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Several studies using brain imaging have demonstrated occipital-cortex activation in blind individuals during tactile and auditory tasks, suggesting that the visual cortex deprived of its normal input has adopted a new role in information processing. So far, however, at what stages of information processing and to which perceptual sub-processes this applies remains unclear. We determined the auditory functions of this cortical region in early-blind humans by means of functional magnetic resonance imaging. We found that these areas were not activated by the mere presence of sound, but were involved in the attentive processing of changes in the auditory environment, which is important in detecting potentially dangerous or other important events in the surroundings, for example.

An event-related potential (ERP) protocol is described that can be used to investigate those sound-evoked neural processes that may be implicated in disrupting immediate memory. Conventional electroencephalogram (EEG) is recorded during the performance of a task that involves ignoring irrelevant sounds while trying to hold in memory lists of numbers. Specific bioelectric measures are made to prevent the contamination of recordings by the movements of articulators. An approach is also outlined which controls the timing of ERP components to sounds with different envelopes. Using this approach, it has been shown that the neural processes involved in the elicitation of the auditory N1 ERP response may be involved in the disruption of memory for serial order produced by irrelevant sound.

We are often aware of the content of distracting sound, although typically remain unaware of the processes by which that sound is disruptive. Disruption can occur even when the sound is ignored and unrelated to the task being performed. In a recent major development, Gisselgård et al. have used positron emission tomography to reveal how distracting sounds recruit the involvement of dorsolateral prefrontal cortex.

Long-term exposure to noise impairs human health, causing pathological changes in the inner ear as well as other anatomical and physiological deficits. Numerous individuals are daily exposed to excessive noise. However, there is a lack of systematic research on the effects of noise on cortical function. Here we report data showing that long-term exposure to noise has a persistent effect on central auditory processing and leads to concurrent behavioral deficits. We found that speech-sound discrimination was impaired in noise-exposed individuals, as indicated by behavioral responses and the mismatch negativity brain response. Furthermore, irrelevant sounds increased the distractibility of the noise-exposed subjects, which was shown by increased interference in task performance and aberrant brain responses. These results demonstrate that long-term exposure to noise has long-lasting detrimental effects on central auditory processing and attention control.

Deficient temporal discrimination and vulnerability to masking effects caused by rapidly succeeding or simultaneous sounds might be one factor underlying the phonological difficulties in dyslexia. We evaluated cortical auditory discrimination in dyslexia by recording the mismatch negativity (MMN) for a simple pitch change, for an order reversal of tone pairs, and for tone-pair order reversals, with a third tone either preceding or following the tone pairs. It was found that when an additional tone followed the pairs the MMN amplitude was attenuated, suggesting elevated backward-masking effects in the auditory cortex of dyslexic individuals. In addition, the MMN elicited by pitch change was diminished over the left hemisphere of the dyslexic individuals suggesting left hemisphere auditory dysfunction. These results suggest impaired cortical discrimination of sounds and lowered tolerance for the masking effects of rapidly following sounds in dyslexia.