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Larry A Abel, Reuben Dyer; Age impairs OKN suppression during divided attention tasks. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5790. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previously we reported that the ability of healthy young subjects to suppress optokinetic nystagmus (OKN) is reduced when they fixate and also respond to a feature of the moving stimulus, particularly when finding the target is hard. We wished to see if finding complex, moving targets was worse in healthy older subjects, consistent with a reduction in their attentional resources.
15 young (19-23 yrs, mean 21.4) and 12 older subjects (65-89 yrs, mean 74) took part. Stimuli 25 deg wide moved right at 26 deg/s; eye movements were recorded at 500 Hz. Complex stimuli were columns of large red Cs and blue Ts with occasional red Ts (the targets) in the middle row. For simple stimuli red Ts were replaced by Xs and all other characters by Os, all black. All trials had a central fixation spot which blinked pseudo-randomly; this was to elicit a key press on central static trials. Peripheral trials had a blinking target 12 deg to the left. Independent variables were complexity (XO vs TC), dynamism (static dot vs moving red T or X passing the relevant dot) and location (attend centre or periphery). Two 3-way ANOVAs were run—one with only the central dot, with age the between-subjects variable and dynamism and complexity as within-subjects variables. The other ANOVA used only dynamic stimuli but some trials used the peripheral spot; within-subjects variables now were locus of attention and complexity.
Older adults were significantly poorer on all tasks. For the dynamic-only ANOVA (Fig 1), there was significantly more breakthrough at centre and for the complex target (p<.001). Age increased the effect of complexity (p=.025), particularly at the centre (p=.013). For the central-only ANOVA (Fig 2), gain was higher for dynamic targets and complex targets; it was even worse for complex, dynamic ones. Older subjects again did worse with dynamic targets (all p<.001), and more so when they were complex (p<.005).
Aging does little to OKN itself but impairs its suppression when attention is directed to the moving target, especially in a conjunction rather than a feature search. Spreading attention spatially did not lead to more breakthrough but rather to the opposite, perhaps due to top-down strengthening of foveal input. When attention was on static dots, age did little, but it markedly impaired OKN suppression when moving targets were attended.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Fig 1-dynamic means
Fig 2-central means
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