Grasping and pointing task comparison in a hemineglect patient. Behavioural and eye-movement measures in an online bisection task

Introduction: The present study aims to explore behavioral and eye movement measures in an unilateral neglect patient in response to online bisection task (unfilled gap line). Previous studies showed that two different representational strategies affected the bisection performance, a pointing and a grasping strategy. It was explored whether these different tasks may influence subject’s behavioral and eye-movement measures in response to different segment features: segment length (from shorter to longer) and segment spatial dislocation (from right to left spatial location). Methods: We describe a 72 years-old patient with left neglect and visual extinction following an ischemic stroke involving right temporo-parietal area; no signs of hemianopia were found. This patient underwent to experimental procedure in which he was asked to indicate midpoint in an unfilled gap between to endpoints. All item varied in length and spatial position. We collected accuracy, reaction times and eye-movement data. We made a comparison with performances of 10 healthy participants. Results: Consistent spatial biases were found for bisection responses, RTs and fixation count and duration, as well as for the first fixation count. However, an “extreme-left” gradient effect was suggested and discussed. Finally, the patient’s performance seems to overlap with the controls’ one in case of a grasping representation in comparison with a pointing representation. The direct link of visual pointing and grasping strategy respectively with the two cortical ventral and dorsal pathways was adduced to explain our results.