Spatial neglect and perseveration in visuomotor exploration

Objective: Right-brain-damaged patients with left spatial neglect make perseveration errors in target cancellation tasks. A recent study (Ronchi, Posteraro, Fortis, Bricolo, & Vallar, 2009) showed that perseveration occurred more frequently in star than in letter cancellation, possibly due to different stimulus disposition. In this study we investigated the role of the spatial organization of targets (scattered vs. arranged) of the star and letter cancellation tasks in eliciting omission and perseveration errors; the role of impairments of divided attentional resources; and the lesion correlates of perseveration. Method: Thirty-three right-brain-damaged patients (27 with neglect, and six without neglect; 17 showing perseveration, 16 of them with spatial neglect) were given two versions of the star and letter cancellation tasks (with stimuli scattered or in rows), and a dual task. Results: A scattered target disposition increased omission and perseveration errors. Target type modulated differently omission and perseveration, with the former being more elicited by verbal targets, and the latter occurring more frequently in the star cancellation task, with scattered stimuli. Perseveration behavior was unrelated to deficits of divided attention, as assessed by the dual task. Lesion analysis indicated damage to the right insula as a neural correlate of perseveration. Conclusions: A display including nonverbal (star) and scattered targets brings about more perseveration errors. Target type and organization modulate in a different fashion omission and perseveration, suggesting the involvement of independent pathological mechanisms, which, however, do not implicate deficits of divided attention. The role of insular damage in motor perseveration in spatial neglect is discussed.