Speech Contrast Research Articles

A modification of play audiometry to assess speech discrimination ability in severe-profoundly deaf 2- to 4-year-old children.

The aim was to develop an assessment procedure that was independent of language and speech production ability, to test speech feature discrimination in severe-profoundly deaf children 2 to 4 yr of age. The procedure being trialed was adapted from existing procedures. The child was required to respond with a game-like motor response to a "change" in a speech stimulus that was being presented repeatedly through a speaker. The change occurred at randomly determined times, and false alarm responses were measured during the waiting periods (while the child waited for the change). Two- to four-yr-old normally hearing children and hearing-impaired children using hearing aids and a group of 4-yr-old hearing-impaired children using cochlear implants were assessed on the task. More than 82% of the 3- and 4-yr-old normally hearing and hearing-impaired children were able to complete the testing for the eight speech sound contrasts within three 20 minute sessions. Fifty percent of the 2-yr-old normally hearing and hearing-impaired children were able to condition and complete the task. All of the normally hearing children who completed the task successfully discriminated all speech sound contrasts. The performance of the hearing-impaired children using hearing aids was influenced by the degree of hearing loss and the type of speech contrast being tested. Similarly, the average performance of the children using cochlear implants was better for easier contrasts such as /ba/bi/ with contrasting vowel formant cues. This procedure has potential for use as a reliable clinical and research tool for assessing the development of auditory discrimination ability in 2- to 4-yr-old severe-profoundly deaf children.

Cognitive evoked potentials to speech and tonal stimuli in children with implants

We investigated late and cognitive (mismatch negativity, P300) auditory potentials in 14 children with cochlear implants between the ages of 4 and 12 years. Length of cochlear implant use ranged from 7 to 84 months. Three types of stimulus contrasts were used: (1) a loudness contrast consisting of a 1500 Hz tone burst presented at 75 (standard) and 90 dB sound pressure level (deviant); (2) a frequency contrast consisting of a 1500 Hz tone burst (standard) and a 3000 Hz tone burst (deviant) presented at 80 dB sound pressure level; and (3) a speech contrast consisting of “heed” (standard) and “who’d” (deviant) delivered with a roving loudness paradigm involving a randomized variation of the levels of the standard and deviant stimuli. Latencies and amplitudes of components N1, P2, N2, and P3 and a mismatch negativity were measured. Overall, there were very few missing or unidentifiable components. P3 and mismatch negativity components were identified for all subjects and all stimuli. The latencies of most components were affected by stimulus type. There was a trend for longer latencies for the speech contrast compared with the loudness or frequency contrasts. This may be a reflection of the increased processing time required for the speech stimuli because of its higher complexity. There were several significant correlations between speech recognition and cognitive evoked potential latencies. These results indicate that the clinical use of cognitive evoked potentials in children with cochlear implants is feasible and informative. (Otolaryngol Head Neck Surg 1997;117:161-9.)

Testing the importance of talker variability in non-native speech contrast training

In contrast to results of training with stimuli produced by 5 talkers, Lively et al. [ 1242–1255 (1993)] reported that Japanese adults trained to perceive English /r/ and /l/ with stimuli produced by a single talker failed to improve from pretest to post-test, or to generalize to novel stimuli. That study was extended by training 5 groups of subjects each with a different talker, and by examining the retention of learning after 3 and 6 months. The previous results were partially replicated: Although all subjects showed significant learning during training, subjects in 3 of the 5 groups did not show significant improvement in a pretest–post-test comparison, did not generalize well to new stimuli, and did not show good retention in 3- and 6-month follow-up tests. Subjects in two of the five groups improved significantly from pretest to post-test, generalized well to new stimuli, and showed retention comparable to that of subjects trained with multiple talkers. The results indicate that while multiple-talker training leads to consistently good results, training with stimuli produced by only one talker may fail to promote generalization to new stimuli and talkers under certain conditions.

A comparison of speech discrimination with cochlear implants and tactile aids

This study investigates patterns of speech discrimination in profoundly hearing-impaired children who have received cochlear implants or tactile aids. The change/no change procedure was used to assess speech discrimination in these children. Three groups of subjects were tested: the first group used 3M/House single-channel cochlear implants; the second group used Nucleus 22-channel cochlear implants; and the third group used two-channel Tactaid II+ vibrotactile aids. Nine contrasts were constructed that assessed discrimination of suprasegmental and segmental speech features. Subjects were presented with stimulus trials in which stimuli changed during the trial or in which stimuli remained the same. Hits, misses, false alarms, and correct rejections were tallied and d' values were calculated for individual subjects for each contrast. Results indicated that different patterns of speech discrimination are provided by the three sensory prosthetic devices. For all contrasts, mean discrimination performance with the Nucleus device was better than that observed for the other two devices, despite the shorter duration of subject experience with this cochlear implant. In addition, interactions between device and speech contrast were not observed. Examination of individual subject performance revealed that each device group had a distribution of good to poor performers. The results suggest that the change/no change procedure is able to provide information regarding speech perception through sensory prosthetic devices despite existing differences in vocabulary and language skills of subjects.

On enhancement of spectral contrast in speech for hearing-impaired listeners

A digital processing method is described for altering spectral contrast (the difference in amplitude between spectral peaks and valleys) in natural utterances. Speech processed with programs implementing the contrast alteration procedure was presented to listeners with moderate to severe sensorineural hearing loss. The task was a three alternative (/b/,/d/, or /g/) stop consonant identification task for consonants at a fixed location in short nonsense utterances. Overall, tokens with enhanced contrast showed moderate gains in percentage correct stop consonant identification when compared to unaltered tokens. Conversely, reducing spectral contrast generally reduced percent correct stop consonant identification. Contrast alteration effects were inconsistent for utterances containing /d/. The observed contrast effects also interacted with token intelligibility.

Computer system for quantitative evaluation of an electrotactile vocoder for artificial hearing

A computer-controlled experimental electrotactile vocoder system is designed to evaluate quantitatively the transmission of speech information and to test various design options for tactual vocoders. The system is composed of a digital speech synthesizer, a digital vocoder, a computer-driven electrotactile display, and an adaptive controller for psychophysical experimentation. Samples of continua representing speech contrast types occurring in natural languages are synthesized by systematically manipulating selected subphonemic features. The synthesized speech stimuli are processed using a programmable vocoder and presented to the skin with an electrotactile display belt worn on the abdomen. Transmission of significant speech parameters is quantitatively evaluated using adaptive psychophysical techniques and labeling tests. The system is used to assess the potential of speech transmission through the skin and to evaluate different vocoder configurations and processing techniques for tactual vocoders to be used as artificial hearing devices by the deaf.

Trading relations in the perception of speech by 5-year-old children

Five-year-old children were tested for perceptual trading relations between a temporal cue (silence duration) and a spectral cue (F 1 onset frequency) for the “say-stay” distinction. Identification functions were obtained for two synthetic “say-stay” continua, each containing systematic variations in the amount of silence following the /s/ noise. In one continuum, the vocalic portion had a lower F 1 onset than in the other continuum. Children showed a smaller trading relation than has been found with adults. They did not differ from adults, however, in their perception of an “ay-day” continuum formed by varying F 1 onset frequency only. The results of a discrimination task in which the two acoustic cues were made to “cooperate” or “conflict” phonetically supported the notion of perceptual equivalence of the temporal and spectral cues along a single phonetic dimension. The results indicate that young children, like adults, perceptually integrate multiple cues to a speech contrast in a phonetically relevant manner, but that they may not give the same perceptual weights to the various cues as do adults.

Auditory perception of speech contrasts by subjects with sensorineural hearing loss.

The goal of these studies was to find out how much of the acoustical information in amplified speech is accessible to children with varying degrees of sensorineural hearing loss. Context-varying, forced-choice tests of speech perception were presented, without feedback on performance, to orally trained subjects with better ear, three-frequency average hearing losses in the range 55-123 dB HL. As expected, average performance fell with increasing hearing loss. The values of hearing loss at which scores fell to 50% (after correction for chance) were 75 dB HL for consonant place; 85 dB HL for initial consonant voicing; 90 dB HL for initial consonant continuance; 100 dB HL for vowel place (front-back); 105 dB HL for talker sex; 115 dB HL for syllable pattern; and in excess of 115 dB HL for vowel height. Performance on the speech contrast tests was significantly correlated with the intelligibility of the subjects' own speech and with the open-set recognition of phonemes in monosyllabic words, even when pure-tone threshold was held constant.

Cross-language speech perception: Evidence for perceptual reorganization during the first year of life

Previous work in which we compared English infants, English adults, and Hindi adults on their ability to discriminate two pairs of Hindi (non-English) speech contrasts has indicated that infants discriminate speech sounds according to phonetic category without prior specific language experience (Werker, Gilbert, Humphrey, & Tees, 1981), whereas adults and children as young as age 4 (Werker & Tees, in press), may lose this ability as a function of age and or linguistic experience. The present work was designed to (a) determine the generalizability of such a decline by comparing adult English, adult Salish, and English infant subjects on their perception of a new non-English (Salish) speech contrast, and (b) delineate the time course of the developmental decline in this ability. The results of these experiments replicate our original findings by showing that infants can discriminate non-native speech contrasts without relevant experience, and that there is a decline in this ability during ontogeny. Furthermore, data from both cross-sectional and longitudinal studies shows that this decline occurs within the first year of life, and that it is a function of specific language experience. © 2002 Published by Elsevier Science Inc.

The Discrimination of Foreign Speech Contrasts by Infants and Adults

TREHUB, SANDRA E. The Discrimination of Foreign Speech Contrasts by Infants and Adults. CHILD DEVELOPMENT, 1976, 47, 466-472. Infants 5-17 weeks of age were presented with foreign speech sounds which were contingent upon their nonutritive sucking. When the infants met a specified criterion of sucking decrement, a contrasting sound was substituted. Significant differences in response recovery for experimental versus control (no sound change) subjects were found for the contrast pairs [pa]-[p-a] and [za]-[ia]. Adults were presented with a comparable discrimination task for the foreign contrasts [za]-[ia] and the English contrasts [li]-[ri]. It was found that adults achieved perfect accuracy with English contrasts but readily confused the foreign contrasts. The implications of these results for theories of perceptual development are discussed.

Surface contrast in children's speech

Surface contrast in children's speech