Abstract
The present study examined age related differences in the perception of global coherent motion when considering available local motion information and stimulus size. The stimuli consisted of random dot cinematograms (RDCs) in which the path of each dot was sampled from a Gaussian distribution of directions with a standard deviation of 36 degrees. 8 younger (mean age 20.9) and 8 older (mean age 78.6) participants were asked to discriminate the coherent direction of motion from two sequentially presented RDCs. Two hypotheses were examined: 1) that older observers are less efficient at incorporating local motion information into a perception of global motion, and 2) that older observers have a decreased ability to spatially integrate motion information. Hypothesis 1 was examined by using 6 or 24 dots in the motion display and three different types of dot motion; continuous, limited lifetime, or random walk. These three motion types can be quantified as containing varying amounts of sampling information based on the number of local motion vectors and amount of angular information presented. To test hypothesis 2 we used RDCs that had circular viewing areas of 1.5, 3, or 6 degrees visual angle in diameter. The results show that younger observers have lower thresholds relative to older participants when 24 dots were present. This result indicates that older observers may not be able to incorporate local motion information into global coherent motion as efficiently as younger observers. This effect was more pronounced when the display size was reduced to 1.5 degrees visual angle. An ideal observer model will be discussed that is used to compare sampling efficiencies in both age groups.
Research supported by NIH AG13419-06