Directed attention after unilateral frontal excisions in humans

We investigated the ability of patients with frontal-lobe lesions to benefit from advance information in a simple reaction-time task. The task involved pressing a button in response to the appearance of a peripheral target (visual angle of 11.5 degrees). A cue, presented in the centre of the screen, preceded the target onset by either a short (average 500 ms) or a long (average 3000 ms) interval. In half of the trials, the cue was an arrow indicating the location, in the left or right hemifield, of the upcoming target; in the other half, the cue was an uninformative plus sign. In addition to patients with unilateral excisions of frontal cortex, we tested patients with anterior temporal-lobe excisions and normal controls. The frontal-lobe group was mildly impaired with respect to the temporal-lobe group in using advance spatial cues to speed response to the visual target. While the size of the cueing effect changed across the range of cue-target intervals tested, there was no variation across intervals in the size of the impairment exhibited by the frontal-lobe group. The site and the volume of the lesions were determined on the basis of magnetic resonance image (MRI) scans in 10 of the 17 patients in the frontal group. There was no correlation between lesion volume and benefit score in these patients.