The post-stimulus modulation of the saccade rate reflects inhibitory control and top-down exploration in young and aging populations

The growth in the world’s aging population has made it increasingly important to understand the cognitive and perceptual changes associated with aging. Studies have suggested that exploratory behavior and motivation decline with age. Here we examine the hypothesis that the characteristics of changes in exploratory behavior can be revealed through examining the saccade rate modulation in response to a new stimulus. It is a replicated finding that following the abrupt presentation of a stimulus, saccades are inhibited for approximately 100-200 ms and then they rebound, before returning to baseline. The post-stimulus inhibition is modulated by low-level features of the stimulus such as contrast and rarity and was suggested to be linked to midbrain inhibitory processes. The rebound phase is hypothesized to represent the initiation of the drive to explore, following the release of inhibition. Young (age 18-35, n=13) and older (age >60, n=12) healthy participants were presented with images of familiar and unfamiliar objects. The objects were first presented during a study phase, and then again during a test phase. The analysis focused on two oculomotor metrics: duration of inhibition and amplitude of the rebound; the first, hypothesized to reflect inhibitory control, and the second to reflect a top-down drive to explore. Analyzing post-stimulus saccade rates revealed that age affected inhibition duration but not the rebound: inhibition duration was found to be shorter in older relative to younger participants, indicating a lower inhibitory control in the aging population. Object familiarity affected the rebound amplitude and not the inhibition, but only in younger participants. This suggests that high-level stimulus characteristics modulate the top-down drive to explore and that this effect deteriorates with aging. We conclude that exploring the post-stimulus modulation of the saccade rate could contribute to the understanding of the exploratory drive and other cognitive functions in different populations.