Contrast and stimulus duration dependence of perceptual surround suppression in older adults.

Most natural visual tasks involve the extraction of visual features from suprathreshold contrast backgrounds, hence an understanding of how ageing impacts on contrast mechanisms is essential to understand elderly visual function. Previous studies have revealed increased perceptual surround suppression of contrast in older adults. We aimed to determine whether such age-related effects depend on the centre or surround stimulus contrast as the neurophysiological mechanisms underpinning contrast-contrast suppression depend on such contrast relationships. We also measured surround suppression of contrast for longer duration and shorter duration stimuli to explore for effects of surround adaptation Fifteen younger and 15 older adults performed a centre-surround contrast discrimination task for a variety of centre-surround contrast combinations (20%, 40% and 80% contrast). Stimulus duration was 500ms. The 40% centre, 80% surround condition was also presented for 100ms duration. Relative to younger adults, perceptual surround suppression was increased for the older group for low, but clearly suprathreshold, central contrasts (20% contrast), whilst both groups performed similarly for stimuli with high centre contrasts. Data was best fit by a model with both increased inhibitory and excitatory weightings in the older group. Reduced stimulus duration increased perceptual surround suppression for both groups consistent with reduced adaptation to the surround, and did not explain the difference in suppression magnitude between groups. Understanding the stimulus parameters that elicit increased surround suppression in older adults is key to directing future work exploring underlying neural substrates, in addition to potentially being useful for predicting performance on more complicated natural visual tasks such as object and scene perception.