Abstract
This study compared the sensitivity of 8 older (mean age - 70.5) and 8 younger (mean age - 20.2) observers to the direction of global motion presented in the retinal periphery. The task was to discriminate between two sequentially presented random-dot cinematograms (RDCs) of different average angular direction. Within the RDCs individual dots moved in a “random-walk” based on a distribution of directions. To manipulate noise the standard deviation of this distribution was set at 0, 4.5, 18, or 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. The results indicate main effects age, eccentricity, and noise level. There were significant interactions between age and eccentricity, age and noise level, as well as eccentricity and noise level. Post-hoc analyses indicated that older observers had increased thresholds at eccentricities of 22 and 40 degrees while younger observer did not differ significantly across eccentricity. This result indicates that there is a loss in sensitivity to global motion direction in the retinal periphery for older observers. 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 eccentricities matching those used in this study. The results indicate a loss in acuity for both age groups as eccentricity was increased. Older and younger observers did not differ significantly in acuity. An ANCOVA was performed to examine if the effect of eccentricity was based on declines in acuity. The results indicate losses in the discrimination of global motion direction for older observers occur independently of losses in acuity.
This work supported by NIH AG13419-06 and NEI EY18334-01.