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Renee Karas, Allison McKendrick; Increased spatial surround suppression in the elderly. Journal of Vision 2011;11(11):464. doi: 10.1167/11.11.464.
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Betts et al. (2005) showed that older observers needed shorter stimulus presentation times than younger adults to determine the motion direction of a large drifting Gabor. This was explained by a reduction in surround suppression in older observers, possibly due to a reduction of cortical inhibition. However, we measured increased surround suppression in older adults using a centre-surround contrast task (Karas and McKendrick, 2009). The magnitude of surround suppression depends on the stimulus parameters of the centre and surround. Here we use a series of stimulus parameters to explore the generality of our finding of increased contrast-contrast suppression in the elderly. Fifteen younger (18–33 years) and 18 older (61–84 years) adults participated. Using a method of constant stimuli, perceived contrast was measured for a sine wave grating (0.67 deg, 4c/deg) with and without an annular surround (4 deg, 4c/deg). The following parameters were varied: a) contrast polarity of centre and surround (70%/40% contrast in centre-surround); b) border in phase and out of phase (180 deg); c) reduced contrast for younger observers (to match saliency to older observers). A second experiment (10 younger and 10 older participants) explored the addition of drift to the grating stimulus (2c/deg, 2 deg/sec). The shift in point of subjective equality (PSE) was measured for each condition. Older participants showed a greater shift in PSE (greater surround suppression) for each condition: lower surround contrast, both in and out of phase [F(1, 31) = 17.4, p < 0.001]; matched contrast saliency [F(1,31) = 19.8, p < 0.001]; and drifting gratings [t(18) = 5.9, p < 0.001)]. For the range of parameters tested, on average older participants demonstrated an increase in surround suppression. Our study demonstrates a robust effect of increased contrast-contrast surround suppression in the elderly for a wide range of stimulus parameters.
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