Abstract
It has been shown that selective attention enhances the activity in visual regions associated with stimulus processing. The left hemisphere seems to have a prominent role when non-spatial attention is directed towards specific stimulus features (e.g., color, spatial frequency). The present electrophysiological study investigated the time course and neural correlates of object-based attention, under the assumption of left-hemispheric asymmetry. Twenty-nine right-handed participants were presented with 3D graphic images representing the shapes of different object categories (wooden dummies, chairs, structures of cubes) which lacked detail. They were instructed to press a button in response to a target stimulus indicated at the beginning of each run. The perception of non-target stimuli elicited a larger anterior N2 component, which was likely associated with motor inhibition. Conversely, target selection resulted in an enhanced selection negativity (SN) response lateralized over the left occipito-temporal regions, followed by a larger centro-parietal P300 response. These potentials were interpreted as indexing attentional selection and categorization processes, respectively. The standardized weighted low-resolution electromagnetic tomography (swLORETA) source reconstruction showed the engagement of a fronto-temporo-limbic network underlying object-based visual attention. Overall, the SN scalp distribution and relative neural generators hinted at a left-hemispheric advantage for non-spatial object-based visual attention.
Highlights
It is known that visual attention can be consciously directed towards a selected location in space, a stimulus as a whole, or specific features of a stimulus
Target stimuli characterized by the prototypical color/shape combination elicited a larger N2 component over posterior sites, during the attention to color condition only. This effect was found over the left but not right hemisphere, as confirmed by the topographic map of voltage distribution computed on the difference wave. These results likely showed specific involvement of the left occipito-temporal cortex for conjoined color and shape processing of real objects
The ANOVA performed on the reaction times (RTs) showed an almost significant trend (F(1,28) = 3.697, p = 0.06, η2p = 0.12) towards a faster response with the right hand (420 ms, SE: 5.96) relative to the left hand (429 ms, SE: 8.15)
Summary
It is known that visual attention can be consciously directed towards a selected location in space (spatial attention [1,2]), a stimulus as a whole (object-based attention [3,4,5]), or specific features of a stimulus (feature-based attention [6,7,8]). While both behavioral and neural correlates of spatial and feature-related attentional processes have been extensively investigated [9,10,11], attentive selection for objects requires further consideration. In two classic fMRI studies by O’Craven and colleagues [3], the participants were presented with stimuli depicting a transparent face superimposed over a house, Brain Sci. 2019, 9, 315; doi:10.3390/brainsci9110315 www.mdpi.com/journal/brainsci
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