Attention to Features Precedes Attention to Locations in Visual Search: Evidence from Electromagnetic Brain Responses in Humans

Single-unit recordings in macaque extrastriate cortex have shown that attentional selection of nonspatial features can operate in a location-independent manner. Here, we investigated analogous neural correlates at the neural population level in human observers by using simultaneous event-related pot...

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Bibliographic Details
Published in:The Journal of neuroscience 2004-02, Vol.24 (8), p.1822-1832
Main Authors: Hopf, Jens-Max, Boelmans, Kai, Schoenfeld, Mircea Ariel, Luck, Steven J, Heinze, Hans-Jochen
Format: Article
Language:English
Subjects:
Adult
Attention - physiology
Behavioral/Systems/Cognitive
Brain - anatomy & histology
Brain - physiology
Brain Mapping
Color
Electroencephalography
Evoked Potentials - physiology
Evoked Potentials, Visual - physiology
Female
Fixation, Ocular - physiology
Humans
Macaca
Magnetoencephalography
Male
Photic Stimulation - methods
Reaction Time - physiology
Reference Values
Task Performance and Analysis
Visual Fields - physiology
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Summary:Single-unit recordings in macaque extrastriate cortex have shown that attentional selection of nonspatial features can operate in a location-independent manner. Here, we investigated analogous neural correlates at the neural population level in human observers by using simultaneous event-related potential (ERP) and event-related magnetic field (ERMF) recordings. The goals were to determine (1) whether task-relevant features are selected before attention is allocated to the location of the target, and (2) whether this selection reflects the locations of the relevant features. A visual search task was used in which the spatial distribution of nontarget items with attended feature values was varied independently of the location of the target. The presence of task-relevant features in a given location led to a change in ERP/ERMF activity beginning approximately 140 msec after stimulus onset, with a neural origin in the ventral occipito-temporal cortex. This effect was independent of the location of the actual target. This effect was followed by lateralized activity reflecting the allocation of attention to the location of the target (the well known N2pc component), which began at approximately 170 msec poststimulus. Current source localization indicated that the allocation of attention to the location of the target originated in more anterior regions of occipito-temporal cortex anterior than the feature-related effects. These findings suggest that target detection in visual search begins with the detection of task-relevant features, which then allows spatial attention to be allocated to the location of a likely target, which in turn allows the target to be positively identified.
ISSN:0270-6474
1529-2401
DOI:10.1523/JNEUROSCI.3564-03.2004