Mitchell S. Sommers

Speech Perception as a Talker-Contingent Process

To determine how familiarity with a talkers voice affects perception of spoken words, we trained two groups of subjects to recognize a set of voices over a 9-day period One group then identified novel words produced by the same set of talkers at four signal-to-noise ratios Control subjects identified the same words produced by a different set of talkers The results showed that the ability to identify a talkers voice improved intelligibility of novel words produced by that talker The results suggest that speech perception may involve talker-contingent processes whereby perceptual learning of aspects of the vocal source facilitates the subsequent phonetic analysis of the acoustic signal

The facilitative influence of phonological similarity and neighborhood frequency in speech production in younger and older adults

A tip-of-the-tongue (TOT) elicitation task and a picture-naming task were used to examine the role of neighborhood frequency as well as word frequency and neighborhood density in speech production. As predicted for the younger adults in Experiment 1, more TOT states were elicited for words with low word frequency and with sparse neighborhoods. Contrary to predictions, neighborhood frequency did not significantly influence retrieval of the target word. For the older adults in Experiment 2, however, more TOT states were elicited for words with low neighborhood frequency. Furthermore, in Experiment 3, pictures with high neighborhood frequency were named more quickly and accurately than pictures with low neighborhood frequency. These results show that the number of neighbors and the frequency of those neighbors influence lexical retrieval in speech production. The facilitative nature of these factors is more parsimoniously accounted for by an interactive model rather than by a strictly feedforward model of speech production.

Inhibitory processes and spoken word recognition in young and older adults: the interaction of lexical competition and semantic context.

Two experiments were conducted to examine the importance of inhibitory abilities and semantic context to spoken word recognition in older and young adults. In Experiment 1, identification scores were obtained in 3 contexts: single words, low-predictability sentences, and high-predictability sentences. Additionally, identification performance was examined as a function of neighborhood density (number of items phonetically similar to a target word). Older adults had greater difficulty than young adults recognizing words with many neighbors (hard words). However, older adults also exhibited greater benefits as a result of adding contextual information. Individual differences in inhibitory abilities contributed significantly to recognition performance for lexically hard words but not for lexically easy words. The roles of inhibitory abilities and linguistic knowledge in explaining age-related impairments in spoken word recognition are discussed.

Auditory-visual speech perception and auditory-visual enhancement in normal-hearing younger and older adults.

Objective: The purpose of the present study was to examine the effects of age on the ability to benefit from combining auditory and visual speech information, relative to listening or speechreading alone. In addition, the study was designed to compare visual enhancement (VE) and auditory enhancement (AE) for consonants, words, and sentences in older and younger adults. Design: Forty-four older adults and 38 younger adults with clinically normal thresholds for frequencies of 4 kHz and below were asked to identify vowel-consonant-vowels (VCVs), words in a carrier phrase, and semantically meaningful sentences in auditory-only (A), visual-only (V), and auditory-visual (AV) conditions. All stimuli were presented in a background of 20-talker babble, and signal-to-babble ratios were set individually for each participant and each stimulus type to produce approximately 50% correct in the A condition. Results: For all three types of stimuli, older and younger adults obtained similar scores for the A condition, indicating that the procedure for individually adjusting signal-to-babble ratios was successful at equating A scores for the two age groups. Older adults, however, had significantly poorer performance than younger adults in the AV and V modalities. Analyses of both AE and VE indicated no age differences in the ability to benefit from combining auditory and visual speech signals after controlling for age differences in the V condition. Correlations between scores for the three types of stimuli (consonants, words, and sentences) indicated moderate correlations in the V condition but small correlations for AV, AE, and VE. Conclusions: Overall, the findings suggest that the poorer performance of older adults in the AV condition was a result of reduced speechreading abilities rather than a consequence of impaired integration capacities. The pattern of correlations across the three stimulus types indicates some overlap in the mechanisms mediating AV perception of words and sentences and that these mechanisms are largely independent from those used for AV perception of consonants.

Stimulus variability and spoken word recognition. I. Effects of variability in speaking rate and overall amplitude

The present experiments investigated how several different sources of stimulus variability within speech signals affect spoken-word recognition. The effects of varying talker characteristics, speaking rate, and overall amplitude on identification performance were assessed by comparing spoken-word recognition scores for contexts with and without variability along a specified stimulus dimension. Identification scores for word lists produced by single talkers were significantly better than for the identical items produced in multiple-talker contexts. Similarly, recognition scores for words produced at a single speaking rate were significantly better than for the corresponding mixed-rate condition. Simultaneous variations in both speaking rate and talker characteristics produced greater reductions in perceptual identification scores than variability along either dimension alone. In contrast, variability in the overall amplitude of test items over a 30-dB range did not significantly alter spoken-word recognition scores. The results provide evidence for one or more resource-demanding normalization processes which function to maintain perceptual constancy by compensating for acoustic-phonetic variability in speech signals that can affect phonetic identification.

Hearing impairment and cognitive energy: the Framework for Understanding Effortful Listening (FUEL)

The Fifth Eriksholm Workshop on “Hearing Impairment and Cognitive Energy” was convened to develop a consensus among interdisciplinary experts about what is known on the topic, gaps in knowledge, the use of terminology, priorities for future research, and implications for practice. The general term cognitive energy was chosen to facilitate the broadest possible discussion of the topic. It goes back to Titchener (1908) who described the effects of attention on perception; he used the term psychic energy for the notion that limited mental resources can be flexibly allocated among perceptual and mental activities. The workshop focused on three main areas: (1) theories, models, concepts, definitions, and frameworks; (2) methods and measures; and (3) knowledge translation. We defined effort as the deliberate allocation of mental resources to overcome obstacles in goal pursuit when carrying out a task, with listening effort applying more specifically when tasks involve listening. We adapted Kahneman’s seminal (1973) Capacity Model of Attention to listening and proposed a heuristically useful Framework for Understanding Effortful Listening (FUEL). Our FUEL incorporates the well-known relationship between cognitive demand and the supply of cognitive capacity that is the foundation of cognitive theories of attention. Our FUEL also incorporates a motivation dimension based on complementary theories of motivational intensity, adaptive gain control, and optimal performance, fatigue, and pleasure. Using a three-dimensional illustration, we highlight how listening effort depends not only on hearing difficulties and task demands but also on the listener’s motivation to expend mental effort in the challenging situations of everyday life.

Effects of stimulus variability on perception and representation of spoken words in memory

A series of experiments was conducted to investigate the effects of stimulus variability on the memory representations for spoken words. A serial recall task was used to study the effects of changes in speaking rate, talker variability, and overall amplitude on the initial encoding, rehearsal, and recall of lists of spoken words. Interstimulus interval (ISI) was manipulated to determine the time course and nature of processing. The results indicated that at short ISIs, variations in both talker and speaking rate imposed a processing cost that was reflected in poorer serial recall for the primacy portion of word lists. At longer ISIs, however, variation in talker characteristics resulted in improved recall in initial list positions, whereas variation in speaking rate had no effect on recall performance. Amplitude variability had no effect on serial recall across all ISIs. Taken together, these results suggest that encoding of stimulus dimensions such as talker characteristics, speaking rate, and overall amplitude may be the result of distinct perceptual operations. The effects of these sources of stimulus variability in speech are discussed with regard to perceptual saliency, processing demands, and memory representation for spoken words.

Formant frequency discrimination by Japanese macaques (Macaca fuscata)

These studies investigated formant frequency discrimination by Japanese macaques (Macaca fuscata) using an AX discrimination procedure and techniques of operant conditioning. Nonhuman subjects were significantly more sensitive to increments in the center frequency of either the first (F1) or second (F2) formant of single-formant complexes than to corresponding pure-tone frequency shifts. Furthermore, difference limens (DLs) for multiformant signals were not significantly different than those for single-formant stimuli. These results suggest that Japanese monkeys process formant and pure-tone frequency increments differentially and that the same mechanisms mediate formant frequency discrimination in single-formant and vowel-like complexes. The importance of two of the cues available to mediate formant frequency discrimination, changes in the phase and the amplitude spectra of the signals, was investigated by independently manipulating these two parameters. Results of the studies indicated that phase cues were not a significant feature of formant frequency discrimination by Japanese macaques. Rather, subjects attended to relative level changes in harmonics within a narrow frequency range near F1 and F2 to detect formant frequency increments. These findings are compared to human formant discrimination data and suggest that both species rely on detecting alterations in spectral shape to discriminate formant frequency shifts. Implications of the results for animal models of speech perception are discussed.

The Structure of Working Memory Abilities Across the Adult Life Span

The present study addresses three questions regarding age differences in working memory: (1) whether performance on complex span tasks decreases as a function of age at a faster rate than performance on simple span tasks; (2) whether spatial working memory decreases at a faster rate than verbal working memory; and (3) whether the structure of working memory abilities is different for different age groups. Adults, ages 20-89 (n = 388), performed three simple and three complex verbal span tasks and three simple and three complex spatial memory tasks. Performance on the spatial tasks decreased at faster rates as a function of age than performance on the verbal tasks, but within each domain, performance on complex and simple span tasks decreased at the same rates. Confirmatory factor analyses revealed that domain-differentiated models yielded better fits than models involving domain-general constructs, providing further evidence of the need to distinguish verbal and spatial working memory abilities. Regardless of which domain-differentiated model was examined, and despite the faster rates of decrease in the spatial domain, age group comparisons revealed that the factor structure of working memory abilities was highly similar in younger and older adults and showed no evidence of age-related dedifferentiation.

Auditory filter shapes in normal‐hearing, noise‐masked normal, and elderly listenersa)

To dissociate the effects of age and hearing impairment on changes in frequency selectivity, auditory filter shapes were measured at 2 kHz in four groups of subjects: (1) normal-hearing young subjects; (2) normal-hearing elderly subjects; (3) elderly hearing-impaired listeners; and (4) young normal-hearing listeners with simulated hearing losses. Filter shapes were derived using a modified version of the notched-noise procedure [Glasberg and Moore, Hear, Res. 47, 103-138 (1990)]. Equivalent rectangular bandwidths (ERBs) of auditory filters were not significantly different in young and elderly subjects with normal 2-kHz hearing. Furthermore, filter widths for young subjects with 20- and 40-dB simulated hearing losses overlapped with those obtained from elderly subjects with corresponding degrees of actual hearing loss. One measure that did show significant differences between actual and simulated hearing losses was the degree of filter asymmetry; auditory filters in hearing-impaired listeners were more asymmetrical than those obtained from noise-masked normal-hearing subjects. The dynamic range of auditory filters, however, was comparable for hearing-impaired and noise-masked listeners. Lastly, post-filter detection efficiency was also similar for young and elderly subjects with equivalent hearing levels. These findings suggest that the reduced frequency selectivity often reported for older listeners can be attributed, primarily, to hearing loss rather than increased age. Implications of the results for speech perception in the elderly and models of hearing impairment are discussed.