Semantic priming by irrelevant speech

Auditory evoked potentials (AEPs) to the subject's own name and to seven other first names were recorded in ten normal adults during wakefulness, in both passive listening and active detection conditions, and during sleep stage II (SII) and paradoxical sleep (PS). All stimuli were disyllabic, equiprobable and presented in random order. During wakefulness, a parietal positive 'P3' component, peaking at about 500 ms, probably equivalent to the endogenous P300 wave, was enhanced in response to the subject's own name, even in the passive condition. During SII, K-complexes (KCs) were evoked by all first names and were formed by two biphasic consecutive waveforms. While the amplitude of the late complex (N3/P4) was identical for both types of stimuli, the early portion of the KC (N2/P3), and notably the positive wave 'SII-P3' at about 600 ms, was selectively enhanced after the subject's own name. This supports the hypothesis that at least two distinct neuronal systems are activated in parallel in response to auditory stimuli during SII, one reflecting the detection of stimulus' salience and the other the processing of its intrinsic relevance. During PS, the AEP morphology was comparable to that observed in wakefulness. Notably, a posterior 'PS-P3' wave appeared exclusively in response to own names at about 550 ms, and was considered as an equivalent of the waking P300. These results suggest that the sleeping brain, during SII and PS, elicits a differential cognitive response to the presentation of the subject's own name, comparable to that occurring during wakefulness, and therefore that the sleeping brain is able to detect and categorize some particular aspects of stimulus significance.

Distraction by irrelevant background sound of visually-based cognitive tasks illustrates the vulnerability of attentional selectivity across modalities. Four experiments centred on auditory distraction during tests of memory for visually-presented semantic information. Meaningful irrelevant speech disrupted the free recall of semantic category-exemplars more than meaningless irrelevant sound (Experiment 1). This effect was exacerbated when the irrelevant speech was semantically related to the to-be-remembered material (Experiment 2). Importantly, however, these effects of meaningfulness and semantic relatedness were shown to arise only when instructions emphasized recall by category rather than by serial order (Experiments 3 and 4). The results favor a process-oriented, rather than a structural, approach to the breakdown of attentional selectivity and forgetting: performance is impaired by the similarity of process brought to bear on the relevant and irrelevant material, not the similarity in item content.