646 S. L, FREUD

3, FREUD, S. L. A study of physiological mechanisms underlying the spiral after effect.
Arlington, Va.: Armed Services Technical Information Agency, 1962. (Document

AD 274-366)
4, FREUD, S. L. The physiological locus of the spiral after effect. Amer. J. Psychol., in
press.

5. HOLLAND, H. C., & BEACH, H, R. The spiral aftereffect as a test of brain damage.
J. ment. Sci., 1958, 104, 466-471.

6. Hoppe, J. J. Studien zur Erklarung gewisser Scheinbewegungen, Z. Psychol. Physiol.
Sinnesorg., 1894, 7, 29-37.

7. SERN, A. The latency of the spiral aftereffect and spiral effect as a function of illumi-
nation and speed of rotation. Unpublished doctoral dissertation, Univer. of Con-
necticut, 1959.

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

Accepted September 11, 1963.

GPO 882-976


Reprinted from
Perceptual and Motor Skills, 1963, 17, 643-646. © Southern Universities Press 1963

DURATION AS A MEASURE OF THE SPIRAL AFTEREFFECT

SHELDON L. FREUD*
Washington, D. C+

Summary—The purpose of this experiment was to study the reliability of
duration as a measure of the spiral aftereffect. The results for 10 Ss indicate
that duration is a highly reliable measure and that duration is a simple monotonic
function of exposure-time.

The standard procedure for administering the spiral aftereffect test consists
of rotating the spiral and then having S report whether or not he sees the after-
effect once the spiral has been stopped. This use of a categorical measure of the
spiral aftereffect (SAE) presents a number of difficulties. Reports of the
presence of the effect are highly subjective and often ambiguous. In addition,
precise comparisons of results are not possible since weak responses cannot be
differentiated from strong responses (3, 4).

Duration is a convenient measure of the SAE and appears to be the measure
of choice except that its reliability has been questioned. Thus, the purpose of
this study was to investigate the reliability of duration as a measure of the SAE.

Review of the literature reveals no systematic investigation on the reliability
of duration. Duration has been used as a measure of SAE strength in a number
of studies despite the reservations raised by Hoppe’s (6) report of the tendency
of the effect to wax and wane. This tendency would place doubt upon its reli-
ability as a measure of intensity since Ss might experience difficulty in deter-
mining when the effect had finally stopped. Both Wohlgemuth (8) and Basler
(1) conducted studies of the SAE using duration as a measure of intensity. More
recently, Eysenck (2) used duration, as did Holland and Beach (5). Stern (7),
however, seriously questioned the reliability of duration citing the same objections
raised by Hoppe and, in his own study, used latency of the effect as the strength
measure.

As part of the present experiment, data were also collected with which
to evaluate duration of the effect as a function of exposure time. The purpose
was two-fold. Of immediate concern was the selection of a stimulation period
of sufficient length so as to produce a measureable effect under a variety of
conditions and yet short enough to prevent S's being fatigued. It was also felt
that in future clinical use of the SAE information concerning the relation between
duration and fixation time would be of value.in selecting optimal stimulation

periods.

1Preparation of this paper was facilitated by the assistance of the Epilepsy Foundation. ‘The
author is indebted to A. Robert Rollin for his encouragement and guidance.

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



644 S. L. FREUD

METHOD

Subjects and apparatus—Ten Ss with visual acuity of 20/25 or better were
used. The apparatus utilized a table upon which was mounted vertically a sheet
of peg-board. Through the center of the peg-board protruded the drive-shaft of
the standard spiral aftereffect apparatus with a 920° Archimedes spiral, 714 in.
in diameter, and connected to a DC power supply. Speed of rotation was fixed
at 80 rpm by means of a Strobotac, and recalibration was done by adjustment of
voltage and amperage readings on the power supply prior to testing each S.
Starting and stopping of the spiral rotation was controlled by an X-ray timer
built into the main control panel. 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’s view. All of the exposed portions of the apparatus, with the
exception of the spiral disc itself, were painted a flat light gray. An interval
timer was mounted on the main control panel and was controlled by a push but-
ton on S's table so that the timer started when S pressed and stopped when S
released the button. By this means, S reported the duration of the effect. 5 was
seated at a table 8 ft. from the spiral, with his head fixed in a chin rest which
was mounted on the table edge and centered so that both eyes were focused equi-
distant from the center of the spiral.

Procedure-—S was given the following instructions: “Look at the center of”
the spiral. Iam going to spin it and when it stops, I want you to tell me what
you see.” The spiral was then rotated for 15 sec. and after S responded with,
“It’s expanding,” or a similar response to indicate that he had observed the after-
effect, he was told, “Now I’m going to spin the spiral again. After the machine
has stopped, if you sce it expanding in the same way as you just did, I want you
to press this button and hold it down until the spiral stops expanding.”

S was then given one trial for each of four different durations of exposute
time, 5, 15, 30, and 60 sec. The conditions were presented in random order
with a 1-min. rest between trials, and aftereffect-duration times were recorded.
The entire procedure was repeated 48 hr. later to obtain the test-retest reliability.

RESULTS?

The Pearson product-moment correlation coefficients for the test-retest
reliability of SAE duration for the periods 5, 15, 30, and 60 sec. were .63 (p <
05), 86 (p < 01), 93 (p < .01), and .82 (p < 01), respectively.

The test-retest group results of Table 1 show duration of SAE increasing
as a monotonic function of exposure time and apparently approaching asymptote.

A simple analysis of variance was performed to test for the presence of a

*Test-retest individual scores for duration of the spiral aftereffect have been deposited
with the American Documentation Institute, Auxiliary Publications Project, Photodupli-
Cation Service, Library of Congress, Washington 25, D. C. Order Document No.
7691, remitting $1.25 for 35-mm. microfilm or photocopies.


DURATION OF SPIRAL AFTEREFFECT 645

TABLE 1
‘Test AND RETEST MEANS AND STANDARD DEVIATIONS OF DURATIONS OF SAE SCORES

Exposure Time Mean sD
(Sec.) Trial i ‘Trial 2 Teal 1 Trial 2
5 4.09 4.03 1.67 2.03
15 11.98 11.29 449 3.89
30 19.10 17.12 6.08 5.59
60 23.09 21.85 5.17 6.74

trend among the effects. Because of heterogeneity of variance, the data were
first subjected to a square root transformation. The results of this analysis
(given in Table 2) show a significant trend between fixation time and duration
of SAE.

TABLE 2
SUMMARY OF ANALYSIS OF VARIANCE OF DURATIONS OF SAE

Source SS df MS F bp
Treatments 25.68 3 8.56 5.94 <.01
Error 51.89 36 1.44
Total 7157 39

This experiment demonstrates that duration of the SAE is a reliable measure.
The correlation coefficients for the 15-, 30-, and 60-sec. fixation periods are all
significant. The lower value of .63 for the 5-sec. period can be attributed to
the restricted range. Even naive Ss experienced no difficulty in consistently
reporting termination of the effect. Such high reliability with naive Ss indicates
that duration of the SAE should prove to be a very useful measure for bath
experimental and applied purposes. In addition, the orderly progression of
duration of SAE with increasing fixation time further adds to our confidence
that duration is a stable measure.

The observed relationship between duration of SAE and fixation time sug-
gests that a relatively shore exposute is sufficient to produce a substantial after-
effect. On the basis of these results, 15 sec. appears to be an optimal fixation
period, This duration has the advantage over the standard 30 sec. used in clinical
practice in that it keeps to a minimum both fatigue and testing time.

REFERENCES
J. BASLER, A. Uber das Sehen von Bewengungen; sechste Mitteilung. Pfleug. Arch. ges.
Physiol., 1911, 139, 611-622.
2. EYSENCK, H. J. Cortical inhibition, figural aftereffect and theory of personality. J.
abnorm. soc. Psychol., 1955, 51, 94-106.