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Lisa R. Betts, Christopher P. Taylor, Patrick J. Bennett, Allison B. Sekuler; Evidence for reduced inhibition in the aging visual system revealed by a motion discrimination task. Journal of Vision 2004;4(8):206. doi: 10.1167/4.8.206.
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© ARVO (1962-2015); The Authors (2016-present)
Elderly observers perform worse than their younger counterparts on many perceptual tasks, including contrast detection, orientation discrimination, and motion discrimination. These performance deficits may be linked to age-related changes in cortical perceptual mechanisms, such as the deterioration of inhibitory connections that help to fine-tune the selectivity of visual neurons (Leventhal et al., 2003). Recent psychophysical research with young observers suggests that such inhibitory processes impair motion discrimination for large, high-contrast stimuli (Tadin et al., 2003). We predicted that an age-related reduction in inhibitory processing would therefore benefit elderly observers in a discrimination task using large, high-contrast targets. Stimuli consisted of 1 cpd Gabor gratings drifting at a rate of 2 deg/s. The gratings were presented at two different sizes (0.7 and 2.7 deg) and at three different contrast levels (2.8%, 11% and 43%). A staircase procedure varied stimulus duration to obtain motion discrimination thresholds at 77% accuracy. Consistent with previous findings, duration thresholds for younger observers with low-contrast stimuli improved with increasing stimulus size, whereas thresholds in the high-contrast condition worsened with increasing stimulus size. Elderly observers showed the same pattern of results for low contrast gratings, with a greater improvement as a function of stimulus size compared to young observers. More importantly, as predicted, elderly duration thresholds for high-contrast gratings increased only marginally with increasing stimulus size. Furthermore, elderly thresholds were lower than young thresholds in the condition using the largest, high-contrast stimulus. Additional control experiments showed that the results were not due to age differences in retinal illuminance. The results are consistent with the hypothesis that intra-cortical inhibitory mechanisms, perhaps in area MT, are less potent in elderly observers.
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