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Abstract:
Background: In extinction, a frequent sequel of brain damage,
patients report only the more ipsilesional stimulus of a pair of
simultaneously presented stimuli, and disregard ("extinguish") the
contralesional stimulus. Extinction may be visual, auditory or
tactile, and is often discussed within the context of unilateral
neglect (UN). Several explanations were suggested to explain
extinction, ranging from disruption of sensory pathways to higher
order attention deficits. Experimental data, mainly from the visual
modality, suggested extensive implicit processing of the
extinguished stimuli. Nevertheless, a critical theoretic question
remains the stage(s) at which the processing of neglected or
extinguished stimuli does fail. Goal: We investigated the
possibility of a dissociation between impaired
detection/localization and intact identification of extinguished
phonemes in the auditory modality. Methods: Fourteen right
hemisphere damaged patients with severe auditory extinction were
examined using bilateral simultaneous pairs of phonemes, in a task
that required the detection/localization of auditory stimuli and
the identification of their phonetic content. Results: The patients
overtly reported the identity of left-sided phonemes significantly
above chance level, while 'extinguishing' these stimuli at the same
time, in the traditional sense of the term. Conclusions: This
dissociation joins our ERP results suggesting that auditory
extinction (and probably UN) is more about spatial encoding of a
stimulus in the contralesional hemispace than about the actual
processing of the content of the stimulus.
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