlines a strategy for measuring a psychological
variable, in the present example determining the combinations of distance and added gray that
leave the sensation of the mixture invariant. The determination of the physical variables that
leave a sensation invariant constitutes one of the most basic problems of psychophysics. Such
measurement can help to understand how the senses work--in the present example learning
how saturation depends on the size of the retinal image and, ipso facto, the distribution of
retinal receptors. Thus, from the start Smitty saw psychophysics as handmaiden to the sensory
psychologist and physiologist.
This same strategy for determining equal sensation functions was next applied to the
measurement of tonal volume, which won him the PhD in 1933. This abrupt change from
vision to hearing was occasioned by the chance acquisition of an electronic oscillator for the
production of pure tones. The field of hearing was the place to be, owing to the recent
invention of the vacuum-tube amplifier.
Science of Hearing
New interest in hearing led him into postdoctoral research on the electrophysiology of
hearing, with Hallowell Davis, at the Harvard Medical School. Their work culminated in the
publication of their book Hearing in 1938.It served as the authoritative text on hearing for
three decades or more thereafter. Some have even compared it with Helmholz’s
Tonempfindungen.
Around 1940 was born the Psychoacoustic Laboratory. The laboratory found its home
in the basement of Harvard’s Memorial Hall, which after the war years came also to house the
Department of Psychology, in close physical and intellectual proximity. Under Smitty’s
directorship the Psychoacoustic Laboratory took on preeminent status worldwide. Over the
years it boasted prominent scientists too many to name here. Its most famous member,
recruited by Smitty and E. B. Newman, was Georg von Békésy, who in 1960, was awarded
the Nobel Prize in Physiology and Medicine, for his many early studies of the ear. Those of us
then resident in Memorial Hall recall the pride we felt the day of the announcement.
Measurement and Scales of Measurement
Already in the 1930’s Smitty addressed the second major problem of psychophysics, namely,
how does sensation magnitude depend on stimulus magnitude? His first candidates for study
of this problem were loudness and pitch. His first attempt to scale loudness was derived by
having observers adjust a stimulus to sound half as loud as a standard stimulus, at successive
levels of the standard. The resulting “sone” function as it was dubbed did not quite conform to
a power function, likely because of bias associated with the halving procedure.
Attempts to measure psychological attributes like loudness and pitch led the way to an
almost obsessioned search into the fundamental nature of measurement. In this search he was
motivated by proponents at Harvard of logical positivism, a philosophical school that
flourished between the two wars. Born of this search was Smitty’s ordering of the domain of
measurement, which, in my view, transcends its philosophical ancestry. This was his four-fold
hierarchical classification of scales of measurement: nominal, ordinal, interval, and ratio. A
noteworthy practical implicationo of this claassification is that it clarifies what statistical tests
are permissible for a particular scale type (S. S. Stevens, 1951). Although practically every
reader will be familiar with this classification, it’s possible that some may not have known
that its author was S.S. Stevens. It made its way into the forefront of many a textbook on
statistics but oddly detached from his name, perhaps, he conjectured, because it had been so
widely accepted that “many authors feel it unnecessary to cite its origin”. (S.S. Stevens,
1973). Yet he considered this classification and his psychophysical power law to be his two
most enduring contributions to science. This caused him some pain. He once related to me
that at a pool party hosted by B.F. Skinner he fell into conversation with Tom Lehrer. Tom
Lehrer was a Harvard mathematician, to my generation “infamous” for his naughty satirical
songs. When Smitty referred to “My classification of scales of measurement” Lehrer replied,
“What do you mean your classification.” That hurt. But perhaps consolation came with his
election to the National Academy of Science while he was still in his thirties.
Constitutional Psychology: Somatotyping
Measurement led Smitty also along another quite different path, into the domain of
constitutional psychology and the scaling of physiques and temperament. A psychiatrist, Dr.
William H. Sheldon, had assembled a stack of photographs and data relating body types and
temperament. He classified physiques into three categories: endomorphy, mesomorphy and
eectomorphy.
Corresponding to these types were posited to be three types of temperament,
viscerotonia, somatatonia, and cerebrotonia. Under what circumstances I don’t know, Smitty
hooked up with Sheldon and collaborated in the writing of two books, Varieties of Human
Physique (1940) and Varieties of Human Temperament (1942). I think Smitty’s main
contribution here was to instill some quantitative order by means of category scaling of each
of the components of physique and of temperament. Any male person can be assigned a
number between one and seven for each component of his physique and his temperament,
thereby permitting the computation of correlation coefficients relating body types and
temperament. Shown here (Fig. 2) are examples of the extreme somatotypes, namely 711s,
171s, and 117s. Obviously most persons have intermediate scores on these components, such
as 345, or 256, or whatever
.
Fig. 2. Extreme somatotypes: A: 711, B: 171, C: 117. A balanced somatotype D: 444
One noteworthy somatotype, also shown in Fig. 2, is the 444, a person of average
score on all three components—actually a relatively uncommon somatotype, about 42 of
every 1000 males. I show it here because it was Smitty’s own somatotype. I am getting back
on him here because he was always going around somatotyping other people (including me)
with sometimes snickering comment. Sheldon (1954) wrote that the 444 “seems to suggest the
predicament of a man trying to drive three equally powerful horses whom nature has pointed
in almost orthogonally opposed directions.” “A few 444’s become eminent, gifted people. But
many are found in the mental hospitals…”
However that may be, Smitty was insistent that a person’s somatotype is invariant
over his life span and significantly determines his behavioral dispositions. As to the naturenurture apposition, Smitty came down hard on the side of nature.
Views like this, aggressively asserted, set him at odds with many a colleague and
student of “softer” persuasion in the Department of Psychology. So did his disparagement of
undergraduate teaching. And so did his insistence that mathematics, as well as statistics, be
required for the PhD. These things threatened promotion to tenure. But in 1944 Harvard’s
President James Conant, discounting departmental dissatisfaction with him, and waiving the
customary review by an outside ad hoc committee of peers, awarded Smitty tenure, saying
that he sometimes felt competent to judge things on his own.
Educator
Now some words about Smitty as educator. In my 13 years at Harvard he never taught an
undergraduate course. He reviled the undergraduate major in psychology and prophesized that
its proliferation signaled the demise of psychology as a “hard” science. In my opinion this
prophecy has been largely fulfilled. Admission to graduate school, he thought, should require
a good background in general science and mathematics, and maybe a course or two in
experimental psychology, but a major in psychology was irrelevant. At his request in1962
Harvard changed his title from Professor of Psychology to Professor of Psychophysics. He
was proud to call himself the first Professor of Psychophysics
At the graduate level Smitty did teach small groups, seated around a table in the style
of a pro-seminar. His course on mathematics for psychologists was a highlight of my
education. It was tough, interesting, and useful. Throughout my entire career it has proved
invaluable. I daresay that other participants might say the same.
An enduring contribution to education was the scrupulous editing of the Handbook of
Experimental Psychology (1953), which brought together essays by some thirty eminent
authors. It swiftly became the bible of serious students of experimental psychology. My own
copy holds together by liberal strips of Scotch tape. It lives on in three volumes, now titled
S.S. Stevens’ Handbook of Experimental Psychology.
As pedagogue Smitty was at his best in one-on-one sessions, in his office or at the
laboratory bench. He himself said that he took great joy in them. For the student, however
they could be scary as they were enlightening, alike for the graduate student, the post-doc, or
the visiting scholar. He showed little patience for small talk, no mercy for sloppy thought or
muddled writing. He could be brutally frank. With me, and I think with others he often began
these sessions in a confrontational style that I, at least, found intimidating. My colleague
Larry Marks recounts his first session of this kind. He proposed to Smitty that he would like
to compare the brightness functions for rods and cones. Smitty snarled: You mean the socalled rods and the so-called cones. Not a good start for Larry, but Smitty later gave his
imprimatur to the project, and Larry published three articles on the subject. It was typical of
Smitty to mellow as these interactions progressed. Smitty loved data, especially when they
could be plotted, and re-plotted, until their meaning displayed itself. Sometimes he turned
these sessions into brutal lessons in writing. But those who stuck them out learned that he had
a lot to teach about both experimenting and writing.
Over the years Smitty drew many a visiting scholar, just passing through, or on
sabbatical. About a dozen of them, in my time and memory, ended up doing experiments
leading to publications jointly authored with Smitty. Each in its own way exhibited the utility
of psychophysical scaling methods to elucidate sensory processes. My list includes Len
Diamond (vision), Tarow Indow (vision), Hannes Eisler (proprioception), Eugene Galanter
(psychophysical scaling), Roland Harper (somatosensory), Tom Aiba (vision), Christopher
Poulton (hearing), Hilda Greenbaum (scaling) and Miguelina Guirao (hearing, vision,
proprioception), and surely others before and after my time at Harvard.
The Psychophysical Power Law
In Fig. 3 are plotted three power functions for three different sensory continua. They vary
greatly in shape depending on the size of the exponent. In log-log coordinates these power
functions are straight lines with various slopes. The power law states that perceived
magnitude grows as a power function of stimulus magnitude, but also that each sensory
continuum, here electric shock, apparent length, and brightness, has a characteristic exponent
(or slope in log-log axes), as shown here. The up-down position of these functions is denoted
by the value of log k. It is often devoid of empirical meaning, but not always, as I demonstrate
later on.
Fig. 3. Three power functions in A: linear coordinates, and B: log-log coordinates
In the fall of my first year of graduate school (1953) Smitty gave a departmental
seminar titled “Brightness is just like loudness.” (Stevens, S.S, 1953) In it he recounted his
previous summer’s research, with Richard Herrnstein, on subjective brightness. They revived
methods used for the construction of the first sone scale back in 1936. One of these was to set
a variable stimulus to appear half as intense as a standard stimulus, at several levels of the
standard. It turned out that the halving data for brightness were nearly identical to those for
loudness. Thus the title for the seminar.
I do not remember whether in this talk Smitty stated that brightness and loudness were
both power functions of stimulus energy. He may well have, because by November of 1953
he claimed in a two-paragraph note to Science that they were (SS. Stevens, 1953). To be
honest I doubt that at that time I even knew what a power function was. But I took to mind
one thing: brightness is just like loudness. From this I had an inspiration: brightness ratios
should match loudness ratios. In other words, two lights that differ from each other by, say,
10-fold in luminance should match two sounds that differ by 10-fold in energy level. In still
other words, decibel differences of lights should match decibel differences of sound.
With trepidation I proposed to Smitty that I might do an experiment along this line. To
my relief he responded rather warmly to the idea. He set me up with the same homemade
brightness apparatus that he and Herrnstein had fabricated, together with light filters, white
noise generator, attenuator, earphones, a pair of switches that gated two levels of the noise,
and devices and instructions for calibrating the stimuli. What an education!
The subject faced two lights spaced wide apart to the left and right, one B1 brighter
than the other B2. With the two switches he could access either of two levels of white noise,
the first L1 at fixed loudness, the second L2 adjustable by turning a knob. The instruction was
to adjust L2 so that the loudness ratio L1/L2 matched the brightness ratio B1/B2 so that B1
/B2 = L1/L2, Fifteen subjects had their hand at this task, and their average results (Fig 4)
showed that to a first approximation decibel differences in light do indeed match decibel
differences in sound. (J. C. Stevens, 1953; S. S. Stevens and J.C. Stevens, 1960.)
Fig. 4. dB light vs dB sound
This was the first experiment in our laboratory to employ a cross-modality matching
paradigm. It strengthened the power law by sidestepping altogether the use of numerical
instruction. Soon thereafter Smitty presented these results to the International Society of
Psychology in Montreal. Piéron was there and he and Smitty dialoged in French about these
matters, which I couldn’t understand, but I was nonetheless full of “graduate-student pride.”
The experiment became part of my doctoral dissertation in 1957, which was a comparison of
loudness and brightness. I demonstrated there that the slope and intercept (i.e.. up-down
position) of the brightness function vary with such factors as contrast, adaptation, and target
size.
Here I made liberal use of Smitty’s newly invented method, magnitude estimation (in
1953), as well as its complementary method, magnitude production. In magnitude estimation
the subject matches numbers to stimulus magnitudes, in magnitude production the subject
matches stimulus magnitudes to numbers. He believed that these complementary procedures
together helped to control for biases inherent in each alone. The same for other scaling
methods, such as halving and doubling. This caution was later often ignored, even by Smitty,
perhaps because of the beguiling simplicity of magnitude estimation. With it one could scale
not only sensory magnitudes but also any other human feature that appears to vary in
degree—such as the seriousness of various crimes, prestige of various occupations, utility of
money, and many others. Doubtless one or more of my colleagues in the Round Table will see
fit to enlarge on these applications to what Smitty called “Scaling the Social Consensus”—the
title of a whole chapter of his last book (S.S. Stevens, 1975)
In June of 1956 Gene Galanter came on board in Memorial Hall. And the flurry of
research on sensory magnitude turned into a gale, both in our lab and abroad, too, especially
notably in `Gosta Ekman’s laboratory in Stockholm. In May of 1957 Smitty published his
first major statement of the general power law: 14 sensory continua were shown to conform to
a powerfunction, each continuum having its own exponent, ranging between 0.3 and 2.0. In
December of that same year Smitty and Gene published a second major statement of the
power law, together with clarification of the relationship between ratio scales and category
scales.
My own contributions to the Power Law lay in two areas mainly. The first was its
validation by cross-modality matching, the second various applications of the Power Law to
the study of sensory and perceptual processes.
After I got my PhD I had to teach undergraduates, whether Smitty liked it or not. In
those days Harvard seniors in psychology had to do a research project under the mentorship of
a faculty member. Since at that time we were scaling every sensory continuum we could think
of, I suggested to a senior Joel Mack that he might scale the subjective force of handgrip.
Smitty at first turned down our request to buy a good dynamometer, so we hooked up a
handle with a dairy scale. Joel called out numbers and the subject would pull on the handle to
match the numbers. The results conformed well to a power function with an exponent of
about l.7. This means that to double any subjective force of handgrip required an increase of
only half again the physical level.
By this time Smitty was beginning to take interest, and he honored our request to buy
a good dynamometer. Ironically, the dairy scale and the new dynamometer gave the same
results. We published the findings in The Journal of Experimental Psychology (J.C. Stevens
and Mack (1959)
Later I came up with the idea that handgrip could conveniently be substituted for
magnitude estimation to scale any sensory continuum, and we proceeded to do so for some
seven continua. The relative slopes of these functions in Fig. 5 turned out to be nearly
identical to the relative slopes obtained by magnitude estimation. (Stevens, J. C. et al., 1960).
This same kind of result was also obtained by matching loudness to ten different sensory
continua (Stevens, S. S., 1966). In his autobiography of 1970 Smitty wrote “Already more
than 40 perceptual continua have been scaled by simple number matching—magnitude
estimation as it is called. Equally important, the human subject can match any variable to any
other variable, such as apparent loudness to apparent brightness, or force of handgrip to
warmth on the skin, or apparent duration to apparent area, and so on.The demonstrated
success of such cross-modality matching means that the interrelations among all subjective
variables can be quantified.”
Fig 5. Nine continua scaled by handgrip. The dotted line has a slope of 1.0
As I stated earlier Smitty believed that the goal of psychophysics is to elucidate
sensory and physiological processes. That goal was stamped on almost all of my publications
from Smitty’s lab and later. Armchair psychophysics never interested me much. I was far
more interested in learning how sensory phenomena measured in the laboratory reveal
themselves in the parameters of the power law.
Already in my doctoral research on brightness I had shown how adaptation and
contrast could change the brightness function. Much later I hit on a way of using magnitude
estimation to show how the brightness function depends on any state of adaptation of the eye.
The trick was to keep one eye dark-adapted, the other light-adapted to some fixed level. From
time to time target lights were presented briefly to one or the other eye for magnitude
estimation of brightness. Then the whole process was repeated for another level of adaptation
until all desired levels of adaptation had been studied. In other words the dark-adapted eye
provided a constant brightness yardstick by which to measure brightness in the light-adapted
eye. At first Smitty was, typically, skeptical of the method and prodded me to spot-check the
results by conventional matching—a tedious and intricate operation for this kind of problem.
But in the end he was won over and in 1963 together we jointly published the results in the
Journal of the Optical Society of America (J.C. Stevens and S.S. Stevens, 1963).
Fig. 6. Brightness as a function of luminance for an eye adapted to darkness (far left) and to
various adapting luminances. Circles show the brightness of a light having the same
luminance as the adapting stimulus.
Fig. 6 shows the idealized family of brightness functions. Note that as the adaptation
level increases the slope of the brightness function increases, the intercept decreases (i.e. updown position goes down), and the absolute threshold increases. As a bonus the experiment
shows that the method of magnitude estimation can serve conveniently to generate equalsensation functions. Any horizontal line intersecting this family of brightness functions
specifies the combinations of target luminance and level of adaptation that arouse the same
brightness. From this I saw that the method of magnitude estimation can be used as an
efficient means of generating equal-sensation functions. It is sometimes the method of choice,
as for example when matching by adjustment is difficult or impossible.
These findings in the domain of vision have left me a bit uneasy with the assertion that
every modality has its own “characteristic” exponent. Indeed, we see here a whole family of
brightness functions that differ from each other in slope, intercept, and threshold. And there
are other psychophysical families like these, not only in vision but also hearing and thermal
sensation. For some this constitutes an unwelcome complication of the power law, but to me
it is an exciting, fresh way to describe sensory phenomena. Later in 1972 Lawrence Marks
gave a comprehensive account of such research in a book, whose title, I think, says a lot—
Sensory Processes: The New Psychophysics.
Postscripts
In 1972, about a year before his death, Smitty wrote to his old friend and colleague, Hallowell
Davis: “Do I have any advice, you ask, for those approaching retirement? Yes. Try to
formulate an exciting campaign that promises to stretch far into the years ahead. My own
project looms as three different books to expound the beauties of a simple power law hat
seems to relate the strength of the stimulus to that of the sensation. The power law appears to
govern all the sense modalities. Accounts are beginning to seep into the textbooks under the
rubric Stevens’ Law. That in itself is enough to urge me on.”
One can only speculate about Smitty’s vision of two of the three books he promised.
The last book, Psychophysics: Introduction to its perceptual, neural, and social prospects was
published posthumously in 1975, meticulously edited by his widow, Geraldine (Didi) Stone.
From the beginnings of the Psychoacoustic Laboratory around 1940 Didi had been his
assistant, editor, organizer, and companion. As Gene Galanter put it she was a “pillar of
Smitty’s laboratory.” They were married in 1963, and the reception was held on the
snowfields atop Mt. Washington in New Hampshire. If you weren’t a skier you weren’t
invited.
Smitty took up skiing at age 42. Passion for the sport drove him to purchase an
abandoned farmhouse in New Hampshire that came to lodge many a skier: students,
colleagues, friends. Some, like me, were initiated into the sport on a gentle slope behind the
barn, at first reluctant and terrified. Ever the experimenter, Smitty challenged conventional
properties of skis, and proposed new ones in ski magazines. Skis, he felt, were too long for
the amateur skier.
This idea may have come to him when he examined a short metal ski used by the
French ski militia on account of its maneuverability. We lodgers at the farm served as guinea
pigs to learn just how long a ski should be. Smitty’s answer was, about half the length
dictated by the authorities! “Shorties” as the scoffers termed them, enabled me—no natural
athlete indeed—to take on some of the toughest slopes of the Alps and the Andes.
Smitty died suddenly in his sleep on the eighteenth of January 1973, in his 67th year,
at Vail, Colorado. There he and Didi were combining attendance at the annual meeting of the
Winter Conference on Brain Research with their favorite sport skiing. He was survived by his
wife Didi, his son, Peter, and three grandchildren. Didi died in 2004.
In the three decades plus following Smitty’s death there have been slews of
commentaries, replications, extensions, and criticisms of his work, especially the power law.
Each of these in its own way pays tribute, I think, to his creative genius, perhaps as much as
the many formal honors bestowed on him in his lifetime. He will be ever remembered as the
first, and perhaps foremost Professor of Psychophysics.
References
Marks, L. E. (1974). Sensory Processes: The New Psychophysics. New York: Academic
Press.
Sheldon, W.H. (1940). The varieties of temperament. New York: Harper.
Sheldon, W. H. (1954). Atlas of men. New York: Wiley.
Sheldon, W.H. and Stevens, S.S.(1942). The varieties of human physique. New York: Harper.
Stevens J.C. (1957). A comparison of ratio scales for the loudness of white noise and the
brightness of white light. PhD dissertation, Harvard University.
Stevens, J.C, Mack, J.D., and. Stevens S.S, (1960) Growth of sensation magnitude on seven
continua measured by force of handgrip, Journal of Experimental Psychology, 59,
60-67.
Stevens, J.C. and Stevens, S.S. 1963 Brightness function: effects of adaptation, Journal of
the Optical Society of America, 53, 375-385.
Stevens, S. S., and Davis H. (1938). Hearing: Its Psychology and Physiology New York:
Wiley.
Stevens, S.S (1951). Handbook of Experimental Psychology (Ed). New York: Wiley.
Stevens, S.S. (1953). On the brightness of lights and the loudness of sounds, Science. 118, no.
3072, p 576.
Stevens, S.S. and Stevens, J.C. (1960). The dynamics of visual brightness. Psychophysical
Laboratory Monograph, Harvard University, 1960.
Stevens, S.S. (1974). Notes for a life story, In H.R. Moskowitz, B. Scharf, and J.C.
Stevens
(Eds), Sensation and Measurement: Papers in honor of S.S. Stevens. Boston:
Reidel. 423-455.
Stevens, S.S., (1975). Psychophysics: Introduction to its perceptual, neural, and social
prospects. New York: Wiley.