Blas Espinoza‐Varas

Simulating the effect of spread of excitation in cochlear implants

A model was developed to simulate acoustically the effects of excitation spread in cochlear implants (CI). Based on neurophysiologic data, the proposed model simulates the electrical-current decay rate associated with broad and narrow types of excitation, such as those produced by monopolar and bipolar electrode configurations. The effect of excitation spread on speech intelligibility was simulated in normal-hearing subjects by varying the slopes of the synthesis bands in the noise vocoder. Sentences and monosyllabic words processed via 4-16 channels of stimulation with varying degrees of excitation spread were presented to normal-hearing listeners for identification. Results showed significant interaction between spectral resolution (number of channels) and spread of excitation. The effect of narrowing the excitation spread was minimal when the spectral resolution was sufficiently good (>8 channels) but it was significant when the spectral resolution was poor (4 channels). A significant decrement in performance was observed for extremely narrow excitation spread. This outcome is partly consistent with behavioral data obtained with cochlear implant studies in that CI users tend to do as well or better with monopolar stimulation than with bipolar stimulation.

Otoacoustic emissions, auditory evoked potentials and self-reported gender in people affected by disorders of sex development (DSD)

Both otoacoustic emissions (OAEs) and auditory evoked potentials (AEPs) are sexually dimorphic, and both are believed to be influenced by prenatal androgen exposure. OAEs and AEPs were collected from people affected by 1 of 3 categories of disorders of sex development (DSD) - (1) women with complete androgen insensitivity syndrome (CAIS); (2) women with congenital adrenal hyperplasia (CAH); and (3) individuals with 46,XY DSD including prenatal androgen exposure who developed a male gender despite initial rearing as females (men with DSD). Gender identity (GI) and role (GR) were measured both retrospectively and at the time of study participation, using standardized questionnaires. The main objective of this study was to determine if patterns of OAEs and AEPs correlate with gender in people affected by DSD and in controls. A second objective was to assess if OAE and AEP patterns differed according to degrees of prenatal androgen exposure across groups. Control males, men with DSD, and women with CAH produced fewer spontaneous OAEs (SOAEs) - the male-typical pattern - than control females and women with CAIS. Additionally, the number of SOAEs produced correlated with gender development across all groups tested. Although some sex differences in AEPs were observed between control males and females, AEP measures did not correlate with gender development, nor did they vary according to degrees of prenatal androgen exposure, among people with DSD. Thus, OAEs, but not AEPs, may prove useful as bioassays for assessing early brain exposure to androgens and predicting gender development in people with DSD.

Aging Impairs the Ability to Ignore Irrelevant Information in Frequency Discrimination Tasks

Age effects on the ability to ignore irrelevant auditory information were studied using frequency discrimination threshold (FDT) tasks. FDTs were determined in an unmasked condition with target tones in isolation, and in two backward-masked conditions with a nontarget masking tone presented 20 to 240 ms after the target.One masked condition included irrelevant variability in the masker frequency, but the other did not. The no-variability condition yielded more masking in older than in young adults. Masker variability induced large FDT elevations in both groups; however, the improvement in FDTs with training was large in young but only minimal in older adults.

Low commonality between tests of auditory discrimination and of speech perception

The relation between measures of speech processing and of fine auditory discrimination abilities was investigated by means of factor analyses of the performance of normal listeners on the Test of Basic Auditory Capabilities, TBAC [Watson et al., J. Acoust. Soc. Am. Suppl. 1 71, S72 (1982)]. The eight subtests of the TBAC include syllable identification in noise and discrimination of (a) changes in frequency, intensity, and duration in 1.0‐kHz sinusoids; (b) “jitter” within a pulse train; (c) temporal order for sinusoids and nonsense syllables; and (d) detection of single‐component changes in word‐length tonal patterns. Data were collected in a field (n = 127) and using earphones (n = 119). Test reliability was high in both presentation conditions. Average performance was slightly higher with earphones for discrimination of intensity, of tonal patterns, and in the two speech subtests. Both groups showed large ranges of individual performance on all subtests. Factor analyses revealed similar structures for ...

Measurements of monopolar and bipolar current spreads using forward-masking with a fixed probe.

Abstract Objectives This research employed a forward-masking paradigm to estimate the current spread of monopolar (MP) and bipolar (BP) maskers, with current amplitudes adjusted to elicit the same loudness. Since the spatial separation between active and return electrodes is smaller in BP than in MP configurations, the BP current spread is more localized and presumably superior in terms of speech intelligibility. Because matching the loudness requires higher current in BP than in MP stimulation, previous forward-masking studies show that BP current spread is not consistently narrower across subjects or electrodes within a subject. Methods The present forward-masking measures of current spread differ from those of previous studies by using the same BP probe electrode configuration for both MP and BP masker configurations, and adjusting the current levels of the MP and BP maskers so as to match them in loudness. With this method, the estimate of masker current spread would not be contaminated by differences in probe current spread. Forward masking was studied in four cochlear implant patients, two females and two males, with speech recognition scores higher than 50%; that is, their auditory-nerve survival status was more than adequate to carry out the experiments. Results The data showed that MP and BP masker configurations produce equivalent masking patterns (and current spreads) in three participants. A fourth participant displayed asymmetrical patterns with enhancement rather than masking in some cases, especially when the probe and masker were at the same location. Discussion This study showed equivalent masking patterns for MP and BP maskers when the BP masker current amplitude was increased to match the loudness of the MP masker, and the same BP probe configuration is used with both maskers. This finding could help to explain why cochlear implant users often fail to accrue higher speech intelligibility benefit from BP stimulation.

Sequential interactions in the discrimination of frequency increments co‐occurring with irrelevant increments in frequency, duration, or level

Discrimination of target frequency increments co‐occurring with irrelevant increments in frequency, duration, or level was studied. Pairs (t1,t2) of 1500‐Hz, 80‐ms pure tones separated by 20–120 ms of silence (ITI) were presented in a three‐interval, two‐alternative, forced‐choice (3I/2AFC) task. On each trial, a ‘‘standard’’ pair of tones (interval 1) was followed by two ‘‘comparison’’ pairs (intervals 2 and 3), with 500 ms of silence between observation intervals. One (randomly chosen) comparison pair contained a target increment in the frequency of either t1 or t2; the size of the target increment was controlled by adaptive rules. In addition to the target increment, both comparison stimuli contained identical irrelevant increments in either the duration, frequency, or level of either t1 or t2; there was no correlation between the observation intervals containing target and irrelevant increments. Listeners had to determine which observation interval contained the target increment. Discrimination of t1 ...

Evaluating a model of auditory masking for applications in audio coding

This investigation evaluates the adequacy of an excitation pattern (EP) model of auditory-masking to account for a masking condition commonly observed in the digital coding of audio signals: namely, the masking of quantization noise by either speech or musical sounds. This condition is modeled as a case of masking of a spectrally complex target by a multi-component complex masker (either speech or musical sounds). The evaluation focuses on the extent to which the EP model accounts for the 10-15 dB excess masking observed when multiple maskers occur simultaneously. Excitation-pattern predictions of the masking effects of two-component maskers were compared with predictions of masking-additivity models which closely predict experimental data. The EP model underestimates the combined effects of the two maskers both when the masker frequency components fall within the signal auditory-filter bandwidth, and when they fall outside this bandwidth. A correction for masking additivity may be needed prior to applying the EP model to audio-coding situations.

Optional processing strategies in multidimensional discrimination: Integration versus selective attention

In discrimination of acoustic cues that consist of changes in duration (Δt) and frequency (Δf), listeners can integrate the information from the two dimensions: for any Δf > 0, the just noticeable Δt (d′ = 2.0) can be decreased with Δf, and vice versa [B. Espinoza‐Varas, J. Acoust. Soc. Am. 64, S37(A) (1978)]. This paper presents data which suggest that an alternative strategy that listeners can adopt is to selectively attend to one dimension. As in previous reports, the procedure was to measure the IND in t (or f) as a function of Δf (or Δt) in a “same‐different” discrimination between pure tones. If the listener selectively attends to Δt, then the just noticeable Δt (d′ = 2.0) remains constant with Δf, except for very large Δf; in addition, for Δt = 0 the value of Δf,d′ = 2.0 is considerably larger than that observed with integration. Analogous effects are observed with attention to Δf. Therefore, degraded resolution for the nonattended dimension would be the main result of selective attention. Integrat...

Selective attention to pitch amid conflicting auditory information: context-coding and filtering strategies

An auditory Eriksen-flanker task was used to study how conflicting information interferes with selective attention to task-relevant differences in pure-tone frequency. Across the observation intervals of the discrimination task, the relevant frequency differences between target tones were positive, but within an observation interval, they could appear to be small or negative relative to conflicting differences in flanker tones leading or trailing the target. Being correct required attending to the between-target and ignoring the target–flanker pitch relation (across and within observation-interval, respectively). The interference index was an elevation of conflict-laden frequency discrimination thresholds (FDTs), relative to no-conflict FDTs. When conflicting differences in frequency or level (but not in duration) trailed the relevant differences, interference (i.e., FDT elevation) was large and persistent, increased with the target–flanker time proximity, but decreased with extensive training. Interference occurs when the target–flanker pitch relation is more prominent than the one between targets, and the physical and/or perceptual effects of relevant and conflicting differences tend to cancel one another, as with the above conflicting differences. With untrained participants, the target–flanker pitch relation is most prominent in conditions fostering both the perceptual grouping of the target and flanker (e.g., close time proximity), and the recency and salience of the conflicting differences (e.g., trailing conflicting difference); conversely, by lessening such grouping and salience, prolonged training decreases or nullifies the interference. The interference observed herein does not arise because the relevant and the conflicting differences each prompt separate decisions or responses that are in mutual conflict; instead, it arises from the early-stage interaction between their perceptual effects.

Amplification and training effects in resolution and cross‐spectral integration of redundant cues

Speech recognition of hearing‐aid and cochlear‐implant users is constrained partly by inefficient integration of information conveyed by multiple frequency channels: owing to cross‐channel interference, multi‐channel recognition accuracy is often lower than the sum of single‐channel accuracies, especially if one channel has impaired sensitivity. With complex tones consisting of a mid‐ (M) and a high‐frequency (H) component (1000 and 3127 Hz), the resolution and cross‐spectral integration (CSI) of simultaneous increments in M frequency (IFM) and H duration (ITH) were studied as a function of H amplification and training; M and H impinged, respectively, on normal‐ and impaired‐sensitivity regions of listeners with sensorineural losses. Without amplification, ITH resolution was negligible, the IFM discrimination threshold did not decrease with ITH, and CSI was nil. With H amplification, resolution improved moderately for ITH but decreased for IFM; that is, increasing H audibility interfered with IFM resoluti...