The effects of measurement error and vowel selection on the locus equation measure of coarticulation.

Effects on the slope of introducing error in the F2 Hz values in locus equations (LEs) and of using fewer than ten vowels were investigated. For each of the initial consonants /b, d, g/, 2000 simulated sets were generated using Monte Carlo techniques. The sets were altered with 50, 100, or 200 Hz error being randomly applied to each F2 value within a set. Selected vowels were then removed from the sets and the effects on the slopes were measured. Results suggest that the LE slopes are generally resistant to error and reduced number of vowels. Effects of adding 50 Hz of random error to the F2 values in sets using eight or ten vowels were minimal, yielding a mean absolute change in slope less than 0.07.

Effect of initial-consonant intensity on the speed of lexical decisions.

In the present study, we investigated the effect of initial-consonant intensity on lexical decisions. Amplification was selectively applied to the initial consonant of monosyllabic words. In Experiment 1, young adults with normal hearing completed an auditory lexical decision task with words that either had the natural or amplified initial consonant. The results demonstrated faster reaction times for amplified words when listeners randomly heard words spoken by two unfamiliar talkers. The same pattern of results was found when comparing words in which the initial consonant was naturally higher in intensity than the low-intensity consonants, across all amplification conditions. In Experiment 2, listeners were familiarized with the talkers and tested on each talker in separate blocks, to minimize talker uncertainty. The effect of initial-consonant intensity was reversed, with faster reaction times being obtained for natural than for amplified consonants. In Experiment 3, nonlinguistic processing of the amplitude envelope was assessed using noise modulated by the word envelope. The results again demonstrated faster reaction times for natural than for amplified words. Across all experiments, the results suggest that the acoustic-phonetic structure of the word influences the speed of lexical decisions and interacts with the familiarity and predictability of the talker. In unfamiliar and less-predictable listening contexts, initial-consonant amplification increases lexical decision speed, even if sufficient audibility is available without amplification. In familiar contexts with adequate audibility, an acoustic match of the stimulus with the stored mental representation of the word is more important, possibly along with general auditory properties related to loudness perception.

Simulating the neural correlates of stuttering.

For functional neuroimaging studies of stuttering, two challenges are (1) the elicitation of naturally stuttered versus fluent speech and (2) the separation of activation associated with abnormal motor execution from activation that reflects the cognitive substrates of stuttering. This paper reports on a proof-of-concept study, in which a single-subject approach was applied to address these two issues. A stuttering speaker used his insight into his own stuttering behavior to create a list of stutter-prone words versus a list of "fluent" words. He was then matched to a non-stuttering speaker, who imitated the specific articulatory and orofacial motor pattern of the stuttering speaker. Both study participants performed a functional MRI experiment of single word reading, each being presented with the same lexical items. Results suggest that the generally observed right-hemisphere lateralization appears to reflect a true neural correlate of stuttering. Some of the classically reported activation associated with stuttering appears to be driven more by nonspecific motor patterns than by cognitive substrates of stuttering, while anterior cingulate activation may reflect awareness of (upcoming) dysfluencies. This study shows that it is feasible to match stuttering speakers' utterances more closely to simulated stutters for the investigation of neural correlates of real stuttering. Significant main effects and contrast effects were obtained for the differences between fluent and stuttered speech, and right-hemisphere lateralization associated with real stuttered speech was shown in a single subject.

Effects of consonant-vowel intensity ratio on loudness of monosyllabic words.

Previous research has suggested that speech loudness is determined primarily by the vowel in consonant-vowel-consonant (CVC) monosyllabic words, and that consonant intensity has a negligible effect. The current study further examines the unique aspects of speech loudness by manipulating consonant-vowel intensity ratios (CVRs), while holding the vowel constant at a comfortable listening level (70 dB), to determine the extent to which vowels and consonants contribute differentially to the loudness of monosyllabic words with voiced and voiceless consonants. The loudness of words edited to have CVRs ranging from -6 to +6 dB was compared to that of standard words with unaltered CVR by 10 normal-hearing listeners in an adaptive procedure. Loudness and overall level as a function of CVR were compared for four CVC word types: both voiceless consonants modified; only initial voiceless consonants modified; both voiced consonants modified; and only initial voiced consonants modified. Results indicate that the loudness of CVC monosyllabic words is not based strictly on the level of the vowel; rather, the overall level of the word and the level of the vowel contribute approximately equally. In addition to furthering the basic understanding of speech perception, the current results may be of value for the coding of loudness by hearing aids and cochlear implants.

Brief report: perception and lateralization of spoken emotion by youths with high-functioning forms of autism.

The perception and the cerebral lateralization of spoken emotions were investigated in children and adolescents with high-functioning forms of autism (HFFA), and age-matched typically developing controls (TDC). A dichotic listening task using nonsense passages was used to investigate the recognition of four emotions: happiness, sadness, anger, and neutrality. The participants with HFFA did not differ significantly in overall performance from the TDC, suggesting that the pervasive difficulty in processing emotions is not uniformly present in emotions expressed verbally. Both groups demonstrated a left-ear effect for the perception of emotion in nonsense passages, consistent with overall right-hemisphere superiority for this function.

The consistency of sentence intelligibility across three types of signal distortion.

PURPOSE: To examine the extent to which sentences retain their levels of spoken intelligibility relative to other sentences in a set (the sentence effect) across different types of signal distortion. METHOD: The Central Institute for the Deaf (CID) sentences were rendered difficult to understand through the addition of broadband noise. These intelligibility data were compared with those from previous studies in which the sentences were distorted through filtering and visual-only conditions of speechreading. The extent to which the various sentences retained their intelligibility rankings was examined using an analysis of variance model and by correlating individual sentence means across conditions. RESULTS: The sentences accounted for a large portion of the variance, and individual sentence scores were highly correlated across conditions involving a single distortion type. However, correlations were lower when conditions involving noise were compared with those involving filtering. Surprisingly, correlations across auditory distortions were almost identical to those observed across auditory and visual modalities. These comparisons, reflecting the consistency of sentence difficulty independent of presentation characteristics, accounted for approximately 25% of the variance in sentence-recognition performance. CONCLUSION: There exists a sentence effect that holds across various types of signal distortion, but the strongest form is restricted not only within modalities but within particular forms of distortion.

Consistency of sentence intelligibility across difficult listening situations.

PURPOSE: The extent to which a sentence retains its level of spoken intelligibility relative to other sentences in a list under a variety of difficult listening situations was examined. METHOD: The strength of this sentence effect was studied using the Central Institute for the Deaf Everyday Speech sentences and both generalizability analysis (Experiments 1 and 2) and correlation (Analyses 1 and 2). RESULTS: Experiments 1 and 2 indicated the presence of a prominent sentence effect (substantial variance accounted for) across a large range of group mean intelligibilities (Experiment 1) and different spectral contents (Experiment 2). In Correlation Analysis 1, individual sentence scores were found to be correlated across listeners in each group producing widely ranging levels of performance. The sentence effect accounted for over half of the variance between listener-ability groups. In Correlation Analysis 2, correlations accounted for an average of 42% of the variance across a variety of listening conditions. However, when the auditory data were compared to speech-reading data, the cross-modal correlations were quite low. CONCLUSIONS: The stability of relative sentence intelligibility (the sentence effect) appears across a wide range of mean intelligibilities, across different spectral compositions, and across different listener performance levels, but not across sensory modalities.

Functional communication and executive function in aphasia.

The purpose of this exploratory study was to investigate the relationship between functional communication and executive function ability in aphasia. Twenty-five participants with aphasia underwent examination with an extensive test battery including measures of functional communication, executive function ability, and language impairment. Compared to published norms, most participants did not perform within normal limits on the executive function tests. As expected, the correlation between severity of language impairment and functional communication ratings exceeded that among the executive functioning and functional communication measures. Eight of ten correlation coefficients for the relationship between executive functioning and functional communication reached statistical significance suggesting a clear relationship between scores on the executive functioning measures and functional communication ability. Based on these results, it appears that decreased executive functioning ability may coincide with decreased functional communication ability in persons with aphasia.

Sensitivity to isolated and concurrent intensity and fundamental frequency increments by cochlear implant users under natural listening conditions.

Sensitivity to acoustic cues in cochlear implant (CI) listening under natural conditions is a potentially complex interaction between a number of simultaneous factors, and may be difficult to predict. In the present study, sensitivity was measured under conditions that approximate those of natural listening. Synthesized words having increases in intensity or fundamental frequency (F0) in a middle stressed syllable were presented in soundfield to normal-hearing listeners and to CI listeners using their everyday speech processors and programming. In contrast to the extremely fine sensitivity to electrical current observed when direct stimulation of single electrodes is employed, difference limens (DLs) for intensity were larger for the CI listeners by a factor of 2.4. In accord with previous work, F0 DLs were larger by almost one order of magnitude. In a second experiment, it was found that the presence of concurrent intensity and F0 increments reduced the mean DL to half that of either cue alone for both groups of subjects, indicating that both groups combine concurrent cues with equal success. Although sensitivity to either cue in isolation was not related to word recognition in CI users, the listeners having lower combined-cue thresholds produced better word recognition scores.

Repeated tongue and hand strength measurements in normal adults and individuals with Parkinson's disease.

Changes in tongue and hand strength measurements of men with Parkinson's Disease and aged-matched controls across multiple days were examined. The Iowa Oral Performance Instrument measured tongue and hand strength during four consecutive days and at day 11. Peak tongue strength measurements occurred on day 3 with a small decrease on day 4, which was maintained at day 11, indicating a significant increase in tongue strength measurements with task repetition in multiple days. No change in hand strength measurements was noted over days. Significant differences in mean tongue and hand strength measurements between the PD and age-matched control group were found. Tongue and hand strength measurements were lower for the PD group compared with the control group on average across days.

Perception and production of rise-fall intonation in American English.

At the segmental level, the rate of speaking affects the degree of physical undershoot of articulatory targets and the resulting perception. Little is known regarding evidence of these effects at the suprasegmental level, particularly in intonation. In this study, the effect of rate of speaking on fundamental frequency and on perceptual judgments of peak pitch in a rise-fall intonation pattern was investigated. First, speakers produced rise-fall intonations in sentence contexts at slow, normal, and fast speaking rates. Peak fundamental frequencies (F0) of the slow productions were significantly lower than those of the normal or fast productions. The mean normal rate production of the word Miami was used as a model for the target word in a series of subsequent perceptual experiments. Altering the duration of the target word to represent slow, normal, and fast rates of speaking did not affect listener judgment of peak pitch. Finally, the pitch of the target word was measured in a sentence context. No differences between peak pitch in isolation or in sentence context were found. It was concluded that the production and perception of this form of intonation was not subject to the effects of rate that are seen at the segmental level.