THE PHYSIOLOGICAL LOCUS OF THE SPIRAL AFTER-EFFECT 425

Results. Transfer occurred in all 80 of the homonymous hemiretinal
conditions and in only 4 of the non-hemiretinal conditions. The Chi-square
for these data is 144,76; p < 0.01.

Discussion. The results of Experiment I clearly demonstrate that
homonymous hemiretinas transfer the SAE, while non-homonymous hemi-
retinas fail to do so. The report of transfer in four of the non-homonymous
trials can be accounted for by S's inability to maintain perfect focus upon
the light. If S should glance momentarily at the spiral instead of maintain-
ing his focus upon the light, the after-effect could appear. Another pos-
sibility is the general tendency on the part of the Ss, while engaged in a
difficult discriminative task, to report the presence of an effect when it is
actually absent (false positives). It is to be noted that these four reports
of after-effect in the non-homonymous conditions wete spontaneously de-
scribed by the Ss as “weak” or “different’’ compared to the effect seen in
the demonstration prior to beginning the experiment.

The almost perfect correspondence between these results and the predic-
tions one would make by assuming that the effect takes place at the visual
cortex can be considered as extremely strong evidence for at least a major
central component of the SAE. They do not, however, conclusively rule
out the possibility of a retinal contribution.

In our conditions of transfer, one hemiretina was stimulated with a
moving spiral; when the spiral was stopped, another hemiretina was ex-
posed to the stationary spiral. Transfer was defined as a report of the
SAE under these conditions.

Two physiological explanations for this transfer will be considered.
Presumably, the SAE results from the interaction of neural firings produced
by the present stimulation of the stationary disk with some ‘trace’ in the
nervous system of the previous stimulation produced by the moving disk.
One possibility is that the ‘trace’ represents a neural change or process at
the cortical level and interaction takes place there. An alternative possibility
is that the trace is at the retinal level and these neural changes or processes
result in a particular pattern of firing to the cortex. The SAE would then
occur upon a meeting at the cortex of these firings of the trace from one
hemiretina. It is clear that either explanation requires a cortical or central
process. With the latter explanation the possibility of a major retinal con-
tribution remains.

One alternative experiment suggests itself, which, while not a con-
clusive test of the absence of a retinal contribution as discussed above, could



428 FREUD

between homonymous hemiretinas and almost total absence of transfer
between non-homonymous hemiretinas. In Experiment II, duration of the
SAE was found to be longer for the conditions of non-transfer than for
the conditions of transfer; hence, the possibility of a retinal contribution to
the after-effect could not be conclusively ruled out. In this experiment, a
quantitative study of hemiretinal transfer confirmed the results obtained
in Experiment I. It was concluded from these experiments that a major
central component exists for the Spiral After-Effect.



424 FREUD

a frame 17 X 13 in. Through the center of the peg-board protruded the drive-shaft
of the Spiral After-Effect Apparatus. Attached to the shaft was a standard (920°)
Archimedes spiral, 744 in. in diameter. A Dc power-supply provided the power
to rotate the disk. Speed of rotation was fixed at 80 r.p.m. by means of a Strobotac,
and recalibration was done by adjustment of the readings of voltage and amperage
on the power-supply prior to testing each S. Starting and stopping of the spiral-rota-
tion was controlled by an X-ray timer built into the main control-panel. On either
side of the spiral, at a distance 614 in. from the center of the spiral, was a 6-volt
bulb mounted flush into the peg-board. These bulbs were wired to an on-off-on
switch mounted on the control-panel, thus allowing E to switch lights rapidly. An
AC step-down transformer set at 4 v. served as an independent constant source of
power for the lights. Built into the frame surrounding the apparatus was a sliding
door which, when closed by E after each trial, blocked the entire apparatus from $s
view. All of the exposed portions of the apparatus, with the exception of the spiral-
disk itself, were painted a flat light gray. $ was seated behind a table 8 ft. from the
spiral. Attached to the table on an adjustable shaft was an eye-piece with a sliding
shutter of the focal-plane type, so constructed that S had one eye blocked at all
times. By pulling a cord, 5 exposed the previously covered eye and simultaneously
covered the previously exposed eye.

Procedure. The general procedure was to have S focus upon one of the lights
with one eye, thus causing the image of the rotating spiral to fall upon a predeter-
mined hemiretina, Then, at the end of the period of rotation, § was switched to a
particular eye and a particular focusing light so that the image of the stationary
spiral fell upon either the same or a different hemiretina, as required by the ex-
perimental design.

S was given a demonstration of the after-effect and shown how the eye-piece of
the apparatus was operated. He was instructed to maintain his focus on the selected
light and to avoid looking directly at the spiral itself. General instructions were
given on the procedure for switching eyes and lights, and detailed instructions were
given for all eye-light combinations. § reported presence or absence of after-effect
by responding with ‘yes’ or ‘no.’

For purposes of identification, the four hemiretinas were labeled in the following
manner: left temporal, A; left nasal, B; right nasal, C; and right temporal, D. Hemi-
retinas A and C correspond to the homonymous pair projecting upon the left corti-
cal hemisphere, and hemiretinas B and D correspond to the homonymous pair
projecting upon the right cortical hemisphere.

The following procedure was employed for stimulating and testing the hemiretinas:

Hemiretina Eye Light
A left left
B left right
Cc right left
D right right

The 16 conditions (8 homonymous and 8 non-homonymous) were given in
random order to each S, with a 15-sec. rest-period between trials. A rest-period of
1 min. was given at the end of the eighth trial.


426 FREUD

rule out the possibility of any interaction at the retinal level (/.c. firings of
the trace and firings due to present stimulations interacting in the retina).
If the intensity of the after-effect resulting from the stimulation and testing
of a pair of homonymous hemiretinas (e.g. 4-C) could be shown to be
equal to the intensity of effect obtained when the same hemiretina
(e.g. A-A) was both stimulated and tested, it would follow that no part of
the effect was due to stimulated hemiretina A’s interacting with tested hemi-

TABLE I
Mean Duration or SAE

Homonymous hemiretinas
AA BB cc DD AC CA BD DB

M 7.50 7.65 7.93 8.08 3.92 3.93 3.67 4.08
SD 2.06 2.73 1.95 2,29 1,95 1.71 1.27 1,58

Non-homonymous hemiretinas

AB BA CD DC AD DA BC CB
M 05 0205S (ti 0 0 0
: 0 0 0 0 0 0 0

retina A, What is required, then, is a comparison between the strength of
effect for ‘same’ and ‘different’ hemiretinas. This comparison was included
in Experiment I.

EXPERIMENT II

In an attempt to rule out any retinal contribution to the SAE as discussed
in Experiment I, a test of the SAE for the ‘same-different’ conditions was
conducted. In addition, a measure of the SAE made it possible to evaluate
more precisely the non-homonymous retinal responses.

Method. The Ss were the same as in Experiment I. The same apparatus was used,
except for the addition of an interval-timer attached to a button which S used to
report duration of the SAB. The procedure was basically the same as in Experiment
I, except that 5 reported presence and duration of SAE by means of button and
timer described above.

Results. The results of Experiment II are shown in Table I. The mean
duration of the SAE for the ‘same’ (non-transfer) hemiretinal condition
was 7.79, as opposed to a mean value of 3.90 for the ‘different’ (transfer)
condition.

A comparison of these means resulted in a ¢ of 3.89 (p < 0.01). This
finding demonstrates that the SAE is significantly greater for the ‘same’
(non-transfer) condition.


Founded in 1887 by STANLEY HALL

OFFPRINTED FROM

THE AMERICAN
JOURNAL OF PSYCHOLOGY

EDITED BY

KARL M. DALLENBACH
UNIVERSITY OF TEXAS
AND
M. E. BITTERMAN E. B. NEWMAN
BryN Mawr COLLEGE Harvard UNIVERSITY

WITH THE COGPERATION OF
E. G. Borie, Harvard University; W. K. Estes, Stanford University; J. P.
Guitrorp, University of Southern California; Harry HELSoN, Kansas State
University; E. R. Hitcaro, Stanford University; Francis W. IRWIN, University
of Pennsylvania; F. NOWELL JONES, University of California, Los Angeles;
G. L. Kneezer, Washington University; D. G. MARQUIS, Massachusetts Insti-
tute of Technology; ARTHUR W. MELTON, University of Michigan; W. C. H.

Prentice, Wheaton College; T. A. RvAN, Cornell University

THE PHYSIOLOGICAL LOCUS OF THE
SPIRAL AFTER-EFFECT

By Suexpow L. Frevp, Office of Aviation Medicine,
Federal Aviation Agency, Washington, D.C.

September, 1964, Vol. LXXVII
Pp. 422-428

Published by The American Journal of Psychology, Department of
Psychology, University of Texas, Austin, Tex.

(AAT



THE PHYSIOLOGICAL LOCUS OF THE SPIRAL AFTER-EFFECT 427

The difference between homonymous and non-homonymous hemiretinas
found in Experiment I was confirmed. The after-effect occurred between
the homonymous hemiretinal pairs in all 80 of the trials, but between non-
homonymous pairs in only 5 of the 80 trials. The range for the mean dura-
tion of the SAE for non-homonymous responses (0.02-0.05) was clearly
of a different order of magnitude than the range for the mean duration of
the SAE of homonymous hemiretinal responses (3.67-8.08).

Discussion. With respect to the attempt to rule out retinal interaction by
comparing ‘same’ (non-transfer) and ‘different’ (transfer) hemiretinal
conditions, it is apparent that it is not supported by the results since
‘same’ conditions yield significantly greater durations of the SAE than
‘different’ conditions. In the process of transferring the SAE from one
hemiretina to a different (homonymous) hemiretina, some of the effect is
lost.

Two possibilities will be considered to explain the reduced after-effect
under the condition of transfer. The first, previously considered, is that
retinal interaction contributes to the SAE in the ‘same’ (non-transfer)
conditions, but obviously cannot do so in the ‘different’ (transfer) condi-
tion. An alternative explanation may be made on the basis of very recently
published anatomical evidence regarding projections from the retina to
the visual cortex. According to Teuber, homonymous hemiretinas do not
ptoject to precisely the same points on the visual cortex.* Thus, if hemi-
retina A (left-temporal) projects to Point 1 on the cortex and its homony-
mous hemiretina C (right-nasal) projects to Point 2 (rather than to the
same point), differences such as those obtained might well be expected.

The findings regarding homonymous hemiretinal transfer obtained in
Experiment I are confirmed. The amounts of transfer are almost identical.
In every case of the 80 homonymous hemiretinal pairs, transfer occurred,
and in only 5 of the 80 non-homonymous trials was transfer reported. This
was of very brief duration (0.20 to 0.48 sec.) and of a completely different
order of magnitude from the homonymous scores (1.22 to 14.80 sec.). Thus
again, we have evidence of a major central contribution to the SAE.

SUMMARY

It was the purpose of this study to investigate the physiofogical locus of
the Spiral After-Effect (SAE). Experiment I demonstrated 100% transfer

SH-L. Teuber, W. S. Battersby, and M. B. Benet, Visual Field Defects after
Penetrating Missile Wounds of the Brain, 1960, 113-116.



THE PHYSIOLOGICAL LOCUS OF THE SPIRAL AFTER-EFFECT

By SHELDON L. FREUD, Office of Aviation Medicine,
Federal Aviation Agency, Washington, D.C.

It has long been known that if an Archimedes spiral is rotated, an illu-
sory motion of swelling or shrinking, depending on the direction of rota-
tion, will be perceived. If, after the spiral is rotated, it is stopped and S
looks at a stationary spiral, an after-effect of motion opposite to that pro-
duced by the moving spiral will be seen. This after-effect is called the Spiral
After-Effect (SAE).

Although numerous studies on the use of the SAE as a diagnostic test
for organic brain-damage have been published, these studies have largely
ignored the theory underlying the effect and have not investigated the
crucial question of the physiological locus of the SAE. Theories that have
been proposed to explain the appearance of the effect fall into two general
categories: (1) peripheral theories, which attribute it entirely to processes
within the retina itself; and (2) central theories, which take the position
that the effect is a result of processes within cortical or sub-cortical struc-
tures.

A demonstrated transfer of the effect from a stimulated to an unstim-
ulated eye has been generally accepted as strong evidence of centrality.
Results of a number of studies on interocular transfer, however, have been
far from consistent and the question of this transfer has remained an unre-
solved subject of debate in the literature since 1871, when Dvorak published
a report of observed transfer. Among the early studies, Exner, Von Szily,
and Ehrenstein also reported transfer while Budde, Hunter, and Durop
failed to find it.? More recently, Holland reported 70% transfer, and Day
cites Seagrim as having obtained transfer.

* Received for publication July 11, 1962. This paper is based upon a portion of
a Doctoral dissertation completed at the University of Connecticut. The writer is
indebted to Dr. A. Robert Rollin for his assistance in this study.

*V. Dvorak, Versuche itber Nachbilder von Reizveriinderugen, Sitz. Akad. Wiss.
Wien, 61, 1871, 257-262.

26" Exner, Ueber das Sehen von Bewegungen und die Theorie des zusammenge-
setzten Auges, Sitz. Akad. Wiss. Wien, 72, 1875, 156-189; A. von Szily, Zum
Studium des Bewegungsnachbildes, Z. Psychol. Physiol. Sinnesorg., 42, 1907, 109-
114; Walter Ehrenstein, Versuche tiber die Beziehungen zwischen Bewegungs- und
Gestaltwahrnehmungen, Z. Psychol., 96, 1925, 305-352; E. Budde, Ueber metakine-
tische Scheinbewegungen und tiber die Wahrnehmung von Bewegungen, Arch.
Anat. Physicl., 1884, 127-152; W. S. Hunter, The after-effect of visual motion,

422


THE PHYSIOLOGICAL LOCUS OF THE SPIRAL AFTER-EFFECT 423

Tt is difficult to evaluate these studies, since many variables now known
to be important in determining the intensity of the SAE were often not
reported (e.g. speed of rotation, lighting, size of spiral, testing distance,
and duration of fixation). It is likely that the conflicting results stem from
incomplete control of these variables.

A carefully controlled study of interocular transfer might have resolved
the question. By applying the technique of hemiretinal transfer, however,
it was possible to obtain the same information as in simple interocular
transfer and, in addition, to relate the effect more precisely to the known
neural pathways of the visual system. In the hemiretinal technique, one
hemiretina is stimulated by a rotating spiral and a stationary spiral is then
projected upon a different hemiretina. If cortical processes are crucial,
transfer of the after-effect should occur between homonymous hemiretinas
(i.e. those which project to the same cortical hemisphere) and transfer
should wot occur between non-homonymous hemiretinas (i.e. those which
project to different cortical hemispheres). On the other hand, if the crucial
processes take place at the retinal level, transfer would be expected between
hemiretinas of the same eye rather than between hemiretinas in different
eyes. This latter explanation is based upon the well-known fact that there are
multiple and complex interconnections within a single retina but no known
direct interconnections between the two retinas.®

Two experiments were carried out. In the first, transfer of the SAE was
determined by having S report ‘yes’ or ‘no’ if the effect appeared in the
unstimulated hemiretina after stimulating a homonymous hemiretina. In
the second experiment, S reported presence of effect by pressing a button
connected to an interval-timer. In this way, a measure of the duration of the
effect was obtained.

EXPERIMENT I

Subjects. Ten $s were selected from among undergraduate students, graduate
students, and clerical employees at the University of Connecticut. Included in the
sample were 7 men and 3 women with an age-range of 17 to 49 yr., a mean age of
29.0 yr. and a median age of 28.5 yr. None of the Ss had a history of recent ill-
ness, convulsions, or serious injury.

Apparatus. The apparatus consisted of a table, 50 in. long and 30 in. wide, and
30 in. high, which had mounted vertically upon it a sheet of peg-board enclosed in

Psychol. Rev, 21, 1914, 245-277; G, Durop, Le probléme des impressions de move-
ment consecutives d’ordre visuel, Année Psychol., 29, 1928, 1-56.

* H.C. Holland and H. R. Beech, The spiral aftereffect as a test of brain damage,
J. Ment. Sci., 104, 1958, 466-471.

*R. H. Day, On interocular transfer and the central origin of visual after-effects,
this JouRNAL, 71, 1958, 789.

°S. L. Polyak, The Retina, 1941, 319-348.