Eye movement and online bisection task in unilateral patients with neglect: A new look to the ‘gradient effect’

Primary objective: The present study explored the behavioural and eye-movement measures in spatial unilateral neglect in response to a bisection task. Research design: Four right neglect patients were considered and compared with 11 control subjects during an online task (segment bisection). Methods and procedures: Eye-movements (fixation count and duration) and behavioural responses were monitored during an online bisection task, consisting of unfilled segments (two ending points) to be bisected by subjects. Segment length (six levels) and spatial dislocation (five levels) were modulated to explore a possible ‘gradient effect’” (left-to-right) in neglect bias. Main outcomes and results: Consistent spatial biases were found for both bisection position and eye fixations as a function of segment length (from shorter to longer) and segment spatial dislocation (from right to left). However, only the more eccentric left-positions induced a greater rightward bias in patients, with increasing more right-side bisection and visual right-directed fixations. Also segment length produced significant differences between-groups for behavioural responses, with more right-side bisection for longer segment in patients, and eye movement behaviour, with increased fixation count and duration rightward oriented in response to longer segments. Conclusions: Although a left-to-right and longer-to-shorter ‘continuous-gradient effect’ was not supported by the results, an ‘extreme left-gradient effect’ was suggested and discussed