Healthy aging does not alter centre surround orientation effects in foveal intraocular and interocular contrast suppression

Abstract

Aims/Purpose: Healthy aging alters how the perceived contrast of a pattern is influenced by its surround. Neural mechanisms underlying this aging effect can be disentangled by manipulating stimulus orientation, duration, and by using dichoptic viewing. Here, we tested whether intraocular and interocular center surround contrast suppression demonstrate distinct effects of surround orientation, and if so, whether they are altered by healthy aging.Methods: We measured the perceived contrast of a circular, vertically oriented sine grating (0.67° diameter, 20% contrast) alone and in the presence of annular sinusoidal surround (6° diameter, 40% contrast) in 18 younger (19–32 years) and 18 older adults (61–78 years). Factors explored were: intraocular versus interocular viewing, parallel versus orthogonal surround orientation, and 40 ms versus 200 ms stimulus duration. Surround orientation effect (SOE) was calculated as 1‐ (contrast suppression by orthogonal surround/ contrast suppression by parallel surround). SOE was 0 if contrast suppression was equal between both surround orientations, and the value increased if parallel surround produced stronger suppression than orthogonal surround.Results: The interocular SOE was not influenced by stimulus duration, whereas, intraocular SOE was stronger at 40 ms compared to 200 ms (viewing condition x stimulus duration: F(1,34) = 24.38, p < 0.01). Older and younger adults showed similar SOE under all test conditions (main effect of age: F(1,34) = 0.02, p = 0.89). Age did not affect how stimulus duration influenced intraocular and interocular SOE (age x viewing condition x stimulus duration: F(1,34) = 0.41, p = 0.52).Conclusions: Our results suggest that centre surround orientation effects on intraocular and interocular contrast suppression is dependent on stimulus duration and this relationship is unaltered by healthy aging.