Evidence for an eye-centered spherical representation of the visuomotor map

During visually guided movement, visual coordinates of target location must be transformed into coordinates appropriate for movement. To investigate the representation of this visuomotor coordinate transformation, we examined changes in pointing behavior induced by a local visuomotor remapping. The visual feedback of finger position was limited to one location within the workspace, at which a discrepancy was introduced between the actual and visually perceived finger position. This remapping induced a change in pointing that extended over the entire workspace and was best captured by a spherical coordinate system centered near the eyes.     

Object recognition and object orientation in Alzheimer's disease

There are a wide variety of neuropsychological deficits in Alzheimer's disease (AD), among which are disorders of visual perception and spatial cognition. The present study investigated the ability of 20 mildly to moderately deteriorated patients with AD (and 174 age- and education-matched controls) on tasks that required them to visually identify, provide the canonical orientation of, and mentally rotate common objects. Some 85% of the AD patients performed poorly on all tasks. The authors were able to identify a small number of individual patients whose pattern of performance represented double dissociations between recognizing objects and knowing their canonical orientation. These findings are interpreted in the context of previous findings, especially as to whether information relating to an object's orientation and identity is independently coded.     

An object-centred reference frame for control of grasping: effects of grasping a distractor object on visuomotor control

Previous evidence based on perceptual integration and arbitrary responses suggests extensive cross-modal links in attention across the various modalities. Attention typically shifts to a common location across the modalities, despite the vast differences in their initial coding of space. An issue that remains unclear is whether or not these effects of multisensory coding occur during more natural tasks, such as grasping and manipulating three-dimensional objects. Using kinematic measures, we found strong effects of the diameter of a grasped distractor object on the aperture used to grasp a target object at both coincident and non-coincident locations. These results suggest that interference effects can occur between proprioceptive and visuomotor signals in grasping. Unlike other interference effects in cross-modal attention, these effects do not depend on the spatial relation between target and distractor, but occur within an object-based frame of reference.     

An instrumented object for evaluation of lateral hand grasp during functional tasks

We developed an instrumented object for quantitative evaluation of functional tasks performed with lateral hand grasp. The device was instrumented with three force transducers based on metal foil strain gauges. The transducers allowed simultaneous monitoring of the grasp force, the perpendicular force at the tip, and the force in the long axis of the instrumented object. The device was used for evaluation of a simulated eating task performed by able-bodied subjects and a tetraplegic subject instrumented with an FES hand grasp system. Use of the instrumented object will allow us to gain a more thorough understanding of the application of forces on a tool during important functional tasks of daily living. This knowledge will be used to improve the control of a closed-loop FES hand grasp system incorporating natural sensory feedback.     

An instrumented object for evaluation of lateral hand grasp during functional tasks.

We developed an instrumented object for quantitative evaluation of functional tasks performed with lateral hand grasp. The device was instrumented with three force transducers based on metal foil strain gauges. The transducers allowed simultaneous monitoring of the grasp force, the perpendicular force at the tip, and the force in the long axis of the instrumented object. The device was used for evaluation of a simulated eating task performed by able-bodied subjects and a tetraplegic subject instrumented with an FES hand grasp system. Use of the instrumented object will allow us to gain a more thorough understanding of the application of forces on a tool during important functional tasks of daily living. This knowledge will be used to improve the control of a closed-loop FES hand grasp system incorporating natural sensory feedback.     

Visual recognition of shapes and textures: an fMRi study

Previous literature suggest that processing of visually presented shapes and textures starts in the early visual areas, but subsequently follow different pathways. The purpose of this experiment was to further investigate differential activation for shapes and textures in order elucidate the pathways involved in visual shape and texture matching. In the present study, brain areas involved in discrimination of shapes and textures are mapped, using the same set of stimuli for shape and texture decisions. Texture matching activates more prefrontal regions than shape matching, particularly regions in the left middle frontal gyrus and bilateral inferior frontal gyrus. Shape specific activation includes an occipital/temporal region which is associated with multimodal object matching. The pattern of results suggests that recognition of textures may be based upon different ordering conditions in memory, which involve a prefrontal network and require a great deal more workload than the holistic representation of shape.     

Grab an object with a tool and change your body: tool-use-dependent changes of body representation for action

Along the evolutionary history, humans have reached a high level of sophistication in the way they interact with the environment. One important step in this process has been the introduction of tools, enabling humans to go beyond the boundaries of their physical possibilities. Here, we focus on some “low level” aspects of sensorimotor processing that highlight how tool-use plays a causal role in shaping body representations, an essential plastic feature for efficient motor control during development and skilful tool-use in the adult life. We assess the evidence supporting the hypothesis that tools are incorporated in body representation for action, which is the body schema, by critically reviewing some previous findings and providing new data from on-going work in our laboratory. In particular, we discuss several experiments that reveal the effects of tool-use both on the kinematics of hand movements and the localization of somatosensory stimuli on the body surface, as well as the conditions that are necessary for these effects to be manifested. We suggest that overall these findings speak in favour of genuine tool-use-dependent plasticity of the body representation for the control of action.     

Effect of image orientation and size on object recognition: responses of single units in the macaque monkey temporal cortex

This study examined how cells in the temporal cortex code orientation and size of a complex object. The study focused on cells selectively responsive to the sight of the head and body but unresponsive to control stimuli. The majority of cells tested (19/26, 73%) were selectively responsive to a particular orientation in the picture plane of the static whole body stimulus, 7/26 cells showed generalisation responding to all orientations (three cells with orientation tuning superimposed on a generalised response). Of all cells sensitive to orientation, the majority (15/22, 68%) were tuned to the upright image. The majority of cells tested (81%, 13/16) were selective for stimulus size. The remaining cells (3/16) showed generalisation across four-fold decrease in size from life-sized. All size-sensitive cells were tuned to life-sized stimuli with decreasing responses to stimuli reduced from life-size. These results do not support previous suggestions that cells responsive to the head and body are selective to view but generalise across orientation and size. Here, extensive selectivity for size and orientation is reported. It is suggested that object orientation and size-specific responses might be pooled to obtain cell responses that generalise across size and orientation. The results suggest that experience affects neuronal coding of objects in that cells become tuned to views, orientation, and image sizes that are commonly experienced. Models of object recognition are discussed.     

“Adequate control theory” for human single-joint elbow flexion on two tasks

The control of distance and speed during single-joint human elbow flexion is accomplished by different modes of activating the motoneuron pools. Distance is controlled by modulating the duration of activation, while speed is controlled by modulating the intensity. The experiments reported on here compare movements of different distances under two sets of instructions: subjects moved either as fast and accurately as possible or in a specified time. The first task showed duration modulation, whereas the second, which required simultaneous control of distance and speed, showed both duration and intensity modulation. These results are interpreted in the context of a model for motor control, predicated on the existence of movement plants that use prior knowledge of the dynamics of the movement task to generate muscle activation patterns that produce joint torques. These plans use a simple algorithm based upon parameters of the task such as distance, load, and speed. From this plan, the kinematic trajectory emerges.     

A comparison of children's performance on two recognition memory tasks: Delayed nonmatch-to-sample versus visual paired-comparison

Although 4- to 6-month-old children have a significant tendency to look at new stimuli in a visual paired-comparison task (VPC), they have difficulty in consistently choosing novel objects in a delayed nonmatch-to-sample task (DNMS). To evaluate which factors could account for this difficulty, we tested human infants (10–107 months) and adults (17–25 years) in a DNMS task while monitoring eye fixations. The results indicated that children at all ages reliably looked at (VPC scores) or chose (DNMS scores) the new stimuli about 60% of the time, indicating that both tasks measure visual recognition memory. A videotape analysis of visual attention revealed that children younger than 22 months, but not older children, spent significanlty more time visually exploring the objects rather than looking at the food reward under it. Although this visual attraction to objects in children younger than 22 months of age may have impaired the formation of stimulus-reinforcer association needed to solve the DNMS task, this was not the case for older children, since beyond 22 months of age children consistently looked at the reward while displacing the objects. These results suggest that other cognitive abilities required by the DNMS task may not be fully functional even in children 22 months and older. © 1993 John Wiley & Sons, Inc.     

Direct chromosome preparation and culture using chorionic villi: an evaluation of the two techniques

We present a comparison between direct chromosome preparation and cell culture for first trimester fetal chromosome study using chorionic villi. The 2 techniques have advantages and disadvantages and are demonstrated to be appropriate for routine diagnostic work. The combined use of both methods may optimize the quality of the chromosome study and minimize the possibility of false-positive and false-negative findings.     

The effect of excitotoxic lesions centered on the hippocampus or perirhinal cortex in object recognition and spatial memory tasks

Rats with bilateral ibotenic acid lesions centered on the hippocampus (HPC) or perirhinal cortex (PRC) and sham-operated controls were tested in a series of object recognition and spatial memory tasks. Both HPC and PRC rats displayed reduced habituation in a novel environment and were impaired in an object-location task. HPC rats were severely impaired in both the reference and working-memory versions of the water maze and radial arm maze tasks. In contrast, although PRC rats displayed mild deficits in the reference memory version of the water maze and radial arm maze tasks, they were markedly impaired in the working-memory version of both the tasks. These findings demonstrate that under certain conditions both the HPC and PRC play a role in the processing of spatial memory. Further investigation of these conditions will provide important new insights into the role of these structures in memory processes.     

Oscillatory gamma activity in humans: a possible role for object representation.

The coherent representation of an object has been suggested to be established by the synchronization in the gamma range (20-100 Hz) of a distributed neural network. So-called '40-Hz' activity in humans could reflect such a mechanism. We have presented here experimental evidence supporting this hypothesis, both in the visual and auditory modalities. However, different types of gamma activity should be distinguished, mainly the evoked 40-Hz response and the induced gamma activities. Only induced gamma activities seem to be related to coherent object representations. In addition, their topography depends on sensory modality and task, which is in line with the idea that they reflect the oscillatory synchronization of task-dependent networks. They can also be functionally and topographically distinguished from the classical evoked potentials and from the alpha rhythm. It was also proposed that the functional role of gamma oscillations is not restricted to object representation established through bottom-up mechanisms of feature binding, but also extends to the cases of internally driven representations and to the maintenance of information in memory.     

The effect of action goal hierarchy on the coding of object orientation in imitation tasks: Evidence from patients with parietal lobe damage

In order to explore parietal patients' difficulties in the processing of orientation information, we asked parietal patients (N = 8) and healthy and brain-damaged controls to imitate multicomponent actions where object orientation was one component. In Experiment 1 orientation was not the most relevant aspect of the action to be imitated, and the parietal group showed significant difficulties in processing object orientation. However, in Experiment 2, where orientation was placed at the top end of the goal hierarchy, the parietal group were able to process stimulus orientation sufficiently to place it within the goal hierarchy of the action and to reproduce it accurately. We conclude that patients with parietal lesions might be able to include object orientation in a goal hierarchy, but if their processing of orientation information is impaired they might be disproportionately prone to errors when object orientation is lower in the goal hierarchy and so not prioritized for processing resources.     

The effect of action goal hierarchy on the coding of object orientation in imitation tasks: evidence from patients with parietal lobe damage

In order to explore parietal patients' difficulties in the processing of orientation information, we asked parietal patients (N = 8) and healthy and brain-damaged controls to imitate multicomponent actions where object orientation was one component. In Experiment 1 orientation was not the most relevant aspect of the action to be imitated, and the parietal group showed significant difficulties in processing object orientation. However, in Experiment 2, where orientation was placed at the top end of the goal hierarchy, the parietal group were able to process stimulus orientation sufficiently to place it within the goal hierarchy of the action and to reproduce it accurately. We conclude that patients with parietal lesions might be able to include object orientation in a goal hierarchy, but if their processing of orientation information is impaired they might be disproportionately prone to errors when object orientation is lower in the goal hierarchy and so not prioritized for processing resources.     

Learning a visuomotor rotation: simultaneous visual and proprioceptive information is crucial for visuomotor remapping

Visuomotor adaptation is mediated by errors between intended and sensory-detected arm positions. However, it is not clear whether visual-based errors that are shown during the course of motion lead to qualitatively different or more efficient adaptation than errors shown after movement. For instance, continuous visual feedback mediates online error corrections, which may facilitate or inhibit the adaptation process. We addressed this question by manipulating the timing of visual error information and task instructions during a visuomotor adaptation task. Subjects were exposed to a visuomotor rotation, during which they received continuous visual feedback (CF) of hand position with instructions to correct or not correct online errors, or knowledge-of-results (KR), provided as a static hand-path at the end of each trial. Our results showed that all groups improved performance with practice, and that online error corrections were inconsequential to the adaptation process. However, in contrast to the CF groups, the KR group showed relatively small reductions in mean error with practice, increased inter-trial variability during rotation exposure, and more limited generalization across target distances and workspace. Further, although the KR group showed improved performance with practice, after-effects were minimal when the rotation was removed. These findings suggest that simultaneous visual and proprioceptive information is critical in altering neural representations of visuomotor maps, although delayed error information may elicit compensatory strategies to offset perturbations.     

Presence/absence of original information in the misleading information effect: an investigation using recognition and priming tasks similar to original information presentation

Several previous studies on the misleading information effect employed priming tasks to examine the presence/absence of original information. Given hyperspecificity of priming, however, it is questionable whether or not their priming tasks were sensitive enough to detect original information because their stimuli were perceptually different from the slides in the study phase. In the priming task of this research, we used slides whose perceptual properties were equivalent to those of the studied ones. In addition, we also conducted a yes-no recognition task using the same slides so that the results of these two tasks could be directly compared. The misleading information effect was replicated in the recognition task. Nevertheless, participants correctly recognized the original slides, whereas no priming effect was observed for those slides. These results suggest that although the original information survives the misleading information effect, its representation is modified so that only the yes-no recognition task, not the priming task, has access to it.     

The benefit of offline sleep and wake for novel object recognition

How do we segment and recognize novel objects? When explicit cues from motion and color are available, object boundary detection is relatively easy. However, under conditions of deep camouflage, in which objects share the same image cues as their background, the visual system must reassign new functional roles to existing image statistics in order to group continuities for detection and segmentation of object boundaries. This bootstrapped learning process is stimulus dependent and requires extensive task-specific training. Using a between-subject design, we tested participants on their ability to segment and recognize novel objects after a consolidation period of sleep or wake. We found a specific role for rapid eye movement (REM, n = 43) sleep in context-invariant novel object learning, and that REM sleep as well as a period of active wake (AW, n = 35) increased segmentation of context-specific object learning compared to a period of quiet wake (QW, n = 38; p = .007 and p = .017, respectively). Performance in the non-REM nap group (n = 32) was not different from the other groups. The REM sleep enhancement effect was especially robust for the top performing quartile of subjects, or “super learners” (p = .037). Together, these results suggest that the construction and generalization of novel representations through bootstrapped learning may benefit from REM sleep, and more specific object learning may also benefit from AW. We discuss these results in the context of shared electrophysiological and neurochemical features of AW and REM sleep, which are distinct from QW and non-REM sleep.