Verbal reaction time patterns in aphasic adults: consideration for apraxia of speech

Verbal reaction time patterns were compared in aphasic adults presenting anterior and posterior left hemisphere lesions. Reaction Times were measured from simultaneous recording of the subjects' verbal responses and electromyographic activity from three oral-facial sites. Total Reaction Time was fractionated into Premotor Time and Motor Time components to assess latencies associated with motor speech planning and execution. The results suggested that only anterior lesions result in deficits in motor speech planning and/or execution while posterior lesion patients perform no differently than normal. The evidence supports traditional concepts regarding apraxia of speech as being associated with frontal lobe lesions.     

An interpretation of research on feedback interruption in speech

The controversial question of the scope of sensory control in the voluntary motor patterns involved in speech is examined by reviewing studies in which the auditory, tactile, and proprioceptive feedback channels have been distorted or interrupted. The author makes a case for open loop control of well-learned speech patterns under normal circumstances. The concept of internal feedback is introduced as a possible control system of skilled speech, whereas response feedback and external feedback are viewed as necessary for children developing speech or adults learning new speech patterns.     

An interpretation of research of feedback interruption in speech.

The controversial question of the scope of sensory control in the voluntary motor patterns involved in speech is examined by reviewing studies in which the auditory, tactile, and proprioceptive feedback channels have been distorted or interrupted. The author makes a case for open loop control of well-learned speech patterns under normal circumstances. The concept of internal feedback is introduced as a possible control system of skilled speech, whereas response feedback and external feedback are viewed as necessary for children developing speech or adults learning new speech patterns.     

Converging evidence for the role of relative timing in speech

In an earlier article (Tuller, Kelso, & Harris, 1982a) we suggested that the timing of consonant-related muscle activity was constrained relative to the period between onsets of muscle activity for successive vowels. Here, we reexamine those data based on reservations posed by Barry (1983). Next, we present a kinematic study of articulation that extends and strongly supports our original observations. Finally, we very briefly survey some converging lines of evidence for a functionally significant vowel-to-vowel period in speech and how this may relate to the role of temporal invariance in motor skills in general.     

The role of the perioral reflex in lip motor control for speech.

The analysis of spinal and brainstem reflexes has been shown to be a useful method of quantifying the various inputs to motoneuron pools involved in voluntary motor control. This work is selectively reviewed as a background to a discussion of the role of the perioral reflex in lip motor control for speech. Data on the sensorimotor innervation of the lips and the static and dynamic properties of the perioral reflex are presented in support of the notions that (1) perioral reflex analysis provides a viable technique for analyzing brainstem excitability changes underlying lip muscle contraction for speech, and (2) the perioral reflex loop is an important functional element in lip motor control for speech.     

The effects of simulated stuttering and prolonged speech on the neural activation patterns of stuttering and nonstuttering adults

Functional magnetic resonance imaging was used to investigate the neural correlates of passive listening, habitual speech and two modified speech patterns (simulated stuttering and prolonged speech) in stuttering and nonstuttering adults. Within-group comparisons revealed increased right hemisphere biased activation of speech-related regions during the simulated stuttered and prolonged speech tasks, relative to the habitual speech task, in the stuttering group. No significant activation differences were observed within the nonstuttering participants during these speech conditions. Between-group comparisons revealed less left superior temporal gyrus activation in stutterers during habitual speech and increased right inferior frontal gyrus activation during simulated stuttering relative to nonstutterers. Stutterers were also found to have increased activation in the left middle and superior temporal gyri and right insula, primary motor cortex and supplementary motor cortex during the passive listening condition relative to nonstutterers. The results provide further evidence for the presence of functional deficiencies underlying auditory processing, motor planning and execution in people who stutter, with these differences being affected by speech manner.     

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.     

Some relationships between adaptation and electromyographic activity at laryngeal and masseter sites in stutterers

Cumulative integrated electromyographic (EMG) activity was recorded from laryngeal and masseter sites from ten stutterers during a five trial oral adaptation sequence. Results showed more activity at the laryngeal site than the masseter site. While significant reductions in EMG activity were not found, patterns were shown to be related to the subjects' dysfluency patterns over trials. Results were interpreted as suggesting that reduced muscle activity and adaptation (when they occur) are artifacts of other behavioral modifications resulting from overt motor practice.     

The postnatal development of the motor speech area: a preliminary study

This preliminary study follows the maturation of motor speech areas and their adjacent orofacial motor zones in the right and left hemispheres of the human infant from 3 months to 72 months of age. Quantitative studies of basilar dendrite patterns of layer 5 cortical pyramids are reported in 17 age-graded subjects. The sequence of developmental changes is characterized by early (3 month) prominence of orofacial motor zones over motor speech areas and of the right hemisphere over the left as expressed in total basilar dendritic length and the length of proximal order dendritic segments. The complex series of changes which follow appear to involve increase in number and marked increase in length of the developing distal order segments and possible shortening of the proximal segments. During a variable sequence of apparent growth spurts and resorptions, dendrite arborizations of the motor speech areas overtake and exceed those of orofacial musculature and the total length of dendrite systems on the left finally exceeds those on the right, although even in the most mature group, (42-72 months), distal segment length in the right motor speech area still exceeds that of the left. The early structural primacy of right-sided dendrite systems and the progressive shift to left-sided primacy is considered in the light of the presence of a long phylogenetic and ontogenetic history of gross anatomical asymmetry favoring the left side. The possibility that developmental patterns of the cortical macroenvironment and microenvironment may be dissociated with the microenvironment depending heavily on epigenetic factors receives support from recent data suggesting the existence of a time window or critical period during which primary language proficiency must be attained if normal lateralization of language function is to occur.     

Control of multimovement coordination: sensorimotor mechanisms in speech motor programming

The present paper provides some hypotheses concerning the role of sensorimotor mechanisms in the coordination and programming of multimovement behaviors. The primary database is from experiments on the control of speech, a motor behavior that inherently requires multimovement coordination. From these data, it appears that coordination may be implemented by calibrated, sensorimotor actions which couple multiple movements for the accomplishment of common functional goals. The data from speech and select observations in other motor systems also reveal that these sensorimotor linkages are task-dependent and may underlie the intermovement motor equivalence that characterizes many natural motor behaviors. In this context, it is hypothesized also that motor learning may involve the calibration of these intermovement sensorimotor actions. These observations in turn provide some alternative perspectives on the concept of a motor program, primarily suggesting that individual movements and muscle contractions are not wholly prespecified, but shaped by sensorimotor adjustments.     

Control of Multimovement Coordination

The present paper provides some hypotheses concerning the role of sensorimotor mechanisms in the coordination and programming of multimovement behaviors. The primary database is from experiments on the control of speech, a motor behavior that inherently requires multimovement coordination. From these data, it appears that coordination may be implemented by calibrated, sensorimotor actions which couple multiple movements for the accomplishment of common functional goals. The data from speech and select observations in other motor systems also reveal that these sensorimotor linkages are task-dependent and may underlie the intermovement motor equivalence that characterizes many natural motor behaviors. In this context, it is hypothesized also that motor learning may involve the calibration of these intermovement sensorimotor actions. These observations in turn provide some alternative perspectives on the concept of a motor program, primarily suggesting that individual movements and muscle contractions are not wholly prespecified, but shaped by sensorimotor adjustments.     

Cerebellar structure and function: making sense of parallel fibers

Many parts of the brain have to cooperate in a finely tuned way in order to generate coordinated motor output. Parameters of these cooperations are adjusted during early childhood development and years of motor learning later in life. The cerebellum plays a special role in the concert of these brain structures. With the unusual geometrical arrangement of its neuronal elements, especially of parallel fibers and Purkinje cells the cerebellum is a selective and sensitive detector of a specific class of spatio-temporal activity patterns in the mossy fiber system: sequences of excitatory input which 'move' along the direction of parallel fibers at about 0.5 m/s, i.e. the speed of spike conductance in parallel fibers. Precise spatio-temporal neuronal activity patterns have been shown to occur in two major sources of afference to the cerebellum, the neocortex and the sensory feedback system. Based on our own experimental work and the above-mentioned findings we suggest that the cerebellum detects specific spatio-temporal activity patterns which trigger learned cerebellar output related to motor control and which contributes to the control of precise timing of muscle contraction.     

Synchronized neuronal oscillations and their role in motor processes

Recant data on the relationship of brain rhythms and the simultaneous oscillatory discharge of single units to motor preparation and performance have largely come from monkey and human studies and have failed to converge on a function. However, when these data are viewed in the context of older data from cats and rodents, some consistent patterns begin to emerge. Synchronous oscillatory activity, at any frequency, may be an integrative sensorimotor mechanism for gathering information that can be used to guide subsequent motor actions. There is also considerable evidence that brain rhythms can entrain motor unit activity. It is not clear yet whether the latter influence is a means of organizing muscle phase relationships within motor acts, or is simply a 'test pulse' strategy for checking current muscle conditions. Moreover, although the traditional association of faster brain rhythms with higher levels of arousal remains valid, arousal levels are correlated so tightly with the dynamics of sensorimotor control that it may not be possible to dissociate the two.     

Effects of stimulus response compatibility on covert imitation of vowels

When we observe someone else speaking, we tend to automatically activate the corresponding speech motor patterns. When listening, we therefore covertly imitate the observed speech. Simulation theories of speech perception propose that covert imitation of speech motor patterns supports speech perception. Covert imitation of speech has been studied with interference paradigms, including the stimulus–response compatibility paradigm (SRC). The SRC paradigm measures covert imitation by comparing articulation of a prompt following exposure to a distracter. Responses tend to be faster for congruent than for incongruent distracters; thus, showing evidence of covert imitation. Simulation accounts propose a key role for covert imitation in speech perception. However, covert imitation has thus far only been demonstrated for a select class of speech sounds, namely consonants, and it is unclear whether covert imitation extends to vowels. We aimed to demonstrate that covert imitation effects as measured with the SRC paradigm extend to vowels, in two experiments. We examined whether covert imitation occurs for vowels in a consonant–vowel–consonant context in visual, audio, and audiovisual modalities. We presented the prompt at four time points to examine how covert imitation varied over the distracter’s duration. The results of both experiments clearly demonstrated covert imitation effects for vowels, thus supporting simulation theories of speech perception. Covert imitation was not affected by stimulus modality and was maximal for later time points.

     

Unilateral control of bilaterally symmetrical movement as factor in lateralization of speech.

A number of bilaterally symmetrical motor patterns, preformed in their basic topography at brainstem levels, are most efficiently guided through unilateral input. This concept is related to the lateralization of speech.     

The role of the primary motor cortex during skill acquisition on a two-degrees-of-freedom movement task

One can partially eliminate motor skills acquired through practice in the hours immediately following practice by applying repetitive transcranial stimulation (rTMS) over the primary motor cortex. The disruption of acquired levels of performance has been demonstrated on tasks that are ballistic in nature. The authors investigated whether motor recall on a discrete aiming task is degraded following a disruption of the primary motor cortex induced via rTMS. Participants (N = 16) maintained acquired performance levels and patterns of muscle activity following the application of rTMS, despite a reduction in corticospinal excitability. Disruption of the primary motor cortex during a consolidation period did not influence the retention of acquired skill in this type of discrete visuomotor task.     

Event-related Desynchronization of Mu Rhythms During Concentric and Eccentric Contractions

The purpose of this study was to compare the electroencephalographic (EEG) patterns and reaction times (RTs) of muscle activation between concentric and eccentric biceps brachii contractions under the RT paradigm and to evaluate how the EEG patterns and RTs changed with practice. Sixteen subjects performed 3 sets of 30 repetitions of submaximal voluntary concentric and eccentric biceps contractions. RT, event-related desynchronization (ERD) patterns of mu rhythm onset, and ERD amplitudes were selectively analyzed. Mental demand decreased as familiarity with the motor action increased due to practice regardless of contraction type. However, the 2 types of muscle contractions still have differences in brain activity regardless of decreased mental demand: eccentric contractions require earlier preparation than concentric contractions.     

Atypical speech lateralization in adults with developmental coordination disorder demonstrated using functional transcranial Doppler ultrasound

Research using clinical populations to explore the relationship between hemispheric speech lateralization and handedness has focused on individuals with speech and language disorders, such as dyslexia or specific language impairment (SLI). Such work reveals atypical patterns of cerebral lateralization and handedness in these groups compared to controls. There are few studies that examine this relationship in people with motor coordination impairments but without speech or reading deficits, which is a surprising omission given the prevalence of theories suggesting a common neural network underlying both functions. We use an emerging imaging technique in cognitive neuroscience; functional transcranial Doppler (fTCD) ultrasound, to assess whether individuals with developmental coordination disorder (DCD) display reduced left‐hemisphere lateralization for speech production compared to control participants. Twelve adult control participants and 12 adults with DCD, but no other developmental/cognitive impairments, performed a word‐generation task whilst undergoing fTCD imaging to establish a hemispheric lateralization index for speech production. All participants also completed an electronic peg‐moving task to determine hand skill. As predicted, the DCD group showed a significantly reduced left lateralization pattern for the speech production task compared to controls. Performance on the motor skill task showed a clear preference for the dominant hand across both groups; however, the DCD group mean movement times were significantly higher for the non‐dominant hand. This is the first study of its kind to assess hand skill and speech lateralization in DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance. This fits alongside previous work showing atypical cerebral lateralization in DCD for other cognitive processes (e.g., executive function and short‐term memory) and thus speaks to debates on theories of the links between motor control and language production.     

Effects of physical fatigue and cognitive challenges on the potential for low back injury

There is no question that the motor control system will adapt under fatiguing conditions; however, there is documented evidence showing that when fatigued or challenged, the motor control system will, on occasion, perform inappropriate muscle sequencing, increasing the risk of injury, or directly causing injury. Knowing that inappropriate muscle activations can lead to injury, the purpose of this study was to investigate motor patterns during cognitive and physical challenges. Rather than ensure change with severe challenges, milder challenges were purposefully chosen. Eight male subjects performed a low external load task performed near end ROM while in an unchallenged state, and while in three challenged states: passive tissue creep, muscle fatigue and cognitive distraction. Data were collected using EMG of the trunk muscles and angular displacement of the lumbar spine. Comparison of motor control patterns between the unchallenged state and each of the three challenged conditions showed no systematic differences. However, several random anomalies were observed. A case study of a single subject was chosen to show inappropriate motor control during one trial under the cognitive distraction conditions. The response of the motor control system is very individualized and does on occasion produce inappropriate motor patterns. This supports the notion that injury may also occur as the result of random motor control errors as well as predictable, systematic changes.     

Syllable frequency and syllable structure in apraxia of speech

Recent accounts of the pathomechanism underlying apraxia of speech (AOS) were based on the speech production model of Levelt, Roelofs, and Meyer, and Meyer (1999)1999. The apraxic impairment was localized to the phonetic encoding level where the model postulates a mental store of motor programs for high-frequency syllables. Varley and Whiteside (2001a) assumed that in patients with AOS syllabic motor programs are no longer accessible and that these patients are required to use a subsyllabic encoding route. In this study, we tested this hypothesis by exploring the influence of syllable frequency and syllable structure on word repetition in 10 patients with AOS. A significant effect of syllable frequency on error rates was found. Moreover, apraxic errors on consonant clusters were influenced by their position relative to syllable boundaries. These results demonstrate that apraxic patients have access to the syllabary, but that they fail to retrieve the syllabic motor patterns correctly. Our findings are incompatible with a subsyllabic route model of apraxia of speech.