Evaluating the Sources and Functions of Gradiency in Phoneme Categorization: An Individual Differences Approach

During spoken language comprehension listeners transform continuous acoustic cues into categories (e.g., /b/ and /p/). While long-standing research suggests that phonetic categories are activated in a gradient way, there are also clear individual differences in that more gradient categorization has been linked to various communication impairments such as dyslexia and specific language impairments (Joanisse, Manis, Keating, & Seidenberg, 2000; López-Zamora, Luque, Álvarez, & Cobos, 2012; Serniclaes, Van Heghe, Mousty, Carré, & Sprenger-Charolles, 2004; Werker & Tees, 1987). Crucially, most studies have used 2-alternative forced choice (2AFC) tasks to measure the sharpness of between-category boundaries. Here we propose an alternative paradigm that allows us to measure categorization gradiency in a more direct way. Furthermore, we follow an individual differences approach to (a) link this measure of gradiency to multiple cue integration, (b) explore its relationship to a set of other cognitive processes, and (c) evaluate its role in individuals’ ability to perceive speech in noise. Our results provide validation for this new method of assessing phoneme categorization gradiency and offer preliminary insights into how different aspects of speech perception may be linked to each other and to more general cognitive processes.

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title: Noncategorical perception of stop consonants differing in VOT.
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title: Linear Coding of Voice Onset Time
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title: The effect of subphonetic differences on lexical access
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title: Effects of subphonetic and syllable structure variation on word recognition
abstract: This study explored whether natural acoustic variations as exemplified by either subphonetic changes or syllable structure changes affect word recognition processes. Subphonetic variations were realized by differences in the voice-onset time (VOT) value of initial voiceless stop consonants, and syllable structure variations were realized by vowel deletion in initial unstressed syllables in multisyllable words. An auditory identity priming paradigm was used to determine whether the amount of facilitation obtained to a target stimulus in a lexical decision task was affected by the presence of these acoustic variations in a prime stimulus. Results revealed different patterns for the two types of variability as a function of lexical status. In the case of subphonetic variations, shortening of VOT resulted in reduced facilitation for words but not for nonwords, whereas in the case of syllable structure variation, vowel deletion in an unstressed syllable resulted in reduced facilitation for nonwords and increased facilitation for words. These findings indicate that subphonetic variability interferes with word recognition, whereas syllable structure variability does not, and that this effect is independent of the magnitude of the acoustic difference between a citation form and its variant. Furthermore, the results suggest that the lexical status of the target item plays a crucial role in the processing of both types of variability. Results are considered in relation to current models of word recognition.

title: Echoes of echoes? An episodic theory of lexical access.
abstract: In this article the author proposes an episodic theory of spoken word representation, perception, and production. By most theories, idiosyncratic aspects of speech (voice details, ambient noise, etc.) are considered noise and are filtered in perception. However, episodic theories suggest that perceptual details are stored in memory and are integral to later perception. In this research the author tested an episodic model (MINERVA 2; D. L. Hintzman, 1986) against speech production data from a word-shadowing task. The model predicted the shadowing-response-time patterns, and it correctly predicted a tendency for shadowers to spontaneously imitate the acoustic patterns of words and nonwords. It also correctly predicted imitation strength as a function of "abstract" stimulus properties, such as word frequency. Taken together, the data and theory suggest that detailed episodes constitute the basic substrate of the mental lexicon.

title: A unified account of categorical effects in phonetic perception
abstract: Categorical effects are found across speech sound categories, with the degree of these effects ranging from extremely strong categorical perception in consonants to nearly continuous perception in vowels. We show that both strong and weak categorical effects can be captured by a unified model. We treat speech perception as a statistical inference problem, assuming that listeners use their knowledge of categories as well as the acoustics of the signal to infer the intended productions of the speaker. Simulations show that the model provides close fits to empirical data, unifying past findings of categorical effects in consonants and vowels and capturing differences in the degree of categorical effects through a single parameter.

title: Assimilation and Anticipation in Continuous Spoken Word Recognition
abstract: English coronal place assimilation is one of many productive phonological processes that change the phonological form of words. It may, for example, cause speakers to pronounce green as something approximating [grin] or [grim] in different contexts. The present work examines how listeners recognize words that have undergone this modification. Current accounts are broadly differentiated by two issues: (1) whether listeners generally recognize words that have undergone word-final, single-feature modification, and (2) how context effects in the perception of assimilated speech are interpreted. Experiment 1 employs form priming to demonstrate that listeners tolerate single-feature mismatch resulting from both phonologically plausible and phonologically implausible word form modification when recognizing words heard in context. Experiments 2 and 3 employ phoneme monitoring and negative rhyme priming paradigms, respectively, to demonstrate that listeners use assimilation to anticipate upcoming context. Evidence for anticipation is contrasted with claims that listeners use context to regressively infer the underlying form of place-assimilated segments.

title: Anticipatory coarticulation facilitates word recognition in toddlers
abstract: Children learn from their environments and their caregivers. To capitalize on learning opportunities, young children have to recognize familiar words efficiently by integrating contextual cues across word boundaries. Previous research has shown that adults can use phonetic cues from anticipatory coarticulation during word recognition. We asked whether 18-24 month-olds (n=29) used coarticulatory cues on the word "the" when recognizing the following noun. We performed a looking-while-listening eyetracking experiment to examine word recognition in neutral vs. facilitating coarticulatory conditions. Participants looked to the target image significantly sooner when the determiner contained facilitating coarticulatory cues. These results provide the first evidence that novice word-learners can take advantage of anticipatory sub-phonemic cues during word recognition.

title: Immediate effects of anticipatory coarticulation in spoken-word recognition.
abstract: Two visual-world experiments examined listeners' use of pre word-onset anticipatory coarticulation in spoken-word recognition. Experiment 1 established the shortest lag with which information in the speech signal influences eye-movement control, using stimuli such as "The … ladder is the target". With a neutral token of the definite article preceding the target word, saccades to the referent were not more likely than saccades to an unrelated distractor until 200-240 ms after the onset of the target word. In Experiment 2, utterances contained definite articles which contained natural anticipatory coarticulation pertaining to the onset of the target word (" The ladder … is the target"). A simple Gaussian classifier was able to predict the initial sound of the upcoming target word from formant information from the first few pitch periods of the article's vowel. With these stimuli, effects of speech on eye-movement control began about 70 ms earlier than in Experiment 1, suggesting rapid use of anticipatory coarticulation. The results are interpreted as support for "data explanation" approaches to spoken-word recognition. Methodological implications for visual-world studies are also discussed.

title: Recognition of vowels from information in fricatives: perceptual evidence of fricative-vowel coarticulation.
abstract: Four studies investigated the perceptual effects of spectral variations in fricatives produced in different vowel contexts. The alveolar and palatal fricatives, [s, z, integral of, 3], were produced by two talkers in the context of the vowels [a, i, u], generating 12 fricative-vowel combinations. A computer-controlled editing procedure was used to excise fricative segments of 150-ms duration, as measured back from vowel onset. These excised segments were used as test stimuli in the four experiments. In the first experiment, fricative identification was highly accurate, especially for segments produced in the [a] context. The results of the subsequent three vowel identification experiments, revealed that the high vowels [i] and [u] were identified 60%--80% of the time in all fricative contexts, with the exception of [i] produced in the context of [integral of]. In contrast, identification scores for [a] were close to chance in all fricative contexts. Acoustic analyses of the stimuli revealed that the fricative segments with high vowel identification scores exhibited clear evidence of spectral changes associated with the vowels, while those segments with the highest fricative identification scores exhibited spectra most similar to fricatives produced in isolation. These results, in combination with more extensive acoustic analyses [S. D. Soli,  (1981)] are discussed in terms of variations in the articulatory compatibility of tongue movements required to produce fricative-vowel sequences.

title: On the dissociation of spectral and temporal cues to the voicing distinction in initial stop consonants.
abstract: It has been claimed that a rising first‐formant (F1) transition is an important cue to the voiced–voiceless distinction for syllable‐initial, prestressed stop consonants in English. Lisker [ (1975)] has pointed out that the acoustic manipulations suggesting a role for F1 have involved covariation of the onset frequency of F1 with the duration, and hence the frequency extent, of the F1 transition; he has argued that effects hitherto ascribed to the transition are more properly attributed to its onset. Two experiments are reported in which F1 onset frequency and F1 transition duration/extent were manipulated independently. The results confirm Lisker’s suggestion that the major effect of F1 in initial voicing contrasts is determined by its perceived frequency at the onset of voicing and show that a periodically excited F1 transition is not, per se, a positive cue to voicing. In further experiments, the relative levels and the frequencies at the onset of voicing of both F1...

title: Roles of voice onset time and F0 in stop consonant voicing perception: effects of masking noise and low-pass filtering.
abstract: The contributions of voice onset time (VOT) and fundamental frequency (F0) were evaluated for the perception of voicing in syllable-initial stop consonants in words that were low-pass filtered and/or masked by speech-shaped noise. It was expected that listeners would rely less on VOT and more on F0 in these degraded conditions.



Twenty young listeners with normal hearing identified modified natural speech tokens that varied by VOT and F0 in several conditions of low-pass filtering and masking noise. Stimuli included /b/-/p/ and /d/-/t/ continua that were presented in separate blocks. Identification results were modeled using mixed-effects logistic regression.



When speech was filtered and/or masked by noise, listeners' voicing perceptions were driven less by VOT and more by F0. Speech-shaped masking noise exerted greater effects on the /b/-/p/ contrast, while low-pass filtering exerted greater effects on the /d/-/t/ contrast, consistent with the acoustics of these contrasts.



Listeners can adjust their use of acoustic-phonetic cues in a dynamic way that is appropriate for challenging listening conditions; cues that are less influential in ideal conditions can gain priority in challenging conditions.

title: Gradient sensitivity to within-category variation in words and syllables.
abstract: Five experiments monitored eye movements in phoneme and lexical identification tasks to examine the effect of within-category subphonetic variation on the perception of stop consonants. Experiment 1 demonstrated gradient effects along voice-onset time (VOT) continua made from natural speech, replicating results with synthetic speech (B. McMurray, M. K. Tanenhaus, & R. N. Aslin, 2002). Experiments 2-5 used synthetic VOT continua to examine effects of response alternatives (2 vs. 4), task (lexical vs. phoneme decision), and type of token (word vs. consonant-vowel). A gradient effect of VOT in at least one half of the continuum was observed in all conditions. These results suggest that during online spoken word recognition, lexical competitors are activated in proportion to their continuous distance from a category boundary. This gradient processing may allow listeners to anticipate upcoming acoustic-phonetic information in the speech signal and dynamically compensate for acoustic variability.

title: The Perception of Voice Onset Time: An fMRI Investigation of Phonetic Category Structure
abstract: This study explored the neural systems underlying the perception of phonetic category structure by investigating the perception of a voice onset time (VOT) continuum in a phonetic categorization task. Stimuli consisted of five synthetic speech stimuli which ranged in VOT from 0 msec ([da]) to 40 msec (. Results from 12 subjects showed that the neural system is sensitive to VOT differences of 10 msec and that details of phonetic category structure are retained throughout the phonetic processing stream. Both the left inferior frontal gyrus (IFG) and cingulate showed graded activation as a function of category membership with increasing activation as stimuli approached the phonetic category boundary. These results are consistent with the view that the left IFG is involved in phonetic decision processes, with the extent of activation influenced by increased resources devoted to resolving phonetic category membership and/or selecting between competing phonetic categories. Activation patterns in the cingulate suggest that it is sensitive to stimulus difficulty and resolving response conflict. In contrast, activation in the posterior left middle temporal gyrus and the left angular gyrus showed modulation of activation only to the best fit of the phonetic category, suggesting that these areas are involved in mapping sound structure to its phonetic representation. The superior temporal gyrus (STG) bilaterally showed weaker sensitivity to the differences in phonetic category structure, providing further evidence that the STG is involved in the early analysis of the sensory properties of speech.

title: The cortical organization of speech processing
abstract: Despite decades of research, the functional neuroanatomy of speech processing has been difficult to characterize. A major impediment to progress may have been the failure to consider task effects when mapping speech-related processing systems. We outline a dual-stream model of speech processing that remedies this situation. In this model, a ventral stream processes speech signals for comprehension, and a dorsal stream maps acoustic speech signals to frontal lobe articulatory networks. The model assumes that the ventral stream is largely bilaterally organized — although there are important computational differences between the left- and right-hemisphere systems — and that the dorsal stream is strongly left-hemisphere dominant.

title: Noise differentially impacts phoneme representations in the auditory and speech motor systems
abstract: Contentious debate remains regarding the role of the redundant motor activation during speech perception. In this functional MRI study, multivariate pattern analysis revealed stronger multivoxel phoneme discrimination in speech motor regions than auditory cortices when the speech phonemes were moderately degraded by noise. Our findings provide neuroimaging evidence for the sensorimotor integration account. Preserved phoneme discrimination in speech motor areas may compensate for loss of specificity in noise-impoverished speech representations, which aids speech perception under adverse listening conditions. Although it is well accepted that the speech motor system (SMS) is activated during speech perception, the functional role of this activation remains unclear. Here we test the hypothesis that the redundant motor activation contributes to categorical speech perception under adverse listening conditions. In this functional magnetic resonance imaging study, participants identified one of four phoneme tokens (/ba/, /ma/, /da/, or /ta/) under one of six signal-to-noise ratio (SNR) levels (–12, –9, –6, –2, 8 dB, and no noise). Univariate and multivariate pattern analyses were used to determine the role of the SMS during perception of noise-impoverished phonemes. Results revealed a negative correlation between neural activity and perceptual accuracy in the left ventral premotor cortex and Broca’s area. More importantly, multivoxel patterns of activity in the left ventral premotor cortex and Broca’s area exhibited effective phoneme categorization when SNR ≥ –6 dB. This is in sharp contrast with phoneme discriminability in bilateral auditory cortices and sensorimotor interface areas (e.g., left posterior superior temporal gyrus), which was reliable only when the noise was extremely weak (SNR > 8 dB). Our findings provide strong neuroimaging evidence for a greater robustness of the SMS than auditory regions for categorical speech perception in noise. Under adverse listening conditions, better discriminative activity in the SMS may compensate for loss of specificity in the auditory system via sensorimotor integration.

title: Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients.
abstract: The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.

title: Children with specific language impairments perceive speech most categorically when tokens are natural and meaningful.
abstract: To examine perceptual deficits as a potential underlying cause of specific language impairments (SLI).



Twenty-one children with SLI (8;7-11;11 [years;months]) and 21 age-matched controls participated in categorical perception tasks using four series of syllables for which perceived syllable-initial voicing varied. Series were either words or abstract nonword syllables and either synthesized or high-quality edited natural utterances. Children identified and discriminated (a) digitally edited tokens of naturally spoken "bowl"-"pole", (b) synthesized renditions of "bowl"-"pole", (c) natural "ba"-"pa", and (d) synthetic "ba"-"pa".



Identification crossover locations were the same for both groups of children, but there was modestly less accuracy on unambiguous endpoints for children with SLI. Planned comparisons revealed these effects to be limited to synthesized speech. Children with SLI showed overall reduced discrimination, but these effects were limited to abstract nonword syllables.



Overall, children with SLI perceived naturally spoken real words comparably to age-matched peers but showed impaired identification and discrimination of synthetic speech and of abstract syllables. Poor performance on speech perception tasks may result from task demands and stimulus properties, not perceptual deficits.

title: Categorical speech perception deficits distinguish language and reading impairments in children.
abstract: We examined categorical speech perception in school-age children with developmental dyslexia or Specific Language Impairment (SLI), compared to age-matched and younger controls. Stimuli consisted of synthetic speech tokens in which place of articulation varied from 'b' to 'd'. Children were tested on categorization, categorization in noise, and discrimination. Phonological awareness skills were also assessed to examine whether these correlated with speech perception measures. We observed similarly good baseline categorization rates across all groups; however, when noise was added, the SLI group showed impaired categorization relative to controls, whereas dyslexic children showed an intact profile. The SLI group showed poorer than expected between-category discrimination rates, whereas this pattern was only marginal in the dyslexic group. Impaired phonological awareness profiles were observed in both the SLI and dyslexic groups; however, correlations between phonological awareness and speech perception scores were not significant. The results of the study suggest that in children with language and reading impairments, there is a significant relationship between receptive language and speech perception, there is at best a weak relationship between reading and speech perception, and indeed the relationship between phonological and speech perception deficits is highly complex.

title: Perception of formant transition cues to place of articulation in children with language impairments.
abstract: Discrimination and phonetic identification abilities of 5- to 6-year-old children with language impairments were compared to those of 4-year-olds with normally developing language and to previous findings from 5- to 6-year-olds and adults for synthetic stimuli ranging from [ba] to [da]. Results showed similar discrimination sensitivity to the second- and third-formant transition cues of stimuli by all children, with poorest sensitivity by the youngest. Phonetic categorization by children with language impairments was most different from the groups with normal language abilities, evidenced by a difference in the percent of tokens labeled as "BA" and by greater variability in labeling and in placement of phonetic category boundaries. Results support hypotheses by Gathercole and Baddeley (1990) suggesting that the phonological component of working memory may be disordered in children with language impairments. Results are also suggestive of specific difficulties with left-hemisphere processing associated with language learning rather than with problems related to sensitivity to formant transitions of the speech tokens.

title: Speech perception in severely disabled and average reading children.
abstract: ll has been hypothesized thai children with specific disabilities in reading may have subtle auditory and/or speech perception deficits. To address this question, recent investigations have focussed on whether reading disabled children show categorical speech perception. These efforts have yielded equivocal results. The present study was designed to attempt to help resolve this controversy by comparing the performance of severely disabled readers with normal readers in four speech perception tasks. Results indicated that perception was significantly less categorical among the severely disabled readers in ihrcc of the lour speech perception tasks. The possible implications of this small, but significant, difference arc discussed. KESUME II a ete suggcre que des cnlants ayant des diflicultcs a lire pouvaicnt avoir des deficits subtils d'audition ct/ou de perception du langagc. Les eludes qui se sont aftaquccs a ce problcmc ont produit des rcsultats pour le moins equivoques. L'ctudc presentee ici a tenUS dc rcsoudre cette controverse en comparant la performance d'enfants en difficultc dc lecture avee des enfants normaux dans quatre taches dc perception du langagc. Les resultats ont montrc que la perception etait significativement moins categoriquc the/, les enfants handicapes dans trois des quatre taches. Les implications de cettc difference, petite mais significative, sont discuses. The relation between speech perception and the process of reading has been outlined previously (Godfrey, Syrdal-Lasky, Millay, & Knox, 1981). Basically, in reading, the printed word has to be mapped on to the underlying phonologic representation (Liberman, 1983; Read, 1971). This process includes converting individual graphemes to phonemes and strings of graphemes to the overlapping and highly encoded (Liberman, Cooper, Shankweiler, & Studdert-Kennedy, 1967) larger linguistic units such as syllables and words. In order to make this conversion, the reader must have a stable, context-independent phonological representation available on which to map the linguistic units. Research in speech perception has shown that adults, children, and even prelinguistic infants tend to perceive speech sounds in a categorical fashion. That is, when presented with several varying naturally produced speech syllables or *We wish to thank the students, staff, and board members of the Kenneth Gordon School in New Westminster, B C and the students, staff, and school board ol'licc of the Vancouver Public Schools for their participation and cooperation in this project. Special thanks are extended to Margaret Follis, principal of the Kenneth Gordon School. Our appreciation is also extended to Dr. Alvin M. Liberman, Director, Haskins Laboratory, for making us welcome at Haskins, to Dr. Ignatious Mattingly for help synthesizing the stimuli, and to Dr. Patrice Dunn for serving as a consultant to the grant. Special thanks to Kathy Searcy for all the hours she spent collecting the data and to Margaret Arab for performing the data analyses. This research was supported by a grant from the British Columbia I lealth Care Research Foundation ( # 103(81 2)) to the authors. Address reprint requests to Janet V. Werker, Department of Psychology, The University of British Columbia, Vancouver, BC, Canada V6T IY7

title: Individual differences in language ability are related to variation in word recognition, not speech perception: evidence from eye movements.
abstract: The authors examined speech perception deficits associated with individual differences in language ability, contrasting auditory, phonological, or lexical accounts by asking whether lexical competition is differentially sensitive to fine-grained acoustic variation.



Adolescents with a range of language abilities (N = 74, including 35 impaired) participated in an experiment based on McMurray, Tanenhaus, and Aslin (2002). Participants heard tokens from six 9-step voice onset time (VOT) continua spanning 2 words (beach/peach, beak/peak, etc.) while viewing a screen containing pictures of those words and 2 unrelated objects. Participants selected the referent while eye movements to each picture were monitored as a measure of lexical activation. Fixations were examined as a function of both VOT and language ability.



Eye movements were sensitive to within-category VOT differences: As VOT approached the boundary, listeners made more fixations to the competing word. This did not interact with language ability, suggesting that language impairment is not associated with differential auditory sensitivity or phonetic categorization. Listeners with poorer language skills showed heightened competitors fixations overall, suggesting a deficit in lexical processes.



Language impairment may be better characterized by a deficit in lexical competition (inability to suppress competing words), rather than differences in phonological categorization or auditory abilities.

title: The fragile nature of the speech-perception deficit in dyslexia: Natural vs. synthetic speech
abstract: A number of studies reported that developmental dyslexics are impaired in speech perception, especially for speech signals consisting of rapid auditory transitions. These studies mostly made use of a categorical-perception task with synthetic-speech samples. In this study, we show that deficits in the perception of synthetic speech do not generalise to the perception of more naturally sounding speech, even if the same experimental paradigm is used. This contrasts with the assumption that dyslexics are impaired in the perception of rapid auditory transitions.

title: Categorical perception of speech by children with specific language impairments.
abstract: Previous research has suggested that children with specific language impairments (SLI) have deficits in basic speech perception abilities, and this may be an underlying source of their linguistic deficits. These findings have come from studies in which perception of synthetic versions of meaningless syllables was typically examined in tasks with high memory demands. In this study, 20 children with SLI (mean age = 9 years, 3 months) and 20 age-matched peers participated in a categorical perception task. Children identified and discriminated digitally edited versions of naturally spoken real words in tasks designed to minimize memory requirements. Both groups exhibited all hallmarks of categorical perception: a sharp labeling function, discontinuous discrimination performance, and discrimination predicted from identification. There were no group differences for identification data, but children with SLI showed lower peak discrimination values. Children with SLI still discriminated phonemically contrastive pairs at levels significantly better than chance, with discrimination of same-label pairs at chance. These data suggest that children with SLI perceive natural speech tokens comparably to age-matched controls when listening to words under conditions that minimize memory load. Further, poor performance on speech perception tasks may not be due to a speech perception deficit, but rather to a consequence of task demands.

title: Performance of dyslexic children on speech perception tests.
abstract: Several researchers who have compared the performance of dyslexic and normal-reading children on a variety of different tasks have suggested that dyslexic children may have subtle deficits in the phonemic analysis of spoken as well as written language. Thus it is of interest to know how children who have extraordinary difficulty learning to read can perform explicity auditory-phonetic tasks. Seventeen dyslexic children (10 years of age) and a group of 17 controls were administered tests of identification and discrimination of synthesized voiced stop consonants differing in place of articulation. These were tests of the type used to study categorical perception in adults, adapted for use with young children. Significant differences between dyslexics and controls were found in both kinds of tasks; the pattern of identification and discrimination differences suggests an inconsistency in the dyslexics' phonetic classification of auditory cues. A significant relationship was found between reading level and speech discrimination.

title: Perceptual discrimination of speech sounds in developmental dyslexia.
abstract: 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.

title: Language deficits in dyslexic children: speech perception, phonology, and morphology.
abstract: We investigated the relationship between dyslexia and three aspects of language: speech perception, phonology, and morphology. Reading and language tasks were administered to dyslexics aged 8-9 years and to two normal reader groups (age-matched and reading-level matched). Three dyslexic groups were identified: phonological dyslexics (PD), developmentally language impaired (LI), and globally delayed (delay-type dyslexics). The LI and PD groups exhibited similar patterns of reading impairment, attributed to low phonological skills. However, only the LI group showed clear speech perception deficits, suggesting that such deficits affect only a subset of dyslexics. Results also indicated phonological impairments in children whose speech perception was normal. Both the LI and the PD groups showed inflectional morphology difficulties, with the impairment being more severe in the LI group. The delay group's reading and language skills closely matched those of younger normal readers, suggesting these children had a general delay in reading and language skills, rather than a specific phonological impairment. The results are discussed in terms of models of word recognition and dyslexia.

title: Individual Differences in Categorical Perception Are Related to Sublexical/Phonological Processing in Reading
abstract: This article examines the relationship between individual differences in speech perception and sublexical/phonological processing in reading. We used an auditory phoneme identification task in which a /ba/-/pa/ syllable continuum measured sensitivity to classify participants into three performance groups: poor, medium, and good categorizers. A lexical decision task manipulated syllable and word frequency. We found that the two tasks were associated. Poor categorizers did not present the typical syllable frequency effect; however, the other groups were sensitive to phonological information to differing degrees and showed the inhibitory syllable frequency effect only for low-frequency words. These results suggest that auditory phoneme identification efficiency may be related to the sublexical processes involved in reading words.

title: Word Recognition Variability With Cochlear Implants: “Perceptual Attention” Versus “Auditory Sensitivity”
abstract: Cochlear implantation does not automatically result in robust spoken language understanding for postlingually deafened adults. Enormous outcome variability exists, related to the complexity of understanding spoken language through cochlear implants (CIs), which deliver degraded speech representations. This investigation examined variability in word recognition as explained by “perceptual attention” and “auditory sensitivity” to acoustic cues underlying speech perception.  Thirty postlingually deafened adults with CIs and 20 age-matched controls with normal hearing (NH) were tested. Participants underwent assessment of word recognition in quiet and perceptual attention (cue-weighting strategies) based on labeling tasks for two phonemic contrasts: (1) “cop”–“cob,” based on a duration cue (easily accessible through CIs) or a dynamic spectral cue (less accessible through CIs), and (2) “sa”–“sha,” based on static or dynamic spectral cues (both potentially poorly accessible through CIs). Participants were also assessed for auditory sensitivity to the speech cues underlying those labeling decisions.  Word recognition varied widely among CI users (20 to 96%), but it was generally poorer than for NH participants. Implant users and NH controls showed similar perceptual attention and auditory sensitivity to the duration cue, while CI users showed poorer attention and sensitivity to all spectral cues. Both attention and sensitivity to spectral cues predicted variability in word recognition.  For CI users, both perceptual attention and auditory sensitivity are important in word recognition. Efforts should be made to better represent spectral cues through implants, while also facilitating attention to these cues through auditory training.

title: Using speech sounds to test functional spectral resolution in listeners with cochlear implants.
abstract: In this study, spectral properties of speech sounds were used to test functional spectral resolution in people who use cochlear implants (CIs). Specifically, perception of the /ba/-/da/ contrast was tested using two spectral cues: Formant transitions (a fine-resolution cue) and spectral tilt (a coarse-resolution cue). Higher weighting of the formant cues was used as an index of better spectral cue perception. Participants included 19 CI listeners and 10 listeners with normal hearing (NH), for whom spectral resolution was explicitly controlled using a noise vocoder with variable carrier filter widths to simulate electrical current spread. Perceptual weighting of the two cues was modeled with mixed-effects logistic regression, and was found to systematically vary with spectral resolution. The use of formant cues was greatest for NH listeners for unprocessed speech, and declined in the two vocoded conditions. Compared to NH listeners, CI listeners relied less on formant transitions, and more on spectral tilt. Cue-weighting results showed moderately good correspondence with word recognition scores. The current approach to testing functional spectral resolution uses auditory cues that are known to be important for speech categorization, and can thus potentially serve as the basis upon which CI processing strategies and innovations are tested.

title: Discrimination of speech sounds by children with dyslexia: comparisons with chronological age and reading level controls.
abstract: 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.

title: Allophonic mode of speech perception in dyslexia.
abstract: Perceptual discrimination between speech sounds belonging to different phoneme categories is better than that between sounds falling within the same category. This property, known as "categorical perception," is weaker in children affected by dyslexia. Categorical perception develops from the predispositions of newborns for discriminating all potential phoneme categories in the world's languages. Predispositions that are not relevant for phoneme perception in the ambient language are usually deactivated during early childhood. However, the current study shows that dyslexic children maintain a higher sensitivity to phonemic distinctions irrelevant in their linguistic environment. This suggests that dyslexic children use an allophonic mode of speech perception that, although without straightforward consequences for oral communication, has obvious implications for the acquisition of alphabetic writing. Allophonic perception specifically affects the mapping between graphemes and phonemes, contrary to other manifestations of dyslexia, and may be a core deficit.

title: Effects of syllable-initial voicing and speaking rate on the temporal characteristics of monosyllabic words.
abstract: Two speech production experiments tested the validity of the traditional method of creating voice-onset-time (VOT) continua for perceptual studies in which the systematic increase in VOT across the continuum is accompanied by a concomitant decrease in the duration of the following vowel. In experiment 1, segmental durations were measured for matched monosyllabic words beginning with either a voiced stop (e.g., big, duck, gap) or a voiceless stop (e.g., pig, tuck, cap). Results from four talkers showed that the change from voiced to voiceless stop produced not only an increase in VOT, but also a decrease in vowel duration. However, the decrease in vowel duration was consistently less than the increase in VOT. In experiment 2, results from four new talkers replicated these findings at two rates of speech, as well as highlighted the contrasting temporal effects on vowel duration of an increase in VOT due to a change in syllable-initial voicing versus a change in speaking rate. It was concluded that the traditional method of creating VOT continua for perceptual experiments, although not perfect, approximates natural speech by capturing the basic trade-off between VOT and vowel duration in syllable-initial voiced versus voiceless stop consonants.

title: Effect of speaking rate on the perceptual structure of a phonetic category
abstract: When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener’s adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.

title: Anticipatory Eye Movements Reveal Infants' Auditory and Visual Categories.
abstract: We introduce a new paradigm for the assessment of auditory and visual categories in 6-month-old infants using a 2-alternative anticipatory eye-movement response. Infants were trained by 2 different methods to anticipate the location of a visual reinforcer at 1 of 2 spatial locations (right or left) based on the identity of 2 cuing stimuli. After a training phase, infants were presented with a series of generalization trials in which novel (untrained) stimuli served as the cue to the anticipatory eye movement. Four experiments illustrated that infants can learn the 2-choice discriminative response during training. Infants also showed anticipatory eye movements to novel stimuli, indicating sensitivity to variations along a variety of stimulus dimensions (e.g., color, shape, orientation, spatial frequency, pitch, and duration). In addition, the paradigm can be used to assess categorization in individual infants, thereby revealing the stimulus dimensions to which infants naturally attend.

title: Individual differences in categorical perception of speech: Cue weighting and executive function
abstract: This study examined individual differences in categorical perception and the use of multiple acoustic cues in the perception of the stop voicing contrast. Goals were to investigate whether gradiency of speech perception was related to listeners' differential sensitivity to acoustic cues and to individual differences in executive function. The experiment included two speech perception tasks (visual analogue scaling [VAS] and anticipatory eye movement [AEM]) administered to 30 English-speaking adults in two separate experimental sessions. Stimuli were a /ta/ to /da/ continuum that systematically varied VOT and f0. Findings were that some listeners had a more gradient pattern of responses on the VAS task; the listeners who had a gradient response pattern on the VAS task also showed more sensitivity to f0 on the AEM task. The patterns were consistent across individuals tested on two separate occasions. These results suggest that variability in how categorically listeners perceive speech sounds is consistent and systematic within individuals.

title: Development and Validation of the AzBio Sentence Lists
abstract: The goal of this study was to create and validate a new set of sentence lists that could be used to evaluate the speech perception abilities of hearing-impaired listeners and cochlear implant (CI) users. Our intention was to generate a large number of sentence lists with an equivalent level of difficulty for the evaluation of performance over time and across conditions.  The AzBio sentence corpus includes 1000 sentences recorded from two female and two male talkers. The mean intelligibility of each sentence was estimated by processing each sentence through a five-channel CI simulation and calculating the mean percent correct score achieved by 15 normal-hearing listeners. Sentences from each talker were sorted by percent correct score, and 165 sentences were selected from each talker and were then sequentially assigned to 33 lists, each containing 20 sentences (5 sentences from each talker). List equivalency was validated by presenting all lists, in random order, to 15 CI users.  Using sentence scores from the CI simulation study produced 33 lists of sentences with a mean score of 85% correct. The results of the validation study with CI users revealed no significant differences in percent correct scores for 29 of the 33 sentence lists. However, individual listeners demonstrated considerable variability in performance on the 29 lists. The binomial distribution model was used to account for the inherent variability observed in the lists. This model was also used to generate 95% confidence intervals for one and two list comparisons. A retrospective analysis of 172 instances where research subjects had been tested on two lists within a single condition revealed that 94% of results were accurately contained within these confidence intervals.  The use of a five-channel CI simulation to estimate the intelligibility of individual sentences allowed for the creation of a large number of sentence lists with an equivalent level of difficulty. The results of the validation procedure with CI users found that 29 of 33 lists allowed scores that were not statistically different. However, individual listeners demonstrated considerable variability in performance across lists. This variability was accurately described by the binomial distribution model and was used to estimate the magnitude of change required to achieve statistical significance when comparing scores from one and two lists per condition. Fifteen sentence lists have been included in the AzBio Sentence Test for use in the clinical evaluation of hearing-impaired listeners and CI users. An additional eight sentence lists have been included in the Minimum Speech Test Battery to be distributed by the CI manufacturers for the evaluation of CI candidates.

title: Individual differences in online spoken word recognition: Implications for SLI
abstract: Thirty years of research has uncovered the broad principles that characterize spoken word processing across listeners. However, there have been few systematic investigations of individual differences. Such an investigation could help refine models of word recognition by indicating which processing parameters are likely to vary, and could also have important implications for work on language impairment. The present study begins to fill this gap by relating individual differences in overall language ability to variation in online word recognition processes. Using the visual world paradigm, we evaluated online spoken word recognition in adolescents who varied in both basic language abilities and non-verbal cognitive abilities. Eye movements to target, cohort and rhyme objects were monitored during spoken word recognition, as an index of lexical activation. Adolescents with poor language skills showed fewer looks to the target and more fixations to the cohort and rhyme competitors. These results were compared to a number of variants of the TRACE model (McClelland & Elman, 1986) that were constructed to test a range of theoretical approaches to language impairment: impairments at sensory and phonological levels; vocabulary size, and generalized slowing. None of the existing approaches were strongly supported, and variation in lexical decay offered the best fit. Thus, basic word recognition processes like lexical decay may offer a new way to characterize processing differences in language impairment.

title: NIH Toolbox for Assessment of Neurological and Behavioral Function
abstract: At present, there are many studies that collect information on aspects of neurologic and behavioral function (cognition, sensation, movement, emotion), but with little uniformity among the measures used to capture these constructs. Further, available measures are generally expensive, normed on homogenous nondiverse populations, not easily administered, do not cover the lifespan (or have easily linked pediatric and adult counterparts for the purposes of longitudinal comparison), and not based on the current thinking in the neuroscience community. There is also a paucity of measurement tools to gauge normal children in the motor and sensation domain areas, and many of these measures rely heavily on proxy reporting. Investigators have expressed the need for brief assessment tools that could address these issues and be used as a form of “common currency” across diverse study designs and populations. This ability to assess functionality along a common metric and “crosswalk” across measures is essential to the process of being able to pool data, which is often necessary when a large and diverse sample is needed. When individual studies employ unique assessment batteries, comparisons between studies and combining data from multiple studies can be problematic. The contract for the NIH Toolbox for the Assessment of Neurological and Behavioral Function (www.nihtoolbox.org) was initiated by the NIH Blueprint for Neuroscience Research (www.neuroscienceblueprint.nih.gov) to develop a set of state-of-the-art measurement tools to enhance collection of data in large cohort studies and to advance the biomedical research enterprise.

title: Effects of noise letters upon the identification of a target letter in a nonsearch task
abstract: During a 1-sec tachistoscopic exposure, Ss responded with a right or left leverpress to a single target letter from the sets H and K or S and C. The target always appeared directly above the fixation cross. Experimentally varied were the types of noise letters (response compatible or incompatible) flanking the target and the spacing between the letters in the display. In all noise conditions, reaction time (RT) decreased as between-letter spacing increased. However, noise letters of the opposite response set were found to impair RT significantly more than same response set noise, while mixed noise letters belonging to neither set but having set-related features produced intermediate impairment. Differences between two target-alone control conditions, one presented intermixed with noise-condition trials and one presented separately in blocks, gave evidence of a preparatory set on the part of Ss to inhibit responses to the noise letters. It was concluded that S cannot prevent processing of noise letters occurring within about 1 deg of the target due to the nature of processing channel capacity and must inhibit his response until he is able to discriminate exactly which letter is in the target position. This discrimination is more difficult and time consuming at closer spacings, and inhibition is more difficult when noise letters indicate the opposite response from the targe

title: Psychometric Functions of Dual-Task Paradigms for Measuring Listening Effort
abstract: The purpose of the study was to characterize the psychometric functions that describe task performance in dual-task listening effort measures as a function of signal to noise ratio (SNR).  Younger adults with normal hearing (YNH, n = 24; experiment 1) and older adults with hearing impairment (n = 24; experiment 2) were recruited. Dual-task paradigms wherein the participants performed a primary speech recognition task simultaneously with a secondary task were conducted at a wide range of SNRs. Two different secondary tasks were used: an easy task (i.e., a simple visual reaction-time task) and a hard task (i.e., the incongruent Stroop test). The reaction time (RT) quantified the performance of the secondary task.  For both participant groups and for both easy and hard secondary tasks, the curves that described the RT as a function of SNR were peak shaped. The RT increased as SNR changed from favorable to intermediate SNRs, and then decreased as SNRs moved from intermediate to unfavorable SNRs. The RT reached its peak (longest time) at the SNRs at which the participants could understand 30 to 50% of the speech. In experiments 1 and 2, the dual-task trials that had the same SNR were conducted in one block. To determine if the peak shape of the RT curves was specific to the blocked SNR presentation order used in these experiments, YNH participants were recruited (n = 25; experiment 3) and dual-task measures, wherein the SNR was varied from trial to trial (i.e., nonblocked), were conducted. The results indicated that, similar to the first two experiments, the RT curves had a peak shape.  Secondary task performance was poorer at the intermediate SNRs than at the favorable and unfavorable SNRs. This pattern was observed for both YNH and older adults with hearing impairment participants and was not affected by either task type (easy or hard secondary task) or SNR presentation order (blocked or nonblocked). The shorter RT at the unfavorable SNRs (speech intelligibility < 30%) possibly reflects that the participants experienced cognitive overload and/or disengaged themselves from the listening task. The implication of using the dual-task paradigm as a listening effort measure is discussed.

title: Cognitive processing load across a wide range of listening conditions: insights from pupillometry.
abstract: The pupil response to speech masked by interfering speech was assessed across an intelligibility range from 0% to 99% correct. In total, 37 participants aged between 18 and 36 years and with normal hearing were included. Pupil dilation was largest at intermediate intelligibility levels, smaller at high intelligibility, and slightly smaller at very difficult levels. Participants who reported that they often gave up listening at low intelligibility levels had smaller pupil dilations in these conditions. Participants who were good at reading masked text had relatively large pupil dilation when intelligibility was low. We conclude that the pupil response is sensitive to processing load, and possibly reflects cognitive overload in difficult conditions. It seems affected by methodological aspects and individual abilities, but does not reflect subjective ratings.