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L. A. Abel, N. R. Rubinstein; OKN Suppression as a Reflection of Divided Attention: Attending Moving or Complex Features Impairs Suppression More. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4760.
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We have previously used suppression of optokinetic nystagmus (OKN) to evaluate the ability of young and old normal subjects to divide visual attention: subjects fixated a central target while covertly attending another location. The stimulus in these studies (a rotating curtain and projected laser targets) could not be readily altered. In the present study we used computer-generated stimuli to vary the nature of both the moving background and static elements, enabling us to examine how suppression is affected by both the location and complexity of attended features.
Horizontal eye movements of 26 subjects (13F) aged 20-26 were recorded with an infrared limbus eyetracker; data were digitized and analysed offline. Subjects were seated 1.55m from a 1.83m by 1.36m front-projected stimulus, subtending 61.1 x 47.4°. OKN stimuli consisted either of rows of red Cs and blue Ts, with 3 red Ts at eye level, or similarly spaced black Xs, with 3 black Os. Shapes-either green squares (simple) or rapidly changing green or orange circles, stars and squares (complex)-were placed at primary position and ±12.5°. The central target was fixated during all tasks. Dynamic tasks required a button press when either a red T or an O passed the attended position, while static tasks required the detection of either a blink (simple) or green star (complex). After computation of OKN gain, effects of within-subjects effects of motion, complexity and location and the between-subject effect of gender were compared with 2-way mixed ANOVAs.
There was no main effect of gender. Attending centrally compared to peripherally caused more breakthrough (i.e., higher gain) for static, dynamic, simple and complex stimuli (p<.001 for all). Complexity did not affect static tasks but caused more breakthrough for dynamic tasks at all locations (p<.001). Dynamic tasks also showed more breakthrough at all locations (p<.001).
Unlike older subjects (Williams et al 2006), these young normal subjects had sufficient attentional reserves to spatially distribute attention. Top-down attention to the OKN stimulus, not to a static feature, significantly increased OKN, perhaps because increased motion processing signals became harder to suppress. This was greatest when these tasks required a conjunction, not a pop-out search, presumably because this diverted attention from OKN suppression. The flexibility of the stimuli will allow further extension of these studies.
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