Adam Buchwald

Consonants and vowels in orthographic representations

It has been argued that orthographic representations—the abstract mental representations of the spellings of words—include orthography-specific information regarding the consonant/vowel (CV) identity of the individual letters that make up a words spelling. This hypothesis has been used to explain the finding that the substitution errors in the spelling of certain dysgraphic individuals exhibit a striking tendency to preserve the CV identity of the target letters. In this paper, we evaluate the adequacy of two alternative hypotheses that do not posit orthography-specific CV representations. One hypothesis proposes that constraints on the nature of letter substitution come from the phonological representation of a word, and a second hypothesis contends that CV-preserving substitutions are driven by orthotactic knowledge—knowledge of the well-formed letter sequences in the orthography of a language. We present novel tests of these hypotheses using data from four case studies of dysgraphic individuals. The results clearly adjudicate in favour of the claim that orthographic representations contain orthography-specific CV information. In this way, the results support the more general claim that abstract categories are represented within the language system.

Finding Levels of Abstraction in Speech Production Evidence From Sound-Production Impairment

A widely held view in linguistics and psycholinguistics is that there are distinct levels of processing for context-independent and context-specific representations of sound structure. Recently, this view has been disputed, in part because of the absence of clear evidence that there are abstract mental representations of discrete sound-structure units. Here, we present novel evidence that separate context-independent and context-specific representations of sound structure are supported by distinct brain mechanisms that can be selectively impaired in individuals with acquired brain deficits. Acoustic data from /s/-deletion errors of 2 aphasic speakers suggest both a phonological level of processing at which sound representations (e.g., /p/) do not specify context-specific detail (e.g., aspirated or unaspirated) and a distinct level at which context-specific information is represented. These data help constrain accounts of sound-structure processing in word production and crucially support the claim that context-independent linguistic information affects language production.

Perceptual adaptation and intelligibility of multiple talkers for two types of degraded speech

Talker intelligibility and perceptual adaptation under cochlear implant (CI)-simulation and speech in multi-talker babble were compared. The stimuli consisted of 100 sentences produced by 20 native English talkers. The sentences were processed to simulate listening with an eight-channel CI or were mixed with multi-talker babble. Stimuli were presented to 400 listeners in a sentence transcription task (200 listeners in each condition). Perceptual adaptation was measured for each talker by comparing intelligibility in the first 20 sentences of the experiment to intelligibility in the last 20 sentences. Perceptual adaptation patterns were also compared across the two degradation conditions by comparing performance in blocks of ten sentences. The most intelligible talkers under CI-simulation also tended to be the most intelligible talkers in multi-talker babble. Furthermore, listeners demonstrated a greater degree of perceptual adaptation in the CI-simulation condition compared to the multi-talker babble condition although the extent of adaptation varied widely across talkers. Listeners reached asymptote later in the experiment in the CI-simulation condition compared with the multi-talker babble condition. Overall, these two forms of degradation did not differ in their effect on talker intelligibility, although they did result in differences in the amount and time-course of perceptual adaptation.

Distinctions between orthographic long-term memory and working memory.

Research in the cognitive and neural sciences has long posited a distinction between the long-term memory (LTM) storage of information and the short-term buffering of information that is being actively manipulated in working memory (WM). This basic type of distinction has been posited in a variety of domains, including written language production—spelling. In the domain of spelling, the primary source of empirical evidence regarding this distinction has been cognitive neuropsychological studies reporting deficits selectively affecting what the cognitive neuropsychological literature has referred to as the orthographic lexicon (LTM) or the graphemic buffer (WM). Recent papers have reexamined several of the hallmark characteristics of impairment affecting the graphemic buffer, with implications for our understanding of the nature of the orthographic LTM and WM systems. In this paper, we present a detailed case series study of 4 individuals with acquired spelling deficits and report evidence from both error types and factors influencing error rates that support the traditional distinction between these cognitive systems involved in spelling. In addition, we report evidence indicating possible interaction between these systems, which is consistent with a variety of recent findings in research on spelling.

Insertion of discrete phonological units: An articulatory and acoustic investigation of aphasic speech

The traditional view that sound structure is mentally represented by discrete phonological units has been questioned in recent years. Much of the criticism revolves around the necessity of positing gradient or continuous sound structure representations to account for certain phenomena. This paper presents evidence in favour of discrete sound structure units in addition to gradient representations. We present a case study of aphasic speaker VBR, whose spoken language production errors include vowel insertions in many word-initial consonant clusters (e.g., bleed → []). An acoustic and articulatory study is reported comparing the inserted vowels with lexical vowels in similar phonological contexts (e.g., b e lieve). The results indicate that these two vowels come from the same population, suggesting discrete insertion of a unit the same size as those used to represent lexical contrast. The implications of these data for theories of sound structure representation are discussed.

Visual speech primes open-set recognition of spoken words

Visual speech perception has become a topic of considerable interest to speech researchers. Previous research has demonstrated that perceivers neurally encode and use speech information from the visual modality, and this information has been found to facilitate spoken word recognition in tasks such as lexical decision (Kim, Davis, & Krins, 2004). In this paper, we used a cross-modality repetition priming paradigm with visual speech lexical primes and auditory lexical targets to explore the nature of this priming effect. First, we report that participants identified spoken words mixed with noise more accurately when the words were preceded by a visual speech prime of the same word compared with a control condition. Second, analyses of the responses indicated that both correct and incorrect responses were constrained by the visual speech information in the prime. These complementary results suggest that the visual speech primes have an effect on lexical access by increasing the likelihood that words with certain phonetic properties are selected. Third, we found that the cross-modality repetition priming effect was maintained even when visual and auditory signals came from different speakers, and thus different instances of the same lexical item. We discuss implications of these results for current theories of speech perception.

Rethinking the graphemic buffer

One of the processes involved in spelling is the short-term buffering of graphemes prior to serial production of their corresponding letter forms in written spelling and letter names in oral spelling. Recent cognitive neuropsychological and computational work has been directed at developing a more detailed understanding of this buffering process (Rapp & Kong, 2002; Sage & Ellis, 2004). Rapp and Kong (2002) argued that graphemic buffering consists of (at least) two major operations: the activation of a word’s constituent graphemes, followed by the serial selection of the graphemes for the temporally ordered production of their names or forms (see also Houghton, Glasspool, & Shallice, 1994). Contrary to a commonly-held position, Sage and Ellis (2004) argued that representations at the level of the graphemic buffer (GB) are sensitive to lexical factors such as lexical frequency, age of acquisition, imageability and neighborhood size. They also questioned the robustness of two common manifestations of GB deficits—length effects, and the bow-shaped accuracy function across letter positions. Sage and Ellis specifically claimed that length effects are largely attenuated when word sets are matched for lexical factors, and that the bowshaped accuracy function may be an artifact of limiting analyses to words with single errors. In the work presented here, we: (1) integrate these two sets of claims by showing that activation deficits are sensitive to lexical frequency, while selection deficits may not be; and (2) report, contra Sage and Ellis, robust length effects and bow-shaped accuracy functions even under conditions they predicted would cause their attenuation or elimination.

On the nature of sonority in spoken word production: Evidence from neuropsychology

The concept of sonority - that speech sounds can be placed along a universal sonority scale that affects syllable structure - has proved valuable in accounting for a wide spectrum of linguistic phenomena and psycholinguistic findings. Yet, despite the success of this concept in specifying principles governing sound structure, several questions remain about sonority. One issue that needs clarification concerns its locus in the processes involved in spoken language production, and specifically whether sonority affects the computation of abstract word form representations (phonology), the encoding of context-specific features (phonetics), or both of these processes. This issue was examined in the present study investigating two brain-damaged individuals with impairment arising primarily from deficits affecting phonological and phonetic processes, respectively. Clear effects of sonority on production accuracy were observed in both individuals testing word onsets and codas in word production. These findings indicate that the underlying principles governing sound structure that are captured by the notion of sonority play a role at both phonological and phonetic levels of processing. Furthermore, aspects of the errors recorded from our participants revealed features of syllabic structure proposed under current phonological theories (e.g., articulatory phonology).

Covert contrast in velar fronting: An acoustic and ultrasound study.

ABSTRACT There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralised. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralised the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed in this article.

Integrating accounts of speech production: the devil is in the representational details

This commentary focuses on two key aspects of Hickoks proposal that distinguish it from other theories of speech production. Unlike many other accounts, auditory targets play a central and early role in speech production. This proposal also adopts a generally reductionist approach to the production of speech, relying almost exclusively on sensory and motor processes to represent sound structure. This eliminates various levels of phonological representation that play key roles in theories motivated by psycholinguistic and cognitive neuropsychological research. The general and specific issues raised by Hickoks approach are examined within two specific areas: the structure of sound representations and patterns of performance in “conduction aphasia.”