We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.

Control of goal-directed and stimulus-driven attention in the brain

Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

A category of stimuli of great importance for primates, humans in particular, is that formed by actions done by other individuals. If we want to survive, we must understand the actions of others. Furthermore, without action understanding, social organization is impossible. In the case of humans, there is another faculty that depends on the observation of others' actions: imitation learning. Unlike most species, we are able to learn by imitation, and this faculty is at the basis of human culture. In this review we present data on a neurophysiological mechanism--the mirror-neuron mechanism--that appears to play a fundamental role in both action understanding and imitation. We describe first the functional properties of mirror neurons in monkeys. We review next the characteristics of the mirror-neuron system in humans. We stress, in particular, those properties specific to the human mirror-neuron system that might explain the human capacity to learn by imitation. We conclude by discussing the relationship between the mirror-neuron system and language.

The mirror-neuron system.

The anterior insular cortex (AIC) is implicated in a wide range of conditions and behaviours, from bowel distension and orgasm, to cigarette craving and maternal love, to decision making and sudden insight. Its function in the re-representation of interoception offers one possible basis for its involvement in all subjective feelings. New findings suggest a fundamental role for the AIC (and the von Economo neurons it contains) in awareness, and thus it needs to be considered as a potential neural correlate of consciousness.

How do you feel--now? The anterior insula and human awareness.

Prior to the twentieth century, theories of knowledge were inherently perceptual. Since then, developments in logic, statis- tics, and programming languages have inspired amodal theories that rest on principles fundamentally different from those underlying perception. In addition, perceptual approaches have become widely viewed as untenable because they are assumed to implement record- ing systems, not conceptual systems. A perceptual theory of knowledge is developed here in the context of current cognitive science and neuroscience. During perceptual experience, association areas in the brain capture bottom-up patterns of activation in sensory-motor areas. Later, in a top-down manner, association areas partially reactivate sensory-motor areas to implement perceptual symbols. The stor- age and reactivation of perceptual symbols operates at the level of perceptual components - not at the level of holistic perceptual expe- riences. Through the use of selective attention, schematic representations of perceptual components are extracted from experience and stored in memory (e.g., individual memories of green, purr, hot). As memories of the same component become organized around a com- mon frame, they implement a simulator that produces limitless simulations of the component (e.g., simulations of purr). Not only do such simulators develop for aspects of sensory experience, they also develop for aspects of proprioception (e.g., lift, run) and introspec- tion (e.g., compare, memory, happy, hungry). Once established, these simulators implement a basic conceptual system that represents types, supports categorization, and produces categorical inferences. These simulators further support productivity, propositions, and ab- stract concepts, thereby implementing a fully functional conceptual system. Productivity results from integrating simulators combinato- rially and recursively to produce complex simulations. Propositions result from binding simulators to perceived individuals to represent type-token relations. Abstract concepts are grounded in complex simulations of combined physical and introspective events. Thus, a per- ceptual theory of knowledge can implement a fully functional conceptual system while avoiding problems associated with amodal sym- bol systems. Implications for cognition, neuroscience, evolution, development, and artificial intelligence are explored.

/pdf/perceptual-symbol-systems-4spsk97r61.pdf

Perceptual symbol systems.

The aim of the present study was to examine the timing of different responses given simultaneously to a single event, the sudden displacement of a visual object occurring at the onset of the grasping movement directed at that object. The subjects were requested to correct their movement in order to reach accurately for the object and to signal the time at which they became aware of its displacement by a simple vocal utterance (Tah!). The onset of the motor adjustment was measured using kinematic landmarks obtained from the hand trajectory. Movements executed during trials where the object was displaced had an earlier peak in acceleration (107 ms) than movements executed during control trials (120 ms). By contrast, the vocal signal occurred 420 ms following object displacement, that was more than 300 ms after the onset of the motor correction. Control experiments were performed in order to verify the influence of possible interferences between the two tasks. Motor corrections performed without vocal utterance had the same timing as when the vocal signal was produced. Vocal signals produced in response to object's displacements but in the absence of reaching movements had the same latency as when movements were performed. We conclude from these results that the two responses were generated independently of each other. Assuming that the vocal responses in this experiment did signal the subject's awareness, the observed delay between motor corrections and these responses suggests that neural activity must be processed during a significant and quantifiable amount of time before it can give rise to conscious experience. This dissociation between motor responses and awareness in normal subjects is discussed in the light of clinical cases where overt behaviour and conscious experience are dissociated by cerebral lesions.

Temporal dissociation of motor responses and subjective awareness. A study in normal subjects.

Beyond consciousness of external reality: A ''who'' system for consciousness of action and self-consciousness

The retinal coordinates of an image are normally insufficient to define the direction of an object in body-centred visual space. Gaze direction, specified by information on the position of eye-in-head and on the position of head-on-torso, is also required. While the source of the eye-in-head signal is controversial, it is clear that proprioceptive signals from neck muscles are sufficient to provide head-on-torso information. Observations by Goodwin et al., beginning in 1972, that vibration of limb muscles modifies proprioception from them, and induces illusory motion and false perception of limb position, suggested this study of the effects of neck muscle vibration on the representation of visual space. Verbal reports, supported by objective measures, revealed that vibration of muscles on one side of the neck induces a visual illusion: contralateral displacement of a small visual target viewed in the dark. Pointing movements towards the target are similarly affected, confirming that the representation of directions in visual space is modified by neck muscle vibration. A second vibration-induced illusion was uncovered when apparent displacement ceased. This is an illusion of pure target motion in the same direction as the previously observed displacement. The magnitudes of both the displacement and pure motion illusions were dependent on vibration amplitude and were unrelated to real or apparent movements of eyes or head. Taken together these observations indicate that vibration of neck muscles can modify independently (1) the central representation of the instantaneous direction of gaze and (2) the signal of the velocity with which this direction is changing.

Neck muscle vibration modifies the representation of visual motion and direction in man.

1 How Do We Direct Our Actions in Space?.- Different Modes of Processing Visual Spatial Information.- Role of the Extraretinal Signal in Perceptual Stability of Visual Space.- The Paralyzed Eye Situation as a Cue for Understanding Visuomotor Localization.- The Role of Registered vs. Actual Gaze Position in Guiding Behavior.- 2 Maintenance of Equilibrium During Movement.- How Is Body Posture Established?.- How Do Movement and Posture Interact?.- Coordination Between Posture and Movement in the Quadruped.- Central Organization of Postural Changes.- Conclusions.- 3 Neural Mechanisms of Visual Orientation in Rodents: Targets Versus Places.- Visually Guided Movements Toward Targets.- Visually Guided Movements Toward Places.- Conclusions.- 4 Role of the Monkey Superior Colliculus in the Spatial Localization of Saccade Targets.- Role of the Superior Colliculus in Saccadic Eye Movements.- Models of the Saccadic Eye Movement System.- Neural Representations of Saccade Targets.- 5 Interface of Visual Input and Oculomotor Command for Directing the Gaze on Target.- Internal Medullary Lamina.- Experimental Examination of the Hypothesis of Adequate Response.- Visual Responses to Target Location in Space.- Discussion.- 6 Coordination of Eye-Head Movements in Alert Monkeys: Behavior of Eye-Related Neurons in the Brain Stem.- Experimental Method.- Behavior of PRF Preoculomotor Neurons During Eye-Head Coordination.- Coordination of Head and Eyes in the Saccadic Changes of Gaze.- Conclusions.- 7 Contribution of Eye Movement to the Representation of Space.- How Is Visual Direction Given?.- What Is the Source of Knowledge of Eye Position?.- Conclusions.- 8 Control of the Optokinetic Reflex by the Nucleus of the Optic Tract in the Cat.- Functional Anatomy of NOT.- Relationship Between NOT Output and OKN.- Conclusions.- 9 Development of Optokinetic Nystagmus and Effects of Abnormal Visual Experience During Infancy.- Human OKN Development.- Other Studies.- Future Research.- 10 Spatially Determined Visual Activity in Early Infancy.- Appreciation of Spatial Relations.- Visual Anticipation of Spatiotemporal Events.- Spatial Sensitivity at Birth.- Conclusions.- 11 Spatial Sense of the Human Infant.- Experiments in Reaching.- Experiments in Intermodal Spatial Coordination.- Orienting to Touch.- Conclusions.- 12 Space, the Organism and Objects, Their Cognitive Elaboration in the Infant.- The Development of Organized Movements for Tracking a Moving Visual Object.- 13 Motion Parallax Sensitivity and Space Perception.- Space Perception.- Psychophysical Observations in Motion Parallax.- Implications for Space Perception.- 14 Perceptual Consequences of Experimental Extraocular Muscle Paralysis.- The Kernel Observation under Partial Paralysis: Perceived Change in Elevation.- Quantitative Measurements of Perceived Eye-Level Horizontal.- Illusory Changes in Visual Localization of the Median Plane.- Influence of Level of Paralysis.- Three-Parameter Model of the Influence of Paralysis on Visual Localization and Oculomotor Control.- Illumination Versus Darkness.- Auditory-Visual Matches.- EEPI and Cancellation Are Not Suppressed in Illumination Visual Localization and Intersensory Localization Are Guided by Cancellation in Darkness.- A Paradox and Its Resolution.- Source of EEPI.- 15 Mechanisms of Space Constancy.- Beyond Corollary Discharge.- Rules of Motion Perception During Saccades Versus During Fixation.- Exploring Space Constancy with Figure-Ground Reversible Images.- Mechanisms of Stabilization.- 16 Visual Information Processing for Saccadic Eye Movements.- Processes Involved in Saccade Generation.- Retinal Eccentricity and Saccade Direction.- Saccade Latency.- Saccade Amplitude.- Conclusions.- 17 Optic Ataxia: A Specific Disorder in Visuomotor Coordination.- Case Reports.- Neuropsychological Symptoms.- Proximal and Distal Deficits in Optic Ataxia.- Comparison with Findings from Experiments in Monkeys.- Effects of Altering Spatial Cues on Reaching Behavior in Optic Ataxia.- Discussion.- 18 Multimodal Structure of the Extrapersonal Space.- Compartments of Extrapersonal Space.- Coordinates of Extrapersonal Space.- Disturbances in the Perception of Objects and Space Following Parietal and Occipital Corex Lesions.- Multimodal Control of Eye Movements.- Conclusions.- Author Index.

Spatially Oriented Behavior

http://www.ddl.ish-lyon.cnrs.fr/fulltext/Boulenger/Boulenger_2008_Neuropsychologia.pdf

Marc Jeannerod

Papers

Temporal dissociation of motor responses and subjective awareness. A study in normal subjects.

Beyond consciousness of external reality: A ''who'' system for consciousness of action and self-consciousness

Neck muscle vibration modifies the representation of visual motion and direction in man.

Spatially Oriented Behavior

Word processing in Parkinson's disease is impaired for action verbs but not for concrete nouns