Cross-modal working memory effect on target identification and the role of posterior parietal cortex

Background: Previous research with healthy participants has established that both verbal and visual items in working memory (WM) modulate attention in a subsequent visual search task. Recent work has suggested that patients with lesions in the posterior parietal cortex (PPC) can show effects of items held in WM on visual selection when items appear in the same modality. Holding a visual stimulus in WM reduces extinction for matching contralesional stimuli. These data suggest that the effects of a visual stimulus in WM are not mediated by the PPC. However, little is known about role of PPC in cross modal attention. Objective: The goal for this study was to investigate the role of PPC in the cross modal effects of WM on target identification. We sought to investigate the necessary roles of posterior parietal cortex (PPC) in cross-modal interactions in WM by examining whether auditory stimuli in WM reduced extinction for contralesional, matching visual targets in patients showing visual extinction after damage to the PPC. Four experiments compared data from 8 patients with the data from two control groups; a group of 5 patients with non-parietal lesions and a group of 7 healthy age-matched control participants. We tested for effects of items held in one form in WM (e.g. auditory WM) on the identification of targets in another format (e.g. visual images). Results: The results indicated that patients with PPC lesions showed stronger extinction of contralesional stimuli than non-parietal patients. Also, while the subsequent allocation of attention to a visual target was affected by a visual cue in WM, it was not affected by the presence of an auditory WM cue. Control participants showed cross-modal effects. Conclusions: The data suggest that the posterior parietal cortex is necessary to generate cross-modal influences on attention from WM.