Parallel and serial search in two teenagers with lesions of the mesial parietal cortex

Visual-spatial attention was examined in two 14-year-olds who had undergone occipital-parietal craniotomies for removal of mesial parietal tumors, one in the right and one in the left hemisphere, Neither patient showed clinic ally significant visual neglect. They were administered two visual search t asks from Treisman and Souther [43] that make significantly different deman ds on visual-spatial attention. In feature-present (parallel) search, they searched for the presence of a feature. In feature-absent (serial) search, they searched for its absence. Search rate was estimated from the slope of the function relating display size to response time. Both patients had flat slopes in feature-present search to target-present (TP) displays, indicati ng that they could conduct parallel search at the same rate as controls. Al though the patient with the right-hemisphere lesion also had a Aat slope to target-absent (TA) displays, the patient with the left-hemisphere lesion h ad a steep slope (30 ms/item) in this condition. In feature-absent search, the patients had equally slow search rates compared to controls, suggesting that the mesial parietal cortex is part of the network that mediates seria l shifts of attention. Results support the distinction between detection of the target in parallel vs serial search and suggest that processes involve d in TP and TA trials in parallel search are also dissociable. (C) 1999 Els evier Science Ltd. All rights reserved.