Functional organization of the auditory cortex is different in stutterers and fluent speakers

Impaired auditory feedback has been suggested to cause stuttering, and subtle irregularities of audition have been reported in behavioural studies. To characterize processing at the auditory cortical level, we recorded neuromagnetic responses to monaural tones in nine stutterers and 10 fluent speakers while the subjects were reading silently, with mouth movements only, aloud, and in chorus with another person. The basic functional organization of the auditory cortices was found to be different in stutterers and controls. The altered interhemispheric balance in stutterers was affected by speech production, due to changes in the left auditory cortical representation, and more severely by self-paced than accompanied speech. This may lead to transient non-optimal interpretation of the auditory input and affect speech fluency.     

P300 event-related potentials in stutterers and nonstutterers

This study investigated possible differences between adult stutterers and nonstutterers in the P300 event-related potential. Responses to tonal stimuli were recorded from electrodes placed over the left (C3) and righ (C4) hemispheres. The two groups exhibited different patterns of interhemispheric activity. Although all 8 participants in the fluent group exhibited P300s that were higher in amplitude over the right hemisphere, 5 of the 8 disfluent participants had higher amplitude activity over the left hemisphere. These results provide evidence that stutterers and nonstutterers may exhibit differences between hemispheres in the processing of some types of nonlinguistic (tonal) stimuli.     

Stuttering as a function of the information value and sentence position of words.

24 stutterers read aloud a 95-word passage of banal prose, and the incidence of stuttering was determined for each word. The information value of each word was estimated by studying the extent to which each word could be predicted from knowledge of the preceeding words by 46 normal speakers. Results indicated that both position in the sentence and information value of words are significantly correlated with stuttering incidence. It is concluded that the positional phenomenon cannot be explained as a redundancy effect. Its nature is discussed briefly from the approach-avoidance conflict and operant viewpoints of stuttering. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morphological structure and hemispheric functioning: The contribution of the right hemisphere to reading in different languages.

This study examined the relationship between morphological structure of languages and performance asymmetries of native speakers in lateralized tasks. In 2 experiments, native speakers of English (concatenative morphology stem plus affix) and of Hebrew and Arabic (nonconcatenative root plus word-form morphology) were presented with lateralized lexical decision tasks, in which the morphological structure of both words and nonwords was manipulated. In the 1st study, stimuli were presented unilaterally. In the 2nd study, 2 stimuli were presented bilaterally, and participants were cued to respond to 1 of them. Three different indexes of hemispheric integration were tested: processing dissociation, effects of distractor status, and the bilateral effect. Lateralization patterns in the 3 languages revealed both common and language-specific patterns. For English speakers, only the left hemisphere (LH) was sensitive to morphological structure, consistent with the hypothesis that the LH processes right visual field stimuli independently but that the right hemisphere uses LH abilities to process words in the left visual field. In Hebrew and Arabic, both hemispheres are sensitive to morphological structure, and interhemispheric transfer of information may be more symmetrical than in English. The relationship between universal and experience-specific effects on brain organization is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orthography and the Hemispheres: Visual and Linguistic Aspects of Letter Processing.

Hebrew and Arabic are Semitic languages with a similar morphological structure and orthographies that differ in visual complexity. Two experiments explored the interaction of the characteristics of orthography and hemispheric abilities on lateralized versions of a letter-matching task (Experiment 1) and a global-local task (Experiment 2). In Experiment 1, native Hebrew readers and native Arabic readers fluent in Hebrew matched letters in the 2 orthographies. The results support the hypothesis that Arabic orthography is more difficult than Hebrew orthography for participants who can read both languages and that this difficulty has its strongest effects in the left visual field. In Experiment 2, native Arabic speakers performed a global-local letter detection task with Arabic letters with 2 types of inconsistent stimuli: different and similar. The results support the hypothesis that the right hemisphere of skilled Arabic readers cannot distinguish between similar Arabic letters, whereas the left hemisphere can. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stuttering, language, and cognition: a review and a model of stuttering as suprasegmental sentence plan alignment (SPA)

Extant models of stuttering do not account for the emergence of stuttering at the onset of productive language use; the greater incidence of stuttering during spontaneous speech, on complex sentences, and at sentence-initial positions; the greater incidence of stuttering in bilinguals' 2nd language; the apparent deficiency of stutterers in expressive and receptive language skills; the prevalence of spontaneous recovery from stuttering; and the lack of chronic physiological or articulatory deficits in stuttering children's fluent speech. The author presents a model of stuttering as points of suprasegmental sentence plan alignment (SPA). Such alignment processes occur when, due to on-line sentence production processes, SPAs adopted prior to utterance initiation need to be aligned with revised SPAs. This model parsimoniously accounts for the findings reviewed in the article.     

Effects of contingent events on stuttering and fluency.

In Study 1 with 4 male 18-20 yr old stutterers, the effect on stuttering frequency of contingent monetary gain and contingent monetary loss for stuttering was examined individually for over 12 hrs, using control periods when no contingency was present. Both contingencies resulted in decreased stuttering, suggesting that the effect of observing and recording instances of stuttering was more powerful than the money. In Study 2, monetary gain and loss was made contingent on units of fluent speech for 5 male and 1 female 17-34 yr old stutterers over 12 hrs. Fluency increased for the group during monetary gain, but monetary loss did not have the predicted effect of decreasing fluency, perhaps because the contigent events served also to enhance self-observation. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right hemisphere performance and competence in processing mental images, in a case of partial interhemispheric disconnection

The objective of this study was to analyze dynamic aspects of right hemisphere implementation in processing visual images. Two tachistoscopic, divided visual field experiments were carried out on a partial split-brain patient with no damage to the right hemisphere. In the first experiment, image generation performance for letters presented in the right visual field (/left hemisphere) was undeniably optimal. In the left visual field (/right hemisphere), performance was no better than chance level at first, but then improved dramatically across stimulation blocks, in each of five successive sessions. This was interpreted as revealing the progressive spontaneous activation of the right hemisphere's competence not shown initially. The aim of the second experiment was to determine some conditions under which this pattern was obtained. The experimental design contrasted stimuli (words and pictures) and representational activity (phonologic and visuo-imaged processing). The right visual field (/left hemisphere: LH) elicited higher performance than the left visual field (/right hemisphere, RH) in the three situations where verbal activity was required. No superiority could be found when visual images were to be generated from pictures: parallel and weak improvement of both hemispheres was observed across sessions. Two other patterns were obtained: improvement in RH performance (although LH performance remained superior) and an unexpectedly large decrease in RH performance. These data are discussed in terms of RH cognitive competence and hemisphere implementation.     

Villoglandular adenocarcinoma of the cervix: cytologic presentation

A 69-year-old left-handed man developed Broca aphasia and jargon agraphia following a right cerebral infarction. He learned to write with his right hand. There is no family history of left-handedness. Neurological examination revealed hemiparesis, sensory impairment, and hyperreflexia with pathological reflexes on the left side. An MRI demonstrated lesions in the area including the pre- and post-central gyri, the posterior part of the middle and inferior frontal gyri, and inferior parietal lobule on the right side. Neuropsychologically he was alert and cooperative. He demonstrated severe Broca aphasia and his verbal output was limited to a few residual words. On the other hand, he could communicate through writing Kanji words. Writing words was relatively preserved with Kanji but not with Kana characters. Asked to write a Japanese folk tale, he showed jargon agraphia mixed with some correct Kanji words. His comprehension of spoken and written sentences was well preserved. He showed mild ideomotor and buccofacial apraxia, left unilateral spatial neglect, and constructional impairment. Dissociation between spoken and written language is a prominent feature of this patient's language output. In this patient, right hemisphere seems to be dominant for language and praxis, and left hemisphere for motor engram of writing. Learning to write with the right hand may have enhanced the establishment and maintenance of motor engram for writing in the left hemisphere. The intact motor engram of characters in the left hemisphere could be retrieved by the right hand without control from the language area in the diseased right hemisphere, resulting in jargon agraphia especially with Kana characters. In left handed people, the hand with which they learn to write may effect interhemisphere lateralization of language functions.     

Level of aspiration in stutterers and nonstutterers.

"Forty adult stutterers were compared with sixty normal speakers on three dimensions of their performance on the Rotter Level of Aspiration Board… . The stutterers were significantly lower in average D score, or discrepancy between aim and accomplishment… . They predicted more modest performances and showed in general a lower level of aspiration… . To a greater extent than the normal population, stutterers avoid even the threat of failure… . Within the normal group, there was no significant sex difference in D score. Within the stuttering group, the females were strikingly low." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual half-field Stroop effects with spatial separation of words and color targets

Past inconsistencies in the occurrence of differential visual half-field Stroop effects were addressed in two experiments using a visual half-field presentation technique incorporating brief displays (100 ms) and a fixation task designed to ensure proper eye fixation at display onset. Experiment 1 used displays in which distractor words and color targets were presented in contralateral visual fields. Experiment 2 compared contralateral with ipsilateral displays where words and color targets appeared one above the other in the same visual field. Stroop effects were larger whenever a word occupied the right as opposed to the left visual field, regardless of whether the color target was left or right. Results are consistent with the idea that words are processed more efficiently or automatically in right visual field/left hemisphere presentations.     

The Lateralized Emotional Stroop Task: Left Visual Field Interference in Women.

In a visual hemifield emotional Stroop task, 54 women were asked to name the color of laterally flashed emotional and neutral words while ignoring their semantic content. Vocal reaction times for color naming were recorded. The participants exhibited significant emotional interference effects in the left visual field, which tended to be larger for negative words than for positive words. Participants with higher trait anxiety scores exhibited larger interference for positive words in the left relative to the right visual field. The outcome indicates that, in women, emotional Stroop interference arises in the right rather than in the left hemisphere, with a larger impact of negative than of positive words, and with trait anxiety modulating the lateralized interference for positive words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual and semantic processing in reading Kanji.

A. Nakagawa (see record 1992-15549-001) showed hemispheric asymmetries during semantic processing of single English words. The right hemisphere passively maintained both strong and weak associations, whereas the left hemisphere maintained only strong associations when Ss were left free to attend. The present study extends the methodology to the study of Kanji characters. Contrary to the study of English characters, there was a general right-hemisphere advantage in single-character Kanji words. A study using a visual cue to direct attention suggested that the right-hemisphere advantage of Kanji was due to better representation of visual features by the posterior right hemisphere. However, the pattern of semantic priming found in English was replicated. Semantic analysis, mediated by more anterior systems, appears similar in the 2 languages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interhemispheric communication is via direct connections

Two priming experiments, using normal university students as subjects, independently projected low imagery primes and concrete target words to the left or right visual fields (LVF or RVF) to examine the merits of three spreading activation models of interhemispheric communication: (i) callosal relay of a semantically encoded prime; (ii) transfer of products activated as a result of the spread of activation; and (iii) direct connections between the hemispheres. The first experiment temporally separated pairs by a stimulus onset asynchrony (SOA) of 250 ms and obtained strong support for the direct connections model. Priming effects were obtained only when the prime was projected to the RVF and the target to the LVF. The pattern of priming effects suggested that low imagery words projected to the left hemisphere can activate concrete associates in the right hemisphere via direct callosal connections between the two. In the second experiment, the SOA was increased to 450 ms. This time, RVF-RVF priming was obtained along with RVF-LVF priming. The findings are interpreted within a modification of Bleasdale's (1987) framework, where abstract/low imagery words and concrete/high imagery words are represented in separate subsystems in the left hemisphere lexicon. Support was also found for the view that the left hemisphere is comprised of a complex network of abstract and concrete words, while the right hemisphere operates as a subsidiary word processor, subserving linguistic processing with a limited, special purpose lexicon comprised of associative connections between concrete, imageable words (e.g., Zaidel, 1983a; Bradshaw, 1980). Interhemispheric communication in the priming procedure appears to occur at the semantic level, via direct connections between the hemispheres.     

Word repetition within- and across-visual fields: an event-related potential study

A divided visual field (DVF) procedure was used to investigate the scalp distribution of the event-related potential (ERP) repetition effect. ERPs were recorded from 27 scalp sites whilst subjects (n = 20) discriminated between words and non-words presented to either the left (LVF) or the right (RVF) visual field. A proportion of the words were repeated on the trial immediately following their first presentation. In two within-field repetition conditions the two encounters with a word occurred in the same visual field (LVF or RVF). In two across-field repetition conditions, the two encounters with a word occurred in different visual fields. For both words and non-words, task performance was better for RVF presentations than for LVF presentations. In each repetition condition there was a positive-going shift in the ERP elicited by repeated words compared to that elicited by words on their first presentation. This ERP repetition effect was equivalent in magnitude and lateralised to the right hemisphere to an equivalent degree in all four repetition conditions. It is suggested that the ERP effects largely reflect the processing of visual form thought to occur predominately in the right hemisphere.     

Right Hemisphere Sensitivity to Word- and Sentence-Level Context: Evidence From Event-Related Brain Potentials.

Researchers using lateralized stimuli have suggested that the left hemisphere is sensitive to sentence-level context, whereas the right hemisphere (RH) primarily processes word-level meaning. The authors investigated this message-blind RH model by measuring associative priming with event-related brain potentials (ERPs). For word pairs in isolation, associated words elicited more positive ERPs than unassociated words with similar magnitudes and onset latencies in both visual fields. Embedded in sentences, these same pairs showed large sentential context effects in both fields. Small effects of association were observed, confined to incongruous sentences after right visual hemifield presentation but present for both congruous and incongruous sentences after left visual hemifield presentation. Results do not support the message-blind RH model but do suggest hemispheric asymmetries in the use of word and sentence context during real-time processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Form-specific visual priming in the right cerebral hemisphere.

Results of 4 experiments indicate that both within-modality and case-specific visual priming for words are greater when test stimuli are presented initially to the right cerebral hemisphere (RH). In contrast, neither within-modality nor case-specific explicit memory for words is greater when stimuli are presented initially to the RH. Priming is measured using word-stem completion, and explicit memory is measured using word-stem cued recall. In both cases, Ss first rate how much they like words, and then word stems are presented briefly to the RH (in the left visual field) or to the left hemisphere (in the right visual field). Results suggest that at least 2 separate systems encode the visual representations that produce priming. The system that is more effective in the RH is better at representing form-specific information, whereas another system that is not more effective in the RH does not distinguish among distinct instances of word forms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A PET study of the neural systems of stuttering

The cause of stuttering is unknown. Failure to develop left-hemispheric dominance for speech is a long-standing theory although others implicated the motor system more broadly, often postulating hyperactivity of the right (language nondominant) cerebral hemisphere. As knowledge of motor circuitry has advanced, theories of stuttering have become more anatomically specific, postulating hyperactivity of premotor cortex, either directly or through connectivity with the thalamus and basal ganglia. Alternative theories target the auditory and speech production systems. By contrasting stuttering with fluent speech using positron emission tomography combined with chorus reading to induce fluency, we found support for each of these hypotheses. Stuttering induced widespread overactivations of the motor system in both cerebrum and cerebellum, with right cerebral dominance. Stuttered reading lacked left-lateralized activations of the auditory system, which are thought to support the self-monitoring of speech, and selectively deactivated a frontal-temporal system implicated in speech production. Induced fluency decreased or eliminated the overactivity in most motor areas, and largely reversed the auditory-system underactivations and the deactivation of the speech production system. Thus stuttering is a disorder affecting the multiple neural systems used for speaking.     

Form-specific priming and functional brain asymmetries in perceptual identification

Word form representations in intact cerebral hemispheres were studied by a lateralized perceptual identification priming task. During the study phase, word forms were primed by displaying words visually in uppercase or lowercase letters. During the test phase, perceptual identification of non-studied baseline words and studied words (presented in same or different lettercase as studied) was tested by displaying targets in the left or right visual field. Experiment 1 showed that the hemispheric pattern of priming effects was dependent on the lettercase at test. For uppercase test items, only the left visual field/right hemisphere was sentitive to study-test changes in lettercase, replicating an earlier result obtained in word-stem completion (Marsolek, Kosslyn and Squire, 1992). However, lowercase test items did not reveal any asymmetries in the form-dependent priming component indicating that in some conditions form-specific representations are computed in the left hemisphere also. No asymmetries were found in the abstract, form-independent component of priming. Experiment 2 revealed that use of explicit memory in the perceptual identification task eliminated the form-specific priming effects and suggested that the results of Experiment 1 were uncontaminated by explicit memory.