Different causes explain pathological visual search in spatial neglect

Overview and aim. In visual search tasks, neglect patients tend to explore and repeatedly re-cancel stimuli on the ipsilesional side, as if they did not realize that they had previously examined the rightward location favored by their lateral bias. Re-cancellation behaviors have been related to spatial working memory (SWM) impairment (Husain et al., 2001) but some authors have recently called into question this interpretation (Wansard et al., 2014). Difficulties planning a visual search (Mark et al., 2004) but also abnormal inhibition of return (IOR, Bourgeois et al., 2012) frequently observed in neglect patients could exacerbate neglect behaviors (i.e. omissions and re-cancellations), leading to repetitive searching towards the right side of space. The aim of our study was to investigate the cognitive functions involved in re-cancellation behaviors.
Methods. We assessed twenty-nine right-damaged patients suffering from left neglect on experimental tasks evaluating SWM (Corsi Block test), IOR (Bartolomeo et al., 1999), and visual search planning (cancellation task without visual feedback).
Results. Results showed that the IOR index and the planification of visual search are the two factors that better explain the re-cancellations behavior, while the measure of SWM significantly predict left omissions.
Discussion and conclusion. Re-cancellation behavior cannot be explained by a spatial working memory deficit in neglect patients. In our study, we observed that the lack of IOR and difficulties to plan a visual search observed in neglect patients exacerbate the rightward bias and thus failures to explore the left space. The influence of neglect’s severity and clinical implications of our findings are discussed.