Eric A. Roy

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.

Manual asymmetries in aimed movements

Three hypotheses for the right-hand advantage in aiming movements were examined in these experiments: (1) the right-hand system is more efficient at processing visual information during the movement; (2) subjects make more use of visual information prior to movement initiation when using the right hand; (3) the right hand is less variable in generating force in initiating the pointing response as force demands increase. In the first experiment subjects pointed at a target located directly in front of them from two starting positions which defined short (25-cm) and long (35-cm) movements. The movements were made in three movement times, fast (150 to 249 msec), medium (250 to 349 msec) and slow (350 to 449 msec), under three vision conditions—full vision, and no vision (lights out) with immediate or delayed movement initiation. Performance was measured in movement time and accuracy in amplitude of movement. The results did not completely support any of the hypotheses regarding the right-hand advantage, although the left hand was generally more variable than the right. Also, variability increased with increases in movement length and decreases in movement time. The second experiment was designed to examine further the hypotheses regarding the right-hand advantage. In this experiment the same three visual conditions were used; however, subjects made only fast (<250-msec) movements. Also six rather than two starting positions were used. The increased variability of the left hand was observed again here. Further pointing accuracy with the left hand was more adversely affected in the no-vision delay condition. The implications of these results were discussed as they pertain to understanding the processes involved in visual aiming and the observed manual asymmetries.

Pantomimed actions may be controlled by the ventral visual stream.

Abstract. Several studies have demonstrated that while perceptual judgements of object size can be biased by visual illusions, actions remain more closely scaled to true object properties. This dissociation is often cited in support of a two-stream model of visual processing, in which visual perception is thought to be mediated by a ventral stream, while goal-directed actions are controlled by a dorsal stream. Evidence suggests that pantomimed actions (i.e., actions directed toward remembered targets) are controlled differently to natural actions; indeed, it has been proposed that pantomimed actions are mediated by the ventral rather than the dorsal stream. To test this hypothesis, we examined the effect of a visual size illusion (a variation of the Müller-Lyer figure) on manual aperture formation during natural and pantomimed prehension (i.e., action) and aperture scaling (i.e., perception). As found in earlier studies, mean peak aperture (MPA) was significantly affected by the illusion in the perception task but not the natural action task. In the pantomime condition, action and perception were equally affected by the illusion as reflected by MPA. These results provide support for the hypothesis that pantomimed actions are mediated by the ventral visual processing stream, while natural actions depend on the dorsal stream.

Delayed grasping of a Müller-Lyer figure.

Abstract. Grasping movements are more sensitive to the Müller-Lyer (ML) illusion when the response is made after a brief period of visual occlusion. It is unclear whether this effect is due to (1) the elimination of on-line visual feedback, or (2) reliance on a stored perceptual representation of the target for movement planning. Here participants grasped objects from within two forms of a ML figure in four visual conditions (full vision, open-loop, brief delay, and 2-s delay) and estimated object size in the full-vision condition. Peak grasping aperture was influenced by the ML figure in the full-vision condition, although to a much smaller extent than was true for manual size estimation. The effect of the ML figure on peak grasping aperture was substantially increased in the open-loop and delay conditions, which did not differ from one another. These findings highlight the importance of on-line visual feedback for the resistance of grasping to the ML illusion and also call to attention the relevance of task factors such as target previewing, the visuomotor relevance of illusion-inducing elements, and participant strategies.

Using hand performance measures to predict handedness.

Handedness is defined by the individuals preference to use one hand predominately for unimanual tasks and the ability to perform these tasks more efficiently with one hand (Corey, Hurley, & Foundas, 2001). It is important to use performance variables to measure handedness because they are more objective than traditional hand preference questionnaires (Bryden, Pryde, & Roy, 2000a). The current study develops a predictive model of handedness as measured by the Waterloo Handedness Questionnaire (WHQ) using several performance indicators of handedness. A total of 120 individuals (60 right-handers and 60 left-handers) were asked to complete four performance-based tasks: the Grooved Pegboard (GP), the Annett pegboard (AP), finger tapping (FT), and grip strength (GS) as well as an observational measure of preference, the Wathand Box Test (WBT). Backward linear regression analysis showed that the Wathand Box measure and the laterality quotients for several performance measures (GP place, AP, and FT) combined to act as the most accurate predictors of hand preference. The predictive model of handedness developed is as follows: WHQ = -2.760- – 0.667(GP place) + 0.809(FT) + 0.234(WBT) – 0.748(AP) with an explained variance of 0.836. These results illustrate, as Corey et al. (2001) suggested, that the best predictive model of handedness combines preference measures and several performance measures that tap into different elements of motor performance. By developing this model, it is possible to get an accurate measure of handedness using objective measures.

No Evidence for Accurate Visuomotor Memory: Systematic and Variable Error in Memory-Guided Reaching

Abstract The authors explored whether the motor system has access to highly accurate information about the aiming environment after visual occlusion. Participants (N = 14) reached to 1 of 3 midsagittal targets in 4 visual conditions (open-loop, brief-delay, 500-ms delay, and 2,000-ms delay). In all conditions, the aiming environment was first viewed for 2,000 ms. Movements were cued immediately after the initial viewing period in the open-loop and brief-delay conditions. Vision was not occluded until movement onset in the open-loop condition, whereas vision was occluded coincidentally with the movement cue in the brief-delay condition. In the 2 longer delay conditions, the movement was cued following a 500- or a 2,000-ms no-vision delay period. Participants overshot the target in the open-loop condition, but that tendency was significantly reduced in the 3 delay conditions. Moreover, end-point variability was greater in the 3 delay conditions than in the open-loop condition. A speed-accuracy tradeoff account could not explain the differences between open-loop and delayed reaching. Those findings suggest that the motor system does not have access to highly accurate information about the aiming environment for any appreciable period of time following visual occlusion, consistent with the view that the visuomotor system operates in real time.

Dopaminergic modulation of timing control and variability in the gait of Parkinson's disease

The basal ganglia have been implicated in timing control, yet the nature of timing disturbances in Parkinsons disease (PD) is poorly understood. We evaluated the influence of timing cues on spatiotemporal aspects of gait control and its variability, and the impact of dopaminergic treatment on timing. Three separate groups: 19 PD (OFF state); 24 PD (ON state); and 30 control participants were tested. Participants walked on a computerized carpet at four randomized and metronome‐controlled rates: self‐paced, 60, 80, or 100 steps/min. To our knowledge, this is the first study to demonstrate that medicated PD patients had poorer timing control than patients withdrawn from medication and healthy participants when modulating timing to an external stimulus. Increased step‐to‐step timing variability and deficits in mean temporal gait characteristics revealed that the medicated PD group (in contrast to nonmedicated PD group) performed least like healthy participants. This was observable in externally‐cued conditions, but not during self‐paced gait. Similar to previous research, step length contributed to overall slowness in PD, while temporal characteristics of gait did not. Interestingly, healthy participants increased stride length with each increase in cue rate, whereas both PD groups locked their step length regardless of temporal demand. Step‐to‐step variability differences between PD and healthy (e.g. step and double‐support time measurements) may be indicative of specific basal ganglia involvement in temporal control of gait.

Neuropsychological Profile of Acute Alcohol Intoxication during Ascending and Descending Blood Alcohol Concentrations

Numerous studies have investigated the effects of alcohol on motor processes during rising and declining blood alcohol concentrations (BAC), however, relatively little research has examined the alcohol-induced impairment of cognitive performance on the two limbs of the BAC curve. This experiment administered a neuropsychological test battery to assess the degree to which rising and declining BACs during an acute dose of alcohol impair nine cognitive processes within an individual. In all, 20 healthy male social drinkers (university students) were assigned to one of two groups (n=10) who received a beverage containing either 0.0 g/kg (placebo) or 0.65 g/kg alcohol and performed the test battery when BAC was increasing and was decreasing. Comparisons of alcohol and placebo groups revealed impairment (slower response and/or increased errors) in seven of the cognitive processes: long-term verbal memory; information processing; declarative memory; inhibitory control; short-term visual memory; long-term visual memory, and visual-spatial working memory. However, some processes were impaired only during rising BACs whereas the impairment of others during declining BACs was evident only by an increase in errors. These results show cognitive tasks performed by an individual are not similarly affected by rising and declining BACs, and call attention to the importance of assessing both speed and accuracy on both limbs of the BAC curve. The particular cognitive processes differentially affected by rising vs declining BACs raised the possibility that acute alcohol intoxication may impair one cerebral hemisphere to a greater degree than the other, and this could be explored by neuroimaging techniques.

Analysis of task demands in apraxia.

Several task demands were examined in a battery of praxis tests: the movement system (limb versus axial), input modality (command versus imitation), movement complexity (single gestures versus a sequence of gestures), type of limb gesture (transitive versus intransitive), and the representational nature of the gestures. Performance accuracy for a group of left hemisphere patients was significantly lower than for two other groups of patients with either right hemisphere damage or no brain damage on all gestures. The right hemisphere patients were significantly different from the normals only for the most complex gestures involving a three movement sequence. Within the left hemisphere group performance to command was not different from imitation. Representational and nonrepresentational gestures were not different, and axial gestures was not different from the limb gestures. The transitive and complex gestures were not different but were both performed less accurately than the intransitive gestures. The implications of these findings for understanding apraxia were discussed.

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.