Some Parameters in the Perception of the Spiral Aftereffect

Abstract

Previous work with figural aftereffects has indicated that retarded adolescent males do not satiate as readily as normal males ( 2 ) . If neural satiation underlies motion aftereffects ( I ) , retarded males should not perceive the spiral aftereffect (AE) as readily as normal males. The spiral, spun at 100 rpm, was an 8-in. disc with a %-in. black line making 2% clockwise rotations on a white ground. Ss were seated approximately 7 ft. from the spiral under an overhead fluorescent room fixture. Ss fixated the center of the spiral which was spun inwardly for 30 sec., after which a description was requested, and then outwardly for 30 sec. While all 32 normals (16 males, 16 females; tested in groups of 4; mean age 16 yr., 0 mo.) wrote descriptions indicating they perceived both AE., 9 (6 males, 3 females, mean age 16 yr., 10 mo.) of the 41 individually tested retardates failed to report both AEs The mean IQ of 49 for the retardates not reporting the AE was significantly lower than the mean IQ of 60 for the retardates (16 males, 16 females, mean age 16 yr., 9 rno.) reporting the AE ( f i < .01). For all Ss correctly reporting both AEs, the spiral was then spun alternately inwardly, then outwardly, in a random time order varying from 2 to 20 sec. (excluding odd numbers). Results indicate a significant interaction between sex and intelligence. The 16 male normals reported more total AEs than the 16 male retardates (# < .O5), confirming the hypothesis. In contrast, however, female retardates reported more total AEs than female normals (# < .01). Among the normals, males reported more total AEs than females ( p < .05)a finding consistent with sex differences in kinesthetic AEs (3)-while, in contrast, the retarded females reported more total AEs than retarded males ( p < .01). Because of the above interaction, no significant differences were found between all normals and all retardates in the temporal threshold (approximately 50% Ss reporting AE) or at any point on the temporal curve. However, direction of rotation was a significant variable. Combining both groups, the threshold for inward rotation was 6 sec., for outward rotation (interpolated) 13 sec., and in both groups far more total AEs were reported after inward rotation ( p < .001). In the normals, significant differences between AEs after inward as compared with outward rotation were found at each 2-sec. interval from 6 through 14 sec.; for retardates from 10 through 16 sec.