An optimal period for setting sustained variability levels.

In two experiments, we investigated how explicit reinforcement of highly variable behavior at different points in training affected performance after the requirement was eliminated. Two versions of a computer game, differing in the number of possible solution paths, were used. In each, an optimal period of training for producing sustained high variability was found. Exposure to a high lag requirement shortly after acquisition sustained variability. Rewarding variability at other times did not have a sustained effect. The implications for learning and problem solving are discussed.

Variability, constraints, and creativity. Shedding light on Claude Monet.

Recent experimental research suggests 2 things. The first is that along with learning how to do something, people also learn how variably or differently to continue doing it. The second is that high variability is maintained by constraining, precluding a currently successful, often repetitive solution to a problem. In this view, Claude Monet's habitually high level of variability in painting was acquired during his childhood and early apprenticeship and was maintained throughout his adult career by a continuous series of task constraints imposed by the artist on his own work. For Monet, variability was rewarded and rewarding.

Kinematic analysis of tongue movements in dysarthria following traumatic brain injury using electromagnetic articulography.

Electromagnetic articulography (EMA), a technique that uses alternating magnetic fields to track the movement of miniature receiver coils affixed to the articulators, was used to assess the speed and accuracy of tongue movements exhibited by an individual with dysarthria following severe traumatic brain injury (TBI). Three receiver coils were attached to the TBI subject's tongue and the movements of these coils were recorded during five productions of three single syllable real words consisting of the lingual consonants /t, s, k/ in the word-initial position. A non-neurologically impaired adult male served as a control subject. A range of kinematic parameters was analysed from the consonant productions including the movement trajectories, velocity, acceleration, distance, and duration of tongue movements. Examination of the complex interactions between the kinematic parameters recorded for the TBI subject revealed a disturbance in the 'control' of tongue speed rather than a disturbance in speed per se, as it was found that the TBI subject exhibited difficulty in decelerating his tongue movements appropriately on the approach up to the palate during consonant production. The difficulty noted in deceleration resulted in inaccurate tongue movements that overshot the point of intent (in the case of /t/) and may have been instrumental in reducing the length of time that the tongue remained at the palate (in the case of /s/ and /k/) in comparison to the control subject. The disturbances identified in the kinematic parameters recorded provided objective insights into the nature of the articulatory disturbances responsible for the deviant speech feature, consonant imprecision, perceived in the TBI subject's speech. The study stresses the importance of examining a range of kinematic parameters and the interactions between these parameters in attempting to determine the nature of articulatory disturbances exhibited by individuals with dysarthria following TBI.

Variability in the perceptual and physiological features of dysarthria following severe closed head injury: an examination of five cases.

The perceptual and physiological features of the dysarthric speech of five severely closed-head-injured (CHI) subjects were examined in a case-by-case analysis. The five male CHI subjects included in the study were selected to reflect the range of severity and types of dysarthria evident in the CHI population. The perceptual profiles of each subject consisted of the findings of a perceptual speech analysis, the Frenchay Dysarthria Assessment (FDA) and the Assessment of the Intelligibility of Dysarthric Speakers (ASSIDS). The subjects' physiological profiles included the results of instrumental assessments of the respiratory, laryngeal, velopharyngeal and articulatory subsystems of the speech-production mechanism. The case studies highlighted the variability among the individual subjects with respect to the location, physiological nature, and severity of impairment in their speech-production mechanisms. In addition, the interdependence of the various speech subsystems in determining speech outcome, the presence of differential subsystem impairment in dysarthria following CHI, and the varied therapeutic requirements of the individual subjects were identified. Clinically, the case studies highlighted the importance of developing individual treatment programmes based on comprehensive perceptual and physiological evaluations of the speech mechanism in each CHI subject with dysarthric speech.

Lip function in subjects with upper motor neuron type dysarthria following cerebrovascular accidents.

The lip function of 16 speakers with upper motor neuron damage following cerebrovascular accident (CVA), was investigated using instrumental measures. Sixteen, non-neurologically impaired adults matched for age and sex served as controls. The results of the instrumental investigations revealed that the CVA speakers had patterns of lip function that were significantly different from the control speakers. Specifically, on maximum force tasks, the CVA speakers were found to produce significantly lower maximum lip force values. Maximum rate of attempts at lip movement was also slower in the CVA speakers. In addition, the instrumental investigation revealed that the CVA speakers demonstrated a significant decline in pressure over the course of the task involving 10 attempts at maximum lip force. In contrast, the control speakers maintained a consistent level of force throughout the 10 repetitions/attempts. Overall, the findings suggest that the CVA speakers have deficits in maximum lip force, endurance of lip strength and rate of lip movements. Correlations conducted between instrumental measures of maximum lip strength and the perceptual ratings of overall intelligibility, precision of consonants, precision of vowels and length of phonemes revealed no significant relationship.

Impaired tongue strength and endurance in developmental verbal dyspraxia: a physiological analysis.

Tongue strength and endurance measures were obtained from six children with developmental verbal dyspraxia (DVD) aged between 5;6 years and 11;5 years and compared to those achieved by six normal speaking controls matched for age and sex. The instrument for measuring tongue strength comprised an air-filled soft rubber bulb connected to a pressure transducer. The results indicated that the DVD group had weaker lingual musculature than the controls. In addition the DVD subjects exhibited significantly reduced tongue strength endurance compared with the controls. Overall the findings support the hypothesis that a motor impairment forms at least part of the basis of DVD and may be indicative of the presence of a concomitant dysarthria in children with DVD, or may reflect an underspecification of the motor programme. The need for revision of contemporary taxonomies relating to childhood motor speech disorders is discussed.

Abnormal patterns of speech breathing in dysarthric speakers following severe closed head injury.

The respiratory abilities of a group of 20 subjects with a speech disorder resulting from severe closed head injury (CHI) were assessed using both spirometric and kinematic techniques and compared with those of a group of 20 non-neurologically impaired controls matched for age and gender. Results of the spirometric assessment showed that the CHI subjects as a group had lower vital capacities and lower forced expiratory volumes 1 second than the controls. Kinematic assessment also showed that the CHI subjects had problems co-ordinating the action of the rib-cage and abdomen when carrying out speech tasks such as vowel prolongations, syllable repetitions and reading. Results are discussed in terms of the effects of CHI on neuromuscular function.

Hypernasality in dysarthric speakers following severe closed head injury: a perceptual and instrumental analysis.

Hypernasality in the dysarthric speech of 20 severely closed-head-injured (CHI) subjects was investigated using both perceptual and instrumental techniques. A perceptual analysis of the speech of the CHI subjects was performed using a four-point rating scale for hypernasality. Instrumental assessment was carried out using a computerized accelerometric technique yielding a nasal coupling index. Results revealed a high incidence of perceived hypernasality (95%) in the speech of subjects in the CHI group. More than half of these subjects exhibited hypernasality of speech to a moderate to severe degree. When compared with a control group matched for age and sex the severely CHI subjects were perceived as being significantly more hypernasal. Instrumental assessment revealed that the functioning of the velopharyngeal valve in the group of CHI subjects was significantly impaired compared to the control group. The study highlighted the need to evaluate the perceptual and instrumental assessment results for the severely CHI subjects on an individual basis. The clinical implications of these findings are discussed.

Respiratory kinematics in speakers with cerebellar disease.

The respiratory abilities of a group of 12 speech disordered subjects with cerebellar disease were assessed using both spirometric and kinematic techniques and compared to those of a group of 12 non-neurologically impaired controls matched for age and gender. Results of the spirometric assessment showed that although all of the cerebellar-diseased subjects had normal total lung capacities, almost half had vital capacities below normal limits. All except 1 of the cerebellar-diseased subjects exhibited irregularities in their chest wall movements while performing sustained vowel and syllable repetition tasks. Over half of the cerebellar-diseased subjects also displayed similar irregularities when reading and conversing. The same irregularities were not present in the chest wall movements exhibited by the control subjects suggesting that their presence was caused by the cerebellar disease. Results are discussed in terms of the effects of cerebellar disease on neuromuscular function.

Effects of reinforcing preselected approximations on the topography of the rat's bar press.

The effects of different shaping approximations on the topography of the rat's bar press were investigated in two experiments. Behavior was classified into discrete components, and changes in components and their sequential organization were analyzed. Experiment 1 examined response form early in training and found that specific components reinforced during shaping were incorporated into press sequences. Experiment 2 investigated how response form changed when a shaping contingency was relaxed later in training. Two topographies were selected for reinforcement, and both appeared in the press sequences of all subjects by the end of shaping. Subsequently, all variations of bar pressing were reinforced, and neither topography was necessary to satisfy the contingency. Although the frequency of the topographies reinforced during shaping declined for 3 of 4 subjects during this phase, the most frequent press sequence for 2 rats at the end of training included both unnecessary topographies. Variability in press topographies declined when all emitted variants were reinforced. However, all subjects emitted novel response forms throughout training. The results demonstrate that specific response-reinforcer contingencies influence response form by modulating component availability and organization.