Temporal dynamics of parietal cortex involvement in visual search.
The functional-neuroanatomic relationship that describes the involvement of the parietal cortex in visual search was investigated using repetitive transcranial magnetic stimulation (rTMS; 10 Hz, 500 ms in duration). Twelve adult participants performed feature-based visual search for a unique letter-without eye movements-under conditions that involved manipulations of search efficiency (efficient versus inefficient) and target-selection demands (set-size: 4 versus 10). rTMS was applied over the right posterior parietal cortex at the onset of the search array for all factorial conditions (0-500 ms); stimulation was additionally administered at 500 ms post-array onset (500-1000 ms) during inefficient search (set-size 10). Stimulation over the primary sensorimotor cortex served as a within-subjects control condition, and eye movements were monitored continuously. Significant increases in reaction time were restricted to parietal stimulation during inefficient search (set-size 10), with interference observed when rTMS was administered at the onset of the search array and at 500 ms post-array onset. The early effect was confined to target-present trials and the late effect was confined to target-absent trials, which may indicate temporally dissociable parietal involvement in target detection and response-based selection and/or search termination, respectively. Error rates did not vary significantly as a function of any of the independent variables. Taken together, these results are consistent with evidence from functional magnetic resonance studies indicating that inefficient feature-based visual search requires an intact parietal cortex, and also indicate that the parietal cortex is involved in inefficient search later than has been previously reported.
Rosenthal
Clive R
CR
Department of Visual Neuroscience, Charing Cross Campus, Imperial College London, St. Dunstan's Road, London W6 8RP, UK. c.rosenthal@imperial.ac.uk
Walsh
Vincent
V
Mannan
Sabira K
SK
Anderson
Elaine J
EJ
Hawken
Malcolm B
MB
Kennard
Christopher
C
D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology*; D001931:Brain Mapping; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010296:Parietal Lobe / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods