Abstract
In this single case study, visuospatial neglect patient P1 demonstrated a dissociation between an intact ability to make appropriate reflexive eye movements to targets in the neglected field with latencies of <400 ms, while failing to report targets presented at such durations in a separate verbal detection task. In contrast, there was a failure to evoke the usually robust Remote Distractor Effect in P1, even though distractors in the neglected field were presented at above threshold durations. Together those data indicate that the tight coupling that is normally shown between attention and eye movements appears to be disrupted for low-level orienting in P1. A comparable disruption was also found for high-level cognitive processing tasks, namely reading and scene scanning. The findings are discussed in relation to sampling, attention and awareness in neglect.
Highlights
Unilateral neglect is a condition in which patients fail to respond to, orient towards, or report, stimuli located on the side of space contralesional to brain damage in the absence of sensory motor deficits [1]
These data were used in the experiment to examine whether stimuli presented in P1’s neglected hemifield had to be presented at durations at which he showed some awareness for in the verbal detection task, in order to program an eye movement to those targets
Using the Remote Distractor Effect (RDE) paradigm we examined the effects of the prior allocation of attention to either ipsilesional or contralesional space on saccadic orienting in P1, and evaluated whether there was any dissociation between the saccadic orienting system and conscious awareness for stimuli presented in P1’s ‘neglected’ hemifield
Summary
Unilateral neglect is a condition in which patients fail to respond to, orient towards, or report, stimuli located on the side of space contralesional to brain damage in the absence of sensory motor deficits [1] It is observed most frequently and is of longer duration following damage to the right hemisphere of the brain [2], resulting most commonly in the left side of space being ‘neglected’. These include multi-stepping hypometric (short) saccades of long latency into the neglected field, failure to fixate upon visual information presented in that field, and failure to report information that may be successfully fixated, in the neglected hemispace These and later studies have provided evidence for hyperattention to the ipsilesional side in neglect The effects of contralesional distractors on the time taken to initiate saccades to targets presented in ipsilesional space [8] has resulted in the suggestion that an imbalance in the saccadic system can underpins neglect, and this has received recent support [12]
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