Sublexical Conversion Research Articles

Multi-step treatment for acquired alexia and agraphia (Part I): efficacy, generalisation, and identification of beneficial treatment steps

ABSTRACTReading and writing impairments are common in individuals with post-stroke aphasia. Treatment typically aims to improve the function of one of these modalities by strengthening aspects of either lexical or sublexical processing. In the present study, eight adults with acquired alexia and agraphia were administered a comprehensive treatment targeting specific lexical and sublexical processes underlying reading and/or writing. Two participants were trained in reading and six were trained in writing. Throughout treatment, reading and writing accuracy were monitored for trained items, as well as untrained but orthographically and semantically related items. Linear mixed effects models indicated that the most substantial gains were made on trained items in the trained modality; generalisation to trained items in the untrained modality and untrained but related items in both modalities was also observed. Participants improved significantly on a subset of treatment steps intended to address lexical access and representations, sublexical conversion mechanisms, and the graphemic and/or phonological buffer processes in both modalities. These results demonstrate the efficacy of a novel, comprehensive treatment protocol and suggest that targeting multiple reading and writing processes in conjunction may facilitate widespread generalisation.

Neural correlates reveal sub-lexical orthography and phonology during reading aloud: a review.

The sub-lexical conversion of graphemes-to-phonemes (GPC) during reading has been investigated extensively with behavioral measures, as well as event-related potentials (ERPs). Most research utilizes silent reading (e.g., lexical decision task) for which phonological activation is not a necessity. However, recent research employed reading aloud to capture sub-lexical GPC. The masked priming paradigm avoids strategic processing and is therefore well suitable for capturing sub-lexical processing instead of lexical effects. By employing ERPs, the on-line time course of sub-lexical GPC can be observed before the overt response. ERPs have revealed that besides phonological activation, as revealed by behavioral studies, there is also early orthographic activation. This review describes studies in one’s native language, in one’s second language, and in a cross-language situation. We discuss the implications the ERP results have on different (computational) models. First, the ERP results show that computational models should assume an early locus of the GPC. Second, cross-language studies reveal that the phonological representations from both languages of a bilingual become activated automatically and the phonology belonging to the context is selected rapidly. Therefore, it is important to extend the scope of computational models of reading (aloud) to multiple lexicons.

Training phoneme to grapheme conversion for patients with written and oral production deficits: A model‐based approach

Background: A previous study (Kiran, Thompson, & Hashimoto, 2001) investigated the effect of training sublexical conversion on improving oral reading of regular words in two individuals with aphasia. Results revealed that training grapheme to phoneme conversion improved acquisition of trained items and facilitated generalisation to trained and untrained stimuli during oral naming, written naming, and writing to dictation as well. Aims: The aim of the present study was to extend this work to investigate if training phoneme to grapheme conversion would result in improvement of writing to dictation of trained items and facilitate generalisation to untrained stimuli and untrained tasks. Methods & procedures: Using a single subject experimental design across three participants with aphasia, the effects of phoneme to grapheme conversion treatment were evaluated by periodic probing of both trained and untrained regular words across lexical tasks: writing to dictation, written naming, oral spelling, and oral naming. Outcomes & Results: Results indicated that training phoneme to grapheme conversion resulted in improved writing to dictation of trained and untrained words in two out of three patients. In addition, improved written naming and oral spelling of trained words was observed. Marginal improvements were observed for untrained stimuli on written naming, oral spelling, and oral naming. Conclusions: The results of this experiment demonstrate the effectiveness of training sublexical conversion to improve written production deficits and to facilitate generalisation to untrained stimuli and untrained tasks. These results also complement findings of our previous study to suggest a more efficient method of improving single word production deficits than training each modality successively.

Neuronal correlates of consistency and frequency effects on Chinese character naming: an event-related fMRI study

This event-related functional magnetic resonance imaging (efMRI) study aims to investigate the central representations of Chinese orthography-to-phonology transformation (OPT) by simultaneously manipulating character frequency and consistency. Bilateral inferior frontal cortices (including Broca's area and insula), the left temporoparietal region (superior parietal gyrus and supramarginal gyrus), and the left temporal-occipital junction showed greater activation, especially in low-frequency conditions, when naming inconsistent characters as compared to consistent ones. These findings suggest that these regions are involved in the sublexical conversion of orthographic input into phonological codes in naming Chinese. The similar activation pattern found in these three regions suggests a distributed process, rather than separate neural routes, for lexical and sublexical OPT. In addition, the regions involved in Chinese OPT are congruent with the findings for reading alphabetic scripts and indicate that the neuronal mechanisms for orthography-to-phonology transformation is domain universal across different writing systems.

Do Phonological Codes Constrain the Selection of Orthographic Codes in Written Picture Naming?

Sound-to-print consistency of picture labels was manipulated in five experiments to investigate whether phonological codes constrain the selection of orthographic codes in written picture naming. In Experiments 1 and 2, participants wrote down picture names which were inconsistent or consistent in the phono-orthographic mapping defined either at the level of the word unit, i.e., heterographic homophones versus nonhomophones (Experiment 1), or at the sublexical level (Experiment 2). In neither experiment did phonographic consistency affect written latencies. Although more errors were observed for inconsistent than for consistent picture names, the observation of a similar error pattern in an untimed written picture naming (control) task suggests that errors resulted from inaccurate orthographic knowledge. In Experiment 3, the position of the inconsistent units within the picture name (initial versus middle or final) was manipulated. The results indicated that only initial inconsistencies affected written latencies. Ruling out the hypothesis that this finding merely results from the fact that handwriting starts before the orthographic encoding of the word endings, Experiments 4 and 5 showed that middle or final inconsistencies influenced written latencies in a spelling-to-dictation task. The findings are discussed as suggesting that the build-up of orthographic activation from pictures is phonologically constrained through the sequential operation of sublexical conversion.

SUBLEXICAL CONVERSION PROCEDURES AND THE INTERACTION OF PHONOLOGICAL AND ORTHOGRAPHIC LEXICAL FORMS

In double naming tasks requiring the production of consecutive spoken and written responses to the same picture, subject ECA produced inconsistent lexical responses in the say-then-write (stimulus: organ; spoken response: “church;” written response: piano) but not in the write-then-say condition (organ → piano → “piano”). This observation, together with the fact that ECA had damage to the semantic system and to sublexical phoneme-grapheme conversion but not to sublexical grapheme-phoneme conversion procedures, is used to constrain claims about the organisation of lexical form knowledge. It is proposed that phonological and orthographic lexical forms are accessed autonomously, but interact via sublexical conversion procedures. In ECA, the one-way interaction between phonological and orthographic word forms is prevented by damage to phoneme- grapheme procedures (hence, inconsistent responses in the say-then-write naming condition); the reverse interaction can take place because grapheme-phoneme conversion processes are spared (hence, the absence of inconsistent responses in the write-then-say naming condition).

The neural circuitry involved in the reading of German words and pseudowords: A PET study.

Silent reading and reading aloud of German words and pseudowords were used in a PET study using (15O)butanol to examine the neural correlates of reading and of the phonological conversion of legal letter strings, with or without meaning. The results of 11 healthy, right-handed volunteers in the age range of 25 to 30 years showed activation of the lingual gyri during silent reading in comparison with viewing a fixation cross. Comparisons between the reading of words and pseudowords suggest the involvement of the middle temporal gyri in retrieving both the phonological and semantic code for words. The reading of pseudowords activates the left inferior frontal gyrus, including the ventral part of Broca's area, to a larger extent than the reading of words. This suggests that this area might be involved in the sublexical conversion of orthographic input strings into phonological output codes. (Pre)motor areas were found to be activated during both silent reading and reading aloud. On the basis of the obtained activation patterns, it is hypothesized that the articulation of high-frequency syllables requires the retrieval of their concomitant articulatory gestures from the SMA and that the articulation of low-frequency syllables recruits the left medial premotor cortex.

Semantic Errors as Neuropsychological Evidence for the Independence and the Interaction of Orthographic and Phonological Word Forms

For some time, it has been assumed that writing requires phonological mediation (orthographic word forms cannot be activated directly from semantics, but only indirectly from phonological word forms). More recently, phonological mediation has been questioned, due to the observation that on tasks that require the production of spoken and written responses on the same naming attempt, some aphasic subjects produce different words (e.g. a correct written response and a spoken semantic error, or vice versa; or, two distinct semantic errors). This pattern of performance cannot be accounted for by phonological mediation, but is easily accommodated by the orthographic autonomy hypothesis, which allows the direct activation of orthographic word forms from semantics. However, the observation that damage to word meaning or to word form usually results in comparable difficulties in spoken and written output, suggests that phonological and orthographic word forms, albeit autonomous, can interact. The available data are compatible both with a “weak” version of orthographic autonomy (orthographic word forms are activated both directly from semantics and indirectly from phonological word forms), and with a “strong” version of the same hypothesis (orthographic forms are directly activated from semantics; they do not receive direct activation from phonological forms; and they are allowed to interact with phonological forms via sublexical conversion mechanisms).

The Independence of Phonological and Orthographic Lexical Forms: Evidence from Aphasia

WMA suffers from damage to the semantic component of the lexical semantic system and from damage to sublexical phonology-orthography and orthography-phonology conversion procedures. His performance on picture naming tasks that require two consecutive responses was used to explore issues concerning the relations between the phonological and orthographic components of the lexical system. Responses to tasks requiring responses in different modalities (one oral and one written) often resulted in lexically "inconsistent" responses. For example, to a picture representing pliers, WMA said "pincers," but wrote saw; and, to a picture representing peppers, he wrote tomato but said "artichoke." By contrast, inconsistent responses never occurred in tasks that required two consecutive responses in the same modality (oral or written). In these tasks, WMA always produced the same (correct or incorrect) word twice. These results rule out the hypothesis thatphonological mediation is necessary for writing, and suggest instead that orthographic word forms are autonomous from phonological forms, and that they are activated directly from lexical semantic information. However, the results do not allow us to distinguish between a weak version of the orthographic autonomy hypothesis- that there are direct connections between phonological and orthographic forms, which are impaired in WMA-and a strong version of the same hypothesis-that phonological and orthographic word forms are completely autonomous but that the selection of a word form for output in a given modality can be constrained by sublexical conversion mechanisms, which are impaired in WMA.

Morphological errors and the representation of morphology in the lexical—semantic system

Neuropsychological studies support the hypothesis that morphology is represented autonomously, both at the level of word meaning and at the level of word form. In output processes, morphologically organized semantic information activates lexical representations of roots and affixes, which are composed before production. In input processes, the stimulus is parsed along the morphological dimension, to access root and affix lexical representations, which in turn activate morphologically organized semantic information. Inflectional and derivational morphology are represented independently in the lexicon. Inflected words are fully decomposed; derived words are decomposed into base form+inflection. In aphasia, morphological errors in transcoding tasks always co-occur with semantic and/or phonemic errors. Morphological errors in transcoding tasks require combined damage to morphological representations in the semantic-lexical system and to sublexical conversion procedures; they co-occur with semantic errors when also root representations are damaged. The co-occurrence of morphological and phonemic errors can be accounted for by several hypotheses, but its theoretical meaning is still uncertain.

The interaction of lexical and sublexical processes in reading, writing and repetition

It has recently been proposed that in the course of repetition, reading aloud and writing to dictation, lexical representations are activated and selected for output by the joint operation of the semantic system and of sublexical conversion mechanisms—the Summation Hypothesis [ Hillis and Caramazza, Brain Lang. 40, 106–144, 1991]. The hypothesis predicts that semantic errors in oral reading and in writing to dictation should only occur when both the semantic system and the sublexical component involved in that task (orthography to phonology and phonology to orthography conversion, respectively) are damaged. The performance of Italian patient E.C.A. indicates damage to the semantic system, and to sublexical phonology to phonology and phonology to orthography conversion mechanisms, but with substantial sparing of sublexical orthography to phonology conversion processes. In agreement with expectations derived from the Summation Hypothesis, E.C.A. produced semantic errors in repetition and in writing to dictation, but not in reading aloud. The paucity of semantic errors in speakers of languages with relatively transparent orthographies is discussed in the context of the Summation Hypothesis.