Visuomotor Actions Research Articles

Drawing cartoon faces – a functional imaging study of the cognitive neuroscience of drawing

We report a functional imaging study of drawing cartoon faces. Normal, untrained participants were scanned while viewing simple black and white cartoon line drawings of human faces, retaining them for a short memory interval, and then drawing them without vision of their hand or the paper. Specific encoding and retention of information about the faces were tested for by contrasting these two stages (with display of cartoon faces) against the exploration and retention of random dot stimuli. Drawing was contrasted between conditions in which only memory of a previously viewed face was available versus a condition in which both memory and simultaneous viewing of the cartoon were possible, and versus drawing of a new, previously unseen, face. We show that the encoding of cartoon faces powerfully activates the face-sensitive areas of the lateral occipital cortex and the fusiform gyrus, but there is no significant activation in these areas during the retention interval. Activity in both areas was also high when drawing the displayed cartoons. Drawing from memory activates areas in posterior parietal cortex and frontal areas. This activity is consistent with the encoding and retention of the spatial information about the face to be drawn as a visuo-motor action plan, either representing a series of targets for ocular fixation or as spatial targets for the drawing action.

Visual stimulus presentation using fiber optics in the MRI scanner

Imaging the neural basis of visuomotor actions using fMRI is a topic of increasing interest in the field of cognitive neuroscience. One challenge is to present realistic three-dimensional (3-D) stimuli in the subject's peripersonal space inside the MRI scanner. The stimulus generating apparatus must be compatible with strong magnetic fields and must not interfere with image acquisition. Virtual 3-D stimuli can be generated with a stereo image pair projected onto screens or via binocular goggles. Here, we describe designs and implementations for automatically presenting physical 3-D stimuli (point-light targets) in peripersonal and near-face space using fiber optics in the MRI scanner. The feasibility of fiber-optic based displays was demonstrated in two experiments. The first presented a point-light array along a slanted surface near the body, and the second presented multiple point-light targets around the face. Stimuli were presented using phase-encoded paradigms in both experiments. The results suggest that fiber-optic based displays can be a complementary approach for visual stimulus presentation in the MRI scanner.

Tracing sequential waves of rapid visuomotor activation in lateralized readiness potentials

Feedforward activation processes are widely regarded as crucial for the automatic initiation of motor responses, whereas recurrent processes are often regarded as crucial for visual awareness. Here, we used a set of behavioral criteria to evaluate whether rapid processing in the human visuomotor system proceeds as would be expected of a feedforward system that works independent of visual awareness. We measured lateralized readiness potentials (LRPs) for key-press responses to color targets (“masks”) preceded by masked color primes mapped onto the same or opposite response, and traced the time-course of motor activation as a function of different prime and mask characteristics. LRP time-courses showed that initial motor activation occurred in prime direction and was time-locked to prime onset. Response activation was then captured on-line by the mask signal, with motor activation now time-locked to the mask and proceeding in mask direction. Crucially, the time-course of early activation by the prime was independent of all mask characteristics. This invariance in early priming effects contrasted with large differences in visual awareness for the prime produced by different masks. Results suggest that primed responses to color stimuli are controlled by feedforward waves of activation sequentially elicited by prime and mask signals traveling rapidly enough to escape the recurrent processes leading to backward masking.

Do visual illusions probe the visual brain?: Illusions in action without a dorsal visual stream

Visual illusions have been shown to affect perceptual judgements more so than motor behaviour, which was interpreted as evidence for a functional division of labour within the visual system. The dominant perception–action theory argues that perception involves a holistic processing of visual objects or scenes, performed within the ventral, inferior temporal cortex. Conversely, visuomotor action involves the processing of the 3D relationship between the goal of the action and the body, performed predominantly within the dorsal, posterior parietal cortex. We explored the effect of well-known visual illusions (a size-contrast illusion and the induced Roelofs effect) in a patient (IG) suffering bilateral lesions of the dorsal visual stream. According to the perception–action theory, IG's perceptual judgements and control of actions should rely on the intact ventral stream and hence should both be sensitive to visual illusions. The finding that IG performed similarly to controls in three different illusory contexts argues against such expectations and shows, furthermore, that the dorsal stream does not control all aspects of visuomotor behaviour. Assuming that the patient's dorsal stream visuomotor system is fully lesioned, these results suggest that her visually guided action can be planned and executed independently of the dorsal pathways, possibly through the inferior parietal lobule.

An fMRI approach to particularize the frontoparietal network for visuomotor action monitoring: Detection of incongruence between test subjects’ actions and resulting perceptions

Contemporary theories of motor control assume that motor actions underlie a supervisory control system which utilizes reafferent sensory feedbacks of actions for comparison with the original motor programs. The functional network of visuomotor action monitoring is considered to include inferior parietal, lateral and medial prefrontal cortices. To study both sustained monitoring for visuomotor incongruence and the actual detection of incongruence, we used a hybrid fMRI epoch-/event-related design. The basic experimental task was a continuous motor task, comprising a simple racing game. Within certain blocks of this task, incongruence was artificially generated by intermittent takeover of control over the car by the computer. Fifteen male subjects were instructed to monitor for incongruence between their own and the observed actions in order to abstain from their own action whenever the computer took over control. As a result of both sustained monitoring and actual detection of visuomotor incongruence, the rostral inferior parietal lobule displayed a BOLD signal increase. In contrast, the prefrontal cortex (PFC) exhibited two different activation patterns. Dorsolateral (BA 9/46) and medial/cingulate (BA 8, BA 32) areas of the PFC displayed a greater increase of activation in sustained monitoring, while ventrolateral PFC showed greater event-related activation for the actual detection of visuomotor incongruence. Our results suggest that the rostral inferior parietal lobule is specifically involved in the reafferent comparison of the test subjects’ own actions and visually perceived actions. Different activation patterns of the PFC may reflect different frontoparietal networks for sustained action monitoring and actual detection of reafferent incongruence.

Moving Farther but Faster

Fitts's law holds that movement time (MT) increases with longer distances. Here we report a violation of this law: When the target appears in a structured, linear display with placeholders indicating the possible target locations, MT to the most distant target is not longer than MT to the second most distant target, but rather tends to be shorter. Furthermore, the presence of placeholders attenuates the range effect that occurs in the absence of placeholders. These findings suggest that Fitts's law may be limited to egocentric visuomotor action, and that the visual control of hand movements may use allocentric, in addition to egocentric, spatial information.

The role of parietal cortex in visuomotor control: What have we learned from neuroimaging?

Research from macaque neurophysiology and human neuropsychology has implicated the parietal cortex in the sensory control of action. Functional neuroimaging has been very valuable in localizing and characterizing specific regions of the human brain involved in visuomotor actions involving different effectors, such as the eyes, head, arms and hands. Here, we review the areas discovered by human neuroimaging, including the putative functional equivalents of the following macaque regions: parietal eye fields (PEF), ventral intraparietal (VIP) area, parietal reach region (PRR) and the anterior intraparietal (AIP) area. We discuss the challenges of studying realistic movements in the imaging environment, the lateralization of visuomotor function, caveats involved in proposing interspecies homologies and the limitations and future directions for neuroimaging studies of visuomotor control.

Action selectivity in parietal and temporal cortex

The sensory–action theory proposes that the neural substrates underlying action representations are related to a visuomotor action system encompassing the left ventral premotor cortex, the anterior intraparietal (AIP) and left posterior middle temporal gyrus (LPMT). Using fMRI, we demonstrate that semantic decisions on action, relative to non-action words, increased activation in the left AIP and LPMT irrespective of whether the words were presented in a written or spoken form. Left AIP and LPMT might thus play the role of amodal semantic regions that can be activated via auditory as well as visual input. Left AIP and LPMT did not distinguish between different types of actions such as hand actions and whole body movements, although a right STS region responded selectively to whole body movements.

Influence of the Poggendorff illusion on manual pointing.

The results of recent studies indicate that certain visuomotor actions, such as grasping and pointing, are unaffected by visual size illusions. The present study investigated whether the Poggendorff illusion of alignment influences pointing to a target's location. 15 subjects pointed with their unseen hands to the apparent location of the extension of the oblique line onto the target line of a version of the Poggendorff illusion. Analysis indicated the pointing action was influenced by the Poggendorff illusion. The implications of this finding for the claim that different cortical streams of visual processing subserve visuomotor actions and conscious visual perception are discussed.

Neuronal activity related to the visual representation of arm movements in the lateral cerebellar cortex.

Testing the hypothesis that the lateral cerebellum forms a sensory representation of arm movements, we investigated cortical neuronal activity in two monkeys performing visually guided step-tracking movements with a manipulandum. A virtual target and cursor image were viewed co-planar with the manipulandum. In the normal task, manipulandum and cursor moved in the same direction; in the mirror task, the cursor was left-right reversed. In one monkey, 70- and 200-ms time delays were introduced on cursor movement. Significant task-related activity was recorded in 31 cells in one animal and 142 cells in the second: 10.2% increased activity before arm movements onset, 77.1% during arm movement, and 12.7% after the new position was reached. To test for neural representation of the visual outcome of movement, firing rate modulation was compared in normal and mirror step-tracking. Most task-related neurons (68%) showed no significant directional modulation. Of 70 directionally sensitive cells, almost one-half (n = 34, 48%) modulated firing with a consistent cursor movement direction, many fewer responding to the manipulandum direction (n = 9, 13%). For those "cursor-related" cells tested with delayed cursor movement, increased activity onset was time-locked to arm movement and not cursor movement, but activation duration was extended by an amount similar to the applied delay. Hence, activity returned to baseline about when the delayed cursor reached the target. We conclude that many cells in the lateral cerebellar cortex signaled the direction of cursor movement during active step-tracking. Such a predictive representation of the arm movement could be used in the guidance of visuo-motor actions.

Visual Experience and Motor Action: Are the Bonds Too Tight?

How should we characterize the functional role of conscious visual experience? In particular, how do the conscious contents of visual experience guide, bear upon, or otherwise inform our ongoing motor activities? According to an intuitive and (I shall argue) philosophically influential conception, the links are often quite direct. The contents of conscious visual experience, according to this conception, are typically active in the control and guidance of our fine-tuned, real-time engagements with the surrounding three-dimensional world. But this idea (which I shall call the Assumption of Experience-Based Control) is hostage to empirical fortune. It is a hostage, moreover, whose safety is in serious doubt. Thus Milner and Goodale (1995) argue for a deep and abiding dissociation between the contents of conscious seeing, on the one hand, and the resources used for the online guidance of visuomotor action, on the other. This “dual visual systems” hypothesis, which finds many echoes in various other bodies of cognitive scientific research, poses a prima facie challenge to the Assumption of Experience-Based Control. More importantly, it provides (I shall argue) fuel for an alternative and philosophically suggestive account of the functional role of conscious visual experience.

Task-Independent Effect of Time on rCBF

Positron emission tomography was used to identify brain regions that showed general increase or decrease in regional cerebral blood flow (rCBF) across time that was task-independent. Twelve male subjects were scanned eight times: the first and last scans were taken while subjects performed a baseline fixation task and the middle six scans were taken while subjects performed a visuomotor activation task. To determine whether there was a consistency across different studies in the regions that showed this time-related change in rCBF two additional datasets were analyzed. There were similarities across all three studies in the regions that showed a monotonic task-independent change in activity. In all three studies there was a general bilateral decrease in rCBF of occipital and temporal areas across scans that might be related to habituation in the visual domain. Increases in rCBF were found in anterior cingulate, postcentral gyrus, and precentral gyrus across studies. It is likely that these changes reflect motor learning and motor program retrieval. This implies that, unless the experimenter controls for time-dependent changes in brain activity, the interpretation of task-related changes in rCBF may be confounded by these monotonic changes in rCBF. We present analytic strategies to identify experimental effects that are independent of nonspecific time effects, which can be used when it is not possible to control these effects through counterbalancing the experimental design. Nonspecific confounds are particularly relevant in functional MRI studies in which the number of scans acquired per study is much larger.

Temporal hierarchy of the visual perceptive systems in the Mondrian world.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50-100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure--an abstract multi-coloured scene with no recognizable objects--against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.

The Effects of Videogame Playing on Neuropsychological Performance of Elderly Individuals

To determine the effects of sensory-perceptual stimulation (videogame playing) on neuropsychological performance, measures of reaction time (RT), visual sensitivity, cognition, and affect were obtained from 60 healthy 60- to 79-year-old individuals before and after their 11-week participation in videogame (VG) playing, movie viewing, or as controls. Only RT demonstrated an activity specific change, being significantly faster at posttesting for the VG subjects. The RT results indicate that the central nervous system of elderly people can be modified by activation procedures. We speculate that VG playing may improve efficiency of cell assemblies stimulated by visuomotor activities common to both VG playing and RT.

Restricting the Field of View: Perceptual and Performance Effects

Visual perception involves both the high acuity of foveal vision and the wide scope of overlapping peripheral information. The role of peripheral vision in competent performance of the adult visuomotor activities of walking, reaching, and forming a cognitive map of a room was examined using goggles which limited the scope of the normal field of view to 9 degrees, 14 degrees, 22 degrees, or 60 degrees. Each restriction of peripheral field information resulted in some perceptual and performance decrements, with the 9 degrees and 14 degrees restriction producing the most disturbance. In addition, bodily discomfort, dizziness, unsteadiness and disorientation, were reported as the subjects moved around with restricted fields of view.