Search PubMed⌕ Search

Biomedical subjects

David P Carey

Publications and source records attributed to David P Carey.

8 recordsLinked to original sources
PubMed2006

Visual-proprioceptive mismatch and the Taylor illusion.

When a participant moves a hand-held target in complete darkness after an afterimage of that target has been obtained, an illusory increase (with movements away from the participant) or decrease (with movements towards the participant) in the apparent size of the afterimage is reported (the Taylor illusion, reported first in Taylor, J Exp Psychol 29: 1941). Unlike typical Emmert's Law demonstrations, the Taylor illusion shows that a motor-related signal can be used to specify distance for the computation of real size. A study by Carey and Allan (Exp Brain Res 110: 1996) found that the Taylor illusion did not occur in a condition where an afterimage of one hand was obtained while the other hand performed a movement away from the participant from directly behind the first. It was proposed that, for the illusion to manifest itself, proprioceptive and visual information must be in strict "register" when the afterimage is obtained. To evaluate this hypothesis, 14 participants performed "towards" and "away" movements after obtaining afterimages of hand-held cards. Participants wore either plain lenses or prism lenses during the trials, the latter of which displaced visual stimuli 10 degrees to the left. No significant difference was found between the two lens conditions in terms of the effect on the perception of the Taylor illusion. It was concluded that the illusory size distortions may depend on register of visual and proprioceptive position in terms of depth, rather than in the picture plane. Several suggestions for future studies of the Taylor illusion are proposed, and limitations of size judgements of afterimages are outlined.

Afterimage↗
PubMed2006

Pointing to places and spaces in a patient with visual form agnosia.

Previous investigations of visuospatial abilities in the visual form agnosic patient D.F. suggest that her egocentric sensorimotor processing is intact while her 'allocentric' judgments of spatial position are impaired. The current investigation extends these previous observations by comparing D.F.'s performance at pointing to a set of spatially distributed stimuli, either directly or by 'pantomiming' the responses in an adjacent homologous workspace. The results showed accurate sensorimotor localization when D.F. pointed directly to single targets or to sequences of targets, presumably as she could use egocentric visual coding. In spite of making relatively spared spatial judgments about the arrays, however, D.F. performed quite poorly when copying them and on the pantomimed pointing task. In this latter task good performance presumably depends on an ability to represent both the categorical and coordinate properties of the array (as does copying them), and to translate these into the effector-based coordinates required for accurate action. D.F.'s pantomimed pointing was similar to her copies of target arrays, as in both tasks there was evidence of spared (although somewhat degraded) appreciation of the relative spatial positions of the stimuli. Remarkably, her accuracy in this allocentric task was not worsened by longer pointing sequences. It is possible that D.F.'s degraded performance reflects a relative (though not complete) preservation of categorical coding within the ventral stream, despite a loss of coordinate coding there.

Adult↗
PubMed2005

Visuomotor 'immunity' to perceptual illusion: a mismatch of attentional demands cannot explain the perception-action dissociation.

Recent findings of visuomotor immunity to perceptual illusions have been attributed to a perception-action division of labour within two anatomically segregated streams in the visual cortex. However, critics argue that such experimental findings are not valid and have suggested that the perception-action dissociations can be explained away by differential attentional/processing demands, rather than a functional dissociation in the neurologically intact brain: perceptual tasks require processing of the entire illusion display while visuomotor tasks only require processing the target that is acted upon. The present study examined whether grasping of the Müller-Lyer display would remain immune to the illusion when the task required the direction of attention or a related resource towards both Müller-Lyer shafts. Twelve participants were required to match and grasp two Müller-Lyer shafts bimanually (i.e. one with each hand). It was found that bimanual grasping was not significantly affected by the illusion, while there was a highly significant illusion effect on perceptual estimation by matching. Furthermore, it was established that this dissociation did not result from a differing baseline rate of change in manual estimation and grasping aperture to a change in physical object size. These findings provide further support for the postulated perception-action dissociation and fail to uphold the idea that grasping 'immunity' to the Müller-Lyer illusions merely represents an experimental artefact.

Adult↗
PubMed2005

Tapping, grasping and aiming in ideomotor apraxia.

Very few studies have investigated sensorimotor control in apraxia using tasks that differ in movement complexity. Nevertheless, there is some evidence to suggest that spontaneous behaviour, although relatively preserved, can be rather clumsy or awkward, and that patients with ideomotor apraxia may have subtle kinematic abnormalities in movements made in the laboratory. It remains unclear whether patients with ideomotor apraxia perform normally on movements such as visually guided aiming, that may not depend on higher-order, more cognitive, processes and that are relatively unguided by overlearned contexts. In this study, three different sensorimotor tasks were given to the same sample of patients with quantified apraxic disturbance. Finger tapping, goal-directed grasping and aiming with and without visual feedback were examined in these patients. A clear dissociation was found between grossly impaired gesture imitation and intact motor programming of goal-directed movements with visual feedback. Apraxic patients were, however, impaired on aiming movements without visual feedback, suggesting that apraxia is associated with an increased reliance on integration of online visual information with feedforward/feedback somatosensory and motor signals. Furthermore, patients were impaired on single finger tapping which was a surprisingly good predictor of apraxia severity.

Aged↗
PubMed2004

Processing biases towards the preferred hand: valid and invalid cueing of left- versus right-hand movements.

A Posner-like paradigm was employed to investigate the effects of valid and invalid cueing of each hand on reaction time, movement time and peak velocity in an aiming task. Given claims of left hemisphere superiority in movement selection and inhibition (and the privileged within-hemisphere access of the right hand to such systems), it was hypothesised that invalidly cueing the left hand (i.e. right-hand movement precued, left-handed movement required by a go signal) would result in increased reaction time relative to invalid right-hand cueing. The hypothesis was not confirmed as reaction times of both hands were slowed equivalently by invalid cueing. Nevertheless, it was found that the movement duration of the left hand was increased substantially by invalid cueing, while the right hand was unaffected on this measure, suggesting a possible intentional rather than attentional difference between the two hands. These results are discussed in terms of a possible asymmetry of intentional processes related to hand movement and the right-hand advantage in movement duration.

Adult↗
PubMed2002

Neuropsychological perspectives on eye-hand coordination in visually-guided reaching.

Substantial progress has been made in understanding the neural control of movement in the past 30 years. Lower cost technology for tracking movements of the eyes and the hands has increased our understanding of these two systems and their interactions in both neurologically intact individuals and non-human primates. Nevertheless the neuropsychology of eye-hand coordination during visually-guided tasks such as reaching and grasping remains relatively understudied. This chapter reviews some of the relevant neurophysiology and neuropsychology of eye-hand coordination during visually-guided reaching. Current models emphasising coordinate transformations are discussed in light of new patient data showing a particular type of failure of eye-hand coordination during reaching.

Animals↗