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Neuropsychologia. 2009 Dec;47(14):3255-64. doi: 10.1016/j.neuropsychologia.2009.08.004. Epub 2009 Aug 12.

Attentional and sensory effects of lowered levels of intrinsic alertness.

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General and Experimental Psychology, Ludwig-Maximilians-University, Leopoldstr. 13, 80802 Munich, Germany.


Low levels of intrinsic alertness are associated with lateralized performance in visual tasks, similar to neglect of the left (ipsilesional) visual hemi-field. However, it is unclear whether reduced alertness produces a specific lateralization of spatial-attentional processes in terms of the prioritization of right- over left-side stimuli, or whether it affects more basic functions of visuo-sensory coding, and/or higher function of the top-down control of selection, of stimuli on the left side. To decide between these alternatives, the present study examined the effects of lowered alertness, induced by a 50-min vigilance task, in a partial-report paradigm of briefly presented letter displays. With only one (unilateral) stimulus in display, no specific hemi-field effects were found under low-alertness conditions, indicating that reduced alertness impairs neither sensory effectiveness nor the top-town control of selection. However, with dual, bilateral stimuli, report accuracy was specifically affected for left-side targets (in subjects who showed comparable performance for both sides under normal-alertness conditions). This pattern can be interpreted in terms of a specific bias in spatial-attentional weighting, where prioritization of stimuli on the right leads to (mild) extinction of targets on the left. Moreover, participants who had a lower general level of alertness also showed a more pronounced re-distribution of weights, evidenced by a more severe imbalance in report accuracy, in a low compared to a normal state of alertness. This suggests that a low general level of intrinsic alertness engenders a specific vulnerability to neglect-like performance with a (mild) left-side extinction.

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