Biomedical subjects

Steve Hansen

Publications and source records attributed to Steve Hansen.

10 recordsLinked to original sources

PubMed2006

Inferring online and offline processing of visual feedback in target-directed movements from kinematic data.

Vision plays an important role in the planning and execution of target-directed aiming movements. In this review, we highlight the limitations that exist in detecting visual regulation of limb trajectories from traditional kinematic analyses such as the identification of discontinuities in velocity and acceleration. Alternative kinematic analyses that involve examining variability in limb trajectories to infer visual control processes are evaluated. The basic assumption underlying these methods is that noise exists in the neuromotor system that subsequently leads to variability in motor output. This leads to systematic relations in limb trajectory variability at different stages of the movement that are altered when trajectories are modified during movement execution. Hence, by examining the variability in limb trajectories and correlations of kinematic variables throughout movement for vision and no vision conditions, the contribution of visual feedback in the planning and control of movement can be determined.

Animals↗

PubMed2006

Optimizing rapid aiming behaviour: Movement kinematics depend on the cost of corrective modifications.

Recent studies have shown that the initial impulse associated with goal-directed aiming movements typically brings the limb to a position short of the target. This is because target overshooting is associated with greater temporal and energy costs than target undershooting. Presumably these costs can be expected to vary not only with the muscular forces required to move the limb, but also the gravitational forces inherent in the aiming task. In this study we examined the degree to which primary movement endpoint distributions depend on the direction of the movement with respect to gravity. We hypothesized that the magnitude of an undershoot bias would be greatest for downward movements because target overshooting necessitates a time and energy consuming movement reversal against gravity. Participants completed rapid aiming movements toward targets located above and below, as well as proximal and distal to a central home position. Movements were made both with and without additional mass attached to the limb. Although movement time did not vary with experimental condition, primary movement endpoint distributions were consistent with our predictions. Specifically, both greater undershooting and greater endpoint variability was associated with downward aiming movements. As well, a greater proportion of the overall movement time was spent in the corrective phase of the movement. These results are consistent with models of energy minimization that posit an inherent efficiency of control and hold that movements are organized to minimize movement time and energy expenditure and maximize mechanical advantages.

Adult↗

PubMed2006

The influence of advance information about target location and visual feedback on movement planning and execution.

This study was designed to determine if movement planning strategies incorporating the use of visual feedback during manual aiming are specific to individual movements. Advance information about target location and visual context was manipulated using precues. Participants exhibited a shorter reaction time and a longer movement time when they were certain of the target location and that vision would be available. The longer movement time was associated with greater time after peak velocity. Under conditions of uncertainty, participants prepared for the worst-case scenario. That is, they spent more time organizing their movements and produced trajectories that would be expected from greater open-loop control. Our results are consistent with hierarchical movement planning in which knowledge of the movement goal is an essential ingredient of visual feedback utilization.

Adult↗

PubMed2006

The visual regulation of goal-directed reaching movements in adults with Williams syndrome, Down syndrome, and other developmental delays.

Williams syndrome (WS) is a genetic disorder that causes general cognitive and developmental delays. Compared to persons with Down syndrome (DS) at the same developmental level, individuals with WS generally exhibit superior expressive language abilities, but have difficulty with tasks that require the visual control of movement. Recently it has been suggested that this latter problem reflects a deficit in dorsal stream function. In the present study, this hypothesis was investigated by examining the kinematics of rapid aiming movements. The performance of the participants with WS (n=4) was compared to the performance of participants with DS (n=8), with undifferentiated developmental delays (n=8), and from the general population (n=8). In partial support of the dorsal deficit hypothesis, the results suggest that, compared to people from the other groups, the participants with WS had difficulty in preparing their movements on the basis of the visual and other information available to them. This was particularly evident in their inability to properly scale movement velocities to the amplitude of the movements and in the number of discrete corrections made during movement execution.

Adult↗

PubMed2006

Attentional and motor response priming in a bimanual task.

This study examined the performance of the upper limbs during responses to previously cued and un-cued locations. Participants made unimanual and bimanual responses under homologous and non-homologous muscular control, within a cuetarget (Experiment 1; n = 10), and a target-target (Experiment 2; n = 10) aiming protocol. The inhibition of return (IOR) to a target location was expected to increase with (a) an increase in the organization of the movement response required, and (b) the decrease in the muscular coupling under which the bimanual movement was performed. IOR was observed in both experiments when participants completed their movements in either the unimanual or homologous conditions, but not in the non-homologous condition. In addition, reaction times were significantly shorter when a movement preceded the response than when no manual response was made to the initial visual cue. The results indicate that common processing delays in response to exogenously cued targets are dependent on the muscular control of those responses. Thus, this study provides evidence that IOR is moderated by the muscular control under which the bimanual movement was performed indicating an influential involvement of the motor system in both the movement planning and movement response to multiple target stimuli.

Adolescent↗

PubMed2005

Nomadic inhibition of attention and motor responses.

Klein and MacInnes [Klein, R. M., & MacInnes, W. J. (1999). Inhibition of return is a foraging facilitator in visual search. Psychological Science, 10, 346-352] posited that the function of a phenomenon known as the inhibition of return (IOR) [Posner, M. I., & Cohen, Y. (1984). Components of visual orienting. In H. Bouma, & D. G. Bouwhuis (Eds.), Attention and performance X: Control of language processes (pp. 531-554). Hillsdale, NJ: Erlbaum] is to facilitate the foraging of food and objects in the environment. Once a target object has been identified either the location of that target in space or a movement to that target is inhibited in order to allow the performer to shift his/her attention to something new. Interestingly, in the majority of IOR studies, participants begin their search from a central home position. This research examined IOR in a nomadic target-target paradigm in which the home position randomly appeared at one of three target locations and attentional shifts/movements progressed to other locations. In Experiment 1, participants executed simple manual button presses in response to the sequential presentation of a home position and then two target stimuli. In Experiment 2, participants made manual-aiming movements in response to the same type of presentation. Results obtained from both experiments implicate perceptual-motor mechanisms over and above the inhibition of a specific target location or response. Inhibitory effects appear to be associated with both perceptual and motor processes, and depend not only on the temporal and spatial relations between potential targets, but also on the actions required to detect or engage the targets.

Adolescent↗

PubMed2005

Visual illusions affect both movement planning and on-line control: a multiple cue position on bias and goal-directed action.

Over the last decade, there has been an interest in the impact of visual illusions on the control of action. Much of this work has been motivated by Milner and Goodale's two visual system model of visual processing. This model is based on a hypothesized dissociation between cognitive judgments and the visual control of action. It holds that action is immune to the visual context that provides the basis for the illusion-induced bias associated with cognitive judgments. Recently, Glover has challenged this position and has suggested that movement planning, but not movement execution is susceptible to visual illusions. Research from our lab is inconsistent with both models of visual-motor processing. With respect to the planning and control model, kinematic evidence shows that the impact of an illusion on manual aiming increases as the limb approaches the target. For the Ebbinghaus illusion, this involved a decrease in the time after peak velocity to accommodate the 'perceived' size of the target. For the Müller-Lyer illusion, the influence of the figure's tails increased from peak velocity to the end of the movement. Although our findings contradict a strong version of the two visual systems hypothesis, we did find dissociations between perception and action in another experiment. In this Müller-Lyer study, perceptual decisions were influenced by misjudgment of extent, while action was influenced by misjudgment of target position. Overall, our findings are consistent with the idea that it is often necessary to use visual context to make adjustments to ongoing movements.

Cues↗

PubMed2005

Part and whole practice: chunking and online control in the acquisition of a serial motor task.

A four-component aiming movement was used to examine the relative effectiveness of part and whole practice. Following a pretest, participants were assigned to one of three practice groups. Participants in a "Whole" group practiced the four components together as a unit. A "No Overlap" group practiced the first two and last two components of the task, alternating every fifth trial. An "Overlap" group practiced the transition between the second and third components on every trial by alternating practice of the first three and last three components every five trials. Participants in all groups improved significantly from pretest to immediate posttest and maintained their performance over a 24-hr delay. Contrary to the "chunking hypothesis," participants in the No Overlap group improved as much as those in the other two groups. Kinematic data indicated that participants in all three groups learned to use response-produced feedback earlier in the individual movement trajectories. Moreover, participants appeared to acquire a general ability to make transitions between movement components rather than specific transitions. The results suggest that segmented or segmented "overlap" practice regimes may benefit learning movement sequences of short duration.

Adult↗

PubMed2005

Self-selected visual information during discrete manual aiming.

The authors examined strategic selection of visual samples during manual aiming. Participants (N = 12) wore liquid-crystal goggles while performing discrete movements to a small target. Initially, participants controlled a 40-ms visual sample via a switch in their nonaiming hand. Subsequently, experimenter-imposed strategies required participants to take visual samples before movement initiation or early or late in the movement. Although participants adopted a variety of strategies to optimize the use of vision, they were more likely to select a sample during the early stages of the movement. Experimenter-imposed early and late instructions resulted in longer movement times than did self-selected sampling. Compared with late sampling, early sampling resulted in a temporal advantage with similar accuracy.

Adult↗

PubMed2004

The Ebbinghaus illusion affects on-line movement control.

Changes in the planning and control of discrete aiming movements in response to the introduction and removal of the Ebbinghaus size-contrast illusion were examined. Movements were executed faster to targets that appeared larger following movement initiation. The differences in movement time were associated with the portion of the movement associated with on-line control. The results are inconsistent with the assumptions of the planning and control model [Behav. Brain Sci. (in press); J. Exp. Psychol. Hum. Perc. Perf. 27 (2001) 560], and the perception and action dissociation model of goal-directed movement [A.D. Milner, M.A. Goodale, The Visual Brain in Action, Oxford University Press, New York, Oxford, 1995].

Humans↗