The effects of task switching on age-related differences in shape perception

Abstract

Object and shape perception are important components of vision. However, little is known about how shape perception changes with age. Here, we examined whether aging affects global shape perception: Older and younger observers viewed complete rectangles or line fragments of rectangles (with or without occluders), and judged whether the overall shape was “tall” or “fat”. The aspect ratio of these stimuli was manipulated, and a staircase procedure determined observers' thresholds in each condition at varying stimulus durations. Such a task enables us to compare the relative effects of age and duration under stimulus conditions in which all sensory information is provided (complete), partial information is provided (fragmented), or when partial information leads to integration processes (occluded). Age differences in shape discrimination were found when observers had to switch from one stimulus condition to another every 30 seconds, with older observers requiring larger aspect ratios than younger observers to perform the task. No age differences were found when observers switched less frequently across stimulus conditions. Regardless of switching condition, older observers were not differentially impaired by partial contour information, and both age groups showed similar patterns of performance across stimulus conditions and durations. These results suggest that aging may impact negatively on shape perception, but only under conditions of stimulus or task switching. Such a result fits well with the idea that the true extent of age-related deficits are more likely to be seen under conditions that challenge the visual system (e.g., in divided-attention or task-switching conditions).

Footnotes

 This work was supported by the Canadian Institutes of Health Research and the Canada Research Chair program.