Biomedical subjects

Louis D Braida

Publications and source records attributed to Louis D Braida.

7 recordsLinked to original sources

PubMed2005

Effect of slow-acting wide dynamic range compression on measures of intelligibility and ratings of speech quality in simulated-loss listeners.

The purpose of this study was twofold: (a) to determine the extent to which 4-channel, slow-acting wide dynamic range amplitude compression (WDRC) can counteract the perceptual effects of reduced auditory dynamic range and (b) to examine the relation between objective measures of speech intelligibility and categorical ratings of speech quality for sentences processed with slow-acting WDRC. Multiband expansion was used to simulate the effects of elevated thresholds and loudness recruitment in normal hearing listeners. While some previous studies have shown that WDRC can improve both speech intelligibility and quality, others have found no benefit. The current experiment shows that moderate amounts of compression can provide a small but significant improvement in speech intelligibility, relative to linear amplification, for simulated-loss listeners with small dynamic ranges (i.e., flat, moderate hearing loss). This benefit was found for speech at conversational levels, both in quiet and in a background of babble. Simulated-loss listeners with large dynamic ranges (i.e., sloping, mild-to-moderate hearing loss) did not show any improvement. Comparison of speech intelligibility scores and subjective ratings of intelligibility showed that listeners with simulated hearing loss could accurately judge the overall intelligibility of speech. However, in all listeners, ratings of pleasantness decreased as the compression ratio increased. These findings suggest that subjective measures of speech quality should be used in conjunction with either objective or subjective measures of speech intelligibility to ensure that participant-selected hearing aid parameters optimize both comfort and intelligibility.

Acoustic Stimulation↗

PubMed2005

Comparing different estimates of cochlear compression in listeners with normal and impaired hearing.

A loss of cochlear compression may underlie many of the difficulties experienced by hearing-impaired listeners. Two behavioral forward-masking paradigms that have been used to estimate the magnitude of cochlear compression are growth of masking (GOM) and temporal masking (TM). The aim of this study was to determine whether these two measures produce within-subjects results that are consistent across a range of signal frequencies and, if so, to compare them in terms of reliability or efficiency. GOM and TM functions were measured in a group of five normal-hearing and five hearing-impaired listeners at signal frequencies of 1000, 2000, and 4000 Hz. Compression values were derived from the masking data and confidence intervals were constructed around these estimates. Both measures produced comparable estimates of compression, but both measures have distinct advantages and disadvantages, so that the more appropriate measure depends on factors such as the frequency region of interest and the degree of hearing loss. Because of the long testing times needed, neither measure is suitable for clinical use in its current form.

Adolescent↗

PubMed2005

Neurophysiology and neuroanatomy of pitch perception: auditory cortex.

We present original results and review literature from the past fifty years that address the role of primate auditory cortex in the following perceptual capacities: (1) the ability to perceive small differences between the pitches of two successive tones; (2) the ability to perceive the sign (i.e., direction) of the pitch difference [higher (+) vs. lower (-)]; and (3) the ability to abstract pitch constancy across changes in stimulus acoustics. Cortical mechanisms mediating pitch perception are discussed with respect to (1) gross and microanatomical distribution; and (2) candidate neural coding schemes. Observations by us and others suggest that (1) frequency-selective neurons in primary auditory cortex (A1) and surrounding fields play a critical role in fine-grained pitch discrimination at the perceptual level; (2) cortical mechanisms that detect pitch differences are neuroanatomically dissociable from those mediating pitch direction discrimination; (3) cortical mechanisms mediating perception of the "missing fundamental frequency (F0)" are neuroanatomically dissociable from those mediating pitch perception when F0 is present; (4) frequency-selective neurons in both right and left A1 contribute to pitch change detection and pitch direction discrimination; (5) frequency-selective neurons in right A1 are necessary for normal pitch direction discrimination; (6) simple codes for pitch that are based on single- and multiunit firing rates of frequency-selective neurons face both a "hyperacuity problem" and a "pitch constancy problem"-that is, frequency discrimination thresholds for pitch change direction and pitch direction discrimination are much smaller than neural tuning curves predict, and firing rate patterns change dramatically under conditions in which pitch percepts remain invariant; (7) cochleotopic organization of frequency-selective neurons bears little if any relevance to perceptual acuity and pitch constancy; and (8) simple temporal codes for pitch capable of accounting for pitches higher than a few hundred hertz have not been found in the auditory cortex. The cortical code for pitch is therefore not likely to be a function of simple rate profiles or synchronous temporal patterns. Studies motivated by interest in the neurophysiology and neuroanatomy of music perception have helped correct longstanding misconceptions about the functional role of auditory cortex in frequency discrimination and pitch perception. Advancing knowledge about the neural coding of pitch is of fundamental importance to the future design of neurobionic therapies for hearing loss.

Acoustic Stimulation↗

PubMed2004

Acoustic properties of naturally produced clear speech at normal speaking rates.

Sentences spoken "clearly" are significantly more intelligible than those spoken "conversationally" for hearing-impaired listeners in a variety of backgrounds [Picheny et al., J. Speech Hear. Res. 28, 96-103 (1985); Uchanski et al., ibid. 39, 494-509 (1996); Payton et al., J. Acoust. Soc. Am. 95, 1581-1592 (1994)]. While producing clear speech, however, talkers often reduce their speaking rate significantly [Picheny et al., J. Speech Hear. Res. 29, 434-446 (1986); Uchanski et al., ibid. 39, 494-509 (1996)]. Yet speaking slowly is not solely responsible for the intelligibility benefit of clear speech (over conversational speech), since a recent study [Krause and Braida, J. Acoust. Soc. Am. 112, 2165-2172 (2002)] showed that talkers can produce clear speech at normal rates with training. This finding suggests that clear speech has inherent acoustic properties, independent of rate, that contribute to improved intelligibility. Identifying these acoustic properties could lead to improved signal processing schemes for hearing aids. To gain insight into these acoustical properties, conversational and clear speech produced at normal speaking rates were analyzed at three levels of detail (global, phonological, and phonetic). Although results suggest that talkers may have employed different strategies to achieve clear speech at normal rates, two global-level properties were identified that appear likely to be linked to the improvements in intelligibility provided by clear/normal speech: increased energy in the 1000-3000-Hz range of long-term spectra and increased modulation depth of low frequency modulations of the intensity envelope. Other phonological and phonetic differences associated with clear/normal speech include changes in (1) frequency of stop burst releases, (2) VOT of word-initial voiceless stop consonants, and (3) short-term vowel spectra.

Adult↗

PubMed2004

Integration across frequency bands for consonant identification.

A comparison of the predictions of models of integration to data on the reception of consonants filtered into a variety of frequency bands is reported. New data on the consonant identification are presented. Three experiments were conducted testing the following bands: experiment I, 0-2100 Hz and 2100-4500 Hz; experiment II, 0-700 Hz combined with 700-1400, 1400-2100, 2100-2800, and 2800-4500 Hz; experiment III, all combinations of 700-1400, 1400-2100, 2100-2800, and 2800-4500 Hz. The predictions of four models, Fletcher's [Speech and Hearing in Communication (Van Nostrand, New York, 1950)] independent errors model, Massaro's fuzzy logical model of perception [Proc. Int. Congress of Phonetic Sciences, Stockholm, Vol. 3, pp. 106-113 (1987)], and Braida's pre-labelling and post-labelling models of integration [Q. J. Exp. Psychol. A 43, 647-677 (1991)], were compared in terms of their ability to predict combined-band scores. At least two models were capable of predicting performance for each combined-band condition. For experiment I, all models were able to make satisfactory predictions. For experiment II, a variant of the pre-labelling model was able to make satisfactory predictions. For experiment III, no model was able to make satisfactory predictions, but the fuzzy logical model of perception and a variant of the pre-labelling model made relatively good predictions. Thus the ability of the models to predict performance depended more on whether the condition included the lowest frequency band than on the adjacency or frequency separation.

Adult↗

PubMed2002

Investigating alternative forms of clear speech: the effects of speaking rate and speaking mode on intelligibility.

Sentences spoken "clearly" (and slowly) are significantly more intelligible than those spoken "conversationally" for hearing-impaired listeners in a variety of backgrounds [Picheny, Durlach, and Braida, J. Speech Hear. Res. 28, 96-103 (1985); Uchanski et al., J. Speech Hear. Res. 39, 494-509 (1996); Payton, Uchanski, and Braida, J. Acoust. Soc. Am. 95, 1581-1592 (1994)]. However, it is unknown whether slower speaking rates are necessary for highly intelligible speech or whether an alternative form of clear speech exists at faster (i.e., normal) rates. To investigate this question, talkers with significant public speaking experience were asked to produce clear and conversational speech at slow, normal, and quick rates. A method for eliciting clear speech was introduced that ensured the clearest possible speech was obtained at each of these speaking rates. To probe for other highly intelligible speaking modes, talkers also recorded sentences in two other speaking modes: soft and loud. Intelligibility tests indicated that clear speech was the only speaking mode that provided a consistent intelligibility advantage over conversational speech. Moreover, the advantage of clear speech was extended to faster speaking rates than previously reported. These results suggest that clear speech has some inherent acoustic properties that contribute to its high intelligibility without altering rate. Identifying these acoustic properties could lead to improved signal-processing schemes for hearing aids.

Female↗

PubMed2002

Functional role of auditory cortex in frequency processing and pitch perception.

Microelectrode studies in nonhuman primates and other mammals have demonstrated that many neurons in auditory cortex are excited by pure tone stimulation only when the tone's frequency lies within a narrow range of the audible spectrum. However, the effects of auditory cortex lesions in animals and humans have been interpreted as evidence against the notion that neuronal frequency selectivity is functionally relevant to frequency discrimination. Here we report psychophysical and anatomical evidence in favor of the hypothesis that fine-grained frequency resolution at the perceptual level relies on neuronal frequency selectivity in auditory cortex. An adaptive procedure was used to measure difference thresholds for pure tone frequency discrimination in five humans with focal brain lesions and eight normal controls. Only the patient with bilateral lesions of primary auditory cortex and surrounding areas showed markedly elevated frequency difference thresholds: Weber fractions for frequency direction discrimination ("higher"-"lower" pitch judgments) were about eightfold higher than Weber fractions measured in patients with unilateral lesions of auditory cortex, auditory midbrain, or dorsolateral frontal cortex; Weber fractions for frequency change discrimination ("same"-"different" pitch judgments) were about seven times higher. In contrast, pure-tone detection thresholds, difference thresholds for pure tone duration discrimination centered at 500 ms, difference thresholds for vibrotactile intensity discrimination, and judgments of visual line orientation were within normal limits or only mildly impaired following bilateral auditory cortex lesions. In light of current knowledge about the physiology and anatomy of primate auditory cortex and a review of previous lesion studies, we interpret the present results as evidence that fine-grained frequency processing at the perceptual level relies on the integrity of finely tuned neurons in auditory cortex.

Acoustic Stimulation↗