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L.A. Abel, I.M. Williams, L. Mullhall, J. Mattingley; Optokinetic Nystagmus as an Assessment of Divided Attention . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2398.
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Purpose: To use measures of optokinetic nystagmus (OKN) gain, frequency and amplitude as indicators of the ability to carry out both individual and combined tasks involving allocation of visual attention. If OKN changes corresponded to differing task demands, then it could serve as a means to quantify the ability to allocate visual attention to multiple tasks. Attentional resources are finite and decline with age, which may become particularly apparent during studies of divided attention, when subjects must carry out 2 simultaneous, independent tasks. Methods: We recorded full–field OKN elicited by a curtain bearing large coloured letters. We measured subjects’ (9 M, 2 F, aged 23–69) ability to generate active OKN, to suppress it with fixation of a red laser spot and––to assess the ability to divide visual attention––to continue to suppress it when fixating and simultaneously paying covert attention to a novel–coloured optotype on the stimulus. Results: During fixation all subjects almost fully suppressed OKN. All subjects generated vigorous active OKN. When attempting to suppress the OKN while simultaneously paying covert attention to feature of the stimulus, OKN suppression was less. Gain, frequency and amplitude all showed significant main effects on 1–way repeated measures ANOVA; post–hoc pair–wise comparisons were significantly different in all but one instance. To determine whether performance on any of the tasks was impaired by ageing, linear regression of gain, frequency and amplitude versus age was carried out. Only for the divided attention task were the 3 OKN measures significantly correlated with age, perhaps reflecting an age–related diminution of attentional resources. Conclusions: Simultaneously trying to suppress OKN whilst covertly attending to a feature of the OKN stimulus led to a significant, age–related increase in the "breakthrough" of the nystagmus. Two possible explanations are 1) covert attention to the optokinetic stimulus increased its salience, leading to a stronger and hence harder to suppress motion signal and 2) simply allocating visual attention to two spatially disparate regions meant that insufficient resources were available to adequately suppress the nystagmus. Further experiments would be necessary to choose between these, preferably in a larger population spanning a wide range of ages.
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