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Free keywords:
Visual-Gestalt priming; Object coding; Kanizsa-type figure detection; Reaction time; EEG; Wavelet transform; Evoked gamma-band activity
Abstract:
The detection of reaction-times (RTs) to a target Kanizsa-type square (an illusory square defined by the collinear arrangement of 90° corner junctions) within a matrix of distractor junctions are expedited when the target display is preceded by a 40-Hz flickering display of premask crosses presented prior to, and at the locations subsequently occupied by the junctions of the target display. Priming effects were obtained when four crosses (which together matched the Gestalt arrangement of the target) were presented at the display locations subsequently occupied by the junctions forming the target Kanizsa square (Elliott and Müller, 1998 and Elliott and Müller, 2000). The present study was conducted with the aim of replicating the 40-Hz RT priming effects, while simultaneously recording the observers EEG in order to establish the presence and location of Gestalt priming in the brain. The statistical pattern obtained in the RT data corresponded well with previous studies and was matched by the pattern of target P300 latencies across bilateral central and posterior electrodes. Planned analyses focused upon the evoked 40-Hz activity that co-occurs with the P300, revealing a more specific pattern of 40-Hz priming over the visual cortex. A subsequent series of cross-correlational analyses examined the cortical distribution and timing of Gestalt-prime generation during and subsequent to premask-display presentation. Correlations were revealed between stimulus related 40-Hz activity over a range of cortical loci, including the right temporal lobe, which is considered important for figure coding. Taken together, these findings not only support the role of a distributed 40-Hz mechanism during Gestalt-figure priming, but also suggest that patterns of oscillatory brain activity may be directly influenced by, and interpretable in terms of equivalent temporal patterns of stimulus activity.
