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Digby Elliott

Publications and source records attributed to Digby Elliott.

At least 37 records · Page 2Linked to original sources
PubMed2005

Energy-minimization bias: compensating for intrinsic influence of energy-minimization mechanisms.

Anecdotal and scientific evidence suggest humans tend to undershoot targets in rapid movements. We investigated whether this undershoot bias derives from energy minimization mechanisms. Participants performed 200 trials of two tasks: (1) a simple slider push to a target, and (2) a modified version of (1), designed so overshooting was less energy consuming than undershooting. Results support that the undershoot bias found in (1), as well as the overshoot bias found in (2), results from an energy minimization mechanism. Energy minimization might be inherent to biological systems. Movement biases were un desirable for maximal performance. Nonetheless, participants presented biases despite financial incentives to perform maximally. Participants did, however, appear sensitive to systematic errors produced by the attraction to less energy costly responses. We suggest that the motor system is constrained such that maximal performance trades off with energetic optimality although humans are able to learn and compensate for the energy minimization biases.

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↗
PubMed2004

Gender differences in perception of self-orientation: software or hardware?

We evaluated the contribution of attentional strategy to the perception of self-orientation with and without a body tilt in the median plane. Reinking et al (1974 Journal of Personality and Social Psychology 30 807-811) found that the frame dependence of females on the rod-and-frame test could be mediated by instructions prompting them to focus on internal cues (ie arising from inside of the body). Here, we measured the influence of attentional instructions on the perception of the morphological horizon. Eleven females and thirteen males estimated their morphological horizon in an upright and a 45 degrees body tilt in the median plane under three instruction conditions. All participants first performed without attentional instructions. Then, participants performed under both internal and external attentional instructions. For females, but not for males, perception of morphological horizon was more footward in the supine than in the upright orientation. Although instructions did not eliminate gender differences, internal instructions allowed females to reduce their perceptual bias in the supine orientation.

Attention↗
PubMed2004

Movement trajectories in the presence of a distracting stimulus: evidence for a response activation model of selective reaching.

Consistent with action-based theories of attention, the presence of a nontarget stimulus in the environment has been shown to alter the characteristics of goal-directed movements. Specifically, it has been reported that movement trajectories veer away from (Howard & Tipper, 1997) or towards (Welsh, Elliott, & Weeks, 1999) the location of a nontarget stimulus. The purpose of the experiments reported in this paper was to test a response activation model of selective reaching conceived to account for these variable results. In agreement with the model, the trajectory changes in the movements appear to be determined by the activation levels of each competing response at the moment of response initiation. The results of the present work, as well as those of previous studies, are discussed within the framework of the model of response activation.

Adult↗
PubMed2004

Multimodal inhibition of return effects in adults with and without Down syndrome.

Data from a previous study (Welsh & Elliott, 2001) has been reanalyzed to explore inhibition of return (IOR) effects in adults with and without Down syndrome (DS). Participants were required to react and move with either the left or right hand as quickly as possible to 1 of 2 target locations based on either a visual or a verbal cue. Although persons with DS demonstrated a different pattern of information processing capabilities, they demonstrated the same magnitude of IOR across all conditions of presentation as their peers without DS. This pattern of results provides further support for the multimodal and response-based nature of IOR. Moreover, the results indicate that the inhibitory processes that underlie IOR in the average population seem to be functional in persons with DS.

Acoustic Stimulation↗
PubMed2004

The role of oculomotor information in the learning of sequential aiming movements.

With their eyes initially on either the home, midline, or final end position, 30 participants practiced a 2-target aiming movement. After 120 acquisition trials, participants performed a retention test and were then transferred to each of the other 2 eye conditions. During acquisition, all groups improved over practice, but the home group showed the greatest improvement. The temporal improvement was most pronounced in the times spent after peak velocity. Retention and transfer tests indicated that participants performed best under eye-movement conditions that were the same as the 1 they had practiced in. There was also positive transfer of training between conditions in which the oculomotor information was similar. Thus, to optimize learning, one should practice under the same afferent and oculomotor conditions that will be required for the final performance.

Adult↗
PubMed2004

Learning to optimize speed, accuracy, and energy expenditure: a framework for understanding speed-accuracy relations in goal-directed aiming.

Over the last century, investigators have developed a number of models to explain the relation between speed and accuracy in target-directed manual aiming. The models vary in the extent to which they stress the importance of feedforward processes and the online use of sensory information (see D. Elliott, W. F. Helsen, & R. Chua, 2001, for a recent review). A common feature of those models is that the role of practice in optimizing speed, accuracy, and energy expenditure in goal-directed aiming is either ignored or minimized. The authors present a theoretical framework for understanding speed-accuracy tradeoffs that takes into account the strategic, trial-to-trial behavior of the performer. The strategic behavior enables individuals to maximize movement speed while minimizing error and energy expenditure.

Cognition↗
PubMed2004

Intermittent vision and one-handed catching: the effect of general and specific task experience.

In Experiment 1, 15 skilled and 15 less skilled participants performed 1-handed catching in 4 conditions. For both groups, catching performance deteriorated significantly when no visual information was available for 40 ms between 20-ms visual samples (20/40) and continued to decline with subsequent increases in the duration between visual samples (i.e., 20/80 and 20/120). In Experiment 2, 50 participants performed a pretest and a posttest in a 20/80 condition, separated by 4 blocks of practice (N=80). Participants who practiced with intermittent vision (20/40, 20/80, and 20/120) exhibited a significant improvement between pretest and posttest. Although general practice with intermittent vision enabled some adaptation, posttest performance did not equal performance in the 1st block of continuous vision.

Adult↗
PubMed2003

The Müller-Lyer illusion affects the planning and control of manual aiming movements.

Participants made perceptual judgments about the length of, and manual aiming movements to the opposite end of, formerly visible Müller-Lyer stimuli. The Müller-Lyer illusion affected both perceptual judgments and aiming amplitude. Manipulations of stimulus duration (10 ms or 3000 ms) and memory delay length (10 ms or 3000 ms) had no impact on the illusory effect. Aiming movements executed with vision of the hand were less affected by the illusion than movements executed without vision of the hand. The effect of the illusion on aiming amplitude remained the same between peak velocity and the end of the movement even though participants were engaged in on-line control between peak deceleration and the end of the movement. This latter finding was counter to the predictions of a hypothesis (Glover 2002) stating that illusions should only affect the early (planning) stages of movement and not the late (control) stages of movement. We conclude that a single visual representation is used for perception, motor planning, and motor control.

Adult↗
PubMed2003

Contribution of action to perception of self-orientation in humans.

In this study, we evaluated the effect of action on the perception of an egocentric illusion. Eighteen participants were asked to indicate the perceived morphological horizon under two backward body tilts from upright in the median plane (i.e. pitch) using five different response modes. The response modes varied in the degree of motor and cognitive involvement. Differences in perception of the morphological horizon between the two body tilts were significant only when proximal limb control was not involved. These results suggest that motor involvement and frame of reference may both be important in visual-vestibular illusions.

Adult↗
PubMed2003

Online versus offline processing of visual feedback in the control of movement amplitude.

Researchers have suggested that visual feedback not only plays a role in the correction of errors during movement execution but that visual feedback from a completed movement is processed offline to improve programming on upcoming trials. In the present study, we examined the potential contribution of online and offline processing of visual feedback by analysing spatial variability at various kinematic landmarks in the limb trajectory (peak acceleration, peak velocity, peak negative acceleration and movement end). Participants performed a single degree of freedom video aiming task with and without vision of the cursor under four criterion movement times (225, 300, 375 and 450 ms). For movement times of 225 and 300 ms, the full vision condition was less variable than the no vision condition. However, the form of the variability profiles did not differ between visual conditions suggesting that the contribution of visual feedback was due to offline processes. In the 375 and 450 ms conditions, there was evidence for both online and offline control as the form of the variability profiles differed significantly between visual conditions.

Adolescent↗
PubMed2003

The control of sequential aiming movements: the influence of practice and manual asymmetries on the one-target advantage.

The present experiment was conducted to explore the effect of practice on the one-target advantage in manual aiming, as well as asymmetries in intermanual transfer of training. Reaction and movement times for the first movement were longer in the 2-target than in the 1-target task, regardless of the amount of practice, hand preference and practice hand. When two movements were required, peak velocity was lower and, proportionally, more time was spent after peak velocity. Our kinematic results suggest that the one-target advantage is related to both predefined strategies as well as movement implementation processes during execution. Therefore, an integration of advance planning and on-line explanations for the one-target advantage is suggested. Regarding manual asymmetries, right-handers showed more transfer of training from the left to the right hand than vice versa. Left-handers exhibited a reversed pattern of asymmetric transfer of training to right-handers, but they were more disadvantaged using their non-dominant hand. These latter two findings have implications for models of manual asymmetry and upper limb control.

Adult↗
PubMed2003

Cerebral specialization and verbal-motor integration in adults with and without Down syndrome.

Persons with Down syndrome (DS) tend to exhibit an atypical left ear-right hemisphere advantage (LEA) for the perception of speech sounds. In the present study, a recent adaptation of the dichotic listening procedure was employed to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Although adults with DS (n = 13) demonstrated a right ear-left hemisphere advantage in the dichotic-motor task similar to their peers with (n = 14) and without undifferentiated developmental disabilities (n = 14), they showed an LEA in a free recall dichotic listening task. Based on a comparison of the laterality indices obtained from both dichotic listening procedures, it appears that the manifestation of lateral ear advantages in persons DS may dependent on the response requirements of the task.

Adult↗
PubMed2003

The effects of intermittent vision on prehension under binocular and monocular viewing.

The aim of the present study was to examine the effects of intermittent binocular and monocular vision on the preparation and execution of the transport and grasp phases of prehension, and hence the temporal limit of binocular and monocular integration. Participants in two groups (speed or accuracy) performed prehensile movements of two amplitudes (20 and 40 cm) to either a large or small object (6 x 6 x 2 and 6 x 4x 2 cm) under conditions of binocular and monocular viewing. The interval between visual samples was manipulated with liquid crystal goggles (continuous vision, 20on/60off, and 20on/120off ms). A kinematic analysis indicated that participants modified variables associated with the preparation and execution of prehension in the intermittent vision conditions when instructed to emphasize accuracy. Participants instructed to emphasize speed, modified variables associated with the preparation phase only. The impact of intermittent vision was similar under binocular and monocular viewing. Thus, for prehension, it appears that consecutive binocular or monocular samples need to occur less than 60 ms apart in order to be fully integrated for limb control.

Adult↗
PubMed2003

The utilization of visual feedback in the control of movement direction: evidence from a video aiming task.

The purpose of the present study was to establish the contribution of visual feedback in the correction of errors during movement execution (i.e., online) and the utilization of visual feedback from a completed movement in the programming of upcoming trials (i.e., offline). Participants performed 2 dimensional sweeping movements on a digitizing tablet through 1 of 3 targets, which were represented on a video monitor. The movements were performed with and without visual feedback under 4 criterion movement times (150, 250, 350, 450 msec). We analyzed the variability in directional error at 25%, 50%, 75%, and 100% of the distance between the home position and the target. There were significant differences in variability between visual conditions at each movement time. However, in the 150-msec condition, the form of the variability profiles did not differ between visual conditions, suggesting that the contribution of visual feedback was due to offline processes. In the 250-, 350-, and 450-msec conditions, there was evidence for both online and offline control, as the form of the variability profiles differed between the vision and no vision conditions.

Adolescent↗
PubMed2003

Dichotic ear advantages in adults with Down's syndrome predict speech production errors.

Intellectually challenged adults, with and without Down's syndrome (DS), pointed to drawings of animals following the dichotic presentation of animal names. Although there were no reliable ear differences between the 2 groups, there was tremendous between-persons variability within the group of participants with DS. Moreover, left-ear advantages in persons with DS were associated with more speech production errors when participants either read or repeated a string of 1 syllable words. This was not true for control participants. The relationship between ear advantage and speech errors in persons with DS could reflect their unique pattern of cerebral specialization and brain development.

Adult↗