Abstract
The present study examined sensitivity to the direction of global motion presented to the retinal periphery. The stimuli consisted of two sequentially presented random-dot cinematograms (RDCs) of different average angular directions. The direction of each individual dot was drawn separately from a Gaussian distribution of directions every 6th frame (12 frames total at 85 Hz). The standard deviation of this distribution was manipulated to vary the level of noise. The values used were 0, 4.5, 18, and 36 degrees. To examine the effects of retinal eccentricity the RDCs were offset from a focal point by 0, 8, 22, or 40 degrees of a visual angle. To ensure that that the participants gaze maintained fixation on the focal point, an Eyelink II eye tracking system was employed. 5 college age participants were asked to discriminate between the two sequentially presented displays at all four retinal eccentricities. Additionally, noise was examined to determine if there would be any interaction effects at different retinal eccentricities. The results indicate main effects of eccentricity and noise level. The interaction of noise and eccentricity was not significant. Post hoc analyses indicated significant differences between the 0 and 40 degree eccentricities. These results indicate there is a significant loss in the ability to discriminate global motion only at extreme eccentricities. To assess if this loss could be attributed to a general loss of visual acuity in the retinal periphery a modified Landolt-C test was administered at retinal eccentricities that matched those used in this study. The results indicate a significant decrease in acuity for the 0 and 8 deg retinal eccentricities when compared to the 40 degree eccentricity. These results suggest that pooling velocity to recover global motion is preserved at more eccentric regions in the visual field despite the loss in acuity.
This work supported by NIH AG13419-06 and NEI EY18334-01.