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Paul Dux, Claire Naughtin, Jason Mattingley; Early Cortical Contributions to Object Individuation. Journal of Vision 2015;15(12):905. doi: https://doi.org/10.1167/15.12.905.
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© ARVO (1962-2015); The Authors (2016-present)
In object individuation, spatiotemporal episodic cues are used to register an object as a distinct perceptual event, relative to other stimuli. The present study examined the time course of individuation to assess the information processing stage at which it arises and the extent to which it draws on early sensory cortices. Previous research has failed to provide definitive evidence on these issues, as individuation manipulations have co-varied with other low-level physical differences (e.g., hue, luminance). Similarly, no previous study has had both high spatial and temporal resolution, and consequently has been unable to speak directly to both the neural and cognitive substrates of individuation. Here we used a multi-modal EEG/fMRI approach and a novel enumeration paradigm that equated physical stimulus properties across conditions. We could therefore pinpoint the time window and visual sensory regions associated with individuation for items in attended and unattended locations, as indexed by set-size-dependent changes in activity. P1 (100-140 ms) and N2 (185-250 ms) event-related potentials both increased in amplitude with the number of attended targets, but unattended non-targets only modulated the N2. Using fMRI, we found that V2 and other extrastriate visual areas were the likely source of the early P1 effect observed for attended targets. Thus, object individuation appears to arise at a perceptual stage of processing and can be detected in early sensory brain regions. In addition, individuation of unattended items occurs at a later stage of processing than attended targets, suggesting a role of selective attention in this operation.
Meeting abstract presented at VSS 2015
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