Biomedical subjects

P J Abbas

Publications and source records attributed to P J Abbas.

At least 19 recordsLinked to original sources

PubMed1992

Interpretation of electrocochleography in Menière's disease and normal subjects.

Electrocochleographic recordings were obtained from 20 subjects with normal hearing and 10 subjects with Menière's disease by using an eardrum electrode. Stimuli included clicks and 6,000-Hz tone bursts. Results were not significantly different between the two groups for summating potential (SP) amplitude, action potential (AP) amplitude, or the SP/AP amplitude ratio. Interpreting the results in light of symptoms on the date of assessment or hearing threshold did not appear to improve separation between the two groups. Various SP/AP amplitude ratio criteria have been proposed in order to separate normal patients from those with Menière's disease. Applying these proposed criteria to our data did not successfully separate the two groups.

Acoustic Stimulation↗

PubMed1992

Effects of interaural speech-recognition differences on binaural advantage for speech in noise.

The relationship between interaural differences in speech-recognition performance and binaural advantage for speech in noise was studied. Subjects were five hearing-impaired listeners with symmetrical pure-tone air-conduction audiograms and significant interaural differences in speech recognition. All subjects repeated nonsense syllables in the presence of competing noise in monaural and binaural conditions. Binaural advantage was calculated as the difference in signal-to-noise ratio that afforded 50 percent correct performance between the monaural and binaural conditions. The results were diverse. Although the majority of the subjects retained some degree of binaural advantage, a conclusive relationship between interaural differences in speech recognition and binaural advantage could not be established. The implications for binaural hearing aid fittings are discussed.

Aged↗

PubMed1991

Electrically evoked auditory brainstem response: growth of response with current level.

The electrically evoked brainstem response (EABR) was measured in cochlear implant users who had received either the Ineraid multichannel implant or the Nucleus multichannel implant. Although both implants use a multi-electrode array, they are different in a number of ways. In the Ineraid system the electrodes can be accessed directly through a percutaneous plug and stimulation is generally on four different intracochlear electrodes relative to a common ground outside the cochlea. In the Nucleus implant stimulation is accomplished via an internal coil and stimulation is bipolar between pairs along the 22 electrode array. The ABR waveforms were similar for both groups of subjects, consisting of a series of 3 or 4 positive peaks at the highest levels of stimulation. Using the normal stimulation mode (bipolar for Nucleus and monopolar for Ineraid), users of both devices demonstrated an increase in response amplitude and a decrease in response latency with increases in current level. The threshold of response tended to be higher and growth of the response with level tended to be more gradual for Nucleus users than for Ineraid users. However, with bipolar stimulation for both implant types, when the stimulating electrodes were closely spaced the threshold of response was higher and the growth of amplitude with level was more gradual than the case where the electrodes were separated further. When bipolar stimulation and similar electrode spacing was used, the response growth and threshold were similar for both implant types. Results from neither device showed a strong correlation with performance on word recognition tests.

Adult↗

PubMed1991

Electrically evoked auditory brainstem response: refractory properties and strength-duration functions.

The electrically evoked auditory brainstem potential (EABR) was recorded in users of both the Nucleus cochlear implant and the Ineraid cochlear implant. The refractory properties of the EABR were evaluated by measuring the response amplitude to a two-pulse stimulus where the interpulse interval was varied. The threshold of response for a single pulse stimulus was also measured as a function of the duration of the biphasic pulse. These strength-duration functions were then used to calculate an EABR chronaxie measure. Both of these measures showed a similar range for the monopolar stimulation used with the Ineraid implant and the bipolar stimulation used with the Nucleus implant. Neither of these two measures of the temporal response properties showed any clear relationship to the ability of individual subjects to perform on a speech perception task.

Adult↗

PubMed1990

Neural responses to auditory temporal patterns.

Sets of regularly repeating auditory stimuli elicit unique perceptions; listeners are able to identify specific temporal patterns. Some temporal patterns are unambiguous (only one pattern can be perceived), while others are ambiguous (numerous patterns can be detected). While the psychophysical properties of such percepts have been well studied, little is known about the underlying neurological bases of temporal pattern perception. In this experiment, the role of adaptation in temporal pattern perception is examined by studying neural responses in four cats to a temporal pattern that is perceptually unambiguous and one that is perceptually ambiguous. Measurements were made of the whole-nerve action potential, the auditory brainstem response, and potentials from the surface of the primary auditory cortex. The adaptation patterns corresponded with the perceptual organization of temporal patterns in humans at all levels of the nervous system studied.

Animals↗

PubMed1990

Electrically evoked whole-nerve action potentials: data from human cochlear implant users.

This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615-627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 micro V have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6-0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74-0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.

Cochlear Implants↗

PubMed1990

Electrically evoked whole-nerve action potentials: parametric data from the cat.

In a companion paper [Brown et al., J. Acoust. Soc. Am. 88, 1385-1391 (1990)], a method for recording the electrically evoked whole-nerve action potential in human cochlear implant users was reported. The procedure for recording the response requires that two biphasic current pulses, a "masker" and a "probe," be presented at a rate and level sufficient to drive the auditory nerve into a refractory state. The present study was designed to assess the sensitivity of that recording technique to variations in stimulation parameters. The experiments described in this paper demonstrate that: (1) the EAP as recorded in the cat is triphasic and is defined by two negative peaks occurring at latencies of approximately 0.26 and 0.82 ms; (2) EAP amplitude is independent of the level of the masker stimulus for current levels equal to or greater than the current level of the probe stimulus; and (3) the time course of recovery of the EAP from the refractory state is stable over a range of both probe and masker current levels.

Animals↗

PubMed1990

A signal processing scheme for output limitation.

For both normal listeners and mild to moderately sensori-neurally impaired (probable etiology, presbycusis) listeners a summation of discomfort (S) occurs for complex stimuli, proportional to the logarithm of the number of components. Regression equations of S = 2.05 + 11.51 log n for normals and S = 3.95 + 12.88 log n for hearing impaired (where n equals the number of components or bandwidth in the complex) were found to be significantly different. This change in percept with increased bandwidth (or components) has not been satisfactorily explained in terms of power or amplitude peak density of the stimuli. The regression equations could be applied to future digital hearing aids so that maximum output levels (MPO) would account for this summation.

Hearing Aids↗

PubMed1989

Effects of attention on the auditory evoked potentials recorded from the vertex (ABR) and the promontory (CAP) of human listeners.

Auditory brainstem response (ABR) and the compound whole nerve action potential (CAP) of four human listeners were recorded while they were performing either visual duration or auditory frequency discrimination tasks with both types of stimuli presented simultaneously. The evoking tone bursts had the same center frequency as the standard discrimination tones and were presented between the discrimination tones. Waveforms between the two discrimination tasks did not differ in shape or latency, suggesting that the attention demand of the present task is not a central factor in the control of the auditory efferents.

Adult↗

PubMed1988

Electrically evoked brainstem potentials in cochlear implant patients with multi-electrode stimulation.

The electrically evoked brainstem potential was measured in cochlear implant patients with Symbion multichannel electrode system. In the first experiment, electrodes within the implant were stimulated individually and the responses and sensitivity across electrodes and across subjects were evaluated. The typical response waveform consisted of a series of three peaks, the most prominent occurring at approximately 4 ms after stimulus onset. The amplitude of the largest peak typically showed an orderly increase with increasing current level while latency changes were relatively small. In the second experiment, two electrodes were stimulated simultaneously in order to evaluate the relative independence of the neural populations being stimulated by the different electrode pairs. The responses were compared when two electrode pairs were stimulated simultaneously with current pulses in phase and when the same electrodes were stimulated with current pulses inverted relative to each other. Both stimulation conditions showed similar growth in response amplitude with level but different sensitivity. The differences in sensitivity between these two conditions may be indicative of the degree of overlap in the stimulated neural populations.

Adult↗

PubMed1988

Electrophysiology of the auditory system.

This review has attempted to summarise the properties of electro physiological responses in the auditory system. The treatment was broad and consequently somewhat sketchy. For a more detailed recent treatment of the physiology of the auditory system the reader is referred to Pickles (1982), Møller (1983), or Altschuller et al (1986). The data on acoustic injury have been reviewed recently by Schmiedt (1984). Discussions of a number of topics such as development, hair cell function and speech encoding are found in Berlin (1984).

Action Potentials↗

PubMed1987

A comparison of AP and ABR tuning curves in the guinea pig.

AP and ABR tuning curves were measured using a forward masking paradigm in guinea pigs with chronically implanted electrodes. Measurements were made before exposure to wide-band noise and at several intervals after exposure. The noise exposure was sufficient to produce temporary threshold shifts up to 60 dB lasting several days. Results showed similar reductions in Q10, tip-to-tail ratio and slope of simultaneously recorded AP and ABR tuning curves as a function of threshold shift following noise exposure. Tuning curves based on changes in response latency are presented as well as tuning curves based on changes in response amplitude. AP and ABR latency tuning curves showed similar form and changes with hearing loss as amplitude tuning curves. The similarities between AP and ABR tuning characteristics provide evidence that the ABR is sensitive enough to peripheral changes to be useful as a tool to study auditory frequency selectivity. The similarities between amplitude and latency tuning characteristics suggest that information regarding frequency selectivity of the auditory system can be obtained using response latency as well as response amplitude.

Action Potentials↗

PubMed1987

The effect of stimulus repetition rate on the auditory brainstem response in tumor and nontumor patients.

Auditory brainstem responses were recorded in two groups of adult subjects with asymmetric sensorineural hearing loss. Clicks were presented at repetition rates of 9.7, 39.7, 49.7, and 59.7/s. One group was composed of 20 patients with no known otoneurologic lesion (cochlear group), and one group was composed of 8 patients with a surgically confirmed acoustic neuroma in the ear with poorer hearing sensitivity (retrocochlear group). Detection of wave V at different repetition rates was not significantly different between the two groups. Average wave-V latency shift was not significantly different between the two groups as repetition rate increased from 9.7/s to 39.7/s but was significantly greater for the retrocochlear group as repetition rate increased from 9.7/s to 49.7/s and 59.7/s. However, the wave-V latency shift showed no improvement over the slow-rate interaural wave-V latency difference in discriminating between the two groups of patients. No significant correlation between the amount of wave-V latency shift and hearing loss at 2000 Hz or 4000 Hz was found for the ears with poorer hearing sensitivity.

Acoustic Stimulation↗

PubMed1986

Effects of white noise masking and low pass filtering on speech kinematics.

The effects of reduced auditory information on spatial and temporal parameters of speech production were investigated using cinefluorographic techniques. While subjects read a series of test words embedded in carrier sentences, they received normal auditory information, auditory information regarding only the first formant of their production, or high level noise to mask all formant information. Kinematic analyses indicated that while there were some changes across conditions, these changes were not consistent either within or across the subjects. Parameters that were affected included mean displacement, vocal tract shape, interarticulator timing, and steady state duration. The results suggest that auditory information plays a role in maintaining dynamic aspects of speech kinematics. That is, while speech can be produced without auditory information, the precise action and coordination that characteristic normal production may be altered.

Adult↗

PubMed1986

Detection cues in forward masking and their relationship to off-frequency listening.

Conventional and restricted-listening psychophysical tuning curve paradigms were used to evaluate the masking ability of forward maskers of different envelope characteristics, and the relationship between off-frequency listening effects and the envelope characteristics of both the variable masker and stationary masker used to restrict listening to a narrow region surrounding the probe. Maskers were selected so as to differ widely in the degree of fluctuation in their envelopes. The masker with the largest amplitude fluctuations exhibited greater forward-masking ability than other stimuli; this effect was observed on the high-frequency branch and within the tip region of the tuning curve. It is suggested that differences in masking ability may reflect the use of different signal detection cues. The results are also consistent with previous reports [D. Johnson-Davies and R.D. Patterson, J. Acoust. Soc. Am. 65, 756-770 (1979); B.J. O'Loughlin and B.C.J. Moore, J. Acoust. Soc. Am. 69, 1119-1125 (1981a)] which suggest that off-frequency listening is a factor contributing to the sharpness of psychophysical tuning curves. This effect is largely dependent, however, on the envelope characteristics of both variable and stationary maskers.

Adult↗

PubMed1985

Adaptation in hearing-impaired ears: effects of intermediate duration stimuli.

Recovery from adaptation was measured in acoustically-traumatized ears of cats for pure-tone adapters 1-60 s in duration at levels of 60-100 dB SPL. Adaptation was assessed by measuring the whole nerve action potentials in response to pure-tone stimuli. Effects of changing probe frequency and of changing adapter duration were measured. Impaired ears showed less adaptation than normal ears for adapters of similar SPL, but they showed relatively normal spread of adaptation across probe frequency. The effect was larger for long duration stimuli than for short duration stimuli.

Acoustic Stimulation↗

PubMed1985

Short-term effects of sound exposure on the 2f1-f2 acoustic emission.

The 2f1-f2 acoustic emission (AE) was recorded in the ear canals of cats following exposure to tone bursts of 200-ms duration. Exposures known to result in short-term adaptation (i.e., adaptation lasting under 1 s) at the level of the auditory nerve failed to produce significant post-exposure changes in AE amplitude. Given the apparent cochlear origin of the 2f1-f2 AE, this result is consistent with the view that short-term adaptation in the auditory periphery does not involve substantial changes in cochlear mechanics.

Acoustic Stimulation↗

PubMed1985

Changes in the 2f1-f2 acoustic emission and whole-nerve response following sound exposure: long-term effects.

We examined the effects of 1-min tonal exposures on the amplitude of the 2f1-f2 distortion product in the ear canals of cats. These effects were compared with the changes in the whole-nerve action potential (AP) responses to tone bursts following similar exposures. Both the distortion product and AP amplitudes were reduced following exposure. The time courses of AP and acoustic emission (AE) recoveries were to a certain extent similar, and the post-exposure effects depended in similar ways upon the frequency and intensity of the exposure tone (adapter). Assuming that the 2f1-f2 AE is generated by nonlinearities in the motion of the cochlear partition, the reduction in its amplitude suggests that 1-min sound exposures can alter cochlear mechanics. The analogous aspects of the AP and AE post-exposure effects further suggests that components of long-term adaptation as measured by the AP are associated with changes in the mechanics of transduction. Finally, alterations of the middle ear cavities of the cat by opening the bulla or bony septum can result in marked changes in the effectiveness of an adapter in reducing AE amplitude.

Acoustic Stimulation↗