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Biomedical subjects

G A McCandless

Publications and source records attributed to G A McCandless.

18 recordsLinked to original sources
PubMed1988

Auditory/phonetic categorization with the Symbion multichannel cochlear implant.

The phonetic identification ability of an individual (SS) who exhibits the best, or equal to the best, speech understanding of patients using the Symbion four-channel cochlear implant is described. It has been found that SS: (1) can use aspects of signal duration to form categories that are isomorphic with the phonetic categories established by listeners with normal auditory function; (2) can combine temporal and spectral cues in a normal fashion to form categories; (3) can use aspects of fricative noises to form categories that correspond to normal phonetic categories; (4) uses information from both F1 and higher formants in vowel identification; and (5) appears to identify stop consonant place of articulation on the basis of information provided by the center frequency of the burst and by the abruptness of frequency change following signal onset. SS has difficulty identifying stop consonants from the information provided by formant transitions and cannot differentially identify signals that have identical F1's and relatively low-frequency F2's. SS's performance suggests that simple speech processing strategies (filtering of the signal into four bands) and monopolar electrode design are viable options in the design of cochlear prostheses.

Adult↗
PubMed1986

Differential susceptibility to noise-induced permanent threshold shift between albino and pigmented guinea pigs.

Evidence that reduced levels of cochlear melanin are associated with increased auditory sensitivity, increased levels of auditory fatigue and an increased susceptibility to noise-induced hearing loss led us to investigate the effects of noise exposure on the cochlear microphonic (CM) in albino and pigmented English shorthair guinea pigs. CMs were recorded from the round window prior to and at 90 min and 7 days after exposure to 45 min of 126 dB noise. Thresholds for the first detectable elicitation of the CM for four pure tones were determined and the output voltage of each cochlea was measured in 10 dB steps through intensity levels which produced a maximum voltage amplitude in the CM and voltage rollover. This analysis demonstrated that: albino guinea pigs displayed significantly lower auditory thresholds than did pigmented animals before exposure to noise; thresholds were elevated to comparable levels in both groups 90 min after noise exposure; pigmented guinea pigs showed a reliable recovery in CM thresholds 7 days after exposure to noise while thresholds in the albinos remained elevated to the same degree at both 90 min and 7 days after noise; 90 min after noise exposure, the maximum voltage output of albino cochleas was significantly less than that recorded from the cochleas of the pigmented guinea pigs. These results demonstrate that albino guinea pigs are more susceptible to the ototoxic effects of high intensity noise than pigmented guinea pigs. Converging evidence indicates that some aspects of cochlear function involve melanin pigment and that its absence may produce auditory abnormalities. Reduced melanin pigmentation may also contribute to such phenomena as noise-induced threshold shifts and individual differences in noise-induced hearing loss.

Albinism↗
PubMed1980

Drill- and suction-generated noise in mastoid surgery.

The air-conduction noise levels in the external and middle ear generated by drilling and suction during temporal bone surgery were measured. Variables included diamond burrs, cutting burrs, two different air drills (Hall and Stryker) an electric drill (Emesco), and drilling with and without suction irrigation. The results show that the single factor contributing the highest noise level is suction irrigation, which exposes the ipsilateral ear to noise levels averaging up to 107 dB (A). The average noise levels of drilling range from 65 to 96 dB (A) varying with the drill and burr used. Simultaneous drilling and suction irrigation generated noise levels ranging from 91 to 108 dB (A). Cutting burrs were found to be up to 9 dB (A) more intense than diamond burrs. Exposure to these noise levels may account for shifts in the hearing thresholds sometimes apparent in postoperative audiograms of mastoid surgery patients.

Humans↗
PubMed1980

Action of general anesthesia on middle ear effusions.

An investigation was made of the incidence of "negative myringotomy" or the absence of middle ear effusion when preoperative impedance testing and examination predicted such fluid. The effect of general anesthesia on the clearance of middle ear fluid was studied by comparing preanesthesia and postanesthesia tympanograms with the findings at myringotomy. The effect of nitrous oxide and positive pressure ventilation without nitrous oxide to increase middle ear pressure are mechanisms that could clear low viscosity fluid from the middle ear.

Anesthesia, General↗
PubMed1979

Auditory dysfunction with facial paralysis.

A series of 58 patients with idiopathic facial paralysis were studied to determine if a concomitant cochlear or eight nerve auditory dysfunction could be identified with traditional audiologic tests. Results indicated that only those patients with a facial nerve lesion, proximal to the stapedius branch, experienced reduced tolerance for loud sounds, reduction of speech discrimination at high-intensity levels, and abnormal loudness growth. Such findings suggest that changes in auditory function, accompanying facial nerve paralysis, are a mechanical effect due to absence of stapedial action. Site of lesion tests in this sample failed to demonstrate eighth nerve dysfunction and, thus, does not support a theory of polyneuropathy that involves the auditory nerve.

Adolescent↗
PubMedDate not supplied

Aging and auditory site of lesion.

The purpose of this study was to examine and quantify the functional auditory problems of presbycusis through a battery of recently developed diagnostic tests and to evaluate the usefulness of these tests with an elderly population. Diagnostic measures used were impedence measures, speech discrimination tests, synthetic sentence identification, compressed speech, two measures of tone decay, the short increment sensitivity index, a digit span test, and auditory brain stem response audiometry. Significant differences were found between scores for elderly subjects and those of young subjects who had similar audiograms. Use of the Metz test as an objective measure of recruitment yielded results suggesting a higher incidence of recruitment than evidenced by previous studies using loudness balancing procedures. The Olsen-Noffsinger procedure of quantifying tone decay revealed a greater difference between age groups than did the Suprathreshold Adaptation Test. Synthetic sentence identification revealed the most consistent age effect among the tests of central auditory function. Auditory brain stem response audiometry revealed several examples of abnormally long interpeak latencies. It is concluded that there is both behavioral and electrophysiological evidence of central and peripheral auditory disorder frequently accompanying senescence.

Aged↗
PubMedDate not supplied

Hearing aid performance relative to site of lesion.

This study investigated hearing aid acceptance and use as functions of the probable site of a lesion: conductive, cochlear, neural, and central as determined by an audiometric test battery. Results indicate significantly better acceptance of aids in conductive and cochlear disorders than in more central neural and central disorders.

Adolescent↗
PubMedDate not supplied

Effects of aging on normal hearing loss and noise-induced threshold shift in albino and pigmented guinea pigs.

In a previous investigation into noise-induced hearing loss by comparing 2-month-old albino with pigmented guinea pigs, albinos displayed significantly greater shifts in cochlear microphonic (CM) threshold and less recovery than the pigmented animals 7 days after noise exposure. The present study compared the responses of 14-month-old albino and pigmented guinea pigs to the same noise parameters used previously. Thresholds for the first detectable elicitation of CM for three pure tones were recorded prior to, at 90 min and at 7 days after a 45-min exposure to 126 dB broadband noise. Before exposure to noise, thresholds for pigmented guinea pigs were 24 dB higher than those in the albinos. Following noise exposure, the pigmented animals showed less than half the amount of threshold shift displayed by the albinos. This change ws attributed to the higher pre-exposure thresholds in the pigmented guinea pigs. Converging lines of evidence suggest that cochlear pigmentation may have both protective and toxic influences on the inner ear.

Aging↗
PubMedDate not supplied

Influence of amplification on the discrimination of dichotic consonant-vowel syllables in a population with sensorineural hearing loss.

This study was designed to investigate the premise that the long-term use of monaural amplification influences dichotic listening conditions in a population with sensorineural hearing losses. 30 subjects with moderate, bilateral sensorineural hearing losses and 10 normally-hearing adults were chosen for this study. 20 of the subjects with sensorineural hearing loss had worn amplification successfully for at least 1 year prior to testing. 10 of these subjects had worn amplification only on the right ear while the remaining 10 had worn amplification only on the left ear. All subjects received 60 monaural and dichotic consonant-vowel (CV) nonsense syllables presented at equal loudness levels using the most comfortable level (MCL) as the loudness criteria. While monaural scores revealed nonsignificant differences between ears for all subjects, using percentage of error, dichotic results produced a right-ear advantage for the right-ear-aided, unaided and normally-hearing subjects. A significant left-ear advantage was seen for the left-ear-aided subjects. Results of this study suggest that amplification introduces selective listening effects which alter reported dichotic test scores.

Audiometry, Pure-Tone↗