SPIRAL AFTEREFFECT: RETINAL SIZE, LOCUS, TRANSFER SL

TABLE 3
SUMMARY OF ANALYSIS OF VARIANCE FOR DURATIONS OF SAE

Source SS af MS F p
A (Size) 338.27 2 169.13 105.70 01
B (Place) 186.47 1 186.47 147.99 01
C (Transfer) 197.96 1 197.96 44,58 01
D (Ss) 61.14 9 6.79
AXB 52.16 2 26.08 130.40 1
Axc 16.13 2 8.07 6.06 OL
AxD 28.77 18 1.60
BXxcC 33.22 1 33.22 15.37 01
BX D 11.31 9 1.26
cxD 34.00 9 444
AXBxC 6.20 2 3.10 3.13
AXBxD 3.62 18 .20 .20
AxcxD 23.85 18 1.33 1.34
BxCxD 19.49 9 2.16 2.18
AXBxCxD 17.85 18 99
Total 1030.44 119

Nove- Error terms are A X D for A,B X D for B,C x D for C; A x B X D for
AXB,AX CX DforA X C,B X CX D forB x C, A X B X C x D for second-
order interactions.

Four possibilities concerning the relationship of rods and cones to the
duration of SAE were considered in the introduction. Two of these, (1) that
rods and cones are equally effective in producing the aftereffect and (2) that
the aftereffect is a pure rod phenomenon, can be rejected on the basis of finding
that, in general, longer durations of SAE are found for projections onto cone
areas than for projections onto primarily rod areas, This finding could be ac-
counted for by assuming that the effect is mediated by cones. If this explanation
were correct, decreasing the corie concentration should result in.a corresponding
reduction in duration of effect. As can be seen in Fig. 1, however, the cone
concentration (Bartley, 1951) drops off much more rapidly than does the
strength of the effect. Thus, the latter data do not, then, support mediation by
cones only. Further evidence against this view is the lack of difference between
foveal and peripheral areas for the “large-transfer” condition (Table 2). It
appears then that the SAE is associated with stimulation of either rods or cones
but that cones are more effective.

Other findings of this experiment are consistent with a general knowledge
of rod-cone functioning. The results in Table 2 indicate that rods are more
affected by increasing size of the image than are cones. This would be
expected on the basis of a “ceiling effect” for the cones. The concentration of
cones falls off very rapidly beyond the fovea whereas the concentration of





50 8. L. FREUD

Procedure

The spiral apparatus, lights, eye-piece, and timer button were demonstrated
to S who was then told that he would be focusing at times on the center of the
spiral and at other times directly at one of the 4 lights. He was instructed to
avoid looking directly at the spiral disc unless told to do so, and was given
specific instructions for each test condition.

The angle of focus and size of retinal image were varied independently
by changing the point of focus and the distance between S$ and the spiral. Cal-
culating the image size and angle of focus was done in the standard manner
(Graham, 1951).

Each S was administered a series of 14 trials consisting of variation of con-
ditions along the following three dimensions: (a) place: rod vs cone areas of
the retina; (b) size: small, intermediate, and large areas of the retina; and (c)
transfer: same hemiretina vs different (homonymous) hemiretinae. Hemi-
retinae were labeled for convenience according to the following code: Left tem-
poral “A,” left nasal “B,” right nasal “C,” and right temporal “D.” The 14
conditions (described in Table 1) were randomly assigned.

RESULTS AND DISCUSSION
The results for the group are given in Table 2 and graphically in Fig. 1.
These results show that (1) cone areas give larger effects than rod areas. (2)

TABLE 2
MEANS AND STANDARD DEVIATIONS OF DURATIONS OF SAE
FOR SIZE, PLACE, AND TRANSFER

Rods Cones Rods Cones
Same Diff. Same Diff. Same Diff. Same Diff.

Small Intermediate
M Lil 0 6.13, 3.49 4.62 1.75 7.57 3.18
SD 7 0 1.62 1.00 1.04 130 1.28 1.19
Large

M 6.53 5.95 9.19 5.36
SD 2.29 1.45 1.74 1.43

increasing the size of the image is associated with an increase in duration of SAE,
and (3) larger effects are obtained under the non-transfer condition than under
the transfer condition.

The results of an analysis of variance performed on the estimates of dura-
tion are shown in Table 3. The main effects of size, place, and transfer are all
significant. First order interactions are also significant but not the second-order
interactions.


52 S. L. FREUD

5 1500

4 1200

900

Mean Duration of SAE (econds)
o
Cone Concentration (cones per .OO69sq.mm.)

cones mixed rods
(0) (4.25) (8.5)

Retinal Region (degrees from fovea)

Fic. 1. Comparison of durations of SAE and cone concentrations for 3 retinal regions

tods remains high for large areas of the periphery. A major concentration of
cones is to be found in the 2° foveal area used in the “small-cone” condition.
Increasing size beyond “small” (2°), however, adds relatively fewer cones com-
pared to the increase in rods for a similar change in size of image.

In general, “transfer” weakens the effect but the cones ate more affected
than the rods. It is known (see Polyak, 1941, pp. 319-348) that the cone-
cortical connections approximate a one-to-one system whereas this is not the
case for rods. Thus, for the cones, very precise connections between retinal
points and cortical points exist while for the rods, retinal areas are connected to
cortical points. As has been previously pointed out, homonymous hemiretinae
do not project to precisely the same points on the cortex (Teuber, e¢ al., 1960,
pp. 113-116). For the cones, then, when the effect is transferred between hemi-
retinae, the precise relationship is distorted and a considerable reduction in
effect could be expected. In the case of the rods, since less precise retinal-
cortical correspondence exists, the difference between the retino-cortical projec-
tions for “same” (non-transfer) and “different” (transfer) conditions is rela-
tively small. For this reason, the loss in duration of aftereffect under the transfer
condition should be less for predominantly rod areas.

The effects of size were clearly significant. An increase in size of image
yields an increase in duration of effect. It should be noted that under certain
size conditions the effect is lost for normal Ss. This obviously is of great im-
portance in the diagnostic use of the SAE where failure to observe the aftereffect
is considered evidence of organic brain damage.


Reprinted from
Perceptual and Motor Skills, 1964, 18, 47-53. © Southern Universities Press 1964

DURATION OF SPIRAL AFTEREFFECT AS A FUNCTION OF
RETINAL SIZE, RETINAL PLACE, AND HEMIRETINAL ‘TRANSFER'

SHELDON L. FREUD"
Washington, D.C,

Summary —This experiment has shown that, although both rods and cones
mediate the spiral aftereffect, cone areas give a larger response. Increasing size
of the retinal image results in longer durations of SAE but rods are more affected
by this increase than are cones, There is a general weakening in aftereffect re-
sulting from “transfer” from one hemiretina to another with cone areas showing
greater loss than rod areas. Size of retinal image has been shown to be a potent
variable and, in fact, under some small size conditions, normal Ss fail to observe
any effect whatsoever. In view of these findings, it is apparent that size of retinal
image is a variable which must be carefully controlled if comparable results are
to be obtained. Review of the clinical literature, however, reveals that distance
from S to spiral and objective spiral size often vary from experiment to experi-
ment, This variation could well account for some of the differences in results
of clinical studies. It is proposed that a standard spiral size and testing distance
be introduced for clinical use.

In recent years a large number of studies have been done on the diagnostic
application of the spiral aftereffect (SAE) as a test for organic brain damage.
Little has been done, however, to investigate the underlying physiological mecha-
nisms.

This experiment was designed to study (1) differences in duration of SAE
for areas of the retina differing in rod and cone concentrations, (2) the relation-
ship of retinal image-size and strength of effect, and (3) the effect of these two
variables on both hemiretinal transfer and non-transfer conditions.

The possibility of a difference between peripheral and foveal sensitivity to
the aftereffect was first raised by Aubert (1886). The results of experiments
which were designed to study this difference, however, were contradictory. Cords
and Brucke (1907) reported that the aftereffect was stronger when viewed
peripherally, as did Basler (1909). Wohlgemuth (1911), however, found a
stronger effect in foveal vision using duration as a measure of strength. Colored
discs gave a marked aftereffect both in dim and bright light, suggesting that
both rods and cones were important in the phenomenon. Granit (1928) be-
lieved that, since the peripheral retina was more sensitive to movement, it there-
fore should give a stronger aftereffect.

Other studies have dealt less directly with the question. Kinoshita (1909)
reported that the duration of the effect varied inversely with the intensity of

*Preparation of this paper was facilitated by the assistance of The Epilepsy Foundation,
Washington, D.C. The author wishes to express his appreciation to A. Robert Rollin for
his guidance and encouragement.

*Dr. Freud is with the Division of Research and Education, Office of Aviation
Medicine, Federal Aviation Agency, Washington, D.C.



SPIRAL AFTEREFFECT: RETINAL SIZE, LOCUS, TRANSFER 53

REFERENCES
AUBERT, H. Die Bewegungsempfindung. Pflueg. Arch. ges. Physiol., 1886, 39, 347-
370.

BARTLEY, H. S. The psychophysiolosy of vision. In S. S. Stevens (Ed.), Handbook of
experimental psychology. New York: Wiley, 1951. Pp. 929-930.

BASLER, A. Ueber das Sehen von Bewegungen; dritte mitteilung: Der Ablauf des Be-
wegungsnachibildes. Pflueg. Arch. ges. Physiol., 1909, 128, 145-176.

Corps, R., & BRUCKE, E. T. Ueber die Geschwindigkeit des Bewegungsnachbildes.
Pflueg. Arch. ges. Physiol., 1907, 119, 54-76.

FREUD, S. L. A study of physiological mechanisms underlying the spiral after effect. Un-
published doctoral thesis, Univer. of Connecticut, 1962. (Also available as ASTIA
Document No. AD274-366, Dept. of Defense Document Center, Alexandria, Va.)

GRAHAM, C. H. Visual perception. In S. S. Stevens (Ed.), Handbook of experimental
psychology. New York: Wiley, 1951. Pp. 872-873.

GRANIT, R. en inhibition in the aftereffect of seen movement. Brit. J. Psychol., 1928,
19, 147-157.

HOLLAND, H. C. The Archimedes spiral. Nature, 1957, 179, 432-433;

KINOSHITA, T. Zur Kenntnis der negativen Bewegungsnachbilder. Z. Psychol. Physiol.
Sinnesorg., 1909, 43, 420-442.

PoLyaK, S. L. The retina, Chicago: Univer. of Chicago Press, 1941.

‘TEUBER, H.-L., BATTERSBY, W. S., & BENER, M. B. Visual field defects after penetrating
‘missile wounds of the brain. Cambridge: Harvard Univer. Press, 1960.

Von Szity, A. Zum Studium des Bewegungsnachbildes. Z. Psychol. Physiol. Sinnesorg.,
1907, 42, 109-114.

WOHLGEMUTH, A. On the aftereffect of seen movement. Brit. J. Psychol., Monogr.
Suppl., 1911, 1, 1-117.

Accepted December 16, 1963.

GPo 882-975



48 S. L. FREUD

illumination, suggesting greater sensitivity for the rods. Holland (1957) stated
that the angle of focus was of no importance in producing the aftereffect, thus
denying any sensitivity differences berween rods and cones.

A review of the literature revealed no systematic study of the effect of size
of retinal image upon duration of SAE. Since in clinical application both spiral
size and testing distance are often varied, it was felt that data pertaining to
image size would be of practical as well as theoretical importance. Two previous
studies (Freud, 1962; Von Szily, 1907) yielded significant differences in du-
ration of SAE for hemi-retinal transfer of the effect as opposed to non-transfer.
This raised the possibility of an interaction between this “transfer” variable and
the variables of “retinal size” and “retinal place.”

METHOD
Subjects
Ten Ss were chosen from a group of volunteers. The sample of students
and clerical employees included 7 males and 3 females with an age range of
17-49, a mean age of 29, and a median age of 28.5. None of the Ss had a history
of recent illness, convulsions, or serious injury.

Apparatus

On a table 30 X 50 X 30 in. was mounted vertically a sheet of pegboard
98 X 30 in. Through the center of the pegboard protruded the drive shaft of
the motor used to produce the spiral aftereffect. Attached to the shaft by an
acorn nut was a 920° Archimedes spiral, 7/4 in. in diameter. To the right of
the spiral disc, mounted flush into the pegboard, were four 6-v light bulbs
powered by an AC step-down transformer set at 4 v and wired to a pair of
switches on the main control panel.

The lights were mounted at 15.42, 30.84, 16.57, and 10.05 in. from the
center of the spiral so that when S focused on the lights, the angle of focus, ie.,
the angles subtended from the center of the fovea to the center of the spiral-
image, were 4.5°, 8.5°, 9.5°, and 11.5°, respectively. A DC power supply fur-
nished the power to rotate the disc. By keeping a constant input of 3 v (in
accordance with apparatus manufacturer’s instructions), a rotation speed of 80
rpm (= 2 rpm) was maintained. Stopping and starting rotation of the spiral
was controlled by an X-ray timer built into the main control panel. S was seated
at a table upon which was mounted a chin rest and an eye-piece with a sliding
focal-plane type shutter so constructed that S had one eye blocked at all times.
By pulling a cord, $ exposed the previously covered eye and simultaneously cov-
ered the previously exposed eye. The table was mounted on roller bearings
allowing it to be moved to different distances from the spiral. These distances
were such that the eye was 17 ft. 4 in., 8 ft. 4 in. and 4 ft. 4 in. from the spiral,
producing a retinal image-size of 2°, 4°, and 8°, respectively.


49

SPIRAL AFTEREFFECT: RETINAL SIZE, LOCUS, TRANSFER

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