Diane Kurtzberg

Maturation of mismatch negativity in typically developing infants and preschool children.

Objective 1) To determine whether an adult-like mismatch negativity (MMN) can be reliably elicited in typically developing awake infants and preschool children, and if so 2) to examine whether maturational changes exist in MMN latency and amplitude. Design Two experiments were designed to elicit MMN using an “oddball” paradigm. In Experiment 1, a 1000-Hz tone served as the standard stimulus and a 1200-Hz tone as the deviant. In Experiment 2, a 1000-Hz standard stimulus and a 2000-Hz deviant were presented. Infants’ ages ranged from 2 to 47 and 3 to 44 mo in Experiments 1 and 2, respectively. Results In Experiment 1, a negativity was not elicited in the majority of the infants and preschoolers tested. In Experiment 2, a negativity was reliably elicited in the infants and preschoolers across all ages. A significant negative correlation was observed between age and latency, but not for age and amplitude for this negativity. This negativity was found to decrease at a rate of 1 msec/mo. Infants younger than 12 mo of age showed a significantly larger positivity to the deviant than to the standard between 150–300 and 200–300 msec in Experiments 1 and 2, respectively. Conclusions The discriminative processes indexed by MMN in response to frequency changes are immature in infants and preschool children. Although there is convincing evidence that the negativity elicited in Experiment 2 is an immature MMN, the possibility that it may be an “obligatory effect” indexing recovery from refractoriness cannot be ruled out at this time. The results from these experiments suggest that the MMN component has limited use as a clinical tool at this time for infants and young children.

Developmental studies and clinical application of mismatch negativity : problems and prospects

There is wide interest in the clinical application of mismatch negativity (MMN) to assess discriminative capabilities in individuals whose auditory capacities are difficult to determine, including infants, young children and those with severe cognitive impairment. Before MMN can be used as a clinical electrophysiologic measure, it is necessary to establish that it can be reliably elicited in normal individuals. This chapter describes a detailed analysis of MMN recorded in a group of healthy 8-yr-old children to assess intrasubject and intersubject reliability of the response. We conclude that although statistically reliable results can be obtained with group data, and perhaps even in individuals when large numbers of stimuli can be delivered, the unfavorable signal to noise ratio of individual MMN data currently limits its clinical applicability. Suggestions for approaches to surmount these difficulties are presented for its eventual clinical usefulness.

Topographic analysis of human cortical potentials preceding self-initiated and visually triggered saccades

The topography of human brain potentials preceding self-initiated saccadic eye movements was compared with those preceding visually triggered saccades to examine differences in presaccadic activity under different programming requirements. A slow negative shift beginning approximately 650 ms before eye movement and largest in amplitude over the frontal region was recorded only in the self-initiated condition. This potential presumably reflects preparatory activity occurring predominantly within the frontal eye fields. A ramp-like positivity preceding eye movements by 100-250 ms and a sharp positive potential peaking 10-40 ms before saccades were recorded under both conditions. These potentials were of maximum amplitude over the parietal region. In order to examine the extent to which presaccadic enhancement of parietal activity was related to executive or to attentional mechanisms, the presaccadic visual evoked potential components were compared with activity at the same latency when stimuli were counted without saccades or were ignored. Enhancement of parietal potentials was seen both with counting and with saccades, but was greater in the eye movement condition. Occipital enhancement predominated with counting and parietal enhancement with saccades. These findings suggest that attentional and command mechanisms contribute distinct complementary increments in posterior cortical presaccadic activity associated with visually triggered saccades.

Cortical responses to speech sounds and their formants in normal infants: maturational sequence and spatiotemporal analysis

Cortical auditory evoked potentials (AEPs) to the synthesized syllables [da[ and [ta[ and to the isolated 3 formants of [da[ were obtained from 32 normal infants studied at monthly intervals from birth through 3 months and at 6 months of age. A bilateral array of 16 electrodes referenced to the mid-occiput permitted a topographic analysis of the cortical AEPs at selected latencies. A differential maturational sequence was seen: a predominantly negative cortical AEP wave form became positive, first over the frontocentral region (around term), and then over the temporal region (at 1-2 months). The timing of these electrophysiological changes coincides with a differential anatomical maturational sequence in the auditory cortex, as myelination and synaptogenesis are more advanced in primary than secondary auditory areas at term. All infants in this study followed this developmental sequence. However, there was no systematic effect of the center frequency of the formant stimuli on the maturational level of their respective cortical AEPs, suggesting a relative maturational equivalence in those regions of auditory cortex responding to stimuli across the frequency range present in human speech. In term infants, an initial midline positivity and bitemporal negativities were asynchronous in their peak and offset latencies. suggesting independent generators for each of these components. In infants from 3 to 6 months of age, cortical AEP wave forms consisted of 2 initial positive peaks followed by a negative peak. While the wave forms were similar over midline and lateral scalp, spatiotemporal analysis revealed differences in the latency of onset, duration and in the spatial extent of these components, again suggesting that 2 bilateral, temporally overlapping generators contribute to the cortical AEP. No systematic topographic difference was observed in the cortical AEPs elicited by each of the 3 formants, which differed in center frequencies.

Differential maturation of cortical auditory evoked potentials to speech sounds in normal fullterm and very low-birthweight infants

Cortical auditory evoked potentials (AEP) to the consonant‐vowel syllables /da/ and /ta/ and 800Hz tone were recorded at 40 weeks post‐conceptional age and at one, two and three months after term in normal fullterm and very low‐birthweight infants. As a group, the very low‐birthweight infants exhibited significantly less mature AEPs to consonant‐vowel syllables than the normal‐birthweight infants at 40 weeks post‐conceptional age. Consistent but statistically non‐significant differences also were found for tones at 40 weeks post‐conceptional age, and for all stimuli at one and two months after term. By three months, all the infants exhibited mature AEP morphology and topography.

Maturation of mismatch negativity in school-age children.

Objective: Event‐related potentials were recorded to investigate the maturation of auditory processing in school‐age children. Design: The mismatch negativity (MMN) was obtained in an oddball tone discrimination paradigm in 66 school‐age children and 12 adults. In the childrens data, a prominent negativity to both the standard and deviant tone, peaking around 200 msec, was observed, and compared with the N1 auditory evoked potential component. Results: The MMN was found to decrease with latency by 11 msec/yr from 4 to 10 yr of age. No developmental change in MMN amplitude was seen from 4 to 10 yr of age. However, the MMN amplitude was significantly smaller in adults than in children. The prominent negativity in children was significantly later than the adult N1 component, and did not change in latency from 4 to 10 yr of age. This finding adds to a body of evidence suggesting that this prominent negativity and the adult N1 are not the same component. The magnitude of the prominent negativity in children decreased slightly with age. Conclusion: Changes in the timing of the brain discriminative response, MMN, suggest systematic maturational changes in auditory processing.

Neurobehavioral Performance of Lowbirthweight Infants at 40 Weeks Conceptional Age: Comparison with Normal Full term Infants

This study compares the neurobehavioral status of 118 low‐birthweight infants tested at 40 weeks conceptional age with that of 76 normal fullterm infants. A neonatal neurobehavioral examination comprising 21 test and four summary items was used. The most striking differences between the groups were found in visual and auditory orienting, with approximately two‐thirds of the low‐birthweight infants falling below the range of performance of the fullterm group. Items testing motor performance showed a lower incidence of deviant performance among the low‐birthweight infants. Of the 21 test items, 19 could be assigned cut‐off scores, below which infants can be considered deviant on the specific items.

The effects of decreased audibility produced by high-pass noise masking on cortical event-related potentials to speech sounds /ba/ and /da/

This study investigated the effects of decreased audibility produced by high-pass noise masking on cortical event-related potentials (ERPs) N1, N2, and P3 to the speech sounds /ba/and/da/presented at 65 and 80 dB SPL. Normal-hearing subjects pressed a button in response to the deviant sound in an oddball paradigm. Broadband masking noise was presented at an intensity sufficient to completely mask the response to the 65-dB SPL speech sounds, and subsequently high-pass filtered at 4000, 2000, 1000, 500, and 250 Hz. With high-pass masking noise, pure-tone behavioral thresholds increased by an average of 38 dB at the high-pass cutoff and by 50 dB one octave above the cutoff frequency. Results show that as the cutoff frequency of the high-pass masker was lowered, ERP latencies to speech sounds increased and amplitudes decreased. The cutoff frequency where these changes first occurred and the rate of the change differed for N1 compared to N2, P3, and the behavioral measures. N1 showed gradual changes as the masker cutoff frequency was lowered. N2, P3, and behavioral measures showed marked changes below a masker cutoff of 2000 Hz. These results indicate that the decreased audibility resulting from the noise masking affects the various ERP components in a differential manner. N1 is related to the presence of audible stimulus energy, being present whether audible stimuli are discriminable or not. In contrast, N2 and P3 were absent when the stimuli were audible but not discriminable (i.e., when the second formant transitions were masked), reflecting stimulus discrimination. These data have implications regarding the effects of decreased audibility on cortical processing of speech sounds and for the study of cortical ERPs in populations with hearing impairment.

Neurophysiological Indexes of Speech Processing Deficits in Children with Specific Language Impairment

We used neurophysiological and behavioral measures to examine whether children with specific language impairment (SLI) have deficits in automatic processing of brief, phonetically similar vowels, and whether attention plays a role in such deficits. The neurophysiological measure mismatch negativity (MMN) was used as an index of discrimination in two tasks; one in which children ignored the auditory stimuli and watched a silent video and a second in which they attended to the auditory modality. Children with SLI showed good behavioral discrimination, but significantly poorer behavioral identification of the brief vowels than the children with typical language development (TLD). For the TLD children, two neurophysiological measures (MMN and a later negativity, LN) indexed discrimination of the vowels in both tasks. In contrast, only the LN was elicited in either task for the SLI group. We did not see a direct correspondence between the absence of MMN and poor behavioral performance in the children with SLI. This pattern of findings indicates that children with SLI have speech perception deficiencies, although the underlying cause may vary.

EFFECTS OF SENSORINEURAL HEARING LOSS AND PERSONAL HEARING AIDS ON CORTICAL EVENT-RELATED POTENTIAL AND BEHAVIORAL MEASURES OF SPEECH-SOUND PROCESSING

Objective: To systematically investigate the combined effects of sensorineural hearing loss and prescribed personal hearing aid(s) on cortical event-related potentials (ERPs) (waves N1, MMN, N2b, and P3b) and their related behavioral measures of discrimination (d-prime sensitivity and reaction time) to the speech sounds /ba/ and /da/ presented at 65 and 80 dB peak-to-peak equivalent SPL. Design: Cortical ERPs were recorded to /ba/ and /da/ speech stimuli presented at 65 and 80 dB peak-to-peak equivalent SPL from 20 normal-hearing adults and 14 adults with sensorineural hearing losses. The degree of sensorineural impairment at 1000 to 2000 Hz ranged from moderate losses (50 to 74 dB HL) to severe-profound losses (75 to 120 dB HL). The speech stimuli were presented in an oddball paradigm and cortical ERPs were recorded in both active and passive listening conditions at both stimulus intensities. The adults with hearing impairments were tested in the unaided and aided conditions at each stimulus intensity. Electroacoustic and real-ear testing was performed on each subject’s hearing aid(s) before electrophysiology testing to ensure that the hearing aids were functioning at the time of testing. Results: The use of personal hearing aids substantially improved the detectability of all the cortical ERPs and behavioral d-prime performance scores at both stimulus intensities. This was especially true for individuals with severe-profound hearing losses. At 65 dB SPL, mean ERP amplitudes and d-prime sensitivity scores were all significantly higher or better in the aided versus unaided condition. At 80 dB SPL, only the N1 amplitudes and d-prime sensitivity scores were significantly better in the aided condition. Even though the majority of the hearing-impaired subjects showed increased amplitudes, decreased latencies, and better waveform morphology in the aided condition, the amount of response change (improvements) seen in these measures showed considerable variability across subjects. When compared with the responses obtained from the normal-hearing subjects, both hearing-impaired groups had significantly prolonged aided RT latencies at both stimulus intensities and N2b latencies at the higher stimulus intensities. Conclusions: These results suggest that hearing-impaired individuals’ brains process speech stimuli with greater accuracy and in a more effective manner when these individuals use their personal hearing aids. This is especially true at the lower stimulus intensity. The effects of sensorineural hearing loss and personal hearing aids on cortical ERPs and behavioral measures of discrimination are dependent on the degree of sensorineural loss, the intensity of the stimuli, and the level of cortical auditory processing that the response measure is assessing. The possible clinical significance of these cortical ERP and behavioral findings is discussed.