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Biomedical subjects

M A Goodale

Publications and source records attributed to M A Goodale.

At least 55 records · Page 3Linked to original sources
PubMed1996

Reaching to ipsilateral or contralateral targets: within-hemisphere visuomotor processing cannot explain hemispatial differences in motor control.

Aiming movements made to visual targets on the same side of the body as the reaching hand typically show advantages as compared to aiming movements made to targets on the opposite side of the body midline in the contralateral visual field. These advantages for ipsilateral reaches include shorter reaction time, higher peak velocity, shorter duration and greater endpoint accuracy. It is commonly hypothesized that such advantages are related to the efficiency of intrahemispheric processing, since, for example, a left-sided target would be initially processed in the visual cortex of the right hemisphere and that same hemisphere controls the motor output to the left hand. We tested this hypothesis by examining the kinematics of aiming movements made by 26 right-handed subjects to visual targets briefly presented in either the left or the right visual field. In one block of trials, the subjects aimed their finger directly towards the target; in the other block, subjects were required to aim their movement to the mirror symmetrical position on the opposite side of the fixation light from the target. For the three kinematic measures in which hemispatial differences were obtained (peak velocity, duration and percentage of movement time spent in deceleration), the advantages were related to the side to which the motor response was directed and not to the side where the target was presented. In addition, these effects tended to be larger in the right hand than in the left, particularly for the percentage of the movement time spent in deceleration. The results are interpreted in terms of models of biomechanical constraints on contralateral movements, which are independent of the hemispace of target presentation.

Adult↗
PubMed1996

A neurological dissociation between shape from shading and shape from edges.

We studied the ability of a neurological patient, who has deficits in various aspects of form perception, to perform region segregation tasks requiring discriminations based on several image properties that are related to the three-dimensional structure of objects. The patient could discriminate the apparent three-dimensional structure and orientation of shapes defined by shading gradients, but could not make such discriminations for shapes in which edges were depicted as lines or as luminance discontinuities. These results suggest that the neural pathways that compute shape from shading gradients may be independent of those that compute shape based on edges, and, based on the patient's pattern of brain damage, they also indicate a relatively early functional separation in the requisite inputs.

Adult↗
PubMed1996

Visuomotor modules in the vertebrate brain.

Most accounts of vision assume that its function is largely perceptual, providing an internal model or representation of the external world that serves as the visual foundation for thought and action. However, the evolutionary origins of vision are not representational. Vision evolved not to provide perception of the world but to provide distal control of the many different movements that animals make. Moreover, many of these visuomotor control systems are quite modular in their input-output organization. In humans and other primates, these visuomotor modules function quite independently from the neural mechanisms mediating perception-based knowledge of the world. This division of labour between action systems and perception systems can be seen in the organization of the visual pathways in the primate cerebral cortex. The ventral stream of projections from striate cortex to inferotemporal cortex is critical to the visual perception of objects and is intimately connected with the cognitive operations, while the dorsal stream projecting from striate cortex to the posterior parietal region is essential for the required visuomotor transformations for the on-line control of skilled actions directed at those objects. The perceptual representations constructed by the ventral stream allow us to select a particular course of action with respect to objects and events in the world; the visuomotor transformations carried out by the dorsal stream allow us to program and direct any visually guided movements that are required to carry out that course of action. Thus, to understand the organization of the visual system(s), it is necessary to understand the requirements of the different output systems that vision serves.

Animals↗
PubMed1995

Dissociation between two modes of spatial processing by a visual form agnosic.

We report a dissociation between two aspects of visuospatial processing in a patient with a profound impairment in the visual perception of objects ('visual form agnosia'). The orientation-in-depth of a visual field ('visual pitch') was found to systematically influence the elevation at which she perceived her own eye level, just as it does in normal individuals; but at the same time, she was unable to discriminate perceptually the orientation-in-depth of the same visual field, a trivial task for individuals with normal vision. These results suggest that, in the normal brain, the processes that integrate orientation information from the visual field with extraretinal information about eye position are separable from those supporting the perception of the orientation of the visual field itself. The pattern of brain damage in D.F., in conjunction with the reported dissociation, suggests that the former set of processes maps onto the stream of information flowing from primary visual cortex to the posterior parietal cortex, the so-called dorsal stream, whereas the latter involves the projections from primary visual cortex to the inferotemporal cortex, the so-called ventral stream.

Adult↗
PubMed1995

Size-contrast illusions deceive the eye but not the hand.

BACKGROUND: When we reach out to pick up an object, not only do we direct our moving limb towards the location of the object, but the opening between our fingers and thumb is scaled in flight to the object's size. Evidence obtained from patients with neurological disorders has shown that the visual processing underlying the calibration of grip aperture and other movement parameters during grasping is mediated by visual mechanisms located in the cerebral cortex that are quite distinct from those underlying the experiential perception of object size and other object features. Under appropriate conditions, such dissociations can also be observed in individuals with normal vision. Here we present evidence that the calibration of grasp is quite refractory to pictorial illusions that have large effects on perceptual judgements of size. RESULTS: We used a variation of the familiar 'Titchener circles' illusion in which two target circles of equal size, each surrounded by a circular array of either smaller or larger circles, are presented side by side. Subjects typically report that the target circle surrounded by the array of smaller circles appears to be larger than the target surrounded by larger circles. In our test, two thin 'pokerchip' discs were used as the target circles. The relative size of the two discs was randomly varied so that on some trials the discs appeared perceptually different but were physically equivalent in size, and on other trials they were physically different but appeared perceptually equivalent. The perceptual judgements made by the 14 subjects in our experiment were strongly affected by this size-contrast illusion. However, when asked to pick up a disc, the scaling of the subjects grip aperture (measured opto-electronically before contact with the disc) was largely determined by the true size of the target disc and not its illusory size. CONCLUSIONS: It would seem that the automatic and metrically accurate calibrations required for skilled actions are mediated by visual processes that are separate from those mediating our conscious experiential perception. Earlier studies on patients with neurological deficits suggest that these two types of processing may depend on quite separate, but interacting, visual pathways in the cerebral cortex.

Adult↗
PubMed1995

The McCollough effect reveals orientation discrimination in a case of cortical blindness.

BACKGROUND: The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. RESULTS: Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. CONCLUSIONS: These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.

Adult↗
PubMed1995

Adapting to monocular vision: grasping with one eye.

The aim of the present study was to determine whether normal subjects with one eye covered and patients in whom one eye had been enucleated generate more head movements than subjects using binocular vision during the performance of a visually guided grasping movement. In experiment 1, 14 right-handed normal subjects were tested binocularly and monocularly in a task in which they were required to reach out and grasp oblong blocks of different sizes at different distances. Although the typical binocular advantage in reaching and grasping was observed, the overall head movement scores did not differ between these testing conditions. In experiment 2, seven right-handed enucleated patients were compared to seven age and sex-matched control subjects (tested under binocular and monocular viewing conditions), on the same task as used in experiment 1. While no differences were found in the kinematics of reaches produced by the enucleated patients and the control subjects, the patients did produce larger and faster resultant head movements, composed mainly of lateral and vertical movements. This suggests that enucleated patients may be generating more head movements in order to better utilize retinal motion cues to aid in manual prehension.

Adaptation, Physiological↗
PubMed1995

Preserved visual imagery in visual form agnosia.

We investigated the ability of a patient (D.F.) with profound visual form agnosia to perform a variety of tasks requiring visual imagery. Despite her inability to discriminate between objects and patterns of different shapes, sizes, and orientations, D.F. showed quite normal visual imagery involving these same 'visual' properties when the images were drawn from long-term memory. Thus, she was able both to scan mental images in search of particular features and to form new images by combining several known images. While there is growing evidence that perception and imagery share common neural substrates, the fact that D.F. shows intact visual imagery in the face of a massive perceptual deficit in form vision challenges recent suggestions that these two psychological processes share common input pathways in early vision. It is suggested that regions in the occipitotemporal pathway may be important for the generation of visual images while regions in the posterior parietal system might be involved in the manipulation of these images.

Adult↗
PubMed1995

The development of adaptive head movements following enucleation.

Recent work in our laboratory has revealed that enucleated patients produce large lateral and vertical head movements during visually guided grasping. These movements may allow them to maximise the use of retinal motion cues in planning and controlling their grasp. The aim of the present study was to determine whether the tendency to produce these adaptive head movements increases as a function of time since enucleation. We tested a group of 12 enucleated patients in whom the time between surgery and testing varied from 2 weeks to 35 years (mean = 11.2 years). These patients were required to reach out and grasp oblong blocks of different sizes at different distances. Correlational tests revealed an increase in the proportion of self-generated lateral and vertical head movements versus forward head movements as a function of post-enucleation time (r(s)(12) = 0.68, p < 0.025 and r(s)(12) = 0.65, p < 0.025, respectively). This suggests that enucleated patients may be adapting to living with one eye by learning to increase the proportion of their lateral and vertical head movements during the performance of skilled motor acts.

Adaptation, Physiological↗
PubMed1994

Separate neural pathways for the visual analysis of object shape in perception and prehension.

BACKGROUND: Earlier work with neurological patients has shown that the visual perception of object size and orientation depends on visual pathways in the cerebral cortex that are separate from those mediating the use of these same object properties in the control of goal-directed grasping. We present evidence suggesting that the same dissociation between perception and action is evident in the visual processing of object shape. In other words, discrimination between objects on the basis of their shape appears to be mediated by visual mechanisms that are functionally and neurally distinct from those controlling the pre-shaping of the hand during grasping movements directed at those same objects. RESULTS: We studied two patients with lesions in different parts of the cerebral visual pathways. One patient (RV), who had sustained bilateral lesions of the occipitoparietal cortex, was unable to use visual information to place her fingers correctly on the circumference of irregularly shaped objects when asked to pick them up, even though she had no difficulty in visually discriminating one such object from another. Conversely, a second patient (DF), who had bilateral damage in the ventrolateral occipital region, had no difficulty in placing her fingers on appropriate opposition points during grasping, even though she was unable to discriminate visually amongst such objects. CONCLUSIONS: This double dissociation lends strong support to the idea that the visual mechanisms mediating the perception of objects are functionally and neurally distinct from those mediating the control of skilled actions directed at those objects. It also supports the recent proposal of Goodale and Milner that visual perception depends on a ventral stream of projections from the primary visual cortex to the inferotemporal cortex, whereas the visual control of skilled actions depends on a dorsal stream from the primary visual cortex to the posterior parietal cortex.

Adult↗
PubMed1994

Binocular vision and the on-line control of human prehension.

The contribution of binocular visual feedback to the kinematics of human prehension was studied in two related experiments. In both experiments, the field of view of each eye was independently controlled by means of goggles fitted with liquid-crystal shutters. While wearing these goggles, which permitted either a binocular or a monocular view of the world, subjects were required to reach out and grasp a target object, which varied in size and position from trial to trial. In experiment 1, two viewing conditions were used. In one condition, binocular vision was available throughout the entire trial; in the second condition, the initial binocular view was replaced by a monocular view after the reaching movement had been initiated. When only monocular feedback was available, subjects showed a prolonged deceleration phase, although the time they spent in contact with the object was the same in both conditions. In experiment 2, monocular vision was available throughout a given trial in one condition and was replaced by binocular vision upon movement initiation in the second condition. Subjects in this experiment also displayed a prolonged deceleration phase in the monocular feedback condition relative to their performance in the binocular feedback condition. Unlike experiment 1, however, allowing only monocular feedback resulted in an increase in the amount of time subjects spent in contact with the object. Moreover, the object contact phases under the two conditions of experiment 2 were much longer than those observed in experiment 1, in which subjects received initial binocular views of the object.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Differences in the visual control of pantomimed and natural grasping movements.

In a series of experiments, we studied the differences between natural target-directed grasping movements and 'pantomimed' movements directed towards remembered objects. Although subjects continued to scale their hand opening for object size when pantomiming, grip formation and other kinematic variables differed significantly from those seen in normal target-directed actions. This was true whether the subjects had just seen the target object 2 sec before (Experiments 1 and 2) or whether the target object was still present and they were simply required to pantomime the grasping movement beside it (Experiment 3). We argued that these pantomimed reaches were being driven by stored perceptual information about the object, and were not utilizing the normal visuomotor control systems that direct actions in real time. This interpretation received strong support from observations of a patient with visual form agnosia who was also tested. In an earlier report, we had shown that this patient showed anticipatory scaling of her grasp despite her inability to discriminate between objects perceptually on the basis of size. The present study showed, however, that the requirement to remember an object even briefly, or to pantomime an action beside it, was enough to completely disrupt her visuomotor scaling (Experiments 2 and 3). That this reflected a failure of perception rather than imagery or understanding was supported by the fact that she could convincingly pantomime actions to imagined, familiar objects, the sizes of which were known to her (Experiment 4). All these results suggest that the mechanisms underlying the formation of perceptual representations of objects are quite independent of those mediating on-line visuomotor control.

Adult↗
PubMed1994

The role of surface information in object recognition: studies of a visual form agnosic and normal subjects.

Three experiments were conducted to explore the role of colour and other surface properties in object recognition. The effects of manipulating the availability of surface-based information on object naming in a patient with visual form agnosia and in two age-matched control subjects were examined in experiment 1. The objects were presented under seven different viewing conditions ranging from a full view of the actual objects to line drawings of those same objects. The presence of colour and other surface properties aided the recognition of natural objects such as fruits and vegetables in both the patient and the control subjects. Experiment 2 was focused on four of the critical viewing conditions used in experiment 1 but with a large sample of normal subjects. As in experiment 1, it was found that surface properties, particularly colour, aided the naming of natural objects. The presence of colour did not facilitate the naming of manufactured objects. Experiment 3 was focused on possible ways by which colour could assist in the recognition of natural objects and it was found that object naming was facilitated only if the objects were presented in their usual colour. The results of the experiments show that colour does improve recognition for some types of objects and that the improvement occurs at a high level of visual analysis.

Adult↗
PubMed1994

Control of proximal and distal components of prehension in callosal agenesis.

Classic work with split-brain monkeys suggests that the reaching limb can be controlled by either cerebral hemisphere, but that finger control is largely crossed (Haaxma and Kuypers, 1974). Accordingly, one might predict that acallosal subjects should have little difficulty grasping objects presented in the visual field ipsilateral to the hand used, but should have great difficulty forming their grasp when reaching into crossed space. In the present study, we carried out a kinematic analysis of reaching and grasping movements executed by four acallosal subjects and four matched control subjects. Subjects maintained central fixation while reaching with either hand for objects placed in left, central and right space. Relative to controls, acallosal subjects took longer to complete reaches directed across the body midline, and spent more time decelerating. Moreover, unlike controls, their grip formation appeared to be impaired in all regions of space, although this deficit was most pronounced during reaches into crossed space. These results suggest that congenital absence of the corpus callosum is associated with deficits in the control of both the proximal and distal musculature.

Adolescent↗
PubMed1993

The drawing of objects by a visual form agnosic: contribution of surface properties and memorial representations.

Although edge-based representations of objects are thought to play a central role in object identification, it is clear that real objects convey more information about their form than line drawings. Patients with visual form agnosia, for example, are able to identify real objects more easily than the corresponding line drawings of those objects, even if exactly the same projection planes are used [Goodale et al. Object versus picture identification in a patient with visual form agnosia. Paper presented at the annual meeting of the Association for Research in Vision and Ophthalmology (April, 1991). Sarasota, FL, 1991]. To compare these two modes of representation in another way, we asked a patient (D.F.) with profound visual form agnosia to make line drawings of a series of common objects, either from long-term memory, from the real objects themselves, or from line drawings of those objects. When four independent judges rated the drawings as to how well they represented the target objects, drawings from memory received higher ratings than drawings of real objects which in turn received higher ratings than those based on line drawings. These results complement those of Goodale et al. (1991) and suggest that cues derived from surface properties and depth can assist in the demarcation of the critical features necessary for the accurate portrayal of objects. They also suggest that despite D.F.'s perceptual deficits, her long-term representation of objects is relatively intact.

Adult↗
PubMed1993

Visual pathways supporting perception and action in the primate cerebral cortex.

Behavioral and electrophysiological evidence suggests a new interpretation of the division of labor between the ventral and dorsal streams of visual processing in primate cerebral cortex. It is suggested that the ventral stream mediates the perception of objects while the dorsal stream mediates the on-line control of skilled actions directed at those objects.

Animals↗