Abstract
When a peripheral cue is presented, subsequently presented targets at the cued location first experience facilitated reaction times (RT’s) relative to other locations (a phenomenon classically termed “attentional capture”). Later, a large RT cost occurs (a phenomenon termed “inhibition of return”, IOR). We recently suggested that both attentional capture and IOR are a simple consequence of saccadic system rhythmicity (Tian & Hafed, VSS, 2014). In our simple model, saccades are repetitively generated, including during fixation when they become microsaccades, and they oscillate in direction. When cues appear (typically in a lateralized manner), they “reset” saccadic system phase (Hafed & Ignashchenkova, J. Neurosci., 2013), and whether attentional capture or IOR occurs simply depends on the phase of cue-reset saccadic oscillations at which subsequent targets appear. Here, we aimed to understand one possible source of such oscillations; we hypothesized that purely vertical cues would have weaker impact than horizontal ones because vertical stimuli activate lateralized visuomotor structures (e.g. superior colliculus) in a simultaneous, bilateral manner. We ran two monkeys in a classic Posner cueing paradigm. In each trial, a cue/target (1 deg diameter white circle) appeared at 5 deg eccentricity, either horizontally or vertically. Cue-to-target onset asynchrony (CTOA) was random (between 32 ms and 1532 ms), and the post-cue target could appear either in the “same” or “opposite” cued location. We collected >4000 trials per monkey. We observed strong IOR with purely horizontal cues, as expected. However, with purely vertical cues, IOR was eliminated. Critically, microsaccade analysis revealed significantly weaker influence of vertical cues on post-cue microsaccade frequency and direction, suggesting that microsaccadic oscillations are partly mediated by lateralized visuomotor structures. We also simulated these results with our simple saccadic rhythmicity model. Taken together, our results demonstrate that modulations of spatial attentional performance may simply reflect the dynamics of saccadic/microsaccadic oscillatory rhythms.
Meeting abstract presented at VSS 2015