Improving behavior observation audiometry testing and scoring procedures.

The need exists for improving behavioral testing of low-functioning children, particularly profoundly involved multiply handicapped children. In this study, behavior observation audiometry (BOA) was modified for systematic evaluation of childrens' responses to sound without observer bias. The data were analyzed statistically and a minimum response level was computed. This BOA technique was used to test the hearing of 82 profoundly involved handicapped children. Results suggested that BOA can be helpful in evaluating the hearing of low-functioning children.

Distribution of auditory response behaviors in normal infants and profoundly multihandicapped children.

Responsiveness (yes/no decisions) to sound has been found to be similar for normal infants and profoundly multihandicapped children of comparable developmental ages (Flexer & Gans, 1985). The purpose of this investigation is to extend the comparison of these two groups by examining the distribution of their response behaviors to sound. Ten normal and 10 multihandicapped children were videotaped while various auditory signals were presented. Without knowledge of stimulus type, five judges listed the behaviors that occurred during 24 sound and 24 catch trials for each child. The behaviors were then evaluated as a function of the stimulus parameters of meaningfulness, bandwidth, and intensity. Results revealed that the profoundly multihandicapped children displayed relatively more reflexive than attentive type behaviors and exhibited fewer behaviors per response. The effects of stimulus-type on the numbers and distribution of responses are discussed.

Comparative evaluation of the auditory responsiveness of normal infants and profoundly multihandicapped children.

Responses to sound were observed in two groups of children. One was developmentally normal; the other was older but profoundly multihandicapped. The groups had developmental ages from 2 to 4 months, as assessed by the Kent Infant Developmental Scale (Katoff, Reuter, & Dunn, 1978). Stimuli were speech and random noise, both unfiltered and band-pass filtered at 2000 Hz, presented at 40, 60, and 80 dB HL. Responsiveness was determined from the confidence levels of observers' judgments of videotapes. Results showed that there were no significant differences between the subject groups. In both groups, however, responsiveness was dependent on hearing level and bandwidth but not on meaningfulness. The results support the practice of evaluating auditory responsiveness of multihandicapped children in relation to developmental age.

Effects of acoustic trauma on the cochlear potentials.

The cochlear microphonic, summating potential, and action potential were recorded from all three turns of the gerbil cochlea prior to and following a 1-h exposure to a high-intensity pure tone. Results proved that the depression in the cochlear microphonic was greater when recorded from the upper two turns of the cochlea. The losses for the summating potential were not dependent on recording location. Although the cochlear microphonic and to some extent, the negative summating potential, reflected locally generated activity from the hair cells, the positive summating potential appeared to be dependent on distant electrical activity.

Auditory response behavior of severely and profoundly multiply handicapped children.

Severely and profoundly involved multiply handicapped children present special problems for the audiologist. Although a substantial amount of data is available on the behavioral responses of normal babies, there is a surprising dearth of similar information concerning handicapped children. In the present study, the responses of 31 severely and profoundly involved multiply handicapped children were studied by behavioral observation audiometry. Children's chronological age ranged from 7 to 153 months, while developmental age was estimated as 0 to 24 months. An experienced judge rated each of 9 specific behaviors either absent, strong, or weak on each trial. The stimulus types were a broadband noise, narrowband noises centered at .5 and at 2 kc/s, and speech either unfiltered or high-pass filtered at 1.2 kc/s, presented to S by a loudspeaker at 45 degrees azimuth, at 20, 40, 60, and 80 db re normal HTL. The interrelationships between stimulus variables, types of responses, and developmental level of the children were evaluated. Overall, the children responded differentially to the 5 stimulus types. Furthermore, the higher-functioning children responded much differently to the sounds than did the lower-functioning children. It was recommended that any behavioral technique be used together with objective tests in this most difficult population, and that testing be repeated over an extended period of time.

Observer bias in the hearing testing of profoundly involved multiply handicapped children.

Observer bias was investigated using 27 profoundly involved multiply handicapped children and behavioral observation audiometry. Two observers were in the room with the child, two others viewed via a video monitor, and each of the four observers had full knowledge of stimulus-type and intensity. Two additional observers viewed a videotape without being provided information about the stimuli. Results showed clear bias effects in 85% of the children. At low intensities, observers aware of stimulus events tended to score fewer responses than those judges unaware of stimulus intensity. At high levels, this trend was reversed. It is recommended that the estimation of hearing threshold in handicapped children be made by observers who do not have access to the sequence of stimulus presentations.

The contingent negative variation as an indicator of speech discrimination difficulty.

Recent studies have illustrated the usefulness of the contingent negative variation (CNV) in exploring language processing capabilities. The purpose of this study was to investigate how CNV magnitude is influenced by speech discrimination tasks of graded difficulty. Nine young adult subjects performed easy and difficult speech discrimination tasks while cortical activity was recorded from the vertex. Stimuli consisted of consonant-vowel pairs that were presented in a background of noise. Consistently larger CNV responses were obtained for the difficult versus the easy discrimination task in the nonimperative condition. No consistent trend was found for the imperative condition. There electrophysiological results correspond well with both correct and incorrect discrimination behavior. The clinical implications of these findings are discussed.

Computing auditory fatigue of the whole nerve action potential.

Fatigue at the level of the VIII nerve is often calculated through the measurement of the whole nerve action potential (AP). The losses have been quantified by calculating the dB shift required to record a criterion AP voltage or by determining the ratio of the pre- and post-exposure AP voltages at a constant probe intensity. The issue raised here is whether the two methods produce similar AP losses. Fifteen rats were exposed to a 6000-Hz pure tone at either 100, 105, or 110 dB SPL for five minutes. Input-output functions were determined at five probe frequencies prior to and following exposure. When the probe intensity (i.e., AP voltage) was low, AP losses appeared greater when the AP fatigue was computed at a constant intensity. This trend was reversed at higher probe levels. These results are explained on the basis of the growth behavior of the AP.

An electrophysiological correlate of phonemic discrimination.

Event-related potentials have not, to date, been used to probe speech discrimination processes. The purpose of the present study was to determine whether correct speech discrimination performance was associated with characteristic changes in contingent negative variation (CNV) waveform. 9 paid subjects were placed in a 'go/no-go' discrimination paradigm. Correct perception of phoneme differences (no-go) was associated with an abrupt decrease in 'orienting wave' (O-wave) amplitude. The moment of 'O-wave' resolution generally occurred during presentation of key acoustic features differentiating the 'go' from the 'no-go' stimuli.

Underestimation of auditory fatigue as measured by the compound action potential.

The action potential (AP), summating potential (SP), and cochlear microphonic (CM) were measured in rats in response either to clicks or pure tones prior to and following 3 min of exposure to pure tones at a level 5 db less than that which produced maximum CM. The ratio, in decibels, between pre-exposure and post-exposure potentials, for the same exposure and probe stimulus parameters, was taken as an index of decrement. The relative reduction in voltage resulting from the exposure was greater for the SP than for the AP when these potentials were elicited with 20-msec probe tone bursts between 70-80 db SPL having instantaneous rise times. However, for weaker probe levels within 20 db of that yielding AP potentials of 1 mu V, the AP and SP bpth exhibited similar losses. The CM and the click-evoked AP showed essentially no decrement. These results suggest that the SP might be a better indicator of noise-induced auditory decrement (fatigue?) than the CM. Theories of central auditory fatigue may be based on incorrect interpretations of previously published data obtained from cochlear and neural recordings.

Comparing TROCA and peep-show in testing the hearing of young children.

The hearing of 24 normal hearing children ranging in age from 18 to 32 months was tested by TROCA and peep-show, two operant conditioning technique differing only in the type of reward. Children between 18 and 24 months consistently exhibited poorer thresholds (lowest response levels) than children between 25 and 32 months. The older children required fewer trials for threshold determination and took less time in completing testing. Children tested with TROCA exhibited significantly poorer thresholds (although the differences were small) and took significantly longer to complete testing than for peep-show. No differences were found between the two methods for the number of trials to obtain threshold. The results strongly suggest that the type of reward is not an important factor in testing the hearing of young, normal children.

Attention and respiration audiometry.

The effect of attention on auditory responses obtained with respiration audiometry was examined on twenty normal-hearing adults. Ten subjects were instructed to listen carefully for the auditory stimuli during testing, while the other ten were not instructed. The results revealed that the change in respiration resulting from sound stimuli for the instructed subjects was three times greater than for the uninstructed group during the first 11-tonal sequence. However, during the third sequence, more responses were obtained from the uninstructed subjects. There was little evidence to suggest that the respiratory changes to sound were greater in magnitude or in number as the intensity of the sound approached behavioral threshold. The results suggest that the level of attention affects the number and pattern of respiratory responses to sound.

Normative data on the cochlear microphonic in rat using differential electrodes.

Isopotential (1-muV) cochleograms were obrained from 19 anesthetized rats from electrodes inserted into scala vestibuli and scala tympani of the first turn. The differential electrode technique is suitable for frequencies above 1-2 kc/s in the rat. CM sensitivity in rats as measured with intracochlear electrodes (26 micrometer in diameter) was considerably poorer than in guinea pigs at frequencies below 2 kc/s, but was within 10-14 db at 2 kc/s and above. The shape of the CM input-output functions were similar to those in the guinea pig and chinchilla, except that the intensity level where the CM becomes non-linear is higher in the rat.