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Sandra Utz, Glyn W. Humphreys, Joseph P. McCleery; Neural correlates of central versus peripheral target detection during complex visual search. Journal of Vision 2011;11(11):1294. doi: 10.1167/11.11.1294.
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© ARVO (1962-2015); The Authors (2016-present)
Extensive research has examined behavioural and brain responses during visual search when participants are required to indicate the presence or absence of a pre-defined target. According to Carrasco, Evert, Chang, and Katz (1995) detection of targets in search tasks becomes increasingly less efficient as the target is presented at more distant field eccentricities, reflected in increased reaction times (RTs). To date, however, the neural mechanisms underlying visual search for targets presented in different spatial locations are quite unclear. In the current experiment, adult participants performed a conjunction search task, searching for a red “X” in a field of green “X” and red “T” distractors, while event-related potentials (ERPs) were recorded. Behavioural results revealed significantly higher RTs when either 5 or 15 letters were presented and the target was in the periphery (>10 deg visual angle) compared to when it was in the centre (<10 deg visual angle; p < 0.001). ERP results revealed larger amplitude activity for central versus peripheral targets in a positive-going component recorded from electrodes over the parietal cortex between 400 and 500 ms (p = 0.002). This parietal activity was also larger for targets detected in a field of 5 versus 15 items (p = 0.004). For the 5 item condition only, the earlier N2pc component recorded from electrodes over the occipital cortex also differentiated detected targets identified in the central versus peripheral visual field (interaction p = 0.002). These data reveal differences in neural mechanisms underlying central versus peripheral target detection. Centrally presented targets elicit more parietal cortex activity than peripherally presented targets between 400 and 500 ms, perhaps reflecting increased focus of attention on the target item. For the 5 item condition, this focus of attention appears to be initiated by a bottom-up perceptual process originating in the occipital cortex. Data will also be presented from children aged 6- to 12-years.
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