Competition-induced visual field differences in search

Do visual field effects point to differences in cortical representation, or do they reflect differences in the way these representations are used by o ther brain regions? This study explored three attributes of visual search t hat provide strong evidence in favor of differences in use. Competition ref ers to the finding that visual field differences in search efficiency are l arger in whole- than in half-field displays (both left-right and upper-lowe r half-fields). Task specialization refers to the finding that some tasks f avor one hemisphere whereas other tasks favor the other hemisphere, even th ough the same stimulus displays are used in both tasks. Anatomical alignmen t refers to the finding that competition effects are altered if the quadran ts of the visual display are not aligned with the cortical quadrants of the observer. We propose that visual field specialization in search is the res ult of a competition involving limited access to cortical visual representa tions by the extended neural networks of attention.