A review of the evidence for a disengage deficit following parietal lobe damage
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We review the literature on response times to ipsilesional and contralesional targets following spatial precues in patients with damage involving the left- and right-parietal lobes with the aim of appraising the 'disengage deficit' reported initially by Posner and colleagues (Posner MI, Cohen A, Rafal RD. Neural systems control of spatial orienting. Proceedings of the Royal Society of London, B 1982;298:187-98). The data of individual subjects from a sub-sample of studies were submitted to analyses of variance, and data from all studies meeting our selection criteria were submitted to meta-analytic procedures (Hunter JE, Schmidt FL. Methods of meta-analysis: correcting error and bias in research. Newberg Park: Sagge Publications, 1990). Findings from both types of analysis conducted on data from patients with right-hemisphere lesions indicate that: (1) the disengage deficit phenomenon is robust following peripheral cues, but not following central cues; (2) the disengage deficit is large at shorter cue-target stimulus onset asynchronies (SOAs), and decreases as SOA increases; (3) the disengage deficit is larger in patients with a diagnosis of hemispatial neglect; and (4) although the magnitude of the disengage deficit appears to increase with increases in lesion size, multilobar vs unilobar involvement did not significantly alter the pattern of the disengage deficit. We also show that responses to validly cued targets in the contralesional hemispace were significantly slower than for validly cued targets in ipsilesional hemispace. Similar, but usually smaller, effects were observed in patients with homologous left-hemisphere damage. The implications of these results for current models of the role of the parietal lobes in attentional orienting are discussed.
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