Linda I. Shuster

An fMRI investigation of covertly and overtly produced mono- and multisyllabic words.

Studies suggest that the left insula may play an important role in speech motor programming. We used functional magnetic resonance imaging to investigate the role of the left insula in the production of monosyllabic or multisyllabic words during overt and covert speech conditions. The left insula did not show a BOLD response for multisyllabic words (which should require more speech motor programming) that was different from that for monosyllabic words. Left parietal lobe regions showed a greater response for multisyllabic as compared to monosyllabic words. This is consistent with clinical studies showing that left parietal lobe lesions can produce a deficit in speech programming. Despite similarities, covert and overt speech did not demonstrate the same patterns of BOLD response. The BOLD response was greater during overt speech in areas that have been shown to play an important role in speech production including left premotor cortex/BA6, left primary motor cortex, left insula, and left superior temporal gyrus.

Evoking [r] Using Visual Feedback

An adult who was not able to produce singleton consonantal [r] or any of the r-colored vowels correctly (although he could produce some consonant clusters containing [r]) was enrolled in a treatmen...

Toward a better understanding of the perception of self-produced speech

UNLABELLED The subject of how humans hear their own voices while speaking has received sporadic attention. Previous investigations suggest that the voice is heard substantially via bone conduction, implying a different transfer function to the ear--perhaps a low-pass filter--than for purely air-conducted vocalizations. Determining the characteristics of the transfer function of self-produced speech might contribute to a better understanding of self-perception. Such information may have important implications for treating articulation disorders. The efficacy of training discrimination during the remediation of articulation disorders remains unclear, perhaps because clients are asked to discriminate either speech of others or recorded self-speech samples not readily recognized as their own. This study was conducted to determine preference for filtered self-monitored speech in a delayed feedback paradigm. Participants made immediate comparisons of their real-time speech to delayed-recorded filtered self-speech samples. Participants demonstrated a clear preference for low-pass filtered speech, supporting earlier findings, but we were unable to determine the transfer function itself. LEARNING OUTCOMES As a result of this activity, the learner will be able to describe some reasons why an individuals tape recorded speech typically sounds different to him/her from his/her own, live speech. As a result of this activity, the learner will be able to describe some potential applications for an accurately-characterized transfer function for self-produced speech.

The effect of sublexical and lexical frequency on speech production: An fMRI investigation

There is no consensus regarding the fundamental phonetic units that underlie speech production. There is, however, general agreement that the frequency of occurrence of these units is a significant factor. Investigators often use the effects of manipulating frequency to support the importance of particular units. Studies of pseudoword production have been used to show the importance of sublexical units, such as initial syllables, phonemes, and biphones. However, it is not clear that these units play the same role when the production of pseudowords is compared to the production of real words. In this study, participants overtly repeated real and pseudowords that were similar for length, complexity, and initial syllable frequency while undergoing functional magnetic resonance imaging. Compared to real words, production of pseudowords produced greater activation in much of the speech production network, including bilateral inferior frontal cortex, precentral gyri and supplementary motor areas and left superior temporal cortex and anterior insula. Only middle right frontal gyrus showed greater activation for real words than for pseudowords. Compared to a no-speech control condition, production of pseudowords or real words resulted in activation of all of the areas shown to comprise the speech production network. Our data, in conjunction with previous studies, suggest that the unit that is identified as the basic unit of speech production is influenced by the nature of the speech that is being studied, i.e., real words as compared to other real words, pseudowords as compared to other pseudowords, or real words as compared to pseudowords.

The use of different service delivery models for children with phonological disorders.

A group of 12 preschool children with phonological process errors was selected, and individual subjects were randomly assigned to one of two treatments that differed in relation to service delivery. Group I received a treatment that was administered exclusively by the clinician. Group II received a combination that included clinician administered treatment and parent administered instruction with the Speech Viewer system. Results indicate that both groups improved significantly, but they did not differ significantly from each other in the degree of change. Implications with respect to the service delivery options and their respective components are discussed.

Motor demand-dependent activation of ipsilateral motor cortex

The role of ipsilateral primary motor cortex (M1) in hand motor control during complex task performance remains controversial. Bilateral M1 activation is inconsistently observed in functional (f)MRI studies of unilateral hand performance. Two factors limit the interpretation of these data. As the motor tasks differ qualitatively in these studies, it is conceivable that M1 contributions differ with the demand on skillfulness. Second, most studies lack the verification of a strictly unilateral execution of the motor task during the acquisition of imaging data. Here, we use fMRI to determine whether ipsilateral M1 activity depends on the demand for precision in a pointing task where precision varied quantitatively while movement trajectories remained equal. Thirteen healthy participants used an MRI-compatible joystick to point to targets of four different sizes in a block design. A clustered acquisition technique allowed simultaneous fMRI/EMG data collection and confirmed that movements were strictly unilateral. Accuracy of performance increased with target size. Overall, the pointing task revealed activation in contralateral and ipsilateral M1, extending into contralateral somatosensory and parietal areas. Target size-dependent activation differences were found in ipsilateral M1 extending into the temporal/parietal junction, where activation increased with increasing demand on accuracy. The results suggest that ipsilateral M1 is active during the execution of a unilateral motor task and that its activity is modulated by the demand on precision.

Perceptual and acoustic analyses of speech sound errors in apraxia of speech accompanied by aphasia

In order to carefully characterise their speech errors, two individuals with apraxia of speech and aphasia were audiotape recorded producing 650 monosyllabic words in imitation. Each utterance was transcribed using the methods and diacritics for close phonetic transcription described by Shriberg and Kent (1995). In addition, utterances were analysed acoustically. Although the subjects demonstrated some differences, they also displayed similar patterns. Both produced perceived substitutions as well as perceived distortions. While errors on initial stops tended to be classified as substitutions, errors on initial fricatives were more often classified as distortions or distorted substitutions. Acoustic analyses confirmed and augmented perceptual judgements. The results indicated that this type of approach can be useful for furthering our understanding of the nature and underlying cause of the speech disorder in individuals with aphasia and apraxia. The implications of these findings for the distinction between phonetic and phonemic errors are discussed.

Token‐to‐token variability in adult apraxia of speech: A perceptual analysis

Background: Many researchers and clinicians have suggested that a definitive characteristic of adult apraxia of speech (AOS) is that the speech sound errors are highly variable. Furthermore, it has been argued that error variability is one means of differentially diagnosing AOS from dysarthria. The findings from studies of error variability have been mixed; however, the speech errors have been elicited in different ways and “variability” is not consistently defined across different studies, making comparisons across studies difficult. Aims: The purpose of this investigation was to characterise error variability in two speakers with AOS. Methods & Procedures: Single words were elicited in imitation with repeated trials on the same words over a period of several weeks. The speech samples were transcribed using narrow phonetic transcription and analysed for accuracy of production and consistency of error. Outcomes & Results: We found that the errors were both consistent and inconsistent, depending on how the errors were analysed, e.g., certain sounds were consistently produced in error. In addition, our data suggest that consistency of error may be related to the severity of the AOS. Conclusions: Future research should be aimed at standardising the definitions of consistency, and empirically testing the variables that may affect the observed variability. Furthermore, we need more data on error consistency from a large number of well‐described individuals with a variety of neurogenic disorders, as well as continued refinement of models of speech production that can account for the error patterns that are observed.

Motor demand-dependent improvement in accuracy following low-frequency transcranial magnetic stimulation of left motor cortex.

The role of primary motor cortex (M1) in the control of voluntary movements is still unclear. In brain functional imaging studies of unilateral hand performance, bilateral M1 activation is inconsistently observed, and disruptions of M1 using repetitive transcranial magnetic stimulation (rTMS) lead to variable results in the hand motor performance. As the motor tasks differed qualitatively in these studies, it is conceivable that M1 contribution differs depending on the level of skillfulness. The objective of the present study was to determine whether M1 contribution to hand motor performance differed depending on the level of precision of the motor task. Here, we used low-frequency rTMS of left M1 to determine its effect on the performance of a pointing task that allows the parametric increase of the level of precision and thereby increase the level of required precision quantitatively. We found that low-frequency rTMS improved performance in both hands for the task with the highest demand on precision, whereas performance remained unchanged for the tasks with lower demands. These results suggest that the functional relevance of M1 activity for motor performance changes as a function of motor demand. The bilateral effect of rTMS to left M1 would also support the notion of M1 functions at a higher level in motor control by integrating afferent input from nonprimary motor areas.

Forum Resource theory and aphasia reconsidered: Why alternative theories can better guide our research

Background: For many years, investigators have been exploring the reasons why there appear to be limits to human cognitive abilities. For example, it is difficult or even impossible for humans to perform several tasks simultaneously, depending on the nature of the tasks. Resource theory was developed to account for this limit. Resource theory asserts that humans possess a pool of cognitive resources that can be allocated to various cognitive tasks, but that this pool is limited. In more recent years, many aphasiologists have used resource theory to explain the mechanisms underlying the communication performance deficits of aphasia. However, there are many problems with resource theory and alternative theories exist which can better account for the limits on human cognitive abilities and for the deficits of aphasia. Aims: The first goal of this paper is to review the fundamental problems of resource theory and to describe alternative theories that can better account for the limits of human cognitive performance, especially during the simultaneous performance of two tasks. The second and primary goal of this paper is to critically evaluate studies of aphasia that have used resource theory to account for the findings and to describe how alternative theories can better account for these observations. Main Contribution: This paper provides a review and evaluation of alternative theories to resource theory, which has not been included in previous papers on aphasia and resource theory. It is important for aphasiologists to be aware of these alternative theories, so that they can critically evaluate resource theory as applied to aphasia. Conclusions: Resource theory is not a true scientific theory as defined by Popper. Aphasiologists are investing resources in testing this theory, and this distracts them from testing true scientific theories that can better account for the underlying deficits of aphasia.