The intensity of masking noise affects the mismatch negativity to speech sounds in human subjects

The present study investigated the effects of decreased audibility of the speech sounds 'ba' and 'da' on the mismatch negativity (MMN). Audibility was altered by varying the intensity of the masking noise to be either 0 (no noise), 65, 70 or 75 dB speech perception level. Cortical event-related potentials were recorded while normal listeners (n=7) were instructed to ignore the stimuli. In a separate condition, subjects were asked to signal detection of the deviant stimulus by button-press. As audibility of speech sounds was decreased, MMN peak amplitude decreased and MMN peak latency increased. Behavioral responses were in accordance with the MMN data. Hit rates decreased as audibility decreased. These results suggest that both pre-attentive and attentive speech discrimination deteriorate following a reduction in audibility.

Mismatch negativity to inclusions of noise within complex spectrotemporal sound patterns

Event-related potentials to complex spectrotemporal sound patterns were recorded during non-attend conditions. A high-intensity noise deviant elicited a large negative wave. This is probably a combined mismatch negativity (MMN) and N2b since it was followed by a large amplitude frontal positive wave (P3a). When the noise intensity was reduced, a smaller amplitude negative wave was elicited. This probably corresponds to a true MMN since it was not followed by the positive wave. These findings are consistent with previous research in which N2b is elicited in non-attend conditions when the deviant stimulus was particularly difficult to ignore. These findings demonstrate that complex spectrotemporal sound patterns are represented in auditory memory and that inclusions of noise within these complex stimuli can be passively discriminated.

[Long-term antibiotic therapy in chronic purulent otitis media]

A new therapeutic approach is proposed for chronic purulent otitis media. This clinical condition is often a recurring phenomenon in spite of all forms of treatment. Ten cases are reviewed and the results encourage the authors to pursue this form of treatment consisting of a longterm antibiotherapy of Ampicilline and Cloxacilline in a further study.