Unlike saccades, quick phases of optokinetic nystagmus (OKN) are not preceded by shifts of attention

Abstract

Quick phases of optokinetic nystagmus are often equated to saccades. Indeed, their trajectories resemble the saccadic ‘main sequence’, and both saccade and quick phase control involve the same brainstem circuitry. However, whether and to what extend higher cortical areas associated with saccade programming (e.g. lateral intraparietal area, frontal eye fields) also participate in the control of OKN quick phases remains unknown. One hallmark of saccadic eye movements is the premotor shift of attention towards the saccade goal location, which is assumed to rely on overlapping networks for attention and oculomotor control in these higher cortical areas. Hence, the question arises if quick phases, like saccades, also draw attention towards their endpoint. We measured the spatiotemporal distribution of visual attention during OKN induced by a full-field dynamic pink noise stimulus (which we introduced at VSS 2018), that either moved leftwards or rightwards at a speed of 15°/s. At a random time and position the moving noise stimulus contained a brief orientation signal (50 ms) which participants had to discriminate. Taking visual orientation sensitivity as a proxy of attention, this paradigm allowed us to determine how attention is deployed during quick and slow phases of OKN, without the presence of object-like visual structures. Our results show that, unlike before saccades, visual attention is not enhanced at the endpoint of OKN quick phases. Instead, the data reveal that visual attention during OKN is predominantly allocated to the current gaze position. This suggests that OKN quick phases are reflexive gaze resetting movements controlled by low level, rather than higher, attention-related centers. OKN quick phases are not saccades.