179485; (9 blishing Company Farm without written permission fram the publisher

ILA”

of C~lo~~bia, Bogotd, Colombia,

rformed in order to test hler’s satiation hypothesis. It

n irr the u r half of the visual field would i;r size from tvhe,n seen in the lower half of the visual

duates were required to make size hich W~XVZ. projected on an opaque screen, The design of Constant Stimuli, with controis for response bias

were round (binomial test, p = 0.013) for the field effect, with upwr visual field stimuli judged larger than lower visual field stimuli. The impkatians for man’s knowledge of t’te world were discussed.

Scientific psychology began as the study of sensation within a struc- turalist framework. The early psychologists were also philosophers, and they were interested in understanding the way in which man knows the world. This epistemological concern has disappeared almost completely from contemporary psychology. However the contributions of psychology to the solution of these problems cannot be overemphasized, and they have not yet been studied from a modern point of view.

The present article will describe an experimental study done within the frame of reference of KXihler’s satiation hypothesis. Gestalt theory was in part a revolt against artificial analysis and ‘sensationism’. The theory has been studied at least for 50 years, since 1920 (or even earlier), and it has stimulated a great deal of research by followers and also by enemies. Today Gestalt theory has lost its controversial character and it has almost disappeared as a ‘school’ because it has been incorporated __I(-- -.--.--1_

1 This research owes very much to the direction. of T. Sonderegger, of the University of Nebraska at Lincoln (United States), and to the following people who helped in the planning of the experiment and in the collection of the data: S. Angove, J. Brewer, S. Lip&, G. Lumia, J. Miller, G. Oswalt, 6. Rankin and M. Rodgersqn. Special thanks are due to G. Oswalt.

* Present address: Box 1212, Lincoln, Neb. 68508, U.S.A.

179

180 RUBEN ARDIEA

into general psychology; as BORING (1950) points out, it has been a case of ‘death of success’.

However, many of the possibilities of Gestalt theory have never studieu satisfactorily. One of them is related to satiation effects in the cerebral cortex, and it served as the theoretical problem that the presort. experirrent attempted to solve.

PRENTICE (1959) pointed out that a stand produces a different kind of ‘figure-current’ than before. Ias a later paper (PRENTICX, 1962) he stated that in the case of the figural aftereffects in illusions something connected with the initial way of seeing a figure becomes fatigued or satiated, that the competmg configuration takes over for a while until it also iind gives w’ay to the configuration ori changes are correlated with electrochemical ch could be studied only in the last few years thanks to the development of very refined instruments. A sensory stimulus produces a current flow through the area of the cortex to which the stimulus is relayed, and the current by satiating and fatiguing the current-carrying capacity of that area obstructs its own passage and so it diminishes and fades out.

GIBSON (1933, 1951) independently of Kiihl.er was studying the role of learning in human vision. His results were in agreement with K6hler’s self-limiting neural process as a general element in visual! perception. KGhler proposed that when the impulses set up by a sensory stimulus reach the nerve cells in the appropriate centers of the cerebral cortex, the activity of the cells must generate direct currents through and around the tissue. This current quickly induces a state of polarization at cell interfaces that increases the-resistance o? the tissues of the flow of the current. Because of this the conductivity and polarizability of the tissue are changed, and new impulses from later stimulation act differently.

The hypothesis assumes that the density of the current. should be greater in that section of the cerebral cortex associated with the retinal image of the figtr?e’s edge or contour. It postulates that the br,ain rather than the retina is responsable for figure aftereffects. KiihHer, Held, O’Connell and Wegener dedicated their efforts between 1946 and 1952 to tl’y to confirm this hypothesis. A lot of the success of the task would depend, of course, on the development of adequate recording instruments at the neurophysiological level.

The hypothesis has led to many fruitful investigations (KGHLER and ~ISJ-BMIL, 1950; K~~HLER and HELD, 1949; KZ~HLER et al., 1952 ; Kiiwm

ey:4 this reseat-c

the visual cortex rather than in

int out that the objects in the world are not

vel of straightforward gaze, even in our epoch of j.>ts and rockets. iihler postulated the existence of a

and lower halves of the visual field. it is a well-known fact that the same object appears to have one size when its i e falls in the upper periphery of the retina, and another when the i falls on its center. problem of relatigre sizes of objects in per and lower halves of the visual field had not been srudied before.

TAL PRDCEDURE

The Ss were 17 male and 13 female undergraduate students enrolled at the University of Nebraska (Lincoln, U.S.). It was required that 5% have 20-30 vision or better without corrective lenses.

Apparatus Two small experimental rooms having a common removable partition

were used. An opaque, milk-glass screen was mounted vertically in the opening between the two rocms. A standard overhead projector in the first room flashed stimuli on the screen for a duration of two seconds. Stimulus presentation time was controlled by a Himter electronic timer. The stimuli were seven transparencies, each one consisting of three circles : one very small in the center w ch served as a fixation point;

182 RUBEN ARDILA

and two larger circles, one which varied in size and one ,which remained standard ,across stimuli. Transparencies could be inverted on the projector to interchange the positions of the standard and variable circles. The diameter of the projected ssandurd circle was 3-& inches; le the variable stimuli were: 3,3,;6 3&, 3&, 3r5+, 3&, and 3g. Four tional practice stimuli were 2+$, 2$ 3-& and 34-i inches in diameter. A small dot on the screen corresponded to the projected center circle on the transparencies and served as a screen fixation point betwee presentations. The center-to-center distance of standard a circles was, when projected, 14; inches.

A dental chair with an adjustable headrest faced the screen in the second room. The position and height of the chair could be adjusted so that the subject’s eyes were level with and exactly 22 inches distant from the fixation point on the screen. Normal illumination was provided in the subject’s room, while the other room was semi-dark.

The S was seated before the screen and the chair was adjusted so that the S’s eyes were level with the fixation point. S was instructed by the experimenter, who remained in the same room to observe the S’s eyes, that he would be shown a series of circles. While fixating on the small circle in the center of the screen, 5 was to judge which of the test stimuli was the larger (or the smaller, in another group). S was also instructed to make a choice as quickly as possible, and to always make a choice.

The method of cmstant stimuli was used, with the only possible responses being ‘upper’ or ‘lower’. Four practice trials were presented first, so that S could see that the two circles would be different. Seventy test trials were then presented for two seconds each, thirty-five in which the standard was in the upper position and thirty-five in which it was in the lower. Each of the seven test stimuli were presented randomly five times in each set of thrrty-five. The S had to judge which one of the stimuli was larger (in one group of Ss), or which one was smaller (in other group of Ss). There was an average inter-trial-interval of five seconds, and rest intervals of one minute were given every fourteen trials. After these seventy trials a rest interval of approximately three minutes was given so that S coula move his head and eyes, This interval was followed by the instruction that S was now to judge which one of the stimuli was the smaller (if he had to judge before which one was larger), or larger (if he had to judge before which one was smaller). Another

following the same procedure gments and th.e osition of the standard was

ects seen in the upper visual field should in the lower visual field was

sponses indicating she variable ach stimulus when the standard and when the standard was on

pper portion of the scree pothcsis was tested using a he number of negative diKerences should have

ositivc differences if the null hypothesis was found to be significant

the variable stimuli seen as larger more often when alf of the visual field. A distribution of the

variable stimuli are shown in fig. 1.

St.arldard it-~ iower half of the viyl fie!d

/‘----

/--

f-

& -z in upper half of the visual fteld

---_pI

52 GJ 57

Variable stimuli

Fig. 1. Percent of times that the variable stimulus was indicated as being larger than the standard, when the standard was in the upper and when it was in the lower half

of the visual field.

A possible response bias was examined by comparing the amount of times a variable stimulus was indicated as being krger when Ss were

184 RUBEN ILA

requested to pick the smaller one, aud when they were reque the larger one, There was no significant difference (p = 0. two-tailed binomial test.

Sex differences were also examined and found fp = 0.12) using a two-tailed binomial test. PO were examined by balancing for the position e accuracy for subjects on both halves of the tri diEerence was found, it was non-significant and could for by differences in the number of responses to t Accuracy scores are presented in table 1.

TABLE 1 Accuracy of judgements fix stimuli other than standard.

Males 17 a7 Females 13 86

All subjects Fin&-half of trials Second-half of trials

30 86 30 88

The binomial tests used in the treatment of results are non-parametric and as such considered by some to be conservative tests. However for the data here they seem to be appropriate tests.

Kt would appear that there is indeed a position effect as su by Kiihler. The same stimulus is seen as larger when presented in the upper half of the visual field than when presented in the lower half of

visual field, probably due to more satiation of the lower half because majority of the objects of the real world are in the lower half of the

visual field. The physiological correlates of this phenomenon could be studied using some of the refined recording instruments ava.ilable today in neuropsychology. The epistemological consequences of this satiation eBect have not Wn studied yet, but they would tend to indicate that man alters his visual environment according to what he has seen in the past. A conclusion in agreement with the empiricist notion of ‘learning to see’, and also with Uhler’s Gestalt theory.

2nd. ed. New York:

tion, ~tiation and habituation. Acta

d contract in perception of curved

mp

ISHBACK, 1953. Tb: destruction of the Miller-Lyer illusion in ted trials: I and II. J. exp. Psychol. , 267-281, 398-410.

N. O’C.YONNFLL, 1952. An investigation of cortical currents.

__----_s_s and D. N. 57. Currents of the visual cortex in the cat.,

The r,y&matic psychology of Wolfgang Kohler. In: S. Koch ted.), Psychology. a study of a science, Vol. 1, New York: MeGraw-Hill. 1962. Aftereffects in perception. Scientific American, 206, 44-49.

Yowm~,‘T., 1953. An ex rimental study of figural after-effect. Jap. J. Psychol. 23, 235-238, 287-288.