Biomedical subjects

V Pluvinage

Publications and source records attributed to V Pluvinage.

3 recordsLinked to original sources

PubMed1992

Evaluation of a dual-channel full dynamic range compression system for people with sensorineural hearing loss.

This article describes an evaluation of an in the ear hearing aid, which applies fast-acting full dynamic range compression independently in two frequency bands. This can compensate for the loudness recruitment typically associated with sensorineural hearing loss. The crossover frequency between the two bands and the gain and compression ratio in each band are programmable to suit the individual patient. Twenty subjects with moderate sensorineural hearing loss were tested in a counterbalanced order using the aid programmed as a linear amplifier (condition L) and as a two-band compressor (condition C). All subjects were fitted binaurally. Subjects were also tested without hearing aids (condition U) and using the hearing aids that they normally wore (condition Own). Speech intelligibility was measured in quiet at three sound levels (50, 65, and 80 dB SPL), and speech reception thresholds (SRTs) in 12-talker babble were measured under monaurally and binaurally aided conditions, with the speech and babble both coincident and spatially separated. In condition C, speech intelligibility in quiet was high at all sound levels. Speech intelligibility at the two lower levels decreased in condition L, and decreased still further in conditions Own and U. Condition C gave, on average, better speech intelligibility in babble (lower SRTs) than conditions L, Own, or U. The advantage of condition C over condition L varied across subjects and was correlated with the dynamic range for tones at high frequencies; small dynamic ranges were associated with greater benefit from compression. A significant advantage for binaural aiding was found both when the speech and noise were spatially separated and when they were coincident. The binaural advantage was similar for the C and L conditions, indicating that the independent compression at the two ears did not adversely affect the use of binaural cues. Questionnaires on the subjects' experiences with the aids in everyday life indicated that they generally preferred condition C over condition L.

Adult↗

PubMed1990

Evidence for a power law intensity code in the coupled cones of the turtle.

The hyperpolarizing responses to light were recorded intracellularly from red cones of the turtle, Pseudemys scripta elegans. Pairs of slit stimuli were flashed alone or together at various intensities, one slit positioned on the receptive field center and the other displaced 30 microns. The peak amplitude of the response was measured, and the results analyzed to quantify the relationship between the light intensity and the size of the neural signal evoked prior to the spatial interactions occurring in the network of coupled cones. This signal, E, was found to be described by a compressive power law, E = k.I0.5, where I is slit intensity. Evidence that the inferred excitation function describes a local mechanism independent of the slit position was obtained by measuring the response and the sensitivity receptive field profiles. The response and the sensitivity fields both decreased exponentially, but with space constants that differed by a factor of two, indicating in still another way the existence of an early square-root transformation.

Animals↗

PubMed1990

Square root intensity coding in turtle cones: physiological mechanisms.

The effect of coupling on the intensity-response functions for full field and for slit stimuli was studied by comparing the shapes of the curves obtained from several strongly coupled red cones of turtle with that of one very weakly coupled cone. The full field V-log I curves could be fitted by a Michaelis-Menten relationship, regardless of the strength of the coupling. For the weakly coupled cone the slit V-log I could also be fitted by a Michaelis-Menten curve. For strongly coupled cones a major portion of the curve (1.2-2 log units of intensity) was better fitted by V oc Im. For centered slits "m" was 0.5. With increased distance between the slit and the center of the receptive field "m" was found to increase slightly. The results were analyzed in terms of a theory in which the shape of the slit intensity-response curves arises from scattered light progressively recruiting neighboring cone responses. An analytical formulation of this idea is presented and a plausible light distribution function which supports the recruitment hypothesis is derived. A numerical model of the cone network, which includes the effect of scattering and transduction saturation, accounts well for all of the experimental data obtained with single and paired slits.

Animals↗