Mark Hedrick

Weighting of cues for fricative place of articulation perception by children wearing cochlear implants

Abstract Objective: To determine how children wearing cochlear implants weight cues for fricative perception compared to age-matched children with normal hearing. Design: Two seven-step continua of synthetic CV syllables were constructed, with frication pole varied from /s/ to /∫/ within the continuum, and appropriate formant transition values varied across continua. Relative weights applied to the frication, transition, and interaction cues were determined. Study Sample: Ten 5–7-year-old children with normal hearing and ten 5–8-year-old children wearing cochlear implants participated. Results: Both groups of children gave more perceptual weight to the frication spectral cue than to the formant transition cue. Children with normal hearing gave small but significant weight to formant transitions, but the children wearing cochlear implants did not. The degree of cue interaction was significant for children with normal hearing but was not for children wearing cochlear implants. Conclusions: Children wearing a cochlear implant use similar cue-weighting strategies as normal listeners (i.e. all apply more weight to the frication noise than to the transition cue), but may have limitations in processing formant transitions and in cue interaction. Sumario Objetivo: Determinar el valor que los niños que usan implante coclear le dan a las claves para percibir las fricativas, en comparación con niños normoyentes de la misma edad. Diseño: Se construyeron dos continuos de siete pasos consistentes en sílabas sintéticas CV, con polo fricativo que variaba de /s/ a /∫/ dentro del continuo, y con valores de formato de transición que variaban a través del continuo. Se determinaron los pesos relativos aplicados a la fricación, la transición y la interacción de claves. Muestra: Participaron diez niños de 5 a 7 años de edad con audición normal y diez niños de 5 a 8 años de edad con implante coclear. Resultados: Ambos grupos de niños dieron un mayor valor perceptual a las claves del espectro fricativo que a las claves de transición de los formantes. Los niños normoyentes dieron un valor pequeño pero significativo a las transiciones de las formantes; no así los niños con implante coclear. Conclusiones: los niños con implante coclear utilizan estrategias similares para valorar las claves que los niños normoyentes (i.e. todos dan más valor al sonido fricativo que a la clave de transición, pero tienen limitaciones para procesar las transiciones de las formante en la interacción de claves.

Electrophysiological and behavioral measures of phonological processing of auditory nonsense V–CV–VCV stimuli

An event-related potential, the Phonological Mapping Negativity (PMN), has been reported to reflect recognition of phonological mismatches in speech stimuli. The purpose of the present study was to explore how the PMN response to the auditory nonsense syllable reflects phonological processing in isolation without the letter prime or lexical/semantic context. Sixty-four nonsense syllable stimuli were composed for each of three stimulus conditions: phonological match (PM), phonological mismatch with similar sound (PMMS), and phonological mismatch with different sound (PMMD), making a total of 192 stimuli. The PMN was measured from fourteen normal-hearing listeners. Electroencephalogram (EEG) activity was recorded while subjects were listening to the stimuli and responding behaviorally. Subjects were asked to determine what vowel-consonant-vowel (VCV) (e.g. /apa/) would be formed from the combination of the preceding vowel (V) (e.g. /a/) and consonant-vowel (CV) (e.g. /pa/), and press a correct or incorrect response button as soon as they decided whether the target VCV stimulus matched their expectation. In this way, along with the PMN, behavioral response accuracy and reaction times were obtained. The results were as follows: (1) PMN amplitude was not different by stimulus condition, (2) PMN amplitude was larger over frontal and central than posterior regions, but not different between the left versus right hemisphere, (3) PMN was detected in the absence of N400, and (4) behavioral responses were more accurate and faster in PMMD than PM and PMMS. Results indicate that the PMN can reflect phonological processing of auditory nonsense syllables in isolation. The scalp distribution of PMN is most dominant in the fronto-central regions without lateralization. Lastly, behavioral response accuracy and reaction times appear to be influenced by the extent of the task difficulty or processing demand rather than by the extent of phonological violation.

Effects of physiological internal noise on model predictions of concurrent vowel identification for normal-hearing listeners

Previous studies have shown that concurrent vowel identification improves with increasing temporal onset asynchrony of the vowels, even if the vowels have the same fundamental frequency. The current study investigated the possible underlying neural processing involved in concurrent vowel perception. The individual vowel stimuli from a previously published study were used as inputs for a phenomenological auditory-nerve (AN) model. Spectrotemporal representations of simulated neural excitation patterns were constructed (i.e., neurograms) and then matched quantitatively with the neurograms of the single vowels using the Neurogram Similarity Index Measure (NSIM). A novel computational decision model was used to predict concurrent vowel identification. To facilitate optimum matches between the model predictions and the behavioral human data, internal noise was added at either neurogram generation or neurogram matching using the NSIM procedure. The best fit to the behavioral data was achieved with a signal-to-noise ratio (SNR) of 8 dB for internal noise added at the neurogram but with a much smaller amount of internal noise (SNR of 60 dB) for internal noise added at the level of the NSIM computations. The results suggest that accurate modeling of concurrent vowel data from listeners with normal hearing may partly depend on internal noise and where internal noise is hypothesized to occur during the concurrent vowel identification process.

Effects of language experience on the discrimination of the Portuguese palatal lateral by nonnative listeners.

ABSTRACT The purpose of this study was to investigate (1) whether manner or place takes precedence over the other during a phonological category discrimination task and (2) whether this pattern of precedence persists during the early stages of acquisition of the L2. In doing so, we investigated the Portuguese palatal lateral approximant /ʎ/ since it differs from English /l/ only by the place of articulation, and from English /j/ only by the manner of articulation. Our results indicate that monolinguals’ perception of the non-native sound is dominated by manner while Portuguese learners show a different pattern of results. The results are interpreted as being consistent with evidence suggesting that manner may be neurophysiologically dominant over place of articulation. The study adds further details to the literature on the effects of experience on language acquisition, and has significant clinical implications for bilingualism in general, and foreign accent training, in particular.

Auditory and visual localization accuracy in young children and adults

OBJECTIVEnThis study aimed to measure and compare sound and light source localization ability in young children and adults who have normal hearing and normal/corrected vision in order to determine the extent to which age, type of stimuli, and stimulus order affects sound localization accuracy.nnnMETHODSnTwo experiments were conducted. The first involved a group of adults only. The second involved a group of 30 children aged 3 to 5 years. Testing occurred in a sound-treated booth containing a semi-circular array of 15 loudspeakers set at 10° intervals from -70° to 70° azimuth. Each loudspeaker had a tiny light bulb and a small picture fastened underneath. Seven of the loudspeakers were used to randomly test sound and light source identification. The sound stimulus was the word baseball. The light stimulus was a flashing of a light bulb triggered by the digital signal of the word baseball. Each participant was asked to face 0° azimuth, and identify the location of the test stimulus upon presentation. Adults used a computer mouse to click on an icon; children responded by verbally naming or walking toward the picture underneath the corresponding loudspeaker or light. A mixed experimental design using repeated measures was used to determine the effect of age and stimulus type on localization accuracy in children and adults. A mixed experimental design was used to compare the effect of stimulus order (light first/last) and varying or fixed intensity sound on localization accuracy in children and adults.nnnRESULTSnLocalization accuracy was significantly better for light stimuli than sound stimuli for children and adults. Children, compared to adults, showed significantly greater localization errors for audition. Three-year-old children had significantly greater sound localization errors compared to 4- and 5-year olds. Adults performed better on the sound localization task when the light localization task occurred first.nnnCONCLUSIONSnYoung children can understand and attend to localization tasks, but show poorer localization accuracy than adults in sound localization. This may be a reflection of differences in sensory modality development and/or central processes in young children, compared to adults.

Speech perception in children with cochlear implants for continua varying in formant transition duration

Abstract Purpose: To examine the developmental course of labial and alveolar manner of articulation contrasts, and to determine how that course may be different for typically developing (TD) children with cochlear implants (CI). Method: Eight young adults, eight TD 5–8 year-old children, and seven 5–8 year-old children with CIs participated. Labial /ba/–/wa/ and alveolar /da/–/ja/ continua stimuli were presented, with each continuum consisting of nine synthetic stimuli varying in F2 and F3 transition duration. Participants were asked to label the stimuli as either a stop or glide, and responses were analysed for phonetic boundaries and slopes. Result: For the /ba/–/wa/ contrast, children with CIs required longer transition durations compared to TD children or adults to cross from one phoneme category to another. The children with CIs demonstrated less confidence in labelling the stimuli (i.e. less steep slopes) than the TD children or the adults. For the /da/–/ja/ contrast, the children with CIs showed less steep slope values than adults. Conclusion: These results suggest that there are differences in the way TD children and children with CIs develop and maintain phonetic categories, perhaps differences in phonetic representation or in linking acoustic and phonetic representations.

Relations between speech production, speech perception, and spelling in children with complex communication needs: a preliminary examination

ABSTRACT Purpose: To determine the influence of speech production and speech perception upon spelling abilities in children with complex communication needs (CCN). Methods: Eight children (3 females, 5 males) with cerebral palsy, who did and did not use augmentative and alternative communication (AAC), were recruited to participate. The participants ranged in age from 5 years, 8 months to 11 years, 5 months (Mu2009=u20098 years, 3 months). The children were assessed using clinical tests of speech production (or intelligibility), standardized tests of spelling and receptive vocabulary, and two experimental tasks focusing on spelling generation and spelling identification using pseudo-words matched on phonotactic probability. Results: Using Spearmans correlation, significant relationships were found between the number of pseudo-words spelled and identified correctly. Further examination using a Wilcoxon Signed-Ranks test revealed a significant difference between list presentation type for the percentage of correctly spelled pseudo-words during the spelling generation task, but not for percentage of correctly identified words in the spelling identification task. A significantly greater percentage of consonant and vowel sounds were produced during the spelling generation task when individual sounds of the words were provided; however, there was no difference in performance during the identification task. Conclusions: Results suggest that speech perception has a strong influence than speech production in the development of spelling skills for children with CCN who do and do not use AAC. Further research is required on how to best teach spelling while taking advantage of perceptual abilities.

Vowel Perception in Listeners With Normal Hearing and in Listeners With Hearing Loss: A Preliminary Study

Objectives To determine the influence of hearing loss on perception of vowel slices. Methods Fourteen listeners aged 20-27 participated; ten (6 males) had hearing within normal limits and four (3 males) had moderate-severe sensorineural hearing loss (SNHL). Stimuli were six naturally-produced words consisting of the vowels /i a u æ ɛ ʌ/ in a /b V b/ context. Each word was presented as a whole and in eight slices: the initial transition, one half and one fourth of initial transition, full central vowel, one-half central vowel, ending transition, one half and one fourth of ending transition. Each of the 54 stimuli was presented 10 times at 70 dB SPL (sound press level); listeners were asked to identify the word. Stimuli were shaped using signal processing software for the listeners with SNHL to mimic gain provided by an appropriately-fitting hearing aid. Results Listeners with SNHL had a steeper rate of decreasing vowel identification with decreasing slice duration as compared to listeners with normal hearing, and the listeners with SNHL showed different patterns of vowel identification across vowels when compared to listeners with normal hearing. Conclusion Abnormal temporal integration is likely affecting vowel identification for listeners with SNHL, which in turn affects vowel internal representation at different levels of the auditory system.

Effects of sentence context on phonemic categorization of natural and synthetic consonant-vowel tokens.

The purpose was to assess if phonemic categorization in sentential context is best explained by autonomous feedforward processing or by top-down feedback processing that affects phonemic representation. 11 listeners with normal hearing, ages 20–50 years, were asked to label consonants in /pi/ – /ti/ consonant-vowel (CV) stimuli in 9-step continua. One continuum was derived from natural tokens and the other was synthetically generated. The CV stimuli were presented in isolation and in three sentential contexts: a neutral context, a context favoring /p/, and a context favoring /t/. For both natural and synthetic stimuli, the isolated and neutral context sentences yielded significantly more /t/ responses than sentence contexts primed for either /p/ or /t/. No other conditions were significantly different. Results did not show easily explainable semantic context effects. Instead, data clustering was more readily explained by top-down feedback processing affecting phonemic representation.

Weighting of Static and Transition Cues in Voiceless Fricatives and Stops in Children Wearing Cochlear Implants

Objectives To determine how normal-hearing adults (NHA), normal-hearing children (NHC) and children wearing cochlear implants (CI) differ in the perceptual weight given cues for fricative consonants (having a comparatively long static cue and short transition cue) versus stop consonants (having a comparatively short static cue and long transition cue). Methods Ten NHA, eleven 5- to 8-year-old NHC and eight 5- to 8-year-old children wearing CI were participated. Fricative /su/-/∫u/ and stop /pu/-/tu/continua were constructed by varying the fricative/burst cue and the F2 onset transition cue. A quantitative method of analysis (analysis of variance model) was used to determine cue weighting and measure cue interaction within groups. Results For the fricative consonant, all groups gave more weight to the frication spectral cue than to the formant transition. For the voiceless stop consonant, all groups gave more weight to the transition cue than to the burst cue. The CI group showed similar cue weighting strategies to age-matched NHC, but integration of cues by the CI group was not significant. Conclusion All groups favored the longer-duration cue in both continua to make phonemic judgments. Additionally, developmental patterns across groups were evident. Results of the current study may be used to guide development of CI devices and in efforts to improve speech and language of children wearing CIs.