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The study examined whether the benefit of deactivating stimulation sites estimated to have broad neural excitation was attributed to improved spectral resolution in cochlear implant users. The subjects' spatial neural excitation pattern was estimated by measuring low-rate detection thresholds across the array [see Zhou (2016). PLoS One 11, e0165476]. Spectral resolution, as assessed by spectral-ripple discrimination thresholds, significantly improved after deactivation of five high-threshold sites. The magnitude of improvement in spectral-ripple discrimination thresholds predicted the magnitude of improvement in speech reception thresholds after deactivation. Results suggested that a smaller number of relatively independent channels provide a better outcome than using all channels that might interact. [ABSTRACT FROM AUTHOR]

The decrease of psychophysical detection thresholds as a function of pulse rate for a fixed-duration electrical pulse train is referred to as multipulse integration (MPI). The MPI slopes correlate with anatomical and physiological indices of cochlear health in guinea pigs with cochlear implants. The aim of the current study was to assess whether the MPI slopes were related to the spatial spread of activation by electrical stimulation. The hypothesis was that MPI is dependent on the total number of excitable neurons at the stimulation site, with broader neural excitation producing a steeper threshold decrease as a function of stimulation rate. MPI functions were measured at all stimulation sites in 22-site electrode arrays in human subjects. Some sites with steep MPI functions and other sites with shallow functions were assessed for spatial spread of excitation at 900 pps using a forward-masking paradigm. The results showed a correlation between the slopes of the forward-masking functions and the steepness of MPI, with broader stimulation predicting greater integration. The results are consistent with the idea that integration of multiple pulses in a pulse train relies on the number of excitable neurons at the stimulation site. [ABSTRACT FROM AUTHOR]

The present study evaluated the slopes of threshold-versuspulse-rate functions (multipulse integration, MPI) in humans with cochlear implants in relation to recovery from 300-ms forward maskers. MPI has been correlated with spiral ganglion cell density in animals. The present study showed that steeper MPI functions were correlated with faster recovery from forward masking. The findings suggested that the variations in the MPI slopes are explained not only by the quantity of neurons contributing to the integration process but also by the neurons' temporal response characteristics and possibly central inhibition. [ABSTRACT FROM AUTHOR]

Comparisons of performance with cochlear implants and postmortem conditions in the cochlea in humans have shown mixed results. The limitations in those studies favor the use of within-subject designs and non-invasive measures to estimate cochlear conditions. One non-invasive correlate of cochlear health is multipulse integration, established in an animal model. The present study used this measure to relate neural health in human cochlear implant users to their speech recognition performance. The multipulse-integration slopes were derived based on psychophysical detection thresholds measured for two pulse rates (80 and 640 pulses per second). A within-subject design was used in eight subjects with bilateral implants where the direction and magnitude of ear differences in the multipulse-integration slopes were compared with those of the speech-recognition results. The speech measures included speech reception threshold for sentences and phoneme recognition in noise. The magnitude of ear difference in the integration slopes was significantly correlated with the magnitude of ear difference in speech reception thresholds, consonant recognition in noise, and transmission of place of articulation of consonants. These results suggest that multipulse integration predicts speech recognition in noise and perception of features that use dynamic spectral cues. [ABSTRACT FROM AUTHOR]

The effects of frequency-place shift on consonant recognition and confusion matrices were examined. Frequency-place shift was manipulated using a noise-excited vocoder with 4 to 16 channels. In the vocoder processing, the location of the most apical carrier band varied from the matched condition (i.e., 28 mm from the base of the cochlear) to a basal shift (i.e., 22 mm from the base) in a step size of 1 mm. Ten normal-hearing subjects participated in the 20-alternative forced-choice test, where the consonants were presented in a /Ca/ context. Shift of 3 mm or more caused the consonant recognition scores to decrease significantly. The effects of spectral resolution disappeared when the amount of shift reached ≥3 mm. Information transmitted for voicing and place of articulation varied with spectral shift and spectral resolution, while information transmitted for manner was affected only by spectral shift but not spectral resolution. Spectral shift has shown specific effects on the confusion patterns of the consonants. The direction of errors reversed as spectral shift increased and the patterns of reversal were consistent across channel conditions. Overall, transmission of the consonant features can be accounted for by the acoustic features of the speech signal. [ABSTRACT FROM AUTHOR]

The aim of the study was (1) to develop methods for evaluating tone production of children with cochlear implants (CIs) who speak Mandarin Chinese and (2) to evaluate the efficacy of using these methods to assess tone production. The subjects included two groups of native-Mandarin-Chinese-speaking children: 14 prelingually deafened children who had received CIs and 61 normal-hearing (NH) children as controls. The acoustic analysis focused on quantification of the degree of differentiation among lexical tones based on tonal ellipses and the overall similarity of tone contours produced by the children with CIs to normative contours derived from the 61 NH children. An artificial neural network was used to recognize tones produced by the children with CIs after trained with tone tokens produced by the NH children. Finally, perceptual judgments on the tone production of both groups were obtained from eight native-Mandarin-speaking NH adults to evaluate the efficacy of the methods. The results showed that all measures using the acoustic, neural-network, and perceptual analyses were highly correlated with each other and could be used to effectively evaluate tone production of children with CIs. [ABSTRACT FROM AUTHOR]

We have investigated the shear flow behavior of a dynamically symmetric polymeric bicontinuous microemulsion using rheology and in situ small angle x-ray scattering. The microemulsion consists of a ternary blend of poly (ethylene-alt-propylene) (PEP), poly (butylene oxide) (PBO), and a PEP-PBO diblock copolymer. Steady shear experiments reveal an unusual shear thickening behavior at the onset of the non-Newtonian regime, which is consistent with the strain hardening and frequency thickening (at large strains) under oscillatory shear. Scattering experiments indicate development of anisotropy in the bicontinuous structure within the thickening regime. Subsequent shear thinning is observed at intermediate shear rates. Shear-induced bulk phase separation is detected at very high rates. This work complements previous studies on a dynamically extremely asymmetric bicontinuous microemulsion, and thereby establishes the universal rheological properties of polymeric microemulsions. Possible underlying molecular mechanisms for these rich rheological phenomena are discussed. [ABSTRACT FROM AUTHOR]