Two morphologically distinct auditory middle latency response (MLR) wave forms can be recorded from the surface of the guinea pig brain. The temporal response is recorded from the temporal lobe contralateral to the stimulus ear, and the midline response is recorded over the posterior midline. Experimental evidence suggests that different neural generators contribute to the two responses. Furthermore, it appears that the temporal response principally reflects activity of the primary auditory pathway while the midline response reflects non-primary pathways. Although it is known that neurons throughout the auditory pathway exhibit distinct binaural interaction (BI) properties, thus far there have been no systematic attempts to differentiate the MLR wave forms in response to binaural stimulation. The purpose of this study was to determine if binaural click stimulation could functionally differentiate the midline and temporal MLR responses in the guinea pig. Binaural click stimulation caused a significant decrease in temporal MLR peak amplitudes, and a significant increase in midline MLR amplitudes. The fact that different BI patterns were observed suggests that the two MLR components are functionally distinct. The data further support the hypothesis that the midline and temporal MLR in guinea pigs reflect different neural generators and pathways.

Acoustic Stimulation↗

PubMedDate not supplied

Acoustic versus phonetic representation of speech as reflected by the mismatch negativity event-related potential.

The concept of categorical perception of speech and speech-like sounds has been central to models of speech perception for decades. Event-related potentials (ERPs) provide a neurophysiologic perspective of this important phenomenon. In the present experiment the mismatch negativity (MMN) event-related potential, which is sensitive to fine acoustic differences, was recorded in adults. Of interest was whether the MMN reflects the acoustic or categorical perception of speech. The MMN was elicited by stimulus pairs (along a continuum varying in place of articulation from /da/ to /ga/) which had been identified as the same phoneme /da/ (within category condition) and as different phonemes /da/ and /ga/ (across categories condition). The acoustic differences between these two pairs of stimuli were equivalent. The MMN was observed in all subjects both in the within and across category conditions. Furthermore, the MMN did not differ in latency, amplitude or area within and across categories. That is, the MMN indicated equal discrimination both across and within categories. These results suggest that the MMN appears to reflect the processing of acoustic aspects of the speech stimulus, but not phonetic processing into categories. The MMN appears to be an extremely sensitive electrophysiologic index of minimal acoustic differences in speech stimuli.

Acoustic Stimulation↗

PubMedDate not supplied

Mismatch negativity in school-age children to speech stimuli that are just perceptibly different.

The mismatch negativity event-related potential (MMN) was elicited in normal school-age children in response to just perceptibly different variants of the speech phoneme /da/. A significant MMN was measured in each subject tested. Child and adult MMNs were similar with respect to peak latency and duration. Measures of MMN magnitude (peak-to-peak amplitude and area) were significantly larger in children than in adults. The results of the present study indicate that the MMN can be elicited in response to minimal acoustic stimulus differences in complex speech signals in school-age children. The results support the feasibility of using the MMN as a tool in the study of deficient auditory perception in children.

Acoustic Stimulation↗