Perceptual stabilization is weaker in older adults and correlates with spatial suppression of motion

Spatial suppression and perceptual stabilization are two distinct aspects of motion processing that reduce the influence of redundant motion signals to enhance behaviorally relevant motion. Spatial suppression reduces sensitivity to large, uniform background motion, whereas perceptual stabilization compensates for global retinal motion arising from involuntary eye movements during fixation. Although both mechanisms reduce the influence of redundant motion, it remains unclear whether they are behaviorally related. Comparing younger and older adults provides an opportunity to examine this relationship because spatial suppression is known to be weaker in older adults from previous work. If perceptual stabilization relies on similar motion processing as the spatial suppression of motion, it would be expected to be weaker in older adults. To test this prediction, 34 younger adults (aged 19-35 years) and 34 older adults (aged 60-80 years) performed psychophysical tasks measuring spatial suppression and perceptual stabilization. Spatial suppression strength was measured using a motion direction discrimination task, deriving a suppression index from the duration thresholds for a large stimulus presented at high and low contrast. The influence of perceptual stabilization on motion speed discrimination was assessed by comparing conditions that preserved and disrupted stabilization, with the difference quantified as a stabilization index. Across all participants, the suppression index was positively correlated with the stabilization index, demonstrating a relationship between spatial suppression and perceptual stabilization across both age groups. Older adults exhibited weaker spatial suppression and perceptual stabilization than younger adults. To determine whether the reduced perceptual stabilization reflected age differences in fixational eye movements, fixation stability was assessed and did not differ between the groups. Therefore, our findings provide behavioral evidence that the spatial suppression of motion and the perceptual stabilization of fixational eye movements are linked and may reflect shared motion-processing mechanisms that weaken in older adults.