Abstract
When two objects move toward one another, motion at the point of overlap is ambiguous: the objects may stream past one another or bounce off one another. A sound presented around the time of coincidence biases the percept toward bouncing (Sekuler et al., 1997, Zhou et al., 2007). In contrast, a visual occluder that obscures the motion coincidence biases the percept toward streaming (Sekuler and Sekuler, 1999). Because multisensory integration changes with age (Peiffer et al., 2007, Stephen et al., 2010), we exploited the bouncing-streaming percept to assay age-related changes in the integration of multiple inter- and intra-modal cues. We also examined the temporal development of occlusion by determining the percept for occluders of different durations. In 12 interleaved conditions, younger (n=9; mean age=20) and older (n=9; mean age=68) subjects judged whether two moving gray discs bounced or streamed. The discs were presented on their own (control), or accompanied by a sound, an occluder of varying duration, or both sound and occluder, all centered around the time of the discs’ coincidence. On half the trials, the discs differed in luminance (producing unambiguous streaming or bouncing in control conditions); on other trials, the discs had equal luminance (producing an ambiguous percept in control conditions). Younger, but not older, subjects showed a significant bias toward streaming responses in the ambiguous, control condition. A sound at the point of coincidence biased the percept toward bouncing in both groups, but its effect was reduced in older subjects. The effect of occluders depended on duration: brief occluders promoted bouncing in younger subjects, but not older subjects, whereas long occluders promoted streaming in both groups. The weakened inter- and intra-modal integration seen here could contribute to previously demonstrated age-related deficits in memory, and may be linked to age-related changes in neural processing in the gamma band
Meeting abstract presented at VSS 2012