Spatiotemporal properties of apparent-motion perception in aging

Abstract

Recent studies have found age-related declines in motion perception from random dot kinematograms (e.g. Bennett et al., Vis. Res., 2007; Norman et al., Perception, 2003). However, some temporal integration abilities seem to remain intact (e.g. Andersen & Ni, Vis. Res., 2008). Here, we used random-dot two-frame apparent motion stimuli to investigate whether such age-related changes in motion direction discrimination can be attributed to a decline in the ability to integrate visual information across space and/or time. Previous work using such stimuli has shown that the perception of apparent motion is influenced separately by the duration of the inter stimulus interval (ISI) between the two frames and the magnitude of spatial displacement of the dots (e.g. Baker & Braddick, Perception, 1985). In the current experiment, older (mean age: 69 years) and younger (mean age: 24 years) subjects reported the direction of motion of two sequentially presented random-dot patterns in a two AFC task. The patterns were presented for 100 ms each and were separated by a blank ISI that varied between 10 to 240 ms. The second pattern was identical to the first pattern, but was shifted to the right or to the left by a displacement ranging from 1.9 to 76 arcmin. The effect of age on direction discrimination performance varied with the amount of displacement. At the shortest and longest displacements, older subjects performed significantly worse than young subjects across all ISIs. At medium displacements, both age groups performed near ceiling at short ISIs, but performance decreased with increasing ISIs. This decline was significantly greater, and began at a shorter ISI, in older subjects. These findings indicate that older subjects integrate information across a smaller range of inter-stimulus intervals and spatial displacements compared to younger subjects.