Differential processing of word and color in unilateral spatial neglect

The aim of the present study was to investigate mechanisms underlying processing of contralesional visual stimuli in brain-damaged patients with unilateral spatial neglect (USN). Nine right-hemisphere-damaged stroke patients with left-sided neglect and nine controls performed a reaction-time task involving manual response to a central color patch (target stimulus) flanked to the left or right by a Stroop stimulus they had to ignore. While the word dimension of the flanker affected patients' responses considerably and equally when presented to either side, the color dimension of the flanker had no effect when presented to the left, but had a large effect when presented to the right. Four of the patients performed a control task requiring same/different judgments between either of the two flanker dimensions (color and word) and the central target. Their performance indicated that they were able to process color information from the contralesional field, despite their results in the first experiment. These findings demonstrate a dissociation between how the patients processed different dimensions of the same stimuli and imply that the extent of processing in the contralesional hemifield depends both on task requirements and on the exact features of the stimuli. The implications of these results on normal attentional mechanisms is also discussed.