Patients with Parkinson's disease are less affected than healthy persons by relevant response-unrelated features in visual search

Patients with Parkinson's disease (PD) respond more readily than healthy controls to irrelevant stimuli that contain task-relevant, response-priming features. This behavior may reflect oversensitivity to response-relevant features of irrelevant stimuli or failure to select relevant stimuli. To decide between these alternatives, we investigated in a "contingent-capture" paradigm whether PD patients are also oversensitive to task-relevant features that do not prime responses. PD patients and healthy controls had to report the orientation of bars in target color, presented among bars of other colors. Critically, target arrays were preceded by arrays of rings, all gray except one which might be the target color and might be presented at the same position as the upcoming target. Replicating earlier results from young healthy participants (Eimer, Kiss, Press, & Sauter, 2009), signal rings in target color induced an N2pc component over contralateral visual cortex and some positivity at anterior sites (d-P200), both indicative of attentional capture. Correspondingly, signals in target color facilitated correct responding to upcoming targets presented at the same location and impeded correct responses otherwise. Patients with PD had diminished N2pc, lacked the frontal focus of d-P200, and their responses tended to be less affected than healthy participants' by signal position. Thus PD patients appeared less affected than healthy persons by stimuli with relevant features. This outcome is compatible with the notion that PD patients have poorer internal representations of what is relevant in a given task.