Biomedical subjects

Digby Elliott

Publications and source records attributed to Digby Elliott.

At least 19 recordsLinked to original sources

PubMed2007

Sex differences in judging self-orientation: the morphological horizon and body pitch.

BACKGROUND: Sex differences exist for many spatial tasks. This is true for circular vection, field dependence, and perception of veridical vertical with body tilt. However, explanations for these sex differences is lacking in the literature. In this study, we investigated the nature of individual differences in the perception of self-orientation in humans. Male and female participants were asked to identify their Morphological Horizon (i.e., line perpendicular to saggital plane at eye-level) in different body orientations relative to gravity (i.e., 45 deg and 135 deg body pitch) with and without prior whole body rotation. RESULTS: Sex explained the observed differences in the perception of self-orientation only when blood distribution was least altered (i.e., 45 deg body pitch) and without prior whole body rotation. Specifically, females presented a more footward bias than males in these conditions. CONCLUSION: These results add to the literature on sex differences for spatial orientation tasks. As the differences were only observed with static conditions and when blood distribution was least affected, we concluded that sex differences in the perception of self-orientation are associated with gravireceptors (e.g., otoliths).

Adult↗

PubMed2006

The effect of response uncertainty on illusory biases of perception and action.

When task requirements were known in advance, Glazebrook et al. [C.M. Glazebrook, V.P. Dhillon, K.M. Keetch, J. Lyons, E. Amazeen, D.J. Weeks, D. Elliott, Perception-action and the Müller-Lyer illusion: amplitude or endpoint bias?, Exp. Brain Res. 160 (2005) 71-78.] demonstrated that perceptual biases associated with the Müller-Lyer illusion resulted from a misperception of figure extent, while manual aiming biases resulted from a misperception of vertex position. In this study, we examined the degree to which prior knowledge of task requirements influenced how participants coded visual-spatial information associated with Müller-Lyer configurations. Specifically, we investigated how illusory biases are affected when uncertainty exists as to whether participants will be required to make a perceptual-cognitive decision about the length of a figure or complete a rapid aiming movement to a figure vertex. Although aiming movements were completed in a similar manner regardless of the prior knowledge condition, perceptual biases were associated with a misperception of extent when the task was known and a misperception of both extent and position when the task was unknown. These findings indicate that people are flexible in the manner in which they code visual-spatial information.

Adult↗

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

The type of visual information mediates eye and hand movement bias when aiming to a Müller-Lyer illusion.

Aiming bias typically influences perception but action towards the illusory stimulus is often unaffected. Recent studies, however, have shown that the type of information available is a predictor for the expression of action bias. In the present cyclical aiming experiment, the type of information (retinal and extra-retinal) was manipulated in order to investigate the differential contributions of different cues on both eye and hand movements. The results showed that a Müller-Lyer illusion caused very similar perturbation effects on hand and eye-movement amplitudes and this bias was mediated by the type of information available on-line. Interestingly, the impact of the illusion on goal-directed movement was smaller, when information about the figure but not the hand was provided for on-line control. Saccadic information did not influence the size of the effect of a Müller-Lyer illusion on hand movements. Furthermore, the illusions did not alter the eye-hand coordination pattern. The timing of saccade termination was strongly linked to hand movement kinematics. The present results are not consistent with current dichotomous models of perception and action or movement planning and on-line control. Rather, they suggest that the type of information available for movement planning mediates the size of the illusory effects. Overall, it has been demonstrated that movement planning and control processes are versatile operations, which have the ability to adapt to the type of information available.

Adult↗

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 effect of the Müller-Lyer illusion on the planning and control of manual aiming movements.

Two experiments used Müller-Lyer stimuli to test the predictions of the planning-control model (S. Glover, 2002) for aiming movements. In Experiment 1, participants aimed to stimuli that either remained the same or changed upon movement initiation. Experiment 2 was identical except that the duration of visual feedback for online control was manipulated. The authors found that the figures visible during movement planning and online control had additive effects on endpoint bias, even when participants had ample time to use visual feedback to modify their movements (Experiment 2). These findings are problematic not only for the planning-control model but also for A. D. Milner and M. A. Goodale's (1995) two visual system explanation of illusory bias. Although our results are consistent with the idea that a single representation is used for perception, movement planning, and online control (e.g., V. H. Franz, 2001), other work from our laboratory and elsewhere suggests that the manner in which space is coded depends on constraints associated with the specific task, such as the visual cues available to the performer.

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

A kinematic analysis of how young adults with and without autism plan and control goal-directed movements.

We examined the planning and control of goal-directed aiming movements in young adults with autism. Participants performed rapid manual aiming movements to one of two targets. We manipulated the difficulty of the planning and control process by varying both target size and amplitude of the movements. Consistent with previous research, participants with autism took longer to prepare and execute movements, particularly when the index of difficulty was high. Although there were no group differences for accuracy, participants with autism exhibited more temporal and spatial variability over the initial phase of the movement even though mean peak accelerations and velocities were lower than for control participants. Our results suggest that although persons with autism have difficulty specifying muscular force, they compensate for this initial variability during limb deceleration. Perhaps persons with autism have learned to keep initial impulses low to minimize the spatial variability that needs to be corrected for during the online control phase of the movement.

Acceleration↗

PubMed2006

Integration of intermittent visual samples over time and between the eyes.

The authors investigated the integration of alternate disparate monocular inputs for binocular perception in 1-handed catching experiments (N = 14, 32, 22, and 15 participants, respectively in Experiments 1-4). They varied the no-vision interval between alternate monocular samples to measure catching performance, and they compared the alternating monocular conditions with binocular and monocular conditions with equal no-vision intervals. They found no evidence of a binocular advantage for one-handed catching in the alternating monocular conditions. Performance in monocular and alternating monocular conditions did not differ across no-vision intervals ranging from 0-80 ms and was particularly worse than performance in binocular viewing conditions when the no-vision interval was 40 ms or more. The authors argue that the dissimilarity between disparate monocular inputs created by the approaching object limited the integration of those inputs and subsequent binocular perception.

Adult↗

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

Does Joe influence Fred's action? Inhibition of return across different nervous systems.

Inhibition of return (IOR) refers to the slowing of responses to a target that appears in the same location as a previous event. Many researchers have speculated that IOR arises from inhibitory neural processes that have developed through evolution to facilitate efficient search patterns by biasing the action and/or attention of an individual towards novel locations. Throughout evolution, however, humans conducted searches as individuals as well as members of a group. In this context, we sought to determine if IOR could also be observed in the behavior of one individual after the observation of another's behavior. Consistent with our reasoning, there was no difference in the magnitude of the IOR effect found when participants followed their own response or the response of their partner. These results are discussed in the context of action-based attention and possible underlying neural mechanisms.

Adolescent↗

PubMed2005

The effects of response priming on the planning and execution of goal-directed movements in the presence of a distracting stimulus.

Two models of selective reaching have been proposed to account for deviations in movement trajectories in cluttered environments. The response vector model predicts movement trajectories should deviate towards or away from the location a distractor of little or large salience, respectively. In contrast, the response activation model predicts that a distractor with large salience should cause movement deviations towards it whereas a distractor with little salience should not influence the movement. The precuing technique was combined with the distractor interference paradigm to test these predictions. Results indicate that when the target was presented at the precued (salient) location, movements were unaffected by a distractor. Conversely, when the distractor was presented at the precued location while the target was presented at an uncued (non-salient) location, participants demonstrated increased reaction times and trajectory deviations towards the location of the distractor. These findings are consistent with the model of response activation.

Adult↗

PubMed2005

Perception-action and the Müller-Lyer illusion: amplitude or endpoint bias?

Over the past decade there has been a great deal of controversy regarding the relative impact of visual illusions on cognitive judgments and the control of goal-directed action. We report the results of two experiments indicating that perceptual biases associated with the Müller-Lyer illusion involve a misjudgment of amplitude/extent while aiming biases involve error in the specification of a movement endpoint. This dissociation of perception and action is consistent with some aspects of Milner and Goodale's two visual system model, but not others.

Adult↗

PubMed2005

Between-trial inhibition and facilitation in goal-directed aiming: manual and spatial asymmetries.

Three experiments were conducted with right-handed participants to examine between-trial inhibition and facilitation effects in goal-directed aiming. Participants were required to execute rapid left-hand or right-hand aiming movements upon illumination of a target light in left or right space. Thus, from trial to trial, participants executed movements to either the same target location or a different target location with the either same hand or the other hand. Our reaction time results indicated that participants were particularly slow in initiating their movements when they were required to return to the same target location with the other hand. This was especially the case when the right hand was required to move to a target just occupied by the left hand. For both reaction time and movement time the right hand but not the left hand exhibited an advantage when it was required to perform the same movement two times in a row. Taken together these results suggest that inhibition of return, in a target-target paradigm, is more associated with the particular spatial location of the target than the organization of a specific movement to that location. Moreover, the between-trial facilitation observed for the right hand may reflect the ability of the left cerebral hemisphere to maintain an already parameterized motor program over a short intertrial interval.

Adolescent↗

PubMed2005

Relative processing demands influence cerebral laterality for verbal-motor integration in persons with Down syndrome.

The study of cerebral specialization in the Down syndrome (DS) population has revealed an anomalous pattern of organization. In particular, dichotic-listening studies have suggested a left-ear/right hemisphere dominance for speech perception, whereas motor control research has revealed a left hemisphere dominance for executive-motor control. In the present investigation, we employed a recent adaptation of the dichotic listening procedure to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Specifically, using the selective dichotic-listening procedure, participants were required to complete a rapid left or right hand pointing movement to one of two pictorial icons corresponding to the word presented to their precued ear. We observed that persons with DS (N = 17) and age-matched controls (N = 35) exhibited a right-ear advantage (REA) for our dichotic-aiming task. While these results appear to contradict previous dichotic listening studies, we propose that the manifestation of a lateral ear advantage in the DS population may have more to do with the response requirements of the task than with the characteristics or complexity of the stimulus material.

Acoustic Stimulation↗

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↗