PubMed Health⌕ Search

Biomedical subjects

Melvyn A Goodale

Publications and source records attributed to Melvyn A Goodale.

49 records · Page 3Linked to original sources
PubMed2003

Perceptual illusion and the real-time control of action.

Participants were cued by an auditory tone to grasp a target object from within a size-contrast display. The peak grip aperture was unaffected by the perceptual size illusion when the target array was visible between the response cue and movement onset (vision trials). The grasp was sensitive to the illusion, however, when the target array was occluded from view when the response was cued (occlusion trials). This was true when the occlusion occurred 2.5 s before the response cue (delay), but also when the occlusion coincided with the response cue (no-delay). Unlike previous experiments, vision and occlusion trials were presented in random sequence. The results suggest that dedicated, real-time visuomotor mechanisms are engaged for the control of action only after the response is cued, and only if the target is visible. These visuomotor mechanisms compute the absolute metrics of the target object and therefore resist size-contrast illusions. In other situations (e.g. prior to the response cue, or if the target is no longer visible), a perceptual representation of the target object can be used for action planning. Unlike the real-time visuomotor mechanisms, perception-based movement planning makes use of relational metrics, and is therefore sensitive to size-contrast illusions.

Cues↗
PubMed2002

Target selection for reaching and saccades share a similar behavioral reference frame in the macaque.

The selection of one of two visual stimuli as a target for a motor action may depend on external as well as internal variables. We examined whether the preference to select a leftward or rightward target depends on the action that is performed (eye or arm movement) and to what extent the choice is influenced by the target location. Two targets were presented at the same distance to the left and right of a fixation position and the stimulus onset asynchrony (SOA) was adjusted until both targets were selected equally often. This balanced SOA time is then a quantitative measure of selection preference. In two macaque monkeys tested, we found the balanced SOA shifted to the left side for left-arm movements and to the right side for right-arm movements. Target selection strongly depended on the horizontal target location. By varying eye, head, and trunk position, we found this dependency embedded in a head-centered behavioral reference frame for saccade targets and, somewhat counter-intuitively, for reach targets as well. Target selection for reach movements was influenced by the eye position, while saccade target selection was unaffected by the arm position. These findings suggest that the neural processes underlying target selection for a reaching movement are to a large extent independent of the coordinate frame ultimately used to make the limb movement, but are instead closely linked to the coordinate frame used to plan a saccade to that target. This similarity may be indicative of a common spatial framework for hand-eye coordination.

Animals↗
PubMed2002

Learned perceptual associations influence visuomotor programming under limited conditions: cues as surface patterns.

The present set of three experiments was designed to extend the findings that visuomotor programming can make use of learned size information under some, but not all, conditions. An association was established between the size of square wooden blocks and a perceptual cue in all experiments. In Experiment 1 the perceptual cue to size was a small two-dimensional drawing of a shape affixed to the top of the blocks (e.g. triangle = large; circle = small, or vice versa). In Experiment 2 size and shape were again associated but this time a pattern of two-dimensional shapes covered the visible surface of the blocks. In Experiment 3 block size was associated with the colour of a small circle affixed to the top of the blocks (e.g. red = large; yellow = small, or vice versa). All of the subjects grasped the blocks, and on other trials estimated the size of the blocks by opening their thumb and finger a matching amount. Consistent with previous reports, in all experiments, the learned associations changed the perceived size of two test blocks halfway in size between the large and small blocks: estimations of the test block matched by shape or colour to the group of large objects were smaller than estimations of the test block matched to the group of small objects. The effect appears to result from relative-size comparisons being made between the medium-sized test blocks and the size category (large or small) associated with the matching shape or colour cue. Despite the significant effect of the learned perceptual associations on manual estimations, no effect on grip scaling was seen when the cues associated with size were single small elements centred on the top of the block (Experiment 1 and Experiment 3). Changes in grip scaling corresponded to the change in perceived size only when the cue to size covered the entire block (Experiment 2), forming a surface pattern. These findings suggest that visuomotor programming is more likely to use learned size information when the cue providing the size association covers the visible surface of the target objects, perhaps by acting as a texture that provides reliable information about the target's material and identity.

Association Learning↗
PubMed2002

Learned perceptual associations influence visuomotor programming under limited conditions: kinematic consistency.

Previous findings have suggested that visuomotor programming can make use of learned size information in experimental paradigms where movement kinematics are quite consistent from trial to trial. The present experiment was designed to test whether or not this conclusion could be generalized to a different manipulation of kinematic variability. As in previous work, an association was established between the size and colour of square blocks (e.g. red = large; yellow = small, or vice versa). Associating size and colour in this fashion has been shown to reliably alter the perceived size of two test blocks halfway in size between the large and small blocks: estimations of the test block matched in colour to the group of large blocks are smaller than estimations of the test block matched to the group of small blocks. Subjects grasped the blocks, and on other trials estimated the size of the blocks. These changes in perceived block size were incorporated into grip scaling only when movement kinematics were highly consistent from trial to trial; that is, when the blocks were presented in the same location on each trial. When the blocks were presented in different locations grip scaling remained true to the metrics of the test blocks despite the changes in perceptual estimates of block size. These results support previous findings suggesting that kinematic consistency facilitates the incorporation of learned perceptual information into grip scaling.

Association Learning↗
PubMed2002

Differential effects of viewpoint on object-driven activation in dorsal and ventral streams.

Using fMRI, we showed that an area in the ventral temporo-occipital cortex (area vTO), which is part of the human homolog of the ventral stream of visual processing, exhibited priming for both identical and depth-rotated images of objects. This pattern of activation in area vTO corresponded to performance in a behavioral matching task. An area in the caudal part of the intraparietal sulcus (area cIPS) also showed priming, but only with identical images of objects. This dorsal-stream area treated rotated images as new objects. The difference in the pattern of priming-related activation in the two areas may reflect the respective roles of the ventral and dorsal streams in object recognition and object-directed action.

Adult↗
PubMed2002

Grasping two-dimensional images and three-dimensional objects in visual-form agnosia.

Visually guided prehension is controlled by a specialized visuomotor system in the posterior parietal cortex. It is not clear how this system responds to visual stimuli that lack three-dimensional (3D) structure, such as two-dimensional (2D) images of objects. We asked a neurological patient with visual-form agnosia (patient D.F.) to grasp 3D objects and 2D images of the same objects and to estimate their sizes manually. D.F.'s grip aperture was scaled to the sizes of the 2D and 3D target stimuli, but her manual estimates were poorly correlated with object size. Control participants demonstrated appropriate size-scaling in both the grasping and manual size-estimation tasks, but tended to use a smaller peak aperture when reaching to grasp 2D images. We conclude that: (1) the dorsal stream grasping system does not discriminate in a fundamental way between 2D and 3D objects, and (2) neurologically normal participants might adopt a different visuomotor strategy for target objects that are recognized to be ungraspable. These findings are consistent with the view that the dorsal grasping system accesses a pragmatic, spatial representation of the target object, whereas the ventral system accesses a more comprehensive, volumetric description of the object.

Adult↗
PubMed2002

A temporal analysis of grasping in the Ebbinghaus illusion: planning versus online control.

Recent work has shown that pictorial illusions have a greater effect on perceptual judgements than they do on the visual control of actions, such as object-directed grasping. This dissociation between vision for perception and vision for action is thought to reflect the operation of two separate streams of visual processing in the brain. Glover and Dixon claim, however, that perceptual illusions can influence the control of grasping but that these effects are evident only at early stages of the movement. By the time the action nears its completion any effect of illusions disappears. Glover and Dixon suggest that these results are consistent with what they call a 'planning and control' model of action, in which actions are planned using a context-dependent visual representation but are monitored and corrected online using a context-independent representation. We reanalysed data from an earlier experiment on grasping in the Ebbinghaus illusion in which we showed that maximum grip aperture was unaffected by this size-contrast illusion. When we looked at these data more closely, we found no evidence for an effect of the illusion even at the earliest stages of the movement. These findings support the suggestion that the initial planning of a simple object-directed grasping movement in this illusory context is indeed refractory to the effects of the illusion. This is not to suggest that more deliberate and/or complex movements could not be influenced by contextual information.

Adult↗
PubMed2002

Understanding the contribution of binocular vision to the control of adaptive locomotion.

Abstract. Although the contribution of binocular vision to reach-to-grasp movements has been extensively studied, it has been largely ignored in locomotion. The aim of these studies was to explore the role of binocular vision during the approach phase and step over the obstacle and the contribution of head movements to acquisition of depth information under monocular vision. Binocular and monocular vision was manipulated in different phases using either an eye patch or liquid crystal glasses. Head movement relative to the trunk was restricted in the first experiment by a modified Ferno Universal Head Immobilizer attached to a rigid board strapped to the participant's back. Whole body kinematics were collected by placing infrared diodes on anatomical landmarks and using an Optotrak imaging system. Several measures related to head and limb movement were analyzed. Three major findings emerged from these studies. First, binocular vision is important for the acquisition of accurate information about the surrounding environment: accuracy but not precision of limb elevation over the obstacle was adversely affected when binocular vision was unavailable. Second, motion parallax due to self-motion provides the most critical depth information and it can be used to partially compensate for the loss of binocular vision. Although head movement is not essential to augment depth information, it is important for reorientation of the visual field to obtain the necessary information about the moving limbs when visual field is suddenly limited under monocular vision. Third, step over the obstacle is pre-planned based on visual information acquired during the approach phase: changes in visual condition during the adaptive step do not influence the limb trajectory. Collectively these three studies provide unique insights into the contribution of binocular vision during adaptive locomotion.

Adaptation, Psychological↗
PubMed2002

Haptic study of three-dimensional objects activates extrastriate visual areas.

In humans and many other primates, the visual system plays the major role in object recognition. But objects can also be recognized through haptic exploration, which uses our sense of touch. Nonetheless, it has been argued that the haptic system makes use of 'visual' processing to construct a representation of the object. To investigate possible interactions between the visual and haptic systems, we used functional magnetic resonance imaging to measure the effects of cross-modal haptic-to-visual priming on brain activation. Subjects studied three-dimensional novel clay objects either visually or haptically before entering the scanner. During scanning, subjects viewed visually primed, haptically primed, and non-primed objects. They also haptically explored non-primed objects. Visual and haptic exploration of non-primed objects produced significant activation in several brain regions, and produced overlapping activation in the middle occipital area (MO). Viewing visually and haptically primed objects produced more activation than viewing non-primed objects in both area MO and the lateral occipital area (LO). In summary, haptic exploration of novel three-dimensional objects produced activation, not only in somatosensory cortex, but also in areas of the occipital cortex associated with visual processing. Furthermore, previous haptic experience with these objects enhanced activation in visual areas when these same objects were subsequently viewed. Taken together, these results suggest that the object-representation systems of the ventral visual pathway are exploited for haptic object perception.

Adult↗
PubMed2002

Human fMRI evidence for the neural correlates of preparatory set.

We used functional magnetic resonance imaging (fMRI) to study readiness and intention signals in frontal and parietal areas that have been implicated in planning saccadic eye movements-the frontal eye fields (FEF) and intraparietal sulcus (IPS). To track fMRI signal changes correlated with readiness to act, we used an event-related design with variable gap periods between disappearance of the fixation point and appearance of the target. To track changes associated with intention, subjects were instructed before the gap period to make either a pro-saccade (look at target) or an anti-saccade (look away from target). FEF activation increased during the gap period and was higher for anti- than for pro-saccade trials. No signal increases were observed during the gap period in the IPS. Our findings suggest that within the frontoparietal networks that control saccade generation, the human FEF, but not the IPS, is critically involved in preparatory set, coding both the readiness and intention to perform a particular movement.

Brain Mapping↗
PubMed2002

Selective, non-lateralized impairment of motor imagery following right parietal damage.

Using variants of a visually guided pointing task, in which subjects make pointing movements towards targets of varying sizes, we explored motor imagery in a patient with visual neglect. When this patient actually pointed towards targets of different sizes he showed the normal correlation between movement duration (MD) and target size, such that MD increased as target size decreased. In contrast, his imagined movements did not show the same speed-accuracy trade-off observed for actual movements. This was true regardless of the hand used or the initial direction of movement (left versus right). The patient performed normally on several tasks of visual imagery, including size estimation, perceptual discrimination and localization of cities on an imagined map. This patient's performance suggests that the networks in the right parietal lobe play an important role in the generation of internal models of motor movements regardless of the hand used to perform the task.

Aged↗
PubMedDate not supplied

Behavioral and neuroimaging evidence for a contribution of color and texture information to scene classification in a patient with visual form agnosia.

A common notion is that object perception is a necessary precursor to scene perception. Behavioral evidence suggests, however, that scene perception can operate independently of object perception. Further, neuroimaging has revealed a specialized human cortical area for viewing scenes that is anatomically distinct from areas activated by viewing objects. Here we show that an individual with visual form agnosia, D.F., who has a profound deficit in object recognition but spared color and visual texture perception, could still classify scenes and that she was fastest when the scenes were presented in the appropriate color. When scenes were presented as black-and-white images, she made a large number of errors in classification. Functional magnetic resonance imaging revealed selective activation in the parahippocampal place area (PPA) when D.F. viewed scenes. Unlike control observers, D.F. demonstrated higher activation in the PPA for scenes presented in the appropriate color than for black-and-white versions. The results demonstrate that an individual with profound form vision deficits can still use visual texture and color to classify scenes-and that this intact ability is reflected in differential activation of the PPA with colored versions of scenes.

Adult↗