Biomedical subjects

D K Prasher

Publications and source records attributed to D K Prasher.

7 recordsLinked to original sources

PubMed1990

Effect of simulated bilateral cochlear distortion on speech discrimination in normal subjects.

Bilateral sensorineural hearing loss may introduce grossly dissimilar cochlear distortion at the two ears, causing abnormal demands to be made upon the cortical analytical centres which normally receive congruent information. As a result, the prescription of binaural hearing aids may be a handicap rather than a help. In order to explore this possibility, 10 normal subjects were presented with simulated, dissimilar cochlear distortion at the two ears. Discrimination scores with binaural presentation were poorer than the best monaural score and there were clear indications that in the former, subjects selectively attended to one ear and neglected the other. In contrast, binaural presentation of the same simulated distortion resulted in a significant improvement, compared with the monaural discrimination score. Inability of the cortex to contend with discongruent speech input from the two ears may be a factor contributing to the rejection of binaural hearing aids in some individuals.

Adolescent↗

PubMed1988

The effect of acoustic neuroma removal on hearing in the contralateral ear.

22 patients with unilateral acoustic neuromas were assessed audiometrically pre- and post-operatively. A high proportion (36%) were found to have a hearing loss of 10 dB or more (6 frequency average) in the contralateral ear in the post-operative period. The evidence points to a cochlear site of the loss, and serial audiograms suggest that the hearing deteriorates in the immediate post-operative period. Follow-up audiometry at three months or more showed that the hearing recovered to pre-operative levels. The possible mechanism of the hearing loss is discussed.

Audiometry, Pure-Tone↗

PubMed1986

Electrocochleography and brain-stem potentials in Ramsay Hunt syndrome.

Audiometric investigations and electrophysiologic recordings of cochlear and brain-stem auditory evoked potentials (BAEPs) were performed in 13 patients to elucidate further the type of hearing disorders in Ramsay Hunt syndrome. Transtympanic electrocochleography showed no enhancement of summating potential and did not suggest secondary endolymphatic hydrops. The recording of BAEPs was clearly abnormal in several of the 13 patients. The striking feature of the abnormalities in these patients was the prolongation of the latencies of waves III and V with the preservation of wave I, which clearly suggests retrocochlear involvement. In all the patients tested, abnormalities of the BAEPs were present only on the affected side. It is possible, on the basis of BAEP findings, to suggest that in Ramsay Hunt syndrome both cochlear and retrocochlear involvement may occur.

Adult↗

PubMed1986

Latency variability and temporal interrelationships of the auditory event-related potentials (N1, P2, N2, and P3) in normal subjects.

Peak latency variation and the temporal interrelationships of the auditory event-related potential were investigated in 12 normal adults (ages 28-42). Measures of variation were based on both conventional averages and single trials. Estimates of N1, P2, N2 and P3 latencies were made on a trial-by-trial basis to target stimuli recorded from Fz, Cz and Pz scalp locations. Results showed that single-trial latency variability of the auditory ERP differed both among the various components and between subjects. Larger standard deviations were measured for the later N2 and P3 components than the earlier N1 and P2 components. Regression analyses between various component latencies indicated a strong covarying relationship between N2 and P3, with N2 accounting for up to 61% of the variance of P3 latency at Pz. Earlier N1 and P2 components added little to the overall prediction of either P3 or N2. For the other components, P2 accounted for 9-16% of the variance of N2, while N1 accounted for approximately 1% of the variance of N2; N1 accounted for 8-10% of the latency variation of P2. The correlations between single-trial peak latencies and RTs were positive but of low magnitude. The highest correlations between peak latency and RT were found for N2 (r = 0.33) and P3 (r = 0.24). The low correlations between the single-trial latencies of N1 and P3 suggest that the processes reflected by these components are independent and support a distinction between the earlier and the later components of the ERP. The close temporal coupling between N2 and P3 suggests that N2 may reflect cognitive properties in common to P3 in stimulus evaluation processes.

Adult↗

PubMed1985

Neuro-otological abnormalities in xeroderma pigmentosum with particular reference to deafness.

The neuro-otological findings are described in 3 unrelated patients who had xeroderma pigmentosum. All had impaired hearing. Routine audiometric assessment suggested that the hearing loss was of cochlear origin; brainstem evoked potentials in 2 patients and electrocochleography in 1 support this conclusion. Two adult patients had a supranuclear ophthalmoplegia. Vestibular function was mildly deranged and visual suppression of the vestibulo-ocular reflex impaired.

Adult↗

PubMed1977

A microprocessor controlled multi-channel evoked potential data acquisition system.

A stored program control system is described for the acquisition of evoked potential (EP) data. It is a small, portable and flexible system with a variety of input and output possibilities. The system presents a low cost solution to the problem of acquisition of evoked potential data. A novel method of converting and reducing sixteen channels of EEG analogue data to their digital equivalent is shown. It is adaptable for the inter active control of experiments and is sophisticated enough to deal with the complexities of experimental control as well as data manipulation. One of the major advantages of the system is that both the sequencing of the functions and their detailed make-up can be readily altered by programming to meet the individual requirements of any given situation.

Analog-Digital Conversion↗

PubMedDate not supplied

Auditory function in hereditary motor and sensory neuropathy (Charcot-Marie-Tooth disease).

Fourteen patients with hereditary motor and sensory neuropathy (HMSN), 12 of Type I and 2 of Type II, were assessed for auditory dysfunction. Five patients complained of hearing loss and all had pure-tone audiograms outside the normal range, while one patient who did not complain of hearing impairment also had an abnormal pure-tone audiogram. Assessment of loudness function, speech audiometry and brainstem auditory evoked potentials (BAEP) suggested that the hearing loss was the result of VIII nerve dysfunction, a conclusion supported by the abnormality of the electrocochleogram (ECochG) in one patient.

Adolescent↗