PubMed Health⌕ Search

Biomedical subjects

I Bell

Publications and source records attributed to I Bell.

11 recordsLinked to original sources
PubMed1990

Magnitude of diotic summation in speech-in-noise tasks: performance region and appropriate baseline.

The diotic summation effect is one of the three types of binaural advantage for perceiving speech-in-noise. Using a within-subject design in normally-hearing subjects having no significant noise exposure, we examined its magnitude. The average advantage was +5%, at an overall performance level of 70-80% rising to +9% when an appropriate control was used to exclude order effects introduced by the within-subject design. Diotic summation is an important component of the advantage to be derived from presentation to two ears, but the size of the binaural advantage obtained depends critically on the particular monotic baseline chosen for comparison. The methodological problems of demonstrating binaural advantages (as in binaural aiding studies) are discussed.

Adult↗
PubMed1990

Asymmetrical auditory probe evoked potentials during REM and NREM sleep.

Two experiments were conducted to evaluate interhemispheric differences in late auditory evoked potentials (AEPs) during rapid-eye-movement (REM), Stage 2, and Stage 4 sleep. In the first study, 1,000-Hz stimuli [80 db (SPL)] were presented binaurally at a rate of 1/1.1 s. Analyses of variance were computed on the absolute difference in the amplitude of right and left evoked responses. N1 AEPs were significantly more asymmetrical in Stage 4 sleep compared to either REM or Stage 2 sleep. A second study was conducted with a wider topographical electrode distribution. This study used both a long and a short interstimulus interval with 500-Hz 80-db SPL tone pips. The absolute difference in the amplitude of right and left AEPs was compared across sleep stage. Asymmetries were larger in Stage 4 sleep than in either REM or Stage 2. Examination of these data indicated relative hemispheric balance in REM and Stage 2 sleep with largest asymmetries in Stage 4. The results do not support the view that REM and non-REM sleep stages are associated with differential activation of the two cerebral hemispheres. Rather, they suggest that the sleep cycle is characterized by variations in the degree of asymmetry. Asymmetries in Stage 4 sleep were not consistently in favor of the left hemisphere.

Adolescent↗
PubMed1988

A peak detector program for event-related potentials.

A computer program, developed for peak detection of averaged evoked potential waveforms, is described. The program is able to automatically score up to 200 data files in a single session. The user is asked to define intervals (windows) in which a maximum peak is to be detected. The program can optionally search each EEG channel or a single 'reference' channel from which all other channels will be compared. The mean amplitude of several data points can also be computed within a particular window. When evoked potentials are particularly noisy, it is possible to estimate the 'signal' in the higher frequency background 'noise'. Because the program is written in BASIC, it can be readily transferred to many different computer systems.

Arousal↗
PubMed1988

Electrophysiological monitoring during acoustic neuroma and other posterior fossa surgery.

Techniques used to monitor the function of the seventh and eighth cranial nerves during acoustic neuroma and other posterior fossa surgery are reviewed. The auditory brainstem response (ABR), electrocochleogram (ECochG) and direct recording from the auditory nerve (CNAP) were compared. The best technique is the ECochG, although in many cases, the CNAP should be used as a back-up technique. The CNAP is especially useful for the identification of the auditory nerve. Both can provide real-time feedback on the physiological integrity of the auditory nerve. The ABR may be helpful in monitoring brainstem function. For some procedures, optimal monitoring requires the combined recording of all three techniques. Monopolar constant-voltage intracranial stimulation of the facial nerve is helpful for the identification and preservation of the facial nerve. Audio monitoring of spontaneous electromyographic activity provides real-time feedback on the effect of surgical manipulation of the nerve. Monitoring of ephaptic transmission in the facial nerve during microvascular decompression for hemifacial spasm aids in the identification of the offending vessel.

Action Potentials↗
PubMed1987

Estimation of auditory threshold during sleep using brainstem auditory-evoked potentials.

The brainstem auditory-evoked potential (BAEP) is often employed to determine auditory threshold in subjects who are unable to complete traditional behavioural testing. These responses are usually recorded during natural or drug-induced sleep. The effects of sleep on the BAEP threshold have however not been determined. BAEPs were recorded in 8 young adults in wakefulness and during natural sleep. Click stimuli were presented through a hearing aid device at either 0, 5, 10, 20 or 30 dB above the behavioural threshold. The amplitude of wave V decreased and its latency increased with decreases in stimulus intensity. The BAEP waveform was invariant in sleep. The overall mean BAEP threshold was approximately 16 dB above that determined by behavioural methods. This did not significantly vary in the sleeping subject.

Adult↗
PubMed1985

Subtle neuropsychological deficits in patients with good recovery after closed head injury.

This study demonstrates residual mental deficits in patients who have apparently recovered after closed head injury. Twenty closed head injury patients were compared to 20 normal control subjects matched for age, sex, handedness, education, language, and IQ. All received a series of neuropsychological tests. Discriminant function analysis significantly differentiated the two groups. Correct classification of individuals as having suffered a head injury or not was 85%. The head injury patients did have primary impairment on tests of divided attention. Litigation was not a factor. We propose that this impairment of information processing reflects residual brain damage secondary to the closed head injury.

Adult↗
PubMed1980

A brief communication on bone conduction artefacts.

The various factors which may be involved in the incorrect measurement of bone-conduction threshold are outlined. One of these factors, airborne radiation from the vibrator, has been investigated for three Radioear vibrators, the B70A, B71 and B72. The results indicate that false bone-conduction threshold values could arise, due to the airborne radiation component, mainly with the B72 vibrator.

Audiometry↗