Closing-in behaviour and motor distractibility

This study relates two behaviours, each well documented within its own literature but not previously considered together: closing-in behaviour (CIB) and the effect of visual distractors on reaching. CIB is common in typically developing children, and in adults with dementia, and classically manifests as the tendency to perform graphic copying tasks very close to, or on the top of the model. The effect of visual distractors on reaching has been studied extensively in normal adults. Distractors induce characteristic deviations of the reach, usually away from the distractor, which imply that a competing response towards the distractor is automatically primed, and actively suppressed. It is possible that CIB reflects a failure to inhibit motor distraction, such that the acting hand is attracted automatically to a salient stimulus (the model, during copying tasks). This hypothesis predicts that CIB should be associated with distractor effects during reaching, characterised by veering towards, rather than away from the distractor. We tested this prediction in groups of pre-school children with and without CIB, and in young adults, using task-relevant and task-irrelevant distractors. Both groups of children showed greater veering towards distractors than did adults, implying a lower capacity to inhibit automatic responses. Crucially, this effect was stronger in children with CIB than without CIB when a task-irrelevant distractor was presented. These findings support the idea that CIB reflects a failure to inhibit automatically primed actions towards salient stimuli.