Procedural Considerations of the Spiral Aftereffect Test

Abstract

In Exp. I durations of the aftereffects under the conditions of successive observations of an expanding spiral, successive observations of a contracting spiral, and alternate observations of an expanding and a contracting spiral indicated that alternate observation of an expanding and a contracting spiral yielded spiral aftereffects (SAEs) of shorter duration for both spirals than did successive observations of each spiral alone. The mean duration of the SAE for the non-alternating condition exceeded that for the alternating condition by 4.07 sec. (42%) for the expanding spiral and 3.17 sec. (20%) for the contracting spiral. The contracting spiral yielded SAEs of longer duration than did the expanding spiral under both the conditions of alternation and non-alternation and by about the same absolute amount. No change is expected from repeated exposure to the SAE test, since there was no significant change from the first to the third block of 40 trials. In Exp. II the effect of the width of the spiral on the duration of aftereffect was studied under conditions of successive observations of an expanding and a contracting spiral. Results showed that a spiral composed of equal parts black and white yielded SAEs of longer duration than did a spiral of 25% black and 75% white, or 75% black and 25% white.