Reconsidering classic ideas in speech communication.

The papers in this special issue provide a critical look at some historical ideas that have had an influence on research and teaching in the field of speech communication. They also address widely used methodologies or address long-standing methodological challenges in the areas of speech perception and speech production. The goal is to reconsider and evaluate the need for caution or replacement of historical ideas with more modern results and methods. The contributions provide respectful historical context to the classic ideas, as well as new original research or discussion that clarifies the limitations of the original ideas.

Reconsidering commonly used stimuli in speech perception experiments.

This paper examines some commonly used stimuli in speech perception experiments and raises questions about their use, or about the interpretations of previous results. The takeaway messages are: 1) the Hillenbrand vowels represent a particular dialect rather than a gold standard, and English vowels contain spectral dynamics that have been largely underappreciated, 2) the /ɑ/ context is very common but not clearly superior as a context for testing consonant perception, 3) /ɑ/ is particularly problematic when testing voice-onset-time perception because it introduces strong confounds in the formant transitions, 4) /dɑ/ is grossly overrepresented in neurophysiological studies and yet is insufficient as a generalized proxy for "speech perception," and 5) digit tests and matrix sentences including the coordinate response measure are systematically insensitive to important patterns in speech perception. Each of these stimulus sets and concepts is described with careful attention to their unique value and also cases where they might be misunderstood or over-interpreted.

Vowel and consonant confusions from spectrally manipulated stimuli designed to simulate poor cochlear implant electrode-neuron interfaces.

Suboptimal interfaces between cochlear implant (CI) electrodes and auditory neurons result in a loss or distortion of spectral information in specific frequency regions, which likely decreases CI users' speech identification performance. This study exploited speech acoustics to model regions of distorted CI frequency transmission to determine the perceptual consequences of suboptimal electrode-neuron interfaces. Normal hearing adults identified naturally spoken vowels and consonants after spectral information was manipulated through a noiseband vocoder: either (1) low-, middle-, or high-frequency regions of information were removed by zeroing the corresponding channel outputs, or (2) the same regions were distorted by splitting filter outputs to neighboring filters. These conditions simulated the detrimental effects of suboptimal CI electrode-neuron interfaces on spectral transmission. Vowel and consonant confusion patterns were analyzed with sequential information transmission, perceptual distance, and perceptual vowel space analyses. Results indicated that both types of spectral manipulation were equally destructive. Loss or distortion of frequency information produced similar effects on phoneme identification performance and confusion patterns. Consonant error patterns were consistently based on place of articulation. Vowel confusions showed that perceptions gravitated away from the degraded frequency region in a predictable manner, indicating that vowels can probe frequency-specific regions of spectral degradations.

The neural encoding of formant frequencies contributing to vowel identification in normal-hearing listeners.

Even though speech signals trigger coding in the cochlea to convey speech information to the central auditory structures, little is known about the neural mechanisms involved in such processes. The purpose of this study was to understand the encoding of formant cues and how it relates to vowel recognition in listeners. Neural representations of formants may differ across listeners; however, it was hypothesized that neural patterns could still predict vowel recognition. To test the hypothesis, the frequency-following response (FFR) and vowel recognition were obtained from 38 normal-hearing listeners using four different vowels, allowing direct comparisons between behavioral and neural data in the same individuals. FFR was employed because it provides an objective and physiological measure of neural activity that can reflect formant encoding. A mathematical model was used to describe vowel confusion patterns based on the neural responses to vowel formant cues. The major findings were (1) there were large variations in the accuracy of vowel formant encoding across listeners as indexed by the FFR, (2) these variations were systematically related to vowel recognition performance, and (3) the mathematical model of vowel identification was successful in predicting good vs poor vowel identification performers based exclusively on physiological data.

Talker Versus Dialect Effects on Speech Intelligibility: A Symmetrical Study.

This study investigates the relative effects of talker-specific variation and dialect-based variation on speech intelligibility. Listeners from two dialects of American English performed speech-in-noise tasks with sentences spoken by talkers of each dialect. An initial statistical model showed no significant effects for either talker or listener dialect group, and no interaction. However, a mixed-effects regression model including several acoustic measures of the talker's speech revealed a subtle effect of talker dialect once the various acoustic dimensions were accounted for. Results are discussed in relation to other recent studies of cross-dialect intelligibility.

The Role of the Root in Spoken Word Recognition in Hebrew: An Auditory Gating Paradigm.

Very few studies have investigated online spoken word recognition in templatic languages. In this study, we investigated both lexical (neighborhood density and frequency) and morphological (role of root morpheme) aspects of spoken word recognition of Hebrew, a templatic language, using the traditional gating paradigm. Additionally, we compared the traditional gating paradigm with a novel, phoneme-based gating paradigm. The phoneme-based approach allows for better control of information available at each gate. We found lexical effects with high-frequency words and low neighborhood density words being recognized at earlier gates. We also found that earlier access to root-morpheme information enabled word recognition at earlier gates. Finally, we showed that both the traditional gating paradigm and gating by phoneme paradigm yielded equivalent results.

Measuring return on investment of outreach by community health workers.

Community health workers (CHWs) are effective in improving access to health care, promoting client knowledge and behavior change, and contributing to improved health status of individuals. However, few outreach programs have evaluated the financial impact of CHWs on health care systems and policies. A longitudinal repeated measures design was used to assess the return on investment (ROI) of outreach by CHWs employed by Denver Health Community Voices. Service utilization, charges and reimbursements for 590 underserved men were analyzed 9 months before and after interaction with a CHW. Primary and specialty care visits increased and urgent care, inpatient, and outpatient behavioral health care utilization decreased, resulting in a reduction of monthly uncompensated costs by $14,244. Program costs were $6,229 per month and the ROI was 2.28:1.00, a savings of $95,941 annually. These data provide evidence of economic contributions that CHWs make to a public safety net system and inform policy making regarding program sustainability.

Individual sensitivity to spectral and temporal cues in listeners with hearing impairment.

PURPOSE: The present study was designed to evaluate use of spectral and temporal cues under conditions in which both types of cues were available. METHOD: Participants included adults with normal hearing and hearing loss. We focused on 3 categories of speech cues: static spectral (spectral shape), dynamic spectral (formant change), and temporal (amplitude envelope). Spectral and/or temporal dimensions of synthetic speech were systematically manipulated along a continuum, and recognition was measured using the manipulated stimuli. Level was controlled to ensure cue audibility. Discriminant function analysis was used to determine to what degree spectral and temporal information contributed to the identification of each stimulus. RESULTS: Listeners with normal hearing were influenced to a greater extent by spectral cues for all stimuli. Listeners with hearing impairment generally utilized spectral cues when the information was static (spectral shape) but used temporal cues when the information was dynamic (formant transition). The relative use of spectral and temporal dimensions varied among individuals, especially among listeners with hearing loss. CONCLUSION: Information about spectral and temporal cue use may aid in identifying listeners who rely to a greater extent on particular acoustic cues and applying that information toward therapeutic interventions.

Gastroenteritis and antibiotic-associated diarrhea.

Acute gastroenteritis is a common cause of emergency and office visits. This article reviews causes, pathogenesis, diagnosis, prevention, and treatment. The incidence of antibiotic-associated colitis is increasing worldwide as a consequence of widespread use of broad-spectrum antibiotics for various illnesses. The pathogenic organism, Clostridium difficile, produces two enterotoxins, toxin A and toxin B, that cause colonic mucosal inflammation. C. difficile infection presents with a wide range of clinical manifestations, from asymptomatic carriers to life-threatening pseudomembranous colitis.