Categorical Perception Deficit Research Articles

Categorical Perception of Mandarin Chinese Tones 1-2 and Tones 1-4: Effects of Aging and Signal Duration.

The purpose of this study was to investigate the aging effect on the categorical perception of Mandarin Chinese tones with varied fundamental frequency (F0) contours and signal duration. Both younger and older native Chinese listeners with normal hearing were recruited in 2 experiments: tone identification and tone discrimination on a series of stimuli with the F0 contour systematically varying from the flat tone to the rising-falling tones. Apart from F0 contour, tone duration was manipulated at 3 levels: 100, 200, and 400 ms. Results suggested that, compared with younger listeners, older listeners performed with shallower slope in the identification function and smaller peakedness in the discrimination function, particularly for Tones 1 and 2, whereas for Tones 1 and 4, comparable categorical perception was found between younger and older listeners. The current study suggested that longer duration facilitated categorical perception in the flat-rising tones for the older listeners. Such an aging effect was not found with the flat-falling tones, suggesting that the aging-related deficit in categorical perception might relate to different tone types. Aging resulted in less categoricality of Mandarin tone perception for the flat-rising tones with short duration like 100 ms, possibly due to the aging-related decline in temporal processing.

Speech-specific categorical perception deficit in autism: An Event-Related Potential study of lexical tone processing in Mandarin-speaking children

Recent studies reveal that tonal language speakers with autism have enhanced neural sensitivity to pitch changes in nonspeech stimuli but not to lexical tone contrasts in their native language. The present ERP study investigated whether the distinct pitch processing pattern for speech and nonspeech stimuli in autism was due to a speech-specific deficit in categorical perception of lexical tones. A passive oddball paradigm was adopted to examine two groups (16 in the autism group and 15 in the control group) of Chinese children’s Mismatch Responses (MMRs) to equivalent pitch deviations representing within-category and between-category differences in speech and nonspeech contexts. To further examine group-level differences in the MMRs to categorical perception of speech/nonspeech stimuli or lack thereof, neural oscillatory activities at the single trial level were further calculated with the inter-trial phase coherence (ITPC) measure for the theta and beta frequency bands. The MMR and ITPC data from the children with autism showed evidence for lack of categorical perception in the lexical tone condition. In view of the important role of lexical tones in acquiring a tonal language, the results point to the necessity of early intervention for the individuals with autism who show such a speech-specific categorical perception deficit.

Relationships between Categorical Perception of Phonemes, Phoneme Awareness, and Visual Attention Span in Developmental Dyslexia.

We tested the hypothesis that the categorical perception deficit of speech sounds in developmental dyslexia is related to phoneme awareness skills, whereas a visual attention (VA) span deficit constitutes an independent deficit. Phoneme awareness tasks, VA span tasks and categorical perception tasks of phoneme identification and discrimination using a d/t voicing continuum were administered to 63 dyslexic children and 63 control children matched on chronological age. Results showed significant differences in categorical perception between the dyslexic and control children. Significant correlations were found between categorical perception skills, phoneme awareness and reading. Although VA span correlated with reading, no significant correlations were found between either categorical perception or phoneme awareness and VA span. Mediation analyses performed on the whole dyslexic sample suggested that the effect of categorical perception on reading might be mediated by phoneme awareness. This relationship was independent of the participants’ VA span abilities. Two groups of dyslexic children with a single phoneme awareness or a single VA span deficit were then identified. The phonologically impaired group showed lower categorical perception skills than the control group but categorical perception was similar in the VA span impaired dyslexic and control children. The overall findings suggest that the link between categorical perception, phoneme awareness and reading is independent from VA span skills. These findings provide new insights on the heterogeneity of developmental dyslexia. They suggest that phonological processes and VA span independently affect reading acquisition.

The Categorical Perception Deficit in Dyslexia: A Meta-Analysis

Speech perception in dyslexia is characterized by a categorical perception (CP) deficit, demonstrated by weaker discrimination of acoustic differences between phonemic categories in conjunction with better discrimination of acoustic differences within phonemic categories. We performed a meta-analysis of studies that examined the reliability of the CP deficit in dyslexia. The results show a reliable CP deficit in individuals with dyslexia compared to both chronological-age and reading-level controls. The CP deficit is stronger for discrimination than for identification, suggesting that the latter may only reveal between-category differences that do not fully reflect the CP deficit. The implications of these findings for the allophonic theory of dyslexia are discussed.

Universality of categorical perception deficit in developmental dyslexia: an investigation of Mandarin Chinese tones

While previous studies have shown that children affected by dyslexia exhibit a deficit in categorical perception of segmental features in alphabetic languages, it remains unclear whether the categorical perception deficit generalizes to nonalphabetic languages at the suprasegmental level. In this study, we investigated the occurrence of categorical perception deficit in Mandarin lexical tones in Chinese children with dyslexia. Both behavioral and electrophysiological measures were taken to compare Chinese dyslexic children with age-matched controls. Auditory event-related potentials were collected with a passive listening oddball paradigm. Behavioral data showed that dyslexic children perceived lexical tone contrasts less categorically and less precisely than age-matched controls. Consistent with the behavioral data, the across-category tone contrast elicited larger mismatch negativity than the within-category distinction in the left hemisphere for the age-matched controls but not for the dyslexic children. The behavioral and electrophysiological results demonstrate impaired categorical perception of lexical tones in Chinese children with dyslexia. Our findings support the hypothesis that children affected by dyslexia have a general deficit in categorical perception of speech, which generalizes to nonalphabetic languages at the suprasegmental level.

Discrimination of speech sounds by children with dyslexia: Comparisons with chronological age and reading level controls

Previous studies have shown that children suffering from developmental dyslexia have a deficit in categorical perception of speech sounds. The aim of the current study was to better understand the nature of this categorical perception deficit. In this study, categorical perception skills of children with dyslexia were compared with those of chronological age and reading level controls. Children identified and discriminated /do–to/ syllables along a voice onset time (VOT) continuum. Results showed that children with dyslexia discriminated among phonemically contrastive pairs less accurately than did chronological age and reading level controls and also showed higher sensitivity in the discrimination of allophonic contrasts. These results suggest that children with dyslexia perceive speech with allophonic units rather than phonemic units. The origin of allophonic perception in the course of perceptual development and its implication for reading acquisition are discussed.

Reading & writing

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Categorical perception of speech sounds and dyslexia

Several studies indicate that dyslexics have a deficit in the categorical perception (CP) of phonemes when listening to speech. After reviewing data supporting the reliability of the CP deficit, we examine its possible site in the framework of a three-stage model of speech perception (auditory, phonetic and phonological). Different sources of evidence suggest that the deficit has a speech specific component. Further, the speech perception deficit appears to be phonological in nature insofar as dyslexics appear to be better than control subjects in discriminating allophonic distinctions, i.e. phonetic distinctions irrelevant for lexical processing in their language. Such sensitivity to allophonic variations in dyslexics might arise from a weakness in phonological couplings between phonetic features during perceptual development, which, in turn, can have specific implications for the build up of grapheme-phoneme correspondences. It may explain why dyslexics encounter significant problems in phonologically-demanding tasks like reading without experiencing similar difficulties in speech perception.

Perceptual discrimination of speech sounds in developmental dyslexia.

Experiments previously reported in the literature suggest that people with dyslexia have a deficit in categorical perception. However, it is still unclear whether the deficit is specific to the perception of speech sounds or whether it more generally affects auditory function. In order to investigate the relationship between categorical perception and dyslexia, as well as the nature of this categorization deficit, speech specific or not, the discrimination responses of children who have dyslexia and those of average readers to sinewave analogues of speech sounds were compared. These analogues were presented in two different conditions, either as nonspeech whistles or as speech sounds. Results showed that children with dyslexia are less categorical than average readers in the speech condition, mainly because they are better at discriminating acoustic differences between stimuli belonging to the same category. In the nonspeech condition, discrimination was also better for children with dyslexia, but differences in categorical perception were less clear-cut. Further, the location of the categorical boundary on the stimulus continuum differed between speech and nonspeech conditions. As a whole, this study shows that categorical deficit in children with dyslexia results primarily from an increased perceptibility of within-category differences and that it has a speech-specific component. These findings may have profound implications for learning and re-education.

Impaired categorical perception of synthetic speech sounds in schizophrenia

Background: Simple speech sounds such as /ba/ and /da/ differ in the frequency composition of their underlying formants. Normal volunteers asked to identify intermediate phonemes along the /ba/ to /da/ continuum abruptly switch from perceiving “ba” to perceiving “da”. The present study investigates precision of phonemic processing in schizophrenia. Methods: Categorical perception of speech sounds was evaluated in 15 schizophrenic and 14 control subjects, using a forced-choice phonemic discrimination paradigm. Results: Patients and controls were equally able to recognize endpoint forms of both phonemes, but differed significantly in their perception of intermediate forms near the center of the continuum. Patients also showed a significantly shallower response curve, suggesting an impairment in boundary definition. Despite their impairment in categorical perception, schizophrenic subjects showed normal adaptation of response when test stimuli were preceded by a series of /ba/ or /da/ stimuli from the endpoints of the continuum. Conclusions: The present results suggest that precision of phonemic processing is impaired in schizophrenia. This categorical perception deficit may represent upward generalization of impaired memory-dependent acoustic processing. Deficits in the precision of cortical processing may contribute significantly to cognitive dysfunction in schizophrenia.