The Oblique Effect in Chinese Infants and Adults

Abstract

Lessened acuity for oblique contours as compared with horizontal and vertical contours, the oblique effect, is characteristic of humans and animals. The magnitude of the oblique effect in humans varies with ethnic origin. Three experiments were performed to determine the source and extent of this variation in Chinese and Caucasian subjects. Experiment I. Acuity for vertical and oblique gratings was measured in Chinese infants with a preferential looking technique. The development of visual acuity for Chinese infants was found to be strikingly similar to that reported for Caucasian infants. For infants of both races at about 1 year of age, the magnitude of the oblique effect was about 1 octave. Experiment II. Acuity for main-axis (horizontal and vertical) and oblique gratings was measured in Chinese and Caucasian adults. The oblique effect in Chinese subjects was significantly smaller than in Caucasian subjects. The Chinese also had significantly better acuity for oblique gratings, but not for main-axis gratings. Experiment III. To determine whether differential sensitivity to main-axis and oblique-axis gratings extends to suprathreshold spatial frequencies, contrast sensitivity for four orientations at each of five spatial frequencies was assessed in Chinese and Caucasian adults. There were no significant differences in contrast sensitivity between Chinese and Caucasian subjects at any spatial frequency. The differential sensitivity increased with increasing spatial frequency for both ethnic groups. The difference in the magnitudes of the oblique effect in Chinese and Caucasian subjects appears in acuity thresholds in adults, and may result solely from the Chinese having better acuity for obliquely oriented gratings.