Biomedical subjects

Tim J Anderson

Publications and source records attributed to Tim J Anderson.

6 recordsLinked to original sources

PubMed2003

Tics and developmental stuttering.

BACKGROUND: Developmental stuttering affects 1% of the population but its cause remains unclear. Recent PET studies of metabolism in the central nervous system suggest that it may be related to dysfunction in the basal ganglia or its connections with regions of the cortex associated with speech and motor control. OBJECTIVE: To determine the presence and characteristics of involuntary movements (IMs) in people who stutter and to investigate the hypothesis that these movements may be of a very similar nature to the IMs seen in patients with movement disorders due to basal ganglia dysfunction. METHODS: Sixteen adults with developmental stuttering and 16 controls matched for sex and age were audio-videotaped while freely speaking 300 words in conversation and reading aloud 300 words. The audio data was inspected for dysfluencies and the video data was scrutinised for the presence and characteristics of IMs. RESULTS: Subjects who stuttered produced more IMs than controls during free speech (354 vs 187, p<0.05) and reading (297 vs 47, p<0.001). Most of the IMs in both groups were tics, with a greater number of both simple and complex motor tics (CMTs) in subjects who stuttered. CMTs were more frequent than simple motor tics in those who stuttered, but not in controls. The combination of repetitive eye blink followed by prolonged eye closure was found exclusively in the stuttering group, as were simple tics consisting of eyebrow raise or jaw movement. Dystonia in the form of blepharospasm was identified in a small number of subjects who stuttered. Choreic movements were not associated with stuttering. CONCLUSIONS: Developmental stuttering is associated with the presence of IMs that are predominantly simple and CMTs. This association suggests that tics and stuttering may share a common pathophysiology and supports the view that, in common with tics, stuttering may reflect dysfunction in the basal ganglia or its immediate connections.

Adolescent↗

PubMed2003

Saccadic suppression of displacement: effects of illumination and background manipulation.

In contrast to other functions which are suppressed during saccades, saccadic suppression of displacement (SSD--a decrease in sensitivity to visual displacements during saccades) has often been considered to be due to efferent processes rather than to visual masking. The aim of this study was to explicitly assess the importance of visual conditions in SSD. In two experiments, a small computer-generated target made random horizontal jumps. An infrared eye tracker was used to detect the saccade toward the new position, triggering a smaller centripetal displacement of the target. Subjects reported awareness of these intrasaccadic displacements by pressing a key. In the first experiment, the task was performed in both a well-lit environment and in darkness. In the second experiment these conditions were replicated and additional factors such as the contrast of the background and the effect of moving the target spot alone or the target plus the entire background were investigated. Unlike other forms of saccadic suppression, SSD was stronger in the dark, although subjects also had a greater bias to report detections in that condition. Other background manipulations had no effect. The effect of ambient lighting on SSD is small and subtle. Effects of other background manipulations may be overridden by the focusing of attention on a small moving target.

Adolescent↗

PubMed2002

Saccadic adaptation in neurological disorders.

The role of saccadic adaptive processes in recovery from the effects of various neurological disorders, such as myasthenia gravis, extraocular muscle palsies, and age-related macular degeneration, is reviewed. Studies of clinical populations (e.g. cerebellar disease, mild closed head injury, and opsoclonus) in which intrasaccadic displacement of visual targets has been used to stimulate adaptation are also reviewed. Our own data from such a study of 12 subjects with Parkinson's disease are presented, showing that visually guided adaptation is preserved in PD while memory-guided adaptation is impaired. This supports a model in which different brain regions subserve adaptation in different tasks.

Adaptation, Physiological↗

PubMed2002

Visuoperceptual and visuomotor deficits in developmental stutterers: an exploratory study.

Although the cause of stuttering is unknown, there is strong evidence for it being a neuromotor disorder characterised by an abnormality of higher control encompassing not only speech but other motor systems. The aim of this exploratory study was to look for the presence of non-speech/language deficits--in particular, visuomotor and visuoperceptual deficits--in persons who stutter. Twelve moderate to severe developmental stutterers were compared with a group of fluent speakers, matched for age and sex, on a range of computerized sensory-motor tasks. These tasks covered various aspects of visuomotor function--ballistic movement, dynamic steadiness, and several types of tracking--and visuoperceptual function--acuity, static perception, and dynamic perception. A novel technique was used to remove the visuospatial component from tracking performance. Stutterers had slower reaction times, less accurate random tracking, and impaired dynamic visual perception. Severity of stuttering correlated with reaction time and dynamic perception. Removal of the visuoperceptual component from tracking performance indicated that the impaired tracking in the stutterers was predominantly due to reduced dynamic perception. This is the first study to provide preliminary evidence for the presence of non-linguistic visuoperceptual and upper-limb visuomotor tracking deficits in people with moderate to severe stuttering. These findings support a neurogenic aetiology for stuttering and are compatible with evidence of an overactive dopamine system in stutterers.

Adult↗

PubMed2002

Adaptive modification of saccade amplitude in Parkinson's disease.

The accuracy of saccades (fast eye movements) is maintained over time and is an adaptive ability usually ascribed to the cerebellum. Adaptation might occur elsewhere in certain tasks, such as in the prefrontal cortex for memory-guided saccades. We hypothesized that adaptation of memory-guided saccades would be impaired in Parkinson's disease, as basal ganglia dysfunction can disrupt the operation of the prefrontal cortex, while adaptation of visually guided saccades would be preserved. Adaptation was induced by consistently yet imperceptibly displacing targets as saccades were made toward them, causing artificial saccadic inaccuracy. Twelve Parkinson's disease subjects (OFF medication) and 12 age-matched controls performed 245 visually- and memory-guided horizontal saccades in separate sessions. An infrared eye tracker detected the saccade, during which the target was displaced by 12.5% of the size of the initial jump, either in the same (centrifugal) or the opposite (centripetal) direction. Parkinson's disease subjects made smaller visually guided saccades than did controls [F(1,20) = 9.10, P < 0.01], yet both groups modified saccade size appropriately. Parkinson's disease memory-guided saccades were also smaller than those of controls [F(1,19) = 5.93, P < 0.05]. While controls decreased (by 8.6%) or increased (by 4.1%) the size of these saccades appropriately, Parkinson's disease subjects decreased saccade size in response to both centripetal adaptation (by an excessive 18.3%) and centrifugal adaptation (by 3.5%). Parkinson's disease subjects were less able to modify saccadic size appropriately when the movement size was specified in motor memory: a predilection for excessive hypometria was invoked, regardless of adaptation direction. This indicates that, in certain tasks, saccadic adaptation involves structures other than the cerebellum.

Adaptation, Physiological↗

PubMed2002

A laser-based eye-tracking system.

This paper reports on the development of a new eye-tracking system for noninvasive recording of eye movements. The eye tracker uses a flying-spot laser to selectively image landmarks on the eye and, subsequently, measure horizontal, vertical, and torsional eye movements. Considerable work was required to overcome the adverse effects of specular reflection of the flying-spot from the surface of the eye onto the sensing elements of the eye tracker. These effects have been largely overcome, and the eye-tracker has been used to document eye movement abnormalities, such as abnormal torsional pulsion of saccades, in the clinical setting.

Adolescent↗