Age related changes to perceptual surround suppression of moving stimuli.

Perceptual analogues of centre-surround suppression have been applied as indirect measures of cortical inhibitory function in several clinical disorders. Two tasks have been used: a centre-surround contrast perception task and a motion direction discrimination task, where the stimulus size and contrast is varied to measure surround suppression effects. The tasks are markedly different, yet previous literature implies that both measures indirectly assess inhibitory function and that results will be complementary. This is not the case for age-related effects on surround suppression, however, as previous reports using the different measures are conflicting. Here we use a low-spatial frequency, drifting grating version of the centre-surround contrast perception task, and compare results to those obtained with the motion direction task in a single group of older observers. Older adults demonstrate significantly increased perceptual surround suppression of contrast for drifting, high contrast stimuli. Using the motion discrimination task, older observers showed similar amounts of surround suppression for the largest stimulus. This study confirms that visual surround suppression is altered by ageing. The complexity of neuronal systems involved in centre-surround interactions makes it unlikely that a single perceptual task will be sufficient to describe the effects of clinical disorders on surround suppression.