Search PubMed⌕ Search

Biomedical subjects

G M Clark

Publications and source records attributed to G M Clark.

At least 181 records · Page 10Linked to original sources
PubMed1995

Comparison of monaural acoustic and electric stimulation: unit types in the cat inferior colliculus.

This study has shown that 1) the ratio of excitatory and inhibitory inputs to units in the central nucleus of the inferior colliculus is altered when one cochlea is neomycin-deafened and/or electrically stimulated; 2) prestimulus threshold shift and lateral inhibition mechanisms can be used to explain these results; and 3) at high current levels a leakage current into the modiolus can evoke unit population responses.

Acoustic Stimulation↗
PubMed1995

Model of discharge rate from auditory nerve fibers responding to electrical stimulation of the cochlea: identification of cues for current and time-interval coding.

A model of the response of auditory nerve fibers to electrical stimulation of the cochlea is presented. Auditory nerve fiber responses are described in terms of cochlear regions activated by the stimulus: region A, in which the discharge rate equals a value of the pulse rate plus spontaneous activity, and region B, in which the discharge rate is less than pulse rate plus spontaneous activity but greater than spontaneous activity. The cues for intensity and time-interval coding provided by regions A and B are discussed.

Auditory Pathways↗
PubMed1995

Discharge rate-level functions from dorsal cochlear nucleus single units in response to acoustic and electrical stimulation of the auditory nerve.

Discharge rate-level (I/O) functions possessed by dorsal cochlear nucleus (DCN) units were examined, in response to bipolar electrical stimulation of the cochlea of the barbiturate-anesthetized cat. Spontaneously active units usually possessed nonmonotonic functions with a minimum, and spontaneously inactive units usually possessed monotonic functions or nonmonotonic functions with a maximum (NM+). In response to acoustic high-pass filtered noise, the function relating discharge rate and cutoff frequency resembled the same unit's I/O function to electrical stimulation. The I/O functions to acoustic characteristic tones were usually monotonic or NM+. These results suggest that in the DCN, a prerequisite for the generation of acoustic-like responses with an electrical stimulus may be the matching of the cochlear place and spatial extent activated by each stimulus.

Acoustic Stimulation↗
PubMed1995

Manikin and cochlear implant patient test results with a portable adaptive beamforming processor to suppress the effects of noise.

A simple adaptive beamformer (ABF) was implemented in a real-time portable speech processor and tested with four cochlear implant patients. The ABF algorithm used signals from only two microphones--one behind each ear--to attenuate sounds not arriving from the direction directly in front of the patient, and was compared with a strategy in which the two microphone signals were simply added together (two-microphone broadside strategy). Tests with the four patients were conducted in quiet and in noise. Results at a 0 dB signal-to-noise ratio showed large improvements in speech intelligibility for all patients, when compared to the two-microphone broadside strategy. Physical measurement of the directional characteristics of the ABF processor were made with a Kemar manikin. The effects of reverberation were explored by placing the manikin in different acoustic environments and observing the attenuation of the noise alone at various angles. A near-anechoic environment allowed the noise to be attenuated by as much as 21 dB, whereas in a highly reverberant concrete stairwell, the ABF processor was unable to provide any directional gain beyond about 3 dB.

Cochlear Implants↗
PubMed1995

Loudness summation for two channels of stimulation in cochlear implants: effects of spatial and temporal separation.

An experiment with four implantees with the Mini System 22 device was undertaken to measure the loudness summation across two channels of stimulation, with stimuli in which the current pulses were delivered alternately to each channel. The effects of varying spatial separation, temporal separation, and extent of stimulation were investigated. It was found that the absolute amount of summation varied among subjects, and was in general independent of electrode separation, except for a reduction at zero separation. Widening of the spatial extent of the stimulation did not have a consistent effect. There was a reduction in summation for all subjects at zero electrode separation when the time between the two pulses was increased from less than 1 millisecond to 2 milliseconds. In conclusion, loudness summation did not appear to be highly dependent on parameters that affect the spatial current spread in the cochlea. Further study of the effect of temporal parameters on loudness may help to quantify interaction between stimulation channels.

Adult↗
PubMed1995

Fusion and lateralization study with two binaural cochlear implant patients.

Psychophysical studies have been completed with two binaural cochlear implant patients. Results from a fusion and lateralization experiment with both patients are described. As found in an earlier study with the first binaural patient in Australia, the second patient also showed good sensitivity to interaural amplitude differences but poor sensitivity to interaural time delays when compared with normal-hearing subjects. The implications of this result are discussed.

Cochlear Implants↗