Biomedical subjects

Curtis W Ponton

Publications and source records attributed to Curtis W Ponton.

5 recordsLinked to original sources

PubMed2003

Differential ear effects of profound unilateral deafness on the adult human central auditory system.

This study investigates the effects of profound acquired unilateral deafness on the adult human central auditory system by analyzing long-latency auditory evoked potentials (AEPs) with dipole source modeling methods. AEPs, elicited by clicks presented to the intact ear in 19 adult subjects with profound unilateral deafness and monaurally to each ear in eight adult normal-hearing controls, were recorded with a 31-channel system. The responses in the 70-210 ms time window, encompassing the N1b/P2 and Ta/Tb components of the AEPs, were modeled by a vertically and a laterally oriented dipole source in each hemisphere. Peak latencies and amplitudes of the major components of the dipole waveforms were measured in the hemispheres ipsilateral and contralateral to the stimulated ear. The normal-hearing subjects showed significant ipsilateral-contralateral latency and amplitude differences, with contralateral source activities that were typically larger and peaked earlier than the ipsilateral activities. In addition, the ipsilateral-contralateral amplitude differences from monaural presentation were similar for left and for right ear stimulation. For unilaterally deaf subjects, the previously reported reduction in ipsilateral-contralateral amplitude differences based on scalp waveforms was also observed in the dipole source waveforms. However, analysis of the source dipole activity demonstrated that the reduced inter-hemispheric amplitude differences were ear dependent. Specifically, these changes were found only in those subjects affected by profound left ear unilateral deafness.

Adolescent↗

PubMed2003

Maturation of human central auditory system activity: the T-complex.

OBJECTIVE: The purpose of this study was to evaluate and describe the maturation of a set of auditory evoked potentials (AEPs) described as the T-complex from a large group of children, adolescents, and young adults who ranged in age from 5 to 20 years of age. METHODS: The AEPs evoked by brief trains of clicks presented to the left ear were measured at 30 scalp-electrode locations. Analyses focused on age-related latency and amplitude changes in the T-complex recorded at the temporal electrode sites T3 and T5 over the left hemisphere and T4 and T6 over the right hemisphere. The maturation of the T-complex components Na, Ta, and Tb was contrasted with those of the obligatory AEPs P1, N1b, and P2 measured at electrodes C3 and C4. RESULTS: T-complex activity was present in the grand average AEPs of all 14 age groups spanning ages 5-20 years. T-complex components recorded at electrodes T3 and T4 differed in both morphology and maturation rate from those recorded at T5 and T6. In contrast to the prolonged maturation of AEP latency measured at electrodes T5 and T6, the T-complex components measured at electrodes T3 and T4 did not show a significant overall change in peak latency as a function of age. Consistent amplitude and latency correlations were found between the obligatory AEP components P1, N1b and P2 recorded at C3 and C4 and the T-complex components measured at T5 and T6, but not T3 and T4. CONCLUSIONS: Distinct patterns of AEP maturation were measured at electrode sites commonly used to record the T-complex. At scalp electrodes located over more posterior temporal areas (T5 and T6), the AEPs were characterized by a prolonged pattern of maturation very similar to that measured at the central electrodes C3 and C4. These findings and others reported in this paper provide strong evidence that the AEPs recorded at electrodes T5 and T6 are not T-complex peaks. In contrast, the AEPs measured at electrodes T3 and T4 over more anterior temporal scalp areas appear largely independent of activity measured at the central electrode locations. The T-complex peaks Ta and Tb measured at these scalp locations mature early, with no overall significant age-related changes in peak latencies. SIGNIFICANCE: The T-complex is recorded from the temporal electrodes T3 and T4 represents activity of secondary auditory cortex better than, and independent from, midline potentials. Its robust presence in 5-8 year olds supports its potential usefulness in assessing language impairment.

Adolescent↗

PubMed2003

Auditory-evoked potential studies of cortical maturation in normal hearing and implanted children: correlations with changes in structure and speech perception.

Human auditory system maturation as assessed by means of auditory-evoked potential recording is compared to maturation of axon neurofilaments and some critical stages in speech perception. The parallels strongly suggest that the emergence of the N1 component reflects the maturation of the axons in layer II and upper layer III of the auditory cortex. This is also the time period during which the perception of speech in noise and degraded speech markedly improves. The absence of N1 in cochlear implant subjects who have been deaf for a period of at least 3 years below the age of 6 years suggests a critical period in the maturation of the upper cortical layers and potentially poor future performance in the perception of masked and degraded speech.

Adolescent↗

PubMed2002

Visual speech perception without primary auditory cortex activation.

Speech perception is conventionally thought to be an auditory function, but humans often use their eyes to perceive speech. We investigated whether visual speech perception depends on processing by the primary auditory cortex in hearing adults. In a functional magnetic resonance imaging experiment, a pulse-tone was presented contrasted with gradient noise. During the same session, a silent video of a talker saying isolated words was presented contrasted with a still face. Visual speech activated the superior temporal gyrus anterior, posterior, and lateral to the primary auditory cortex, but not the region of the primary auditory cortex. These results suggest that visual speech perception is not critically dependent on the region of primary auditory cortex.

Acoustic Stimulation↗

PubMedDate not supplied

The neurophysiology of auditory perception: from single units to evoked potentials.

Evoked electric potential and magnetic field studies have the immense benefit that they can be conducted in awake, behaving humans and can be directly correlated with aspects of perception. As such, they are powerful objective indicators of perceptual properties. However, given a set of evoked potential and/or evoked field waveforms and their source locations, obtained for an exhaustive set of stimuli and stimulus contrasts, is it possible to determine blindly, i.e. predict, what the stimuli or stimulus contrasts were? If this can be done with some success, then a useful amount of information resides in scalp-recorded activity for, e.g., the study of auditory speech processing. In this review, we compare neural representations based on single-unit and evoked response activity for vowels and consonant-vowel phonemes with distinctions in formant glides and voice onset time. We conclude that temporal aspects of evoked responses can track some of the dominant response features present in single-unit activity. However, N1 morphology does not reliably predict phonetic identification of stimuli varying in voice onset time, and the reported appearance of a double-peak onset response in aggregate recordings from the auditory cortex does not indicate a cortical correlate of the perception of voicelessness. This suggests that temporal aspects of single-unit population activity are likely not inclusive enough for representation of categorical perception boundaries. In contrast to population activity based on single-unit recording, the ability to accurately localize the sources of scalp-evoked activity is one of the bottlenecks in obtaining an accessible neurophysiological substrate of perception. Attaining this is one of the requisites to arrive at the prospect of blind determination of stimuli on the basis of evoked responses. At the current sophistication level of recording and analysis, evoked responses remain in the realm of extremely sensitive objective indicators of stimulus change or stimulus differences. As such, they are signs of perceptual activity, but not comprehensive representations thereof.

Animals↗