Averaged Electroencephalic Response Research Articles

Maturational effects on the middle components of the averaged electroencephalic response.

Middle component AERs to brief click stimuli were recorded from 60 subjects in four age groups to assess age effects on waveform, latency, and amplitude. Replicable responses similar in waveform to those recorded in adults were observed in 3 - 4-year-old children, full-term newborns, and premature infants tested as early as the 31st postconceptional week. Latencies and amplitudes were compared across ages and significant age effects were evident for amplitude but not latency. Amplitudes of components Po, Pa and Pb were found to increase until 3 - 4 years of age and decline in adulthood. Response amplitudes for premature infants differed significantly from those of adults, but newborns' responses did not differ from either group. Only the responses of 3 - 4-year-old children were clearly differentiated from those of all other groups in this respect. Significant age effects on latency were found only for Po, which is postulated to be synonymous with Wave V of the brainstem response. The absence of a trend for decreasing latency as a function of age in the middle components is surprising in that both early (brainstem) and late (cortical) responses demonstrate this effect. This finding raises questions about the generator sources for middle components.

The use of averaged electroencephalic response techniques in the study of auditory processing related to speech and language

This paper reviews a number of studies done by the authors and others, who have utilized various averaged electroencephalic response (AER) techniques to study speech and language processing. Pertinent studies are described in detail. A relatively new AER technique, auditory brainstem responses (ABR), is described and its usefulness in studying auditory processing activity related to speech and language is outlined. In addition, a series of ABR studies, that have demonstrated significant male—female differences in ABR auditory processing abilities, is presented and the relevance of these data to already established differences in male—female language, hearing, and cognitive abilities is discussed.

Middle component averaged electroencephalic responses to tonal stimuli from normal neonates. Initial report.

Tone-pips, centered at 1,000 Hz, were used to elicit middle component averaged electroencephalic responses (AERs) (8 to 90 ms) from five normal neonates. The stimuli were presented monaurally at 10-, 30-, and 50-dB HL, with regard to adult behavioral thresholds. Averaged electroencephalic responses were also derived for no-stimulus control conditions. The initial portion of the stimulus-elicited AER waveforms was similar to that obtained from adults. An objective, scoring procedure, based on predetermined rules, was used to determine peak latencies and to quantify point-to-point amplitudes. Inspection of the scored data revealed that latencies decreased and amplitudes increased as the stimulus magnitude increased, as has also been reported for adults. Unlike adult responses, the middle components from the neonates in this study were identifiable only when recorded from the side of the head ipsilateral to the ear stimulated.

Middle Components of Human Auditory Averaged Electroencephalic Response: Waveform Variations During Averaging

The bases for variations of the middle-component (8-50 ms) auditory averaged electroencephalic response (AER) to clicks during the averaging process were explored by examining (1) the trend of the mean variance of the averaged waveform, (2) averaged waveforms generated by successive blocks of stimuli fractioned from a total of 512 stimuli, and (3) averaged waveforms generated by successive, but partially overlapping, blocks of responses recorded for a train of 512 stimuli. These analyses indicated no systematic changes in peak latencies or peak-to-peak amplitudes as stimulation progressed. Fluctuations in middle AER waveform are more readily explained by non-stationarity of the background electrophysiologic noise. Previously reported amplitude reduction with increasing stimulus number possibly can be explained by progressive reduction of the background noise on which the consistent-amplitude middle components are superimposed.

Middle Latency Response in Adults and Children

The middle latency response of averaged electroencephalic response to click stimuli were investigated on 8 adults and 8 young children aged from 8 months to 4 years 2 months. The hearing of all subjects were proved to be normal. The results obtained from this studies were as follows:(1) In adults, the great stability was found in the configulations of the response waves and the latency during both awake and asleep, as many authors reported previously. But, there were some inter-subjective variability of the appearance of the response.(2) The response pattern of the young children was unstable during sleep. Especially, Na- and Pa-peak were not consistently detected. It seemed that the appearance of the response tended to depend upon the sleep stage in children. Therefore, the clinical usefulness of the middle latency response, as an objective audiometry for children, may be diminished.(3) It was highly suspected that the origin of Po-peak would be different from that of Na- and Pa-peak.

Recovery of middle components of human auditory averaged electroencephalic responses

Recovery functions of peak-to-peak amplitudes were derived for middle components (latencies approximately 8–80 msec) of auditory AERs recorded from 10 normal-hearing adults. Click stimuli were presented monotically at 50 dB SL in sets of three for 256 repetitions per AER. Interclick interval between the first two clicks of set (delta) was varied between 4 and 256 msec. Third click always followed second click by 256 msec. Amplitudes of responses to second clicks were compared to those of responses to third clicks in stimulus sequence through the use of special computerized scoring procedures. Full recovery of amplitude of the different peaks occurred for delta intervals of 45.6–64 msec and longer. No response was seen for second click of sequence when delta interval was between 4 and 16–22.4 msec. Recovery of amplitude was graded for intermediate delta interval values. Preliminary results of nonlinear curve fits to data suggest that recovery of amplitude is a power function of delta interval. For the middle components, delta interval required for full recovery appears to be less than that for late components and slightly longer than that for early (brainstem) components. No significant shifts of peak latencies occurred as a function of delta interval.

Non-surgical recording of auditory pathway function in cats.

The techniques are described for serial, non-surgical recording of the cochlear microphonic (CM), the electrocochleogram (ECoG) and the averaged electroencephalic response (AER) in cats. The early post-natal period has been systematically studied in a breeding strain of hereditarily deaf white cats, and illustrative examples are presented from animals with histologically normal chochleae, and also from ears with confirmed chochleosaccular degeneration. Transitory potentials have been recorded with the CM and ECoG procedures from some of the latter.

Reexamination of effects of stimulus rate and number on the middle components of the averaged electroencephalic response.

The middle components of the evoked cortical response (8-50 msec) were examined under improved signal processing conditions. 512 click stimuli were presented at 5 rates ranging from 1-16/sec to 10 normal-hearing subjects. The influence of stimulus numbers of 32, 64, 128 and 512 and stimulus rates of 1, 2, 4, 8 and 16/sec was examined. Identifiable and repeatable responses were found with as few as 128 stimuli. Stimulus rate had little effect on middle component waveform or its identifiability. An enhancement of signal-to-noise ratio through improved filter conditions is suggested as one reason for the ability to identify middle components to fewer stimuli.

Early averaged electroencephalic responses to clicks in neonates.

The early (approximately 8–50 msec latency) averaged electroencephalic responses (AER) to 55 dB HL clicks were elicited from ten normal newborns 36 to 72 hours after birth. Early components were observed in all ten babies with 512 clicks presented at 4.5/sec and 9.0/sec. Mean peak latencies in msec were: Po — 11, Na — 17, Pa — 28, Nb — 35, and Pb — 51. The neonates' early component waveforms closely resemble those of adults. The latency and waveform stability of the early components in neonates and adults support the belief in the primary auditory (lemniscal) system as the mediator of these responses. Furthermore, the repeatability of the early components of the AER makes them more reliable response indices than the late components (approximately 50–400 msec) for audiometry with neonates.

Phase Distortion of Averaged Electroencepha

Analog filters employed in most averaged electroencephalic response (AER) recording systems impose some phase distortion on recorded AER. Phase distortion of the response results in a real time shift of peak latencies. The extent of this distortion, in general, is determined by the cutoff frequencies of the filter band in relation to the spectrum of the response. If the filter band employed is quite restrictive, the shift of latencies can be large. For purposes of threshold audiometry, filter-imposed phase shifts will not usually prevent simple response identification. However, if such time shifts in the data are not accounted for in interclinic or published communications, the response information could be misleading and confusing.

Influence of stimulus level and sleep stage on the early components of the averaged electroencephalic response to clicks during all-night sleep.

Ongoing EEG activity was recorded from six adults from an electrode on the vertex referred to the right and left mastoids during nine nights of natural sleep. An electrode placed near the lateral canthus of each eye was used to record eye movements. The effect of stimulus level (0 to 25 dB SL in 5-dB steps) on the early components of the averaged electroencephalic response was examined with clicks presented at a rate of five per second from a loudspeaker. Each response was averaged over 512 stimuli. Responses were sorted into the stage of sleep from which they were obtained. “Light” sleep included Stages REM and 2. “Deep” sleep included Stages 3 and 4. Response latency remained stable, while amplitude generally increased as a function of increasing sensation level. Little difference in peak latency and peak-to-peak amplitude was found when comparing light vs deep sleep. Latency measures for two consecutive nights were similar, but amplitude measures from the first night were significantly larger.

Early components of the averaged electroencephalic response to constant level clicks during rapid eye movement sleep.

The early components of the averaged electroencephalic response (AER) were elicited by click stimuli from each of four subject during completed night of nature sleep. Clicks were presented from a loudspeaker 50 dB above the subject's voluntary threshold at a rate of 4.5/sec continuously throughout the night. Response obtained during sleep stages 2, 3, and 4 were pooled and compared to the responses obtained during rapid eye movement (REM) sleep for each subject. Statistically significant peak-to-peak amplitude difference scores were only obtained for the Pa and Nb peaks. The largest differences, with shorter REM latencies in both cases, were 1.5 msec for Pa and 4.5 msec for Nb. Thus a similar pattern for the early components of the AER was found during REM and non-REM (NREM) sleep. Therefore, the clinical usefulness of the early components was not diminished during stage REM sleep.

Early components of the averaged electroencephalic response to monaural and binaural stimulation.

Early components of the averaged electroencephalic response were recorded in 11 subjects from Cz-A1, Cz-A2, C3-A1, and C4-A2. The early components were examined in response to stimulation of either the left, right, or both ears with 40 dB SL clicks at a rate of 4/sec in awake subjects. Peak latency and peak-to-peak amplitude measures failed to discriminate between stimulus conditions. Left minus right difference scores obtained for each subject showed no consistent relationship to the ear stimulated

Influence of background noise on the early components of the averaged electroencephalic response to clicks.

Early components of the averaged electroencephalic response (AER) were studied in 10 normal-hearing subjects. Clicks were presented monaurally at 24 dB SL in the presence of an ipsilateral white noise whose level was systematically varied. AER peak-to-peak amplitude and peak latency were measured. Response amplitude varied inversely with masker level; latency did not vary systematically. No responses were detectable when the clicks were subjectively masked by the white noise.

Effect of alcohol on the early and late components of the averaged electroencephalic response to clicks.

Early and late components of the averaged electroencephalic response to clicks were studied for eight adult subjects prior to and at regular intervals after ingestion of two ounces of 100 proof bourbon. Latencies of the early and late components did not change over the five to seven hours after alcohol ingestion. No significant changes were noted in the peak-to-peak amplitudes of the early components, while a slight trend toward increased amplitude over time was observed for P 2 -N 2 of the late components.

Short-term habituation of the averaged electroencephalic response in infants.

Short-term habituation of the averaged electroencephalic response (AER) was studied in 12 14- to 18-week-old infants. No evidence of habituation was observed for either pure-tone or broad-band stimuli. This finding is in sharp contrast with the rapid AER habituation observed in adults. The results suggest that the competence reflected by short-term habituation is not fully established at birth, but rather develops with further experience or neurologic maturation.

Early components of the averaged electroencephalic response to constant level clicks during all-night sleep.

Electrical activity was recorded from adult subjects during four consecutive nights of natural sleep. Ongoing EEG activity was recorded from an electrode on the vertex referred to electrodes on the right and left mastoids. An electrode placed near the outer canthus of each eye was referred to the left mastoid and used to record eye movements (EOG). The early components of the averaged electroencephalic response (AER) were examined during the third and fourth nights, with 50 dB SL clicks at a rate of 9.6/sec presented continuously from a loudspeaker during the entire night. Each average consisted of 1024 responses. Sleep stages were subsequently scored from the EEG and EOG, and AERs were selected for analysis based on predetermined sampling rules. The response during sleep differs only slightly in latency from that found in waking subjects. Latencies of the major peaks remain constant regardless of stage of sleep. Amplitude generally varies with stage of sleep: the deeper the stage of sleep, the smaller the amplitude. REM sleep does not interfere with responsivity and, in fact, may enhance clarity of response. In addition, overall response patterns from stages of sleep compared early in the night to those from the early morning show no evidence of long-term habituation during the course of the night.

Early components of the averaged electroencephalic response in relation to rise-decay time and duration of pure tones.

Early components of the averaged electroencephalic response (AER) to auditory stimuli were elicited in 10 normal-hearing subjects. Stimuli were 1000-Hz tones having rise-decay times of 5, 10, and 2...

Induced Biophysical Artifacts in Averaged Electroencephalic Response (AER) Audiometry

Induced biophysical artifacts (myogenic responses) were obtained from six subjects during a test procedure similar to that used for recording the late components of the averaged electroencephalic response (AER) to auditory stimuli. The responses obtained were unlike the characteristic uncontaminated AER to sound with regard to latency and amplitude, determined prior to obtaining the induced biophysical response. However, the variety of voluntary biophysical activities (jaw clenching, eye-blinks, forehead movement) performed while recording the AER to sound tended to obscure the characteristic response. Some possible methods for reducing or eliminating induced biophysical artifacts during AER audiometry are presented.

The Averaged Evoked Response Threshold for Monaural And Binaural Masked Signals

The parameters of the averaged electroencephalic response (AER) are well documented for simple listening situations; this experiment was designed to explore the AER to more complex conditions. The AER and behavioral thresholds were measured for five human subjects. A 500-Hz 20-msec tone (with a rise/fall time of 5 msec) and continuous white noise were delivered through headphones for the following conditions: NmSm, NoSo, NoSm, and NπSo. Behavioral and AER masked thresholds were approximately the same for the NoSo condition but averaged about 6 dB poorer for the AER for the NmSm condition than for the behavioral condition. Both the AER and behavioral thresholds for the NoSm and NπSo were of typical threshold differences (5 dB and 12 dB, or better, respectively) than the NmSm and NoSo conditions. The results indicate that: (1) the AER reflects the signal in the presence of noise background; (2) the AER reflects binaural interaction as demonstrated by the MLD; (3) the AER masked threshold is better with binaural presentation (NoSo) compared to monaural presentation (NmSm).