Functional MRI of haptic face recognition.
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Adult↗
Biomedical subjects
P Servos
Publications and source records attributed to P Servos.
Dynamic visual speech perception in a patient with visual form agnosia.
To examine the role of dynamic cues in visual speech perception, a patient with visual form agnosia (DF) was tested with a set of static and dynamic visual displays of three vowels. Five conditions were tested: (1) auditory only which provided only vocal pitch information, (2) dynamic visual only, (3) dynamic audiovisual with vocal pitch information, (4) dynamic audiovisual with full voice information and (5) static visual only images of postures during vowel production. DF showed normal performance in all conditions except the static visual only condition in which she scored at chance. Control subjects scored close to ceiling in this condition. The results suggest that spatiotemporal signatures for objects and events are processed separately from static form cues.
Adult↗
fMRI-derived cortical maps for haptic shape, texture, and hardness.
We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates involved in haptic processing of texture, shape, and hardness. Subjects performed haptic classification tasks on a set of 27 silicone objects having parametrically defined shape, texture, and hardness. The objects were ellipsoids of revolution in which the ratio of the long to the short axis was varied, producing three different shapes. Three surface textures and three hardness levels were used. In three separate experiments, the same subjects classified each object along the three levels of one of the object properties (shape, texture, or hardness). Texture, shape, and hardness processing led to contralateral activation in the postcentral gyrus (PCG). A common region located within relatively posterior portions of the PCG was observed during shape and texture identification whereas a separate and more anterior region was activated during the hardness identification task. The hardness identification task also produced bilateral activation within the parietal operculum.
Adult↗
Functional neuroimaging of mental chronometry.
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Brain↗
Distance estimation in the visual and visuomotor systems.
Previous work has demonstrated that monocular vision affects the kinematics of skilled visually guided reaching movements in humans. In these experiments, prior to movement onset, subjects appeared to be underestimating the distance of objects (and as a consequence, their size) under monocular viewing relative to their reaches made under binocular control. The present series of experiments was conducted to assess whether this underestimation was a consequence of a purely visual distance underestimation under monocular viewing or whether it was due to some implicit inaccuracy in calibrating the reach by a visuomotor system normally under binocular control. In a purely perceptual task, a group of subjects made similar explicit distance estimations of the objects used in the prehension task under monocular and binocular viewing conditions, with no time constraints. A second group of subjects made these explicit distance estimations with only 500-ms views of the objects. No differences were found between monocular and binocular viewing in either of these explicit distance-estimation tasks. The limited-views subjects also performed a visually guided reaching task under monocular and binocular conditions and showed the previously demonstrated monocular underestimation (in that their monocular grasping movements showed lower peak velocities and smaller grip apertures). A distance underestimation of 4.1 cm in the monocular condition was computed by taking the y intercepts of the monocular and binocular peak velocity functions and dividing them by a common slope that minimised the sum of squares error. This distance underestimation was then used to predict the corresponding underestimation of size that should have been observed in the monocular reaches--a value closely approximating the observed value of 0.61 cm. Taken together, these results suggest that the monocular underestimation in the prehension task is not a consequence of a purely perceptual bias but rather it is visuomotor in nature--a monocular input to a system that normally calibrates motor output on the basis of binocular vision.
Adult↗
The visuomotor system resists the horizontal-vertical illusion.
The effect of the horizontal-vertical illusion on the visual and visuomotor systems was investigated. Participants (N = 8) viewed horizontal and vertical lines in an inverted-T stimulus and judged whether the two line segments were the same or different lengths. Participants also reached out and grasped either the vertical or the horizontal line segment of the stimulus. Perceptually, participants succumbed to the illusion; that is, they judged Ts of equal horizontal and vertical line lengths to be different and Ts of unequal line lengths to be the same. When reaching toward the same stimuli, however, the size of their grip aperture was scaled appropriately for the various line lengths. Thus, whereas the perceptual system succumbed to the illusion, the visuomotor system did not. Those results support a model proposed by M. A. Goodale and A. D. Milner (1992), who posited separate cortical pathways for visual perception and visually guided action.
Adult↗
fMRI evidence for an inverted face representation in human somatosensory cortex.
We provide evidence that the face component of the somatosensory homunculus is actually upside down rather than right-side up along the central sulcus of the human brain. We pneumatically stimulated the forehead or chin of neurologically intact humans while acquiring fMRI images of somatosensory cortex. During forehead stimulation cortical regions along relatively inferior portions of the postcentral gyrus were most active whereas during chin stimulation relatively superior regions were most active. These data are consistent with an inverted face representation along the central sulcus of the human brain.
Adult↗
Somatotopy of the human arm using fMRI.
We describe a technique for mapping out human somatosensory cortex using functional magnetic resonance imaging (fMRI). To produce cortical activation, a pneumatic apparatus presented subjects with a periodic series of air puffs in which a sliding window of five locations moved along the ventral surface of the left arm in a proximal-to-distal or distal-to-proximal direction. This approach, in which the phase-delay of the stimulus can be used to produce somatotopic maps of somatosensory cortex, is based on a method used to generate retinotopic maps of visual cortex. Functional images were acquired using an echoplanar 1.5T scanner and a T2*-weighted spiral acquisition pulse sequence. The periodic series of air puffs created phase-related activation in two cortical regions of the contralateral parietal lobe, the posterior bank of the central sulcus and a more posterior and lateral region.
Adult↗
Monocular and binocular control of human interceptive movements.
Previous work in our laboratory has demonstrated that binocular vision makes an important contribution to skilled reaching and grasping movements directed at static targets. In the present study we examine the contribution of binocular vision to interceptive reaching movements. We monitored such movements using a high-resolution, opto-electronic recording device (WATSMART), while subjects attempted to catch balls projected at them. No differences were found between monocular and binocular viewing conditions using this paradigm - either with respect to the velocity profiles or trajectories of the reaches. Moreover, the grasp was not affected by the type of vision available. It appears, then, that the moving targets provide adequate monocular depth and direction information (on the basis of optic flow) for the control of skilled interceptive movements directed at them. In addition, the time to achieve maximum grip aperture was constant across the trials - a finding consistent with the use of a time-to-contact variable derived from optic flow information. Finally, the transport component of prehension was found to be affected by certain variables that have, in the past, been thought to exclusively affect the grasp component of prehension, whereas the grasp component of prehension was affected by factors that have traditionally been thought to affect only the transport component.
Adult↗
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↗
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↗
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↗
Histamine does not play an essential role in electrocortical activation during waking behavior.
Intraperitoneal injection of alpha-fluoromethylhistidine (alpha-FMH; 200 mg/kg), a specific inhibitor of histidine decarboxylase produced a severe depletion of neocortical and hippocampal histamine 3 h later as determined by a radioenzymatic assay. This treatment had no obvious effect on either low voltage fast activity (LVFA) in the neocortex or on rhythmical slow activity (RSA) in the hippocampus during an 8 h recording period during the rats' light cycle. Scopolamine-sensitive LVFA, scopolamine-resistant LVFA and scopolamine-resistant hippocampal RSA all appeared unaffected. This suggests that any contribution histamine makes to electrocortical activation is probably indirect, acting via other transmitter systems.
Animals↗
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↗
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↗
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↗
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↗
Pressure on the snout immobilizes the spontaneously active, scopolaminized, and amphetaminized hyperactive rat.
Rats that are brought into a novel environment or that are given stimulants or anti-muscarinic drugs exhibit high levels of motor activity. Application of moderate pressure on the sides of the snout of such rats results in immediate cessation of all movements for extended time periods. Hippocampal electrocorticograms show that hippocampal slow wave activity during such induced immobility is equivalent to the hippocampal slow wave pattern typically associated with spontaneous immobility. However, neocortical activity following scopolamine administration contains more 2-6 Hz irregular activity during spontaneous than induced immobility.
Animals↗