The effect of expectation on facilitation of colour/form conjunction tasks by TMS over area V5.
In an earlier paper, we reported task-specific impairments and improvements caused by applying TMS over cortical visual area V5 [Proceedings of the Royal Society of London B 265 (1998) 537]. The phenomenon is further investigated in the present study using two of the previous tasks: a motion/form conjunction in which TMS impaired performance and a colour/form conjunction in which performance was enhanced with TMS. In the earlier experiment, subjects were presented with blocks of trials of one task type perhaps allowing some of the observed effects to arise from knowing the type of stimulus to be discriminated. When blocks of trials consisted of randomly mixed moving/form and colour/form conjunction tasks, TMS over V5 still impaired target-present responses for the moving/form conjunction, but the facilitation seen for colour/form conjunction target-present responses disappeared. We suggest that the competitive inhibition postulated between visual movement areas and colour areas in the brain, in our previous paper, are subject to expectation or knowledge of forthcoming stimulus type.
Ellison
Amanda
A
Cognitive Neuroscience Research Unit, Wolfson Research Institute, University of Durham Queen's Campus, University Boulevard, Stockton-on-Tees TS17 6BH, UK. amanda.ellison@durham.ac.uk
Battelli
Lorella
L
Cowey
Alan
A
Walsh
Vincent
V
D000328:Adult; D000704:Analysis of Variance; D003118:Color Perception / Q000502:physiology* / Q000528:radiation effects; D004558:Electric Stimulation / Q000379:methods*; D005163:Factor Analysis, Statistical; D005556:Form Perception / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D008280:Magnetics / Q000009:adverse effects*; D008875:Middle Aged; D009038:Motion; D009039:Motion Perception / Q000502:physiology* / Q000528:radiation effects; D010775:Photic Stimulation; D011930:Reaction Time; D014793:Visual Cortex / Q000502:physiology*