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Abstract:
Patients with right hemispheric lesions often show
substantial neglect to the contralesional hemispace. Hemineglect is
predominantly associated with lesions of the right posterior
parietal lobe and may occur independent of sensory or motor
impairments. The analyses of priming effects has provided a
feasible way of investigating implicit processing of stimuli in the
neglected hemifield (Ládavas et al., Neuropsychologia, 31,
1307-1320, 1993; Schweinberger & Stief, Neuropsychologia, in
press). Ten patients with left neglect and 10 matched controls
performed lexical decisions for foveally presented targets (common
object names). Target stimuli were preceded by picture primes that
were presented for 150 ms to the left or right visual field. For
word targets, primes could either show a picture of the same or of
a different object. Although RTs were clearly slowed in the
patients, cross-domain repetition priming effects showed a similar
pattern across groups. That is, significant priming was observed
even when picture primes were shown in the neglected left
hemifield. Event- related potentials (ERPs) were recorded from 28
scalp positions. In controls, priming reduced the N400 to word
targets, and this effect was most prominent over right
centroparietal electrodes. Most importantly, priming in the
neglected left hemifield also reduced the N400 in the patients.
Both in terms of latency and scalp topography, this effect was
comparable to that seen in controls. We will also discuss results
from a second study on within-domain (word to word) repetition
priming. Overall, our research suggests preserved and efficient
semantic processing of neglected stimuli at an implicit
level.
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