Visual pathways to perception and action

Predictive information and error processing: The role of medial-frontal cortex during motor control

We have recently provided evidence that an error-related negativity (ERN), an ERP component generated within medial-frontal cortex, is elicited by errors made during the performance of a continuous tracking task (O.E. Krigolson & C.B. Holroyd, 2006). In the present study we conducted two experiments to investigate the ability of the medial-frontal error system to evaluate predictive error information. In two experiments participants used a joystick to perform a computer-based continuous tracking task in which some tracking errors were inevitable. In both experiments, half of these errors were preceded by a predictive cue. The results of both experiments indicated that an ERN-like waveform was elicited by tracking errors. Furthermore, in both experiments the predicted error waveforms had an earlier peak latency than the unpredicted error waveforms. These results demonstrate that the medial-frontal error system can evaluate predictive error information.

Hierarchical error processing: Different errors, different systems

Error processing during motor control involves the evaluation of "high-level" errors (i.e., failures to meet a system goal) by a frontal system involving anterior cingulate cortex and the evaluation of "low-level" errors (i.e., discrepancies between actual and desired motor commands) by a posterior system involving posterior parietal cortex. We have recently demonstrated that high-level errors committed within the context of a continuous tracking task elicited an error-related negativity (ERN) -- a component of the event-related brain potential (ERP) generated within medial-frontal cortex that is sensitive to error commission. The purpose of the present study was to demonstrate that low-level motor errors do not elicit an ERN, but may instead evoke other ERP components associated with visual processing and online motor control. Participants performed a computer aiming task in which they manipulated a joystick to move a cursor from a start to a target position. On a random subset of trials the target jumped to a new position at movement onset, requiring the participants to modify their current motor command. Further, on one half of these "target perturbation" trials the cursor did not respond to corrective movements of the joystick. Consistent with our previous findings, we found that the uncorrectable errors elicited an ERN. We also found that the target perturbations on both correctable and uncorrectable trials did not elicit an ERN, but rather evoked two other ERP components, the N100 and P300. These results suggest that medial-frontal cortex is insensitive to low-level motor errors, and are in line with a recent theory that holds that the P300 reflects stimulus-response optimization by the impact of locus coeruleus activity on posterior cortex.

Mental rotation and object categorization share a common network of prefrontal and dorsal and ventral regions of posterior cortex

The multiple-views-plus-transformation variant of object model verification theories predicts that parietal regions that are critical for mental rotation contribute to visual object cognition. Some neuroimaging studies have shown that the intraparietal sulcus region is critically involved in mental rotation. Other studies indicate that both ventral and dorsal posterior regions are object-sensitive and involved in object perception and categorization tasks. However, it is unknown whether dorsal object-sensitive areas overlap with regions recruited for object mental rotation. Functional magnetic resonance imaging was used to test this directly. Participants performed standard tasks of object categorization, mental rotation, and eye movements. Results provided clear support for the prediction, demonstrating overlap between dorsal object-sensitive regions in ventral-caudal intraparietal sulcus (vcIPS) and an adjacent dorsal occipital area and the regions that are activated during mental rotation but not during saccades. In addition, object mental rotation (but not saccades) activated object-sensitive areas in lateral dorsal occipitotemporal cortex (DOT), and both mental rotation and object categorization recruited ventrolateral prefrontal cortex areas implicated in attention, working memory, and cognitive control. These findings provide clear evidence that a prefrontal-posterior cortical system implicated in mental rotation, including the occipitoparietal regions critical for this spatial task, is recruited during visual object categorization. Altogether, the findings provide a key link in understanding the role of dorsal and ventral visual areas in spatial and object perception and cognition: Regions in occipitoparietal cortex, as well as DOT cortex, have a general role in visual object cognition, supporting not only mental rotation but also categorization.

Brain mechanisms implicated in the preattentive categorization of speech sounds revealed using FMRI and a short-interval habituation trial paradigm

A hallmark of categorical perception is better discrimination of stimulus tokens from 2 different categories compared with token pairs that are equally dissimilar but drawn from the same category. This effect is well studied in speech perception and represents an important characteristic of how the phonetic form of speech is processed. We investigated the brain mechanisms of categorical perception of stop consonants using functional magnetic resonance imaging and a passive short-interval habituation trial design (Zevin and McCandliss 2005). The paradigm takes advantage of neural adaptation effects to identify specific regions sensitive to an oddball stimulus presented in the context of a repeated item. These effects were compared for changes in stimulus characteristics that result in either a between-category (phonetic and acoustic) or a within-category (acoustic only) stimulus shift. Significantly greater activation for between-category than within-category stimuli was observed in left superior sulcus and middle temporal gyrus as well as in inferior parietal cortex. In contrast, only a subcortical region specifically responded to within-category changes. The data suggest that these habituation effects are due to the unattended detection of a phonetic stimulus feature.

Dissociations between reaction times and temporal order judgments: a diffusion model approach

A diffusion model for simple reaction time (RT) and temporal order judgment (TOJ) tasks was developed to account for a commonly observed dissociation between these 2 tasks: Most stimulus manipulations (e.g., intensity) have larger effects in RT tasks than in TOJ tasks. The model assumes that a detection criterion determines the level of sensory evidence needed to conclude that a stimulus has been presented. Analysis of the performance that would be achieved with different possible criterion settings revealed that performance was optimal with a lower criterion setting for the TOJ task than for the RT task. In addition, the model predicts that effects of stimulus manipulations should increase with the size of the detection criterion. Thus, the model suggests that commonly observed dissociations between RT and TOJ tasks may simply be due to performance optimization in the face of conflicting task demands.

Visual recognition and visually guided action after early bilateral lesion of occipital cortex: a behavioral study of a 4.6-year-old girl

We report the case of a 4.6-year-old girl born pre-term with early bilateral occipital damage. It was revealed that the child had non-severely impaired basic visual abilities and ocular motility, a selective perceptual deficit of figure-ground segregation, impaired visual recognition and abnormal navigating through space. Even if the child's visual functioning was not optimal, this was the expression of adaptive anatomic and functional brain modifications that occurred following the early lesion. Anatomic brain structure was studied with anatomic MRI and Diffusor Tensor Imaging (DTI)-MRI. This behavioral study may provide an important contribution to understanding the impact of an early lesion of the visual system on the development of visual functions and on the immature brain's potential for reorganisation related to when the damage occurred.

Dissociating Verbal and Nonverbal Conceptual Processing in the Human Brain

Functional neuroimaging has highlighted a left-hemisphere conceptual system shared by verbal and nonverbal processing despite neuropsychological evidence that the ability to recognize verbal and nonverbal stimuli can doubly dissociate in patients with left- and right-hemisphere lesions, respectively. Previous attempts to control for perceptual differences between verbal and nonverbal stimuli in functional neuroimaging studies may have hidden differences arising at the conceptual level. Here we used a different approach and controlled for perceptual confounds by looking for amodal verbal and nonverbal conceptual activations that are common to both the visual and auditory modalities. In addition to the left-hemisphere conceptual system activated by all meaningful stimuli, we observed the left/right double dissociation in verbal and nonverbal conceptual processing, predicted by neuropsychological studies. Left middle and superior temporal regions were selectively more involved in comprehending words—heard or read—and the right midfusiform and right posterior middle temporal cortex were selectively more involved in making sense of environmental sounds and images. Thus, the neuroanatomical basis of a verbal/nonverbal conceptual processing dissociation is established.

Effects of visual deprivation on space representation: immediate and delayed pointing toward memorised proprioceptive targets

Congenitally blind, late-blind, and blindfolded-sighted participants performed a pointing task at proximal memorised proprioceptive targets. The locations to be memorised were presented on a sagittal plane by passively positioning the left index finger. A 'go' signal for matching the target location with the right index finger was given 0 or 8 s after left-hand demonstration. Absolute distance errors were smaller in the blind groups, with both delays pooled together; signed distance and direction errors were underestimated with the longer delay, and were overestimated by blind groups, whereas the blindfolded-sighted group underestimated them. Elongation of the scatters was stretched but not affected by delay or group. The surface scatter was greater with the longer delay; and orientation of the main axis of the pointing ellipses shows the use of an egocentric frame of reference by the congenitally blind group for both delays, the use of egocentric (0 s) and exocentric (8 s) frame of reference by the blindfolded-sighted group, with the late-blind group using an intermediate frame of reference for both delays. Therefore, early and late visual-deprivation effects are distinguished from transient visual-deprivation effects as long-term deprivation leads to increased capabilities (absolute distance estimations), unaltered organisation (for surface and elongation), and altered organisation (amplitude and direction estimations, orientation of pointing distribution) of the spatial representation with proprioception. Besides providing an extensive exploration of pointing ability and mechanisms in the visually deprived population, the results show that cross-modal plasticity applies not only to neural bases but extends to spatial behaviour.

The potentiation of two components of the reach-to-grasp action during object categorisation in visual memory

Stimulus-Response Compatibility Effects have been reported for several components of the reach-to-grasp action during visual object recognition [Tucker, M., & Ellis, R. (1998). On the relations between seen objects and components of potential actions. Journal of Experimental Psychology: Human Perception and Performance, 24, 830-846; Ellis, R., & Tucker, M. (2000). Micro-affordance: The potentiation of actions by seen objects. British Journal of Psychology, 91, 451-471; Tucker, M., & Ellis, R. (2001). The potentiation of grasp types during visual object categorization. Visual Cognition, 8, 769-800; Creem, S. H., & Proffitt, D. R. (2001). Grasping objects by their handles: A necessary interaction between cognition and action. Journal of Experimental Psychology: Human Perception and Performance, 27, 218-228; Craighero, L. Bello, A. Fadiga, L., & Rizzolatti, G. (2002). Hand action preparation influences the responses to hand pictures. Neuropsychologia, 40, 492-502]. The present study investigates compatibility effects for two elements of reach-to-grasp action during the visual mental imagery of objects-the compatibility of an object for grasping with a power and precision grasp, and the orientation of an object (left/right) for grasping by a particular hand (left/right). Experiment 1 provides further evidence for compatibility effects of a 'seen' object for grasping with a power and precision grasp. The experiment shows that compatibility effects are obtainable when an object is presented in an array of four objects and not just on its own. Experiment 2 provides evidence that compatibility effects of an object for grasping with a power and precision grasp can also be observed when participants make an action response to an object 700 ms after it has been removed from view. Experiment 3 investigates compatibility effects for the orientation of an object for grasping by a particular hand during visual mental imagery, but finds no evidence for such effects. The findings are discussed in relation to two arguments put forward to reconcile ecological and representational theories of visual object recognition.

Visual angle is the critical variable mediating gain-related effects in manual control

Theoretically visual gain has been identified as a control variable in models of isometric force. However, visual gain is typically confounded with visual angle and distance, and the relative contribution of visual gain, distance, and angle to the control of force remains unclear. This study manipulated visual gain, distance, and angle in three experiments to examine the visual information properties used to regulate the control of a constant level of isometric force. Young adults performed a flexion motion of the index finger of the dominant hand in 20 s trials under a range of parameter values of the three visual variables. The findings demonstrate that the amount and structure of the force fluctuations were organized around the variable of visual angle, rather than gain or distance. Furthermore, the amount and structure of the force fluctuations changed considerably up to 1 degrees , with little change higher than a 1 degrees visual angle. Visual angle is the critical informational variable for the visuomotor system during the control of isometric force.

Adjusting reach to lift movements to sudden visible changes in target's weight

People can adjust their reach-to-grasp movements online to sudden changes in the spatial properties of a target. We investigated whether they can also do this when a non-spatial property, weight, suddenly changes. Guiding your movement by using visual cues about an object's weight depends heavily on experience and is expected to be processed by the (slow) ventral stream rather than the (fast) 'online control' dorsal stream. In the first experiment, participants reached out and lifted an object with an expected or an unexpected weight. As predicted, there was an effect of expected weight on the time between the end of the reaching phase and the object's lift-off. In the second experiment, the object sometimes visibly changed weight after the participants had started their movement. The lifting time did not depend on whether the object had changed weight. Thus, participants can make online adjustments to a visually indicated change in weight. These results are interpreted as being contrary to existing theories of online control.

Orienting Attention Based on Long-Term Memory Experience

Attentional orienting and memory are intrinsically bound, but their interaction has rarely been investigated. Here we introduce an experimental paradigm using naturalistic scenes to investigate how long-term memory can guide spatial attention and thereby enhance identification of events in the perceptual domain. In the task, stable memories of objects embedded within complex scenes guide spatial orienting. We compared the behavioral effects and neural systems of memory-guided orienting with those in a more traditional attention-orienting task in which transient spatial cues guide attention. Memory-guided attention operated within surprisingly short intervals and conferred reliable and sizeable advantages for detection of objects embedded in scenes. Event-related functional magnetic resonance imaging showed that memory-guided attention involves the interaction between brain areas participating in retrieval of memories for spatial context with the parietal-frontal network for visual spatial orienting. Activity in the hippocampus was specifically engaged in memory-guided spatial attention and correlated with the ensuing behavioral advantage.

Hemispheric specialization for the visual control of action is independent of handedness

The idea that visually guided action is independent of visual perception has been supported by neurological, neuropsychological, and behavioral studies. In healthy subjects, evidence for this distinction has come from psychophysical studies of the effects of visual illusions on perceptual judgments and object-directed grasping. This evidence is limited, however, by the fact that virtually all studies have involved right-handed subjects using their dominant hand, which is presumably controlled by the left hemisphere. There is tentative evidence from earlier neurological studies that the left hemisphere may in fact play a special role in the integration of visual and motor information during grasping. We designed two experiments to test this idea. The first experiment involved pictorial illusions, which are known to have robust effects on perceptual judgments but little influence on grasping. Right- and left-handed subjects reached out and grasped objects embedded in two different visual illusions with either their dominant or their nondominant hand. For both right- and left-handed subjects, precision grasping with the left hand, but not with the right, was affected by the illusions. In a follow-up experiment, we examined precision grasping in a more natural setting and showed that left-handed subjects use their nondominant (right) hand significantly more as compared with right-handed subjects. We conclude that visuomotor mechanisms encapsulated in the left hemisphere play a crucial role in the visual control of action and that this hemispheric specialization evolved independently of handedness.

Functional clusters in the human parietal cortex as revealed by an observer-independent meta-analysis of functional activation studies

The human parietal cortex is a highly differentiated structure consisting of cytoarchitectonically defined subareas that are specifically connected with other cortical and subcortical areas. Based on evidence from neurophysiological studies in subhuman primates these subareas are supposed to be functionally highly specialized. Here, we reviewed 51 different neuroimaging studies on healthy subjects with activation of the parietal lobe in statistical parametric maps. Running a cluster analysis on the stereotactic coordinates of the centers of gravity of the activation areas and plotting them into Talairach space showed a high consistency of the mean activation foci for similar paradigms across different laboratories and functional imaging modalities. Our meta-analysis exposed seven distinct pairs of quite symmetrically distributed subareas of the parietal cortex of each hemisphere as well as three unpaired regions that are critically involved in the generation of limb and eye movements in egocentric and allocentric coordinates, but also in attention, memory and cognitive problem solving. These data highlights the modular organization of the human parietal lobe. By its locally interspersed distributed circuits it orchestrates specialized cognitive subfunctions interfacing perception and action. Our meta-analysis provides a new framework for understanding information processing in the human parietal cortex.

Intermittent visuomotor processing in the human cerebellum, parietal cortex, and premotor cortex

The cerebellum, parietal cortex, and premotor cortex are integral to visuomotor processing. The parameters of visual information that modulate their role in visuomotor control are less clear. From motor psychophysics, the relation between the frequency of visual feedback and force variability has been identified as nonlinear. Thus we hypothesized that visual feedback frequency will differentially modulate the neural activation in the cerebellum, parietal cortex, and premotor cortex related to visuomotor processing. We used functional magnetic resonance imaging at 3 Tesla to examine visually guided grip force control under frequent and infrequent visual feedback conditions. Control conditions with intermittent visual feedback alone and a control force condition without visual feedback were examined. As expected, force variability was reduced in the frequent compared with the infrequent condition. Three novel findings were identified. First, infrequent (0.4 Hz) visual feedback did not result in visuomotor activation in lateral cerebellum (lobule VI/Crus I), whereas frequent (25 Hz) intermittent visual feedback did. This is in contrast to the anterior intermediate cerebellum (lobule V/VI), which was consistently active across all force conditions compared with rest. Second, confirming previous observations, the parietal and premotor cortices were active during grip force with frequent visual feedback. The novel finding was that the parietal and premotor cortex were also active during grip force with infrequent visual feedback. Third, right inferior parietal lobule, dorsal premotor cortex, and ventral premotor cortex had greater activation in the frequent compared with the infrequent grip force condition. These findings demonstrate that the frequency of visual information reduces motor error and differentially modulates the neural activation related to visuomotor processing in the cerebellum, parietal cortex, and premotor cortex.

Remapping hand movements in a novel geometrical environment

The issue of how the Euclidean properties of space are represented in the nervous system is a main focus in the study of visual perception, but is equally relevant to motor learning. The goal of our experiments was to investigate how the properties of space guide the remapping of motor coordination. Subjects wore an instrumented data glove that recorded the finger motions. Signals generated by the glove operated a remotely controlled endpoint: a cursor on a computer monitor. The subjects were instructed to execute movements of this endpoint with controlled motions of the fingers. This required inverting a highly redundant map from fingers to cursor motions. We found that 1) after training with visual feedback of the final error (but not of the ongoing cursor motion), subjects learned to map cursor locations into configurations of the fingers; 2) extended practice of movement led to more rectilinear cursor movement, a trend facilitated by training under continuous visual feedback of cursor motions; 3) with practice, subjects reduced motion in the degrees of freedom that did not contribute to the movements of the cursor; 4) with practice, subjects reduced variability of both cursor and hand movements; and 5) the reduction of errors and the increase in linearity generalized beyond the set of movements used for training. These findings suggest that subjects not only learned to produce novel coordinated movement to control the placement of the cursor, but they also developed a representation of the Euclidean space on which hand movements were remapped.

Single-neuron theory of consciousness

By most accounts, the mind arises from the integrated activity of large populations of neurons distributed across multiple brain regions. A contrasting model is presented in the present paper that places the mind/brain interface not at the whole brain level but at the level of single neurons. Specifically, it is proposed that each neuron in the nervous system is independently conscious, with conscious content corresponding to the spatial pattern of a portion of that neuron's dendritic electrical activity. For most neurons, such as those in the hypothalamus or posterior sensory cortices, the conscious activity would be assumed to be simple and unable to directly affect the organism's macroscopic conscious behavior. For a subpopulation of layer 5 pyramidal neurons in the lateral prefrontal cortices, however, an arrangement is proposed to be present such that, at any given moment: (i) the spatial pattern of electrical activity in a portion of the dendritic tree of each neuron in the subpopulation individually manifests a complexity and diversity sufficient to account for the complexity and diversity of conscious experience; (ii) the dendritic trees of the neurons in the subpopulation all contain similar spatial electrical patterns; (iii) the spatial electrical pattern in the dendritic tree of each neuron interacts non-linearly with the remaining ambient dendritic electrical activity to determine the neuron's overall axonal response; (iv) the dendritic spatial pattern is reexpressed at the population level by the spatial pattern exhibited by a synchronously firing subgroup of the conscious neurons, thereby providing a mechanism by which conscious activity at the neuronal level can influence overall behavior. The resulting scheme is one in which conscious behavior appears to be the product of a single macroscopic mind, but is actually the integrated output of a chorus of minds, each associated with a different neuron.

Psychophysical test for the independence of perception and action

Research has suggested that perception and action are independent (see M. A. Goodale & A. Haffenden, 1998). The authors used the Ebbinghaus illusion to test this hypothesis in 2 experiments. Verbal reports of perceived size were compared with maximum grip aperture during grasping (Experiment 1) and manual reports of perceived size (Experiment 2). A multidimensional signal detection analysis was used to distinguish among the possible interactions between the two processes in each experiment (H. Kadlec & J. T. Townsend, 1992a, 1992b). In Experiment 1, the percepts were independent, and there were no interactions between processes for verbal and visuomotor responses. In Experiment 2, the percepts associated with verbal and manual reports were independent, but the processes interacted at the levels of the stimulus information and the decision rules used to transform each percept into a response.

Judging relative positions across saccades

When components of a shape are presented asynchronously during smooth pursuit, the retinal image determines the perceived shape, as if the parts belong to the moving object that the eyes are pursuing. Saccades normally shift our gaze between structures of interest, so there is no reason to expect anything to have moved with the eyes. We therefore decided to examine how people judge the separation between a target flashed before and another flashed after a saccade. Subjects tracked a jumping dot with their eyes. Targets were flashed at predetermined retinal positions, with a 67-242 ms interval between the flashes. After each trial subjects indicated where they had seen the targets. We selected the trials on which subjects made a complete saccade between the presentations of the two targets. For short inter-target intervals, subjects' judgements depended almost exclusively on the retinal separation, even when there were conspicuous visual references nearby. Even for the longest intervals, only part of the change in eye orientation was taken into consideration. These findings cannot simply be accounted for on the basis of the mislocalisation of individual targets or a compression of space near saccades. We conclude that the retinal separation determines the perceived separation between targets presented with a short interval between them, irrespective of any intervening eye movements.

Renewal of the neurophysiology of language: functional neuroimaging

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

The role of V5/MT+ in the control of catching movements: an rTMS study

Milner and Goodale described a model which distinguishes between two visual streams in the brain. It is claimed that the ventral stream serves object recognition (i.e. vision for perception), and the dorsal streams provides visual information for the guidance of action (i.e. vision for action). This model is supported by evidence from the domain of spatial vision, but it remains unclear how motion vision fits into that model. More specifically, it is unclear how the motion complex V5/MT contributes to vision for perception and vision for action. We addressed this question in an earlier study with the V5-lesioned patient LM. Can a motion-blind patient reach for moving objects? We found that she is not only impaired in perceptual tasks but also in catching, suggesting a role for V5/MT+ in vision for both perception and action. However, LM's lesion goes beyond V5/MT+ into more dorsal regions. It is thus possible, that the catching deficit was not produced by damage to V5/MT+ itself. In this case, one would expect that selective interference with V5/MT+ would have no effect on catching. In the present study we tested this prediction by applying rTMS over V5/MT+ of the left hemisphere while healthy subjects were either performing a catching or a reaching task. We found that V5-TMS reduced the speed of the catching but not the reaching response. These results confirm that V5/MT+ is not only involved in perceptual but also in visuomotor tasks.

Background visual cues and memory-guided reaching

Recent research [e.g., Carrozzo, M., Stratta, F., McIntyre, J., & Lacquaniti, F. (2002). Cognitive allocentric representations of visual space shape pointing errors. Experimental Brain Research 147, 426-436; Lemay, M., Bertrand, C. P., & Stelmach, G. E. (2004). Pointing to an allocentric and egocentric remembered target. Motor Control, 8, 16-32] reported that egocentric and allocentric visual frames of reference can be integrated to facilitate the accuracy of goal-directed reaching movements. In the present investigation, we sought to specifically examine whether or not a visual background can facilitate the online, feedback-based control of visually-guided (VG), open-loop (OL), and memory-guided (i.e. 0 and 1000 ms of delay: D0 and D1000) reaches. Two background conditions were examined in this investigation. In the first background condition, four illuminated LEDs positioned in a square surrounding the target location provided a context for allocentric comparisons (visual background: VB). In the second condition, the target object was singularly presented against an empty visual field (no visual background: NVB). Participants (N=14) completed reaching movements to three midline targets in each background (VB, NVB) and visual condition (VG, OL, D0, D1000) for a total of 240 trials. VB reaches were more accurate and less variable than NVB reaches in each visual condition. Moreover, VB reaches elicited longer movement times and spent a greater proportion of the reaching trajectory in the deceleration phase of the movement. Supporting the benefit of a VB for online control, the proportion of endpoint variability explained by the spatial location of the limb at peak deceleration was less for VB as opposed to NVB reaches. These findings suggest that participants are able to make allocentric comparisons between a VB and target (visible or remembered) in addition to egocentric limb and VB comparisons to facilitate online reaching control.

Selective rotation of egocentric spatial representation following right putaminal hemorrhage

Although the role of frontoparietal cortex in spatial egocentric processing is well established, recent animal-lesion and human functional imaging studies have suggested that the neostriatum may also be a critical modulator in the processing of body-centred spatial orientation. We describe here a patient with right putamen-centred hemorrhage who exhibited a consistent counterclockwise rotation of approximately 90 degrees when drawing and writing from memory. A more detailed assessment with a series of representational clock tests demonstrated that the rotation was present only in tasks requiring the use of egocentric cues. In the absence of external cues the patient would adopt and maintain a stable but incorrectly-oriented egocentric representation of the imagined or recollected object. By contrast, performance could be rectified by presentation of correctly-oriented stimuli. These findings suggest that the putamen is part of a circuit underlying egocentric, as opposed to allocentric, representation of space in humans.

Action priming by briefly presented objects

Three experiments investigated how visual objects prime the actions they afford. The principal concern was whether such visuomotor priming depends upon a concurrent visual input--as would be expected if it is mediated by on-line dorsal system processes. Experiment 1 showed there to be essentially identical advantages for making afforded over non-afforded responses when these were made to objects still in view and following brief (30 or 50 ms) object exposures that were backward masked. Experiment 2 showed that affordance effects were also unaffected by stimulus degradation. Finally, Experiment 3 showed there to be statistically equal effects from images of objects and their names. The results suggest that an active object representation is sufficient to generate affordance compatibility effects based on associated actions, whether or not the object is concurrently visible.

Effects of redundant visual stimuli on temporal order judgments

Four experiments were conducted in order to compare the effects of stimulus redundancy on temporal order judgments (TOJs) and reaction times (RTs). In Experiments 1 and 2, participants were presented in each trial with a tone and either a single visual stimulus or two redundant visual stimuli. They were asked to judge whether the tone or the visual display was presented first. Judgments of the relative onset times of the visual and the auditory stimuli were virtually unaffected by the presentation of redundant, rather than single, visual stimuli. Experiments 3 and 4 used simple RT tasks with the same stimuli, and responses were much faster to redundant than to single visual stimuli. It appears that the traditional speedup of RT associated with redundant visual stimuli arises after the stimulus detection processes to which TOJs are sensitive.

Cognitive changes after epilepsy surgery in the posterior cortex

OBJECTIVE

The relationship between the posterior cortex and cognitive functions is still a relatively open field. There are no studies on populations in which functions of posterior structures were examined by a standardised neuropsychological examination before and after posterior resections. Changes in cognitive performance are regularly observed after epilepsy surgery in the temporal lobe. However, information about neuropsychological impairments after resections in the posterior cortex is poor, owing to the relatively low proportion of cortical resections in this area.

METHODS

We retrospectively studied changes in cognition in the neuropsychological data of 28 patients prior to and 6 months after posterior cortical resections.

RESULTS

Cognition significantly showed differences in performance intelligence quotient compared with verbal intelligence quotient. Post-operative verbal intelligence consistently increased, whereas performance intelligence decreased. There was no effect regarding the lesion side, continuation of seizures, or reduction of visual field after surgery. Epilepsy surgery in this area did not lead to significant differences in general intelligence after surgery.

CONCLUSION

Functions of posterior areas could be described by standardised neuropsychological measures. Posterior regions contribute to explicit attentional and visuoconstructional abilities. Epilepsy surgery in the posterior cortex bears no risk for substantial decline in general cognition although some discrete impairment in performance intelligence may occur.

Neural basis for the processes that underlie visually guided and internally guided force control in humans

Despite an intricate understanding of the neural mechanisms underlying visual and motor systems, it is not completely understood in which brain regions humans transfer visual information into motor commands. Furthermore, in the absence of visual information, the retrieval process for motor memory information remains unclear. We report an investigation where visuomotor and motor memory processes were separated from only visual and only motor activation. Subjects produced precision grip force during a functional MRI (fMRI) study that included four conditions: rest, grip force with visual feedback, grip force without visual feedback, and visual feedback only. Statistical and subtractive logic analyses segregated the functional process maps. There were three important observations. First, along with the well-established parietal and premotor cortical network, the anterior prefrontal cortex, putamen, ventral thalamus, lateral cerebellum, intermediate cerebellum, and the dentate nucleus were directly involved in the visuomotor transformation process. This activation occurred despite controlling for the visual input and motor output. Second, a detailed topographic orientation of visuomotor to motor/sensory activity was mapped for the premotor cortex, parietal cortex, and the cerebellum. Third, the retrieval of motor memory information was isolated in the dorsolateral prefrontal cortex, ventral prefrontal cortex, and anterior cingulate. The motor memory process did not extend to the supplementary motor area (SMA) and the basal ganglia. These findings provide evidence in humans for a model where a distributed network extends over cortical and subcortical regions to control the visuomotor transformation process used during visually guided tasks. In contrast, a localized network in the prefrontal cortex retrieves force output from memory during internally guided actions.

Perceptual requirements for fast manual responses

The on-line visual control of human movements can be exceptionally fast. Whether it is fast depends on the kind of visual information that is involved. In the present study we examine whether fast on-line control is specific to the magnocellular visual pathway. Fast manual responses become evident when an ongoing movement has to be adjusted, for instance because the target is displaced. We examined whether the response to such perturbations is faster for stimuli that only activate the magnocellular pathway than for equally conspicuous stimuli that only activate the parvocellular pathway. The response was indeed about 35 ms faster for stimuli that activate the magnocellular pathway. However, we argue that the slower response to stimuli that only stimulate the parvocellular pathway is due to the properties of the neurones involved and the less direct connection to the motor areas, rather than to fast reactions being driven exclusively by magnocellular input.

Delayed reaching and grasping in patients with optic ataxia

A series of experiments documenting the reaching and grasping of two patients with optic ataxia is presented. We compare their immediate responses with their behavior when required to delay for a few seconds before responding. When the delayed response is 'pantomimed', i.e. made in the absence of the target object, their performance typically improves. This pattern was predicted from a two-visual-systems model in which the cortical dorsal stream mediates normal visually guided actions while the ventral stream deals with visual information that has to be held in memory. We further found that when a 'preview' task was used in which the patients could use memorized information to guide a response to a still-present target object, they did so in preference to using the visual information facing them.

Neural mechanisms for the recognition of biological movements

The visual recognition of complex movements and actions is crucial for the survival of many species. It is important not only for communication and recognition at a distance, but also for the learning of complex motor actions by imitation. Movement recognition has been studied in psychophysical, neurophysiological and imaging experiments, and several cortical areas involved in it have been identified. We use a neurophysiologically plausible and quantitative model as a tool for organizing and making sense of the experimental data, despite their growing size and complexity. We review the main experimental findings and discuss possible neural mechanisms, and show that a learning-based, feedforward model provides a neurophysiologically plausible and consistent summary of many key experimental results.

Seeing, since childhood, without ventral stream: a behavioural study

We report the case of a 30-year-old man (S.B.) who developed visual agnosia following a meningoencephalitis at the age of 3 years. MRI disclosed extensive bilateral lesions of the occipital temporal visual pathway (ventral stream) and lesions in the right dorsal pathway, sparing primary visual cortices. S.B. showed a severe visual recognition deficit (texture, colour, objects, faces and words), although movement and space perception were largely preserved. His remaining visual capacities illustrate the competence of an isolated dorsal system which essentially functions on the sole basis of magnocellular afferents (low spatial resolution, high sensitivity to low contrast and moving stimuli). Patient S.B. also shows remarkable visuomotor competences, despite his perceptual limitations. It is suggested that his perceptual capacities correspond to the visual processing limitations of the dorsal visual stream, which in this patient have become accessible to perceptual awareness.

A systems model of altered consciousness: integrating natural and drug-induced psychoses

Increasing evidence from neuroimaging and behavioral studies suggests that functional disturbances within cortico-striato-thalamic pathways are critical to psychotic symptom formation in drug-induced and possibly also naturally occurring psychoses. Recent basic and clinical research with psychotomimetic drugs, such as the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, ketamine, and the serotonin-2A (5-HT(2A)) receptor agonist, psilocybin, suggest that the hallucinogenic effects of these drugs arise, at least in part, from their common capacity to disrupt thalamo-cortical gating of external and internal information to the cortex. Deficient gating of sensory and cognitive information is thought to result in an overloading inundation of information and subsequent cognitive fragmentation and psychosis. Cross-species studies of homologues gating functions, such as prepulse inhibition of the startle reflex, in animal and human models of psychosis corroborate this view and provide a translational testing mechanism for the exploration of novel pathophysiologic and therapeutic hypotheses relevant to psychotic disorders, such as the group of schizophrenias.

From three-dimensional space vision to prehensile hand movements: the lateral intraparietal area links the area V3A and the anterior intraparietal area in macaques

The posterior parietal cortex is included in the dorsal cortical visual pathway underlying the three-dimensional (3-D) visual recognition of space and objects. The neurons in the lateral intraparietal area (LIP) respond visually to the three-dimensional objects, whereas those in the anterior intraparietal area (AIP) respond to hand movements to grasp them. LIP receives visual inputs from V3A, whereas AIP projects to the premotor areas; however, it is not known whether the neurons in LIP project to AIP. We herein investigated the connectional substrates that underlie the transformation of three-dimensional vision to prehensile hand movements in the Japanese monkey (Macaca fuscata). After identifying the three-dimensional visually responsive region in the posterior part of LIP by the unit recordings, we injected a bidirectional tracer, wheat germ agglutinin conjugated to horseradish peroxidase, into one of the recording sites. We found that LIP receives neuronal projections from V3A and sends axons to AIP. To confirm our findings, we injected several orthograde tracers into V3A and retrograde tracers into AIP in the same hemispheres. We found that the V3A neurons projecting to LIP terminate in the vicinity of the LIP neurons projecting to AIP. The results suggest that the cortical connections of V3A-LIP-AIP in the lateral bank of the intraparietal sulcus play an important role in the visuomotor transformation for prehensile hand movements.

Object orientation agnosia: a failure to find the axis?

A dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients with vascular lesions. In this article, we describe a 57-year-old man with probable Alzheimer' s disease who shows the same dissociation. Neuroimaging findings indicated marked hypometabolism in the posterior cortical regions, particularly the postero-superior parietal lobes. Clinically, the patient had good object recognition accompanied by severely impaired spatial abilities. The experimental investigations comprised a variety of tasks in which he identified misoriented objects, evaluated the orientation of single objects, or discriminated the orientation of simultaneously presented items. Results revealed that his object recognition was independent of orientation and was largely mediated by salient features. With respect to orientation judgements, the patient displayed a profound inability to judge the orientation of nonupright objects, but remarkably intact (though largely implicit) knowledge of the upright orientation. Strikingly, his orientation judgements were also more accurate for upside-down objects than for other orientations (i.e., 90 degrees ). We interpret these results as evidence that judgements about object orientation are facilitated when the orientation of the principal axis of the object matches that of an internal representation. We propose that the inability to determine other orientations may be due to the failure of an "axis-finding" mechanism implemented in the posterior parietal lobes, that translates between object-centered and eye-centered coordinates appropriate for guiding visual scanning.

Does perception of biological motion rely on specific brain regions?

Perception of biological motions plays a major adaptive role in identifying, interpreting, and predicting the actions of others. It may therefore be hypothesized that the perception of biological motions is subserved by a specific neural network. Here we used fMRI to verify this hypothesis. In a group of 10 healthy volunteers, we explored the hemodynamic responses to seven types of visual motion displays: drifting random dots, random dot cube, random dot cube with masking elements, upright point-light walker, inverted point-light walker, upright point-light walker display with masking elements, and inverted point-light walker display with masking elements. A gradient in activation was observed in the occipitotemporal junction. The responses to rigid motion were localized posteriorly to those responses elicited by nonrigid motions. Our results demonstrate that in addition to the posterior portion of superior temporal sulcus, the left intraparietal cortex is involved in the perception of nonrigid biological motions.

Implication of sensorimotor integration in the generation of periodic dystonic myoclonus in subacute sclerosing panencephalitis (SSPE)

To clarify the mechanism of periodic dystonic myoclonus in subacute sclerosing panencephalitis (SSPE), a 22-year-old patient with a clinical diagnosis of SSPE was electrophysiologically investigated. Involuntary movements consisted of generalized dystonic posturing which occurred quasiperiodically once every 4 to 8 seconds. Effects of sensory stimuli and voluntary movements were studied by means of polygraphic recording of surface electromyogram (EMG), scalp electroencephalogram (EEG), and magnetoencephalogram (MEG). EEG showed quasi-periodic, generalized, transient complexes synchronous to each dystonic myoclonus, which were preceded by a slow negative EEG shift at the parietal region by approximately 5 seconds. Neither external stimuli nor self-paced movements alone influenced the periodicity of dystonic myoclonus or EEG complexes. In the reaction time task, however, the external stimuli given as an imperative cue to execute a motor task elicited dystonic myoclonus and generalized EEG complexes only if they were presented in the latter segment of the interval between the two successive EEG complexes while the slow negative EEG shift appeared. These findings suggest that EEG complexes and periodic movements spontaneously occur when cortical excitability reaches a certain critical level, but both phenomena are elicited even before if the sensory stimuli as an imperative signal requiring motor execution are presented. This finding most likely implies involvement of the sensorimotor integration mechanism in these periodic phenomena.

Motor systems

The field of motor control has broadened considerably over the past decade. Increasingly detailed information has accrued about the cellular and molecular processes involved in motor pattern generation and motor learning while, at the other extreme, the comparison of studies in humans and monkeys has begun to bridge the gap between cognitive and motor functions. The most striking feature of recent research has been the intense use of electrophysiological procedures in behaving monkeys and non-invasive imaging procedures in humans to elucidate details of sensory-motor transformations and the functional roles of different brain regions in the learning, planning and execution of movements.

Ultra-rapid categorisation of natural scenes does not rely on colour cues: a study in monkeys and humans

In a rapid categorisation task, monkeys and humans had to detect a target (animal or food) in briefly flashed (32 ms) and previously unseen natural images. Removing colour cues had very little effect on average performance. Impairments were restricted to a mild accuracy drop (in some human subjects) and a small reaction time mean increase (10-15 ms) observed both in monkeys and humans but only in the detection of food targets. In both tasks, accuracy and latency of the fastest behavioural responses were unaffected, suggesting that such ultra-rapid categorizations could depend on feed-forward processing of early coarse achromatic magnocellular information.

Processing of multiple kinematic signals in the cerebellum and motor cortices

The cerebellum and motor cortices are hypothesized to make fundamentally different but synergistic contributions to the control of movement. Richly interconnected, these structures must communicate and translate salient parameters of movement. This review examines the similarities and differences in the encoding of multiple limb movement parameters in the cerebellum and motor cortices. Also presented are recent data on direction and speed coding by cerebellar Purkinje cells and primary motor and dorsal premotor cortical neurons during a visually-instructed, manual tracking task. Both similarities and differences have been found in the way that these two motor areas process movement parameters. For example, the two motor control structures encode direction with almost identical depths of modulation, which may simplify the exchange of directional signals. Two major differences between the cerebellum and motor cortices consist of the distribution of the preferred directions and the manner in which direction and speed are jointly signaled within the discharge of individual neurons. First, an anterior-posterior distribution of preferred directions has been shown for both reaching and manual tracking, consistent with an intrinsic reference frame and/or the structure of afferent input. In contrast, neurons in the motor cortices have uniformly distributed preferred directions, consistent with general purpose directional calculations. Secondly, Purkinje cells in the cerebellum and motor cortices combine movement direction and speed information differently. For example, Purkinje cell discharge encodes combinations of direction and speed, a 'preferred velocity', while the motor cortical neurons use a temporal parcellation scheme to encode multiple parameters of movement. These results demonstrate that the cerebellum and motor cortices process and use kinematic information in fundamentally different ways that may underlie the functional uniqueness of the two motor control structures.

Can a motion-blind patient reach for moving objects?

It has been claimed that the visual brain is organized in two separate processing streams for spatial vision: one for perception and one for action. To determine whether motion vision is also divided into vision for action and for perception we examined the interceptive behaviour of the motion-blind patient LM. The task for LM and three age-matched control subjects was to reach-and-grasp for an object that moved away. Three experiments were conducted to examine the effects on perfomance of target speed (Expt 1), observation time (Expt 2) and visual feedback (Expt 3). As LM is only able to reach for objects which move at 0.5 m/s or less, her performance is inferior to that of controls who can reach for objects moving at 1.0 m/s, but it is better than would be expected from her performance in psychophysical experiments on her motion vision. Kinematic analysis of LM's reaching movements showed that she adapted the speed of her moving hand to the speed of the target but only when full vision was available. In contrast to normal subjects, LM required long observation times and vision of her moving hand to produce successful reaching responses. Thus, the impairment of both perception and action in LM suggests that the motion area MT/V5 is located at an early stage of the extrastriate hierarchy and provides input to both the perception and the action processing streams.

Ultrastructural organization of transmitters in the cat lateralis medialis-suprageniculate nucleus of the thalamus: an immunohistochemical study

The lateralis medialis-suprageniculate nuclear (LM-Sg) complex of the cat's posterior thalamus receives a rather wide variety of inputs from diverse cortical and subcortical areas. Previous ultrastructural studies of this nucleus demonstrated the presence of four types of vesicle-containing profiles and characterized some of these as gamma-aminobutyric acid (GABA)-containing terminals (Norita and Katoh [1987] J. Comp. Neurol. 263:54-67; Norita and Katoh [1988] Prog. Brain Res. 75:109-118). The present study has extended these observations by examining the immunoreactivity (ir) of LM-Sg, with antibodies raised against aspartate (Asp), glutamate (Glu), GABA, the acetylcholine (ACh) marker, choline acetyltransferase (ChAT), and substance P (SP), by using light and electron microscopy. Neuronal somata immunopositive for the excitatory amino acids (EAAs) Asp and Glu, were of medium size. EAA-ir terminals also were of medium size and contained round synaptic vesicles; they made asymmetrical synaptic contacts with dendritic profiles. Neuronal somata immunopositive for GABA were small. GABA-positive terminals also were small and contained pleomorphic synaptic vesicles; they formed symmetrical synaptic contacts with dendritic profiles. No neurons immunolabeled for ChAT were found. Terminals immunopositive for ChAT were small and contained round synaptic vesicles; these made symmetrical synaptic contacts, asymmetrical synaptic contacts, or both, of the en passant type with dendritic profiles. SP-immunolabeled neuronal somata were not found. Immunolabeled terminals were small, contained round synaptic vesicles, and made asymmetrical synaptic contacts with dendritic profiles. ChAT-ir and SP-ir axon terminals were not expressed evenly within LM-Sg. This difference in distribution suggests that within the LM-Sg, there may be a difference in specific sensory processing functions which correlate with transmitter type.

Dual cytoarchitectonic trends: an evolutionary model of frontal lobe functioning and its application to psychopathology

OBJECTIVE

To introduce and discuss an evolutionary model of frontal lobe functioning (the dual cytoarchitectonic trends theory [DTT]) and its application to understanding the neurobiology of schizophrenia and anxiety disorders.

METHOD

An introduction to the DTT with respect to neural architecture, connectivity, and function is presented. In addition, neurobiologic, neuropathologic, clinical, and cognitive research supporting the application of this model to schizophrenia and anxiety disorders is reviewed.

RESULTS

Traditional neuropsychologic models of acquired brain damage have been limited in their ability to explain frontal lobe dysfunction and its consequences in relation to psychopathology. The DTT offers an appropriately general neural-systems framework that may be better able to account for the diversity of symptoms, widespread neuropathology, and developmental abnormalities that are associated with most forms of psychopathology.

CONCLUSIONS

Research investigating the neurobiology of psychopathology would benefit from adopting models of brain dysfunction that are consistent with neurodevelopmental pathology and evolution. Such efforts would likely lead to a greater understanding of neurobiologic mechanisms and, ultimately, better treatment strategies.

Neurochemical and connectional organization of the dorsal pulvinar complex in monkeys

To investigate the organization of the dorsal pulvinar complex, patterns of neurochemical staining were correlated with cortico-pulvinar connections in macaques (Macaca mulatta). Three major neurochemical subdivisions of the dorsal pulvinar were identified by acetylcholinesterase (AChE) histochemistry, as well as immunostaining for calbindin-D(28K) and parvalbumin. The dorsal lateral pulvinar nucleus (PLd) was defined on histochemical criteria as a distinct AChE- and parvalbumin-dense, calbindin-poor wedge that was found to continue caudally along the dorsolateral edge of the pulvinar to within 1 mm of its caudal pole. The ventromedial border of neurochemical PLd with the rest of the dorsal pulvinar, termed the medial pulvinar (PM), was sharply defined. Overall, PM was lighter than PLd for AChE and parvalbumin and displayed lateral (PMl) and medial (PMm) histochemical divisions. PMm contained a central "oval" (PMm-c) that stained darker for AChE and parvalbumin than the surrounding region. The neurochemically defined PLd was labeled by tracer injections in the inferior parietal lobule (IPL) and dorsolateral prefrontal cortex but not the superior temporal gyrus (STG). Label within PMl was found after prefrontal and IPL and, to a lesser extent, after STG injections. The PMm was labeled after injections of the IPL and STG, but only sparsely following prefrontal injections. The histochemically distinct subregion or module of PMm, PMm-c, was labeled only by STG injections. Overlapping labeling was found in dorsal pulvinar divisions PMl and PLd following paired IPL/prefrontal, but not IPL/STG or these particular STG/prefrontal, injections. Thus, PLd may be a visuospatially related region whereas PM appears to contain several types of territories, some related to visual or auditory inputs, and others that receive directly converging input from posterior parietal and prefrontal cortex and may participate in a distributed cortical network concerned with visuospatial functions.

Manual and verbal responses to completely masked (unreportable) stimuli: exploring some conditions for the metacontrast dissociation

As reported by Neumann and Klotz [1994, in Attention and Performance XV: Conscious and Nonconscious Information Processing Eds C Umiltà, M Moscovitch (Cambridge, MA: MIT Press) pp 123-150], a geometric shape masked by metacontrast can affect response latency (RT) even if it is not visible, i.e. if it yields a d' value of zero in a signal-detection (SD) task (metacontrast dissociation). In the initial study as well as in most subsequent experiments, the RT task was manual and the SD task was verbal. Hence tasks and output modes were confounded. In the present study, two experiments were conducted to find out which of these factors is responsible for the metacontrast dissociation. In experiment 1, participants performed an RT task in either a manual or a verbal output mode. In experiment 2, these output modes were compared in an SD task. Independently of output modes, the masked primes affected RT but could not be detected in the SD task. It is concluded that tasks, but not output modes, are crucial for the metacontrast dissociation. Implications for the mechanisms underlying the metacontrast dissociation and for the functional difference between judgments and responses are discussed.

Generative character of perception: a neural architecture for sensorimotor anticipation

The basic idea of our anticipatory approach to perception is to avoid the common separation of perception and generation of behavior and to fuse both aspects into a consistent neural process. Our approach tries to explain the phenomenon of perception, in particular, of perception at the level of sensorimotor intelligence, from a behavior-oriented point of view. Perception is assumed to be a generative process of anticipating the course of events resulting from alternative sequences of hypothetically executed actions. By means of this sensorimotor anticipation, it is possible to characterize a visual scenery immediately in categories of behavior, i.e. by a set of actions which describe possible methods of interaction with the objects in the environment. Thus, the competence to perceive a complex situation can be understood as the capability to anticipate the course of events caused by different action sequences. Starting from an abstract description of anticipatory perception and the essential biological evidence for internal simulation, we present two biologically motivated computational models that are able to anticipate and evaluate hypothetically sensorimotor sequences. Both models consider functional aspects of those cortical and subcortical systems that are assumed to be involved in the process of sensory prediction and sensorimotor control. Our first approach, the Model for Anticipation based on Sensory IMagination (MASIM), realizes a sequential search in sensorimotor space using a simple model of lateral cerebellum as sensory predictor. We demonstrate the efficiency of this model approach in the light of visually guided local navigation behaviors of a mobile system. The second approach, the Model for Anticipation based on Cortical Representations (MACOR), is actually still at a conceptual level of realization. We postulate that this model allows a completely parallel search at the neocortical level using assemblies of spiking neurons for grouping, separation, and selection of sensorimotor sequences. Both models are intended as general schemes for anticipation based perception at the level of sensorimotor intelligence.