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Biomedical subjects

E A Roy

Publications and source records attributed to E A Roy.

At least 37 records · Page 2Linked to original sources
PubMed1998

A ratio code for vibrotactile pitch.

Subjective impressions of pitch for 80 different sinusoidal vibrotactile stimuli delivered to the index finger were measured by free magnitude estimation in four subjects. In three of the subjects, pitch at a given frequency decreased as stimulus amplitude increased. The data of these subjects were well described by a model of pitch based on the relative levels of activation of the three major tactile channels. The main element in this model was a ratio of P channel activity to the sum of the activity levels of the P, NPI, and NPIII channels. Activity levels of the channels were estimated on the basis of the psychophysical literature, including a study of vibrotactile loudness using the same subjects and stimuli as those employed here. A fourth subject, whose pattern of loudness judgments had previously been shown to differ from those of the other subjects, did not conform to this pitch model: her data revealed significant increases in pitch with increases in amplitude, and appear to reflect an inability to combine signals across vibrotactile channels. Pitch changes resulting from vibrotactile adaptation were directionally consistent with our ratio model: pitch was slightly increased by adaptation to a 25 Hz stimulus, and slightly decreased by 200 Hz adaptation.

Adaptation, Physiological↗
PubMed1998

Influence of spatial mapping on manual aiming asymmetries.

Two experiments were conducted to examine manual asymmetries in a one-dimensional aiming task. In Exp. 1, 10 right-handed adults slid a computer mouse 13 cm on a graphics tablet with both the right and left hands to targets of 3 different diameters. Under these conditions, the movement time for the right hand was significantly faster as expected. In Exp. 2, subjects performed similar movements to move a cursor 13 cm on a computer monitor. Thus the study was identical except the stimulus-response mapping was indirect. In this situation, there were no significant difference for either movement time or movement error between hands despite these performance measures indicating the target aiming was more difficult in Exp. 2. Because increases in task difficulty generally result in a greater advantage for the right hand, as indicated by Todor & Smiley, 1985, the present studies suggest that superiority of the right hand in aiming tasks may be diminished when spatial translation is required. Perhaps the spatial translation requires greater involvement of the right hemisphere, a process associated with manual advantage for the left hand, previously suggested by Roy and MacKenzie.

Adult↗
PubMed1997

On the genetics and measurement of human handedness.

Lateral preferences in humans and other primates may be a key to many important issues in biology and psychology. There is strong evidence that the representation of language functions in the cerebral cortex is different in left-handed (LH) people than in right-handed (RH) people, and an understanding of handedness may lead to valuable clues as to how the brain becomes organised in the way that it does. Although there are clearly cultural effects that influence manual activities, there is nevertheless evidence that human handedness and other lateralities are at least in part genetically determined: compared with two RH parents, one RH and one LH parent are 2-3 times more likely to have an LH child, and two LH parents are 3-4 times more likely to have an LH child. Thus, one might wish to investigate the genetics of laterality with the goal of understanding the biological mechanisms that lead to the preferential use of one hand (or eye or foot). One may also see links between human handedness and footedness and the motor asymmetries found in many nonhuman primate species, and perhaps in lower mammals as well. From this perspective, one might see the study of human laterality as relevant to evolutionary biology. Investigators of both human and nonhuman asymmetries have to grapple with such difficult measurement issues as the relations between preference and performance, and the influences of postural and task demands, and have much to offer each other in the quest for the nature of laterality. Our recent work seems to indicate that the various sensory and motor lateralities may be related, in humans, but not in a simple way. In future work, the challenge will be to identify the relations between the various laterality ''profiles'' and patterns of functional cerebral organisation.

Journal Article↗
PubMed1996

Development of morphological changes and ileal glucagon gene expression in the small intestine of lambs infected with Trichostrongylus colubriformis.

To investigate the consequences of subclinical Trichostrongylus colubriformis infection on the intestinal mucosa and the associated changes in entero-glucagon gene expression, sheep were infected with 30000 larvae and killed 5, 10, 15 or 20 days after infection. Histological and cytological changes were examined. In the main site of infection, the upper duodenum, villous atrophy associated with crypt hyperplasia developed gradually. Cytological changes in the enterocytes appeared concurrently, characterized by a progressive reduction in brush border and in the number of ribosomes in the cytoplasm, changes in the internal structure of mitochondria, and enlargement of the intercellular spaces. Neither histological nor cytological modifications were found before day 15. At the same time, villous hypertrophy developed distally, beyond the main site of infection; this was interpreted as an adaptive response to parasitism. Enteroglucagon gene expression in the ileum was measured in parallel with the mucosal changes but did not reveal any difference between infected and control sheep. The results indicate that this gastrointestinal hormone does not have a major role in the response to nematode parasitism.

Animals↗
PubMed1996

Perceived intensity of vibrotactile stimuli: the role of mechanoreceptive channels.

The perceived intensity of vibrotactile stimuli was studied by means of free magnitude estimation. Eighty different sinusoidal stimuli ranging in frequency from 10 to 200 Hz, and in amplitude from 2.4 to 154 microns, were presented to the left index fingerpad of psychophysical observers through a 5-mm-diameter contactor. Estimates at a given frequency increased with amplitude in all four subjects, and estimates at a given amplitude increased with frequency in three. For the fourth subject, however, intermediate frequencies (25-75 Hz) produced the most intense sensations; the relative sensory effectiveness of different frequencies suggested that in her case, perceived vibrotactile intensity was determined largely by signals in Meissner afferents. From the data of this unusual subject, and from high-frequency (200-Hz) measurements on the normal subjects, quantitative descriptions were derived of the signals in Meissner and Pacinian channels, respectively, that could contribute to subjective intensity. Candidate algorithms by which the signals from the two channels might interact were then evaluated by comparison of modeled and empirically determined subjective intensity values. It was found that subjective intensity is given by the sum of (1) the stronger of the two channels' signals, and (2) half the weaker signal, the latter apparently being reduced by cross-channel suppression that occurs only at suprathreshold levels. Adapting to 25-Hz vibration selectively reduces the perceived intensity of low frequencies, whereas adapting to 200-Hz vibration has a corresponding effect at high frequencies. It is concluded that an understanding of perceived vibrotactile intensity requires knowledge of the signals in vibrotactile channels, and of the interactions between those channels.

Adolescent↗
PubMed1994

Kinematic analyses of manual asymmetries in visual aiming movements.

The right hand advantage has been thought to arise from the greater efficiency of the right hand/left hemisphere system in processing visual feedback information. This hypothesis was examined using kinematic analyses of aiming performance, focusing particularly on time after peak velocity which has been shown to be sensitive to visual feedback processing demands. Eight right-handed subjects pointed at two targets with their left and right hands with or without vision available and either as accurately or as fast as possible. Pointing errors and movement time were found to be smaller with the right hand. Analyses of the temporal components of movement time revealed that the hands differed only in time after peak velocity (in deceleration), with the right hand spending significantly less time. This advantage for the right hand, however, was apparent whether or not vision was available and only when accuracy was emphasized in performance. These findings suggest that the right hand system may be more efficient at processing feedback information whether this be visual or nonvisual (e.g., proprioceptive).

Acceleration↗
PubMed1993

Movement sequencing disorders in Parkinson's disease.

Ten PD patients and ten age-matched normal controls learned a sequence of 3 or 4 different hand movements to a criterion of 5 consecutive correct trials. They also performed a control sequence of 3 or 4 movements which involved the repetition of the same hand posture. Trials to reach criterion, errors, total response time and its components, response time for each movement and inter-response time were examined. There were no group differences in trials to criterion or errors. Total movement time as well as response and inter-response times were significantly longer for the PD patients, however, but only for sequences involving different hand movements not for the repetitive sequences. The relative timing of the responses was also different with the PD patients spending proportionately more time on each response and the controls spending more time between responses. The implications of these findings for understanding the movement sequencing impairments in PD are discussed.

Aged↗
PubMed1992

Ipsilesional disruptions to reciprocal finger tapping.

Impairments in repetitive finger tapping have not been found in the ipsilesional hand, possibly because the performance measure (tapping rate) which has been used is not sufficiently sensitive. In this study, tapping performance of patients with lateralized brain damage was examined using more detailed measures reflecting intertap variability and the relative timing of each tap cycle. In concert with previous findings, neither the left- nor the right-hemisphere-damaged patients exhibited an impairment in tapping rate. An impairment in tapping variability was observed, however, but only for the left hemisphere group. It is argued that intertap variability may be particularly sensitive to left hemisphere damage as this measure reflects the demands for rather precise and consistent phasing or sequencing of muscle activation. Since left hemisphere damage often leads to deficits in making transitions between movements in a sequence, the consistent sequencing of agonist-antagonist muscle activations in tapping may be compromised. Future research directions to examine this hypothesis are discussed.

Journal Article↗
PubMed1989

Isolated and sequenced oral motor posture production under different input modalities by left-hemisphere damaged adults.

The purpose of this investigation was to use a well-refined system of oral movement notation to examine whether the quality of performances for production of elemental oral motor postures as isolated targets was similar to performances of the same postures produced as members of a sequence by left-hemisphere damaged (LHD) and normal adults. The effect of input modality was also examined using three conditions--imitation, photograph and command. Result suggested that "additional movements" and "errors of spatial alignment" prominently characterized both isolated and sequenced postural production errors made by both LHD and normal adults. The frequency of occurrence of these behaviours, however, was dramatically higher among the LHD subjects. Moreover, the quality of productions of oral postures deteriorated in sequences of increasing length among the LHD subjects but not among normal adults. No differential effect for mode of input was found for the LHD subjects but was for the normal adults. Results suggested that the inferior performances of LHD subjects on isolated gesture production are due to exaggerated augmentations and spatial targeting deficits. Sequence production was affected negatively by the same behaviours as well as a disability for "phasing" subcomponents of discrete movements as reflected by a significant increase in "complex" errors on the individual gestures comprising the sequence.

Aged↗
PubMed1988

Limb and oral praxic abilities of children with verbal sequencing deficits.

This study was concerned with children with impaired articulation, with a specific deficit in verbal sequences of consonant-vowel syllables; i.e. verbal sequenced motion rate (SMR). Speech-disordered children with and without this SMR disorder were compared with a group of control children on their performance of single limb and oral gestures and sequences of limb and oral gestures. Performances of an action requiring four different responses and of one requiring the same repeated response were also examined. The children with verbal SMR disorder had greater difficulty in performing both single and sequences of limb and oral gestures compared with the other two groups, as they also had in the task requiring four different responses. There were no differences between the groups in the task requiring the same repeated response. These findings suggest that children with verbal SMR disorder may have a generalized motor disorder which affects performance of both single gestures and sequences of gestures.

Apraxias↗
PubMed1983

Current perspectives on disruptions to limb praxis.

This article briefly presents the disruptions to limb praxis, the clinical features of the disorders, the types of errors observed for each disorder, and the mechanisms proposed to explain these disorders. The paper then focuses on a proposed model of the action system that provides a basis for examining performance of the apraxic patient. The model proposes that the action system requires the operation of two subsystems: a conceptual system and a production system. The former provides a perceptual and linguistic knowledge base for action; the latter provides the mechanisms for performing actions. Within this framework, the conceptual and production bases for disruptions to gesturing and action sequencing observed in patients with apraxia are discussed. Finally, implications for assessment and future research are presented.

Apraxias↗
PubMed1981

Interlimb transfer after adaptation to visual displacement: patterns predicted from the functional closeness of limb neural control centres.

Two experiments were designed to determine whether interlimb transfer of prism adaptation follows a pattern predicted by the functional closeness of limb control centres. Subjects were adapted to a lateral displacing prism with their right arm in conditions known to facilitate interlimb transfer. Negative aftereffect measures of target-pointing shift were taken for all limbs. If transfer to the unadapted limbs is primarily the result of some sort of visual change, scores for those limbs should not differ. However, if the functional cerebral closeness of limb control centres is a factor, the greatest shift should be evidenced in the homologous contralateral limb (left arm), followed by the ipsilateral limb (right leg), with the least shift to the diagonally opposite limb (left leg). No differences in shift among the three unadapted limbs was found in the two experiments.

Adaptation, Ocular↗
PubMed1978

Handedness effects in kinesthetic spatial location judgements.

This experiment examines hemispheric assymetry in reproduction of spatial location in the kinesthetic modality. Using a dichotomous presentation technique, blindfolded, right-handed subjects moved both arms (arm positioning task) or the thumb (thumb positioning task) of each hand simultaneously to predetermined spatial locations and were subsequently asked to reproduce these locations. The results showed a marked left hand advantage only in the thumb positioning task suggesting that the right hemisphere was superior in performing this task. These data were discussed as they relate to other evidence pertaining to cerebral hemispheric specialization in motor activities.

Dominance, Cerebral↗