Abstract
Elderly exhibit accumulating deficits in visual motion perception, which is critical for humans to interact with their environment. Previous studies have suggested that aging generally reduces neuronal inhibition in the visual system. Here, we investigated how aging affects the local intra-cortical inhibition using a motion direction discrimination task based on the motion repulsion phenomenon. Motion repulsion refers to the phenomenon by which observers overestimate the perceived angle when two superimposed dot patterns are moving at an acute angle. The misperception has been interpreted as local mutual inhibition between nearby direction-tuned neurons within the same cortical area. We found that elderly exhibited much stronger motion repulsion than young adults. We then compared this effect to how aging affects the global inter-cortical inhibition by adopting the surround suppression paradigm previously used by Betts et al. (2005). We found that elderly showed less change in the discrimination threshold when the size of a high-contrast drifting Gabor was increased, indicating reduced surround suppression compared to young adults. Our results indicate that aging may not always lead to a decrease of neuronal inhibition in the visual system. These distinct effects of aging on inhibitory functions might be one of the reasons that elderly people often exhibit deficits of motion perception in a real-world situation.
Highlights
As the human lifespan has been continuously increasing over the past century, aging has become a worldwide phenomenon
To investigate aging effects on motion repulsion, we presented young and old observers with two random dot kinematograms (RDKs) moving in different directions
In previous studies (Marshak and Sekuler, 1979; Rauber and Treue, 1999), the visual angle between the perceived motion direction of target RDKs and reference RDKs was generally larger than the actual angle in both the young and old groups (Figure 1B), which is the behavioral correlation of the repulsive interactions between motion directions
Summary
As the human lifespan has been continuously increasing over the past century, aging has become a worldwide phenomenon. The quality of life can be seriously affected by the aging process, because various perceptual abilities generally decline with aging. Because visual motion perception is essential for humans to interact with the environment, aging-induced accumulating deficits in visual motion perception can have profound impacts on normal life, such as inducing a higher risk of car accidents (Boot et al, 2014). Previous studies have shown that elderly exhibit accumulating deficits in the form of reduced sensitivity of motion detection and discrimination (Bennett et al, 2007), impaired perceptual efficiency (Bower and Andersen, 2012), and elevated thresholds for motion speed perception (Snowden and Kavanagh, 2006). Aging increases the thresholds for translational motion but not for radial flow perception (Billino et al, 2008). As the worldwide aged population rapidly expands, it is urgent to determine
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