This paper concerns how motor actions are neurally represented and coded. Action planning and motor preparation can be studied using a specific type of representational activity, motor imagery. A close functional equivalence between motor imagery and motor preparation is suggested by the positive effects of imagining movements on motor learning, the similarity between the neural structures involved, and the similar physiological correlates observed in both imaging and preparing. The content of motor representations can be inferred from motor images at a (...) macroscopic level, based on global aspects of the action (the duration and amount of effort involved) and the motor rules and constraints which predict the spatial path and kinematics of movements. A more microscopic neural account calls for a representation of object-oriented action. Object attributes are processed in different neural pathways depending on the kind of task the subject is performing. During object-oriented action, a pragmatic representation is activated in which object affordances are transformed into specific motor schemas (independently of other tasks such as object recognition). Animal as well as human clinical data implicate the posterior parietal and premotor cortical areas in schema instantiation. A mechanism is proposed that is able to encode the desired goal of the action and is applicable to different levels of representational organization. (shrink)

The emulation theory of representation is developed and explored as a framework that can revealingly synthesize a wide variety of representational functions of the brain. The framework is based on constructs from control theory (forward models) and signal processing (Kalman filters). The idea is that in addition to simply engaging with the body and environment, the brain constructs neural circuits that act as models of the body and environment. During overt sensorimotor engagement, these models are driven by efference copies in (...) parallel with the body and environment, in order to provide expectations of the sensory feedback, and to enhance and process sensory information. These models can also be run off-line in order to produce imagery, estimate outcomes of different actions, and evaluate and develop motor plans. The framework is initially developed within the context of motor control, where it has been shown that inner models running in parallel with the body can reduce the effects of feedback delay problems. The same mechanisms can account for motor imagery as the off-line driving of the emulator via efference copies. The framework is extended to account for visual imagery as the off-line driving of an emulator of the motor-visual loop. I also show how such systems can provide for amodal spatial imagery. Perception, including visual perception, results from such models being used to form expectations of, and to interpret, sensory input. I close by briefly outlining other cognitive functions that might also be synthesized within this framework, including reasoning, theory of mind phenomena, and language. Key Words: efference copies; emulation theory of representation; forward models; Kalman filters; motor control; motor imagery; perception; visual imagery. (shrink)

What is it like to dream? On an orthodox view, dreams involve misleading sensations and false beliefs. I argue, on philosophical, psychological, and neurophysiological grounds, that orthodoxy about dreaming should be rejected in favor of an imagination model of dreaming. I am thus in partial agreement with Colin McGinn, who has argued that we do not have misleading sensory experiences while dreaming, and partially in agreement with Ernest Sosa, who has argued that we do not form false beliefs while dreaming. (...) Rather, on my view, dreams involve mental imagery and propositional imagination. I defend the imagination model of dreaming from objections. (shrink)

Posterior parietal cortex has traditionally been considered to be a sensory association area in which higher-order processing and intermodal integration of incoming sensory information occurs. In this paper, evidence from clinical reports and from lesion and behavioral-electrophysiological experiments using monkeys is reviewed and discussed in relation to the overall functional organization of posterior parietal association cortex, and particularly with respect to a proposed posterior parietal mechanism concerned with the initiation and control of certain classes of eye and limb movements. Preliminary (...) data from studies of the effects of posterior parietal lesions on oculomotor control in monkeys are reported.The behavioral effects of lesions of posterior parietal cortex in monkeys have been found to be similar to those which follow analogous damage of the minor hemisphere in humans, while behavioral-electrophysiological experiments have disclosed classes of neurons in this area which have functional properties closely related to the behavioral acts that are disrupted by lesions of the area. On the basis of current data from these areas of study, it is proposed that the sensory association model of posterior parietal function is inadequate to account for the complexities of the present evidence. Instead, it now appears that many diverse neural mechanisms are locatedin partin parietal cortex, that some of these mechanisms are involved in sensory processing and perceptual functions, but that others participate in motor control, and that still others are involved in attentional, motivational, or emotional processes. It is further proposed that the elementary units of these various neural mechanisms are distributed within posterior parietal cortex according to the columnar hypothesis of Mountcastle. (shrink)

The posterior parietal cortex (PPC) is the most likely site where egocentric spatial relationships are represented in the brain. PPC cells receive visual, auditory, somaesthetic, and vestibular sensory inputs; oculomotor, head, limb, and body motor signals; and strong motivational projections from the limbic system. Their discharge increases not only when an animal moves towards a sensory target, but also when it directs its attention to it. PPC lesions have the opposite effect: sensory inattention and neglect. The PPC does not seem (...) to contain a “map” of the location of objects in space but a distributed neural network for transforming one set of sensory vectors into other sensory reference frames or into various motor coordinate systems. Which set of transformation rules is used probably depends on attention, which selectively enhances the synapses needed for making a particular sensory comparison or aiming a particular movement. (shrink)

According to conventional wisdom, the split-brain syndrome puts paid to the thesis that consciousness is necessarily unified. The aim of this paper is to challenge that view. I argue both that disunity models of the split-brain are highly problematic, and that there is much to recommend a model of the split-brain—the switch model—according to which split-brain patients retain a fully unified consciousness at all times. Although the task of examining the unity of consciousness through the lens of the split-brain syndrome (...) is not a new one—such projects date back to Nagel’s seminal paper on the topic—the time is ripe for a re-evaluation of the issues. (shrink)

In the past decade there has been renewed interest in the study of mental imagery. Emboldened by new findings from neuroscience, many people have revived the idea that mental imagery involves a special format of thought, one that is pictorial in nature. But the evidence and the arguments that exposed deep conceptual and empirical problems in the picture theory over the past 300 years have not gone away. I argue that the new evidence from neural imaging and clinical neuropsychology does (...) little to justify this recidivism because it does not address the format of mental images. I also discuss some reasons why the picture theory is so resistant to counterarguments and suggest ways in which non-pictorial theories might account for the apparent spatial nature of images. (shrink)

6. Seeing With the Mind’s Eye 1: The Puzzle of Mental Imagery .................................................6-1 6.1 What is the puzzle about mental imagery?..............................................................................6-1 6.2 Content, form and substance of representations ......................................................................6-6 6.3 What is responsible for the pattern of results obtained in imagery studies?.................................6-8..

Mental imagery (varieties of which are sometimes colloquially refered to as “visualizing,” “seeing in the mind's eye,” “hearing in the head,” “imagining the feel of,” etc.) is quasi-perceptual experience; it resembles perceptual experience, but occurs in the absence of the appropriate external stimuli. It is also generally understood to bear intentionality (i.e., mental images are always images of something or other), and thereby to function as a form of mental representation. Traditionally, visual mental imagery, the most discussed variety, was thought (...) to be caused by the presence of picturelike representations (mental images) in the mind, soul, or brain, but this is no longer universally accepted. (shrink)

The question of whether conscious experience is restricted by cognitive access and exhausted by report, or whether it overflows it—comprising more information than can be reported—is hotly debated. Recently, we provided evidence in favor of Overflow, showing that observers discriminated the color‐diversity (CD) of letters in an array, while their working‐memory and attention were dedicated to encoding and reporting a set of cued letters. An alternative interpretation is that CD‐discriminations do not entail conscious experience of the underlying colors. Here we (...) argue, based on conceptual considerations and consistency with neuroscience and phenomenology, in favor of the Overflow interpretation. (shrink)

Simulation Theory says we need not rely exclusively on prepositional knowledge of other minds in order to explain the actions of others. Seeking to know what you will do, I imagine myself in your situation, and see what decision I come up with. I argue that this conception of simulation naturally generalizes: various bits of our mental machine can be run‘off‐line’, fulfilling functions other than those they were made for. In particular, I suggest that visual imagery results when the visual (...) system is run off‐line. I briefly review the empirical evidence and consider the philosophical implications, particularly concerning the mode of mental representation in imagery. (shrink)

Patient RB has a peculiar memory impairment wherein he experiences his memories in rich contextual detail, but claims to not own them. His memories do not feel as if they happened to him. In this paper, I provide an explanatory model of RB’s phenomenology, the self-attentional model. I draw upon recent work in neuroscience on self-attentional processing and global workspace models of conscious recollection to show that RB has a self-attentional deficit that inhibits self-bias processes in broadcasting the contents of (...) episodic memories to the global workspace. Typically, self-related contents enjoy a higher salience level than other-related contents. Elimination of bias toward self-related contents diminishes the salience of those contents to the level of other-related contents. Because the typical high salience of self-related content is necessary for the feeling of ownership, RB lacks the feeling of ownership. I also discuss potential applications of the self-attentional model to other psychopathological cases. (shrink)

One of the most compelling questions still unanswered in neuroscience is how consciousness arises. In this article, we examine visual processing, the parietal lobe, and contralateral neglect syndrome as a window into consciousness and how the brain functions as the mind and we introduce a mechanism for the processing of visual information and its role in consciousness. We propose that consciousness arises from integration of information from throughout the body and brain by the thalamus and that the thalamus reimages visual (...) and other sensory information from throughout the cortex in a default three-dimensional space in the mind. We further suggest that the thalamus generates a dynamic default three-dimensional space by integrating processed information from corticothalamic feedback loops, creating an infrastructure that may form the basis of our consciousness. Further experimental evidence is needed to examine and support this hypothesis, the role of the thalamus, and to further elucidate the mechanism of consciousness. (shrink)

A serious crisis is identified in theories of neurocomputation, marked by a persistent disparity between the phenomenological or experiential account of visual perception and the neurophysiological level of description of the visual system. In particular, conventional concepts of neural processing offer no explanation for the holistic global aspects of perception identified by Gestalt theory. The problem is paradigmatic and can be traced to contemporary concepts of the functional role of the neural cell, known as the Neuron Doctrine. In the absence (...) of an alternative neurophysiologically plausible model, I propose a perceptual modeling approach, to model the percept as experienced subjectively, rather than modeling the objective neurophysiological state of the visual system that supposedly subserves that experience. A Gestalt Bubble model is presented to demonstrate how the elusive Gestalt principles of emergence, reification, and invariance can be expressed in a quantitative model of the subjective experience of visual consciousness. That model in turn reveals a unique computational strategy underlying visual processing, which is unlike any algorithm devised by man, and certainly unlike the atomistic feed-forward model of neurocomputation offered by the Neuron Doctrine paradigm. The perceptual modeling approach reveals the primary function of perception as that of generating a fully spatial virtual-reality replica of the external world in an internal representation. The common objections to this picture-in-the-head concept of perceptual representation are shown to be ill founded. Key Words: brain-anchored; Cartesian theatre; consciousness; emergence; extrinsic constraints; filling-in; Gestalt; homunculus; indirect realism; intrinsic constraints; invariance; isomorphism; multistability; objective phenomenology; perceptual modeling; perspective; phenomenology; psychophysical parallelism; psychophysical postulate; qualia; reification; representationalism; structural coherence. (shrink)

Over a decade ago, I introduced a large-scale theory of the cognitive brain which explained for the first time how the human brain is able to create internal models of its intimate world and invent models of a wider universe. An essential part of the theoretical model is an organization of neuronal mechanisms which I have named the Retinoid Model (Trehub, 1977, 1991). This hypothesized brain system has structural and dynamic properties enabling it to register and appropriately integrate disparate foveal (...) stimuli into a perspectival, egocentric representation of an extended 3D world scene including a neuronally-tokened locus of the self which, in this theory, is the neuronal origin of retinoid space. As an integral part of the larger neuro-cognitive model, the retinoid system is able to perform many other useful perceptual and higher cognitive functions. In this paper, I draw on the hypothesized properties of this system to argue that neuronal activity within the retinoid structure constitutes the phenomenal content of consciousness and the unique sense of self that each of us experiences. -/- Trehub, A. (1977). Neuronal models for cognitive processes: Networks for learning, perception, and imagination. _Journal of Theoretical Biology_ 65: 141-169. -/- Trehub, A. (1991). _The Cognitive Brain_. MIT Press. -/- . (shrink)

According to the two visual systems model, the visual processing of objects divides into semantic and pragmatic processing. We provide various criteria for this distinction. Further, we argue that both the semantic and pragmatic processing of visual information about objects should be divided into low-level processing and high-level processing. Finally, we re-evaluate the contribution of the human parietal lobe to the concious visual perception of spatial relations among objects.

Intermediate constructs are required as bridges between complex behaviors and realistic models of neural circuitry. For cognitive scientists in general, schemas are the appropriate functional units; brain theorists can work with neural layers as units intermediate between structures subserving schemas and small neural circuits.After an account of different levels of analysis, we describe visuomotor coordination in terms of perceptual schemas and motor schemas. The interest of schemas to cognitive science in general is illustrated with the example of perceptual schemas in (...) high-level vision and motor schemas in the control of dextrous hands.Rana computatrix, the computational frog, is introduced to show how one constructs an evolving set of model families to mediate flexible cooperation between theory and experiment. Rana computatrix may be able to do for the study of the organizational principles of neural circuitry what Aplysia has done for the study of subcellular mechanisms of learning. Approach, avoidance, and detour behavior in frogs and toads are analyzed in terms of interacting schemas. Facilitation and prey recognition are implemented as tectal-pretectal interactions, with the tectum modeled by an array of tectal columns. We show how layered neural computation enters into models of stereopsis and how depth schemas may involve the interaction of accommodation and binocular cues in anurans. (shrink)

The Global Workspace Theory and Information Integration Theory are two of the most currently accepted consciousness models; however, these models do not address many aspects of conscious experience. We compare these models to our previously proposed consciousness model in which the thalamus fills-in processed sensory information from corticothalamic feedback loops within a proposed 3D default space, resulting in the recreation of the internal and external worlds within the mind. This 3D default space is composed of all cells of the body, (...) which communicate via gap junctions and electrical potentials to create this unified space. We use 3D llustrations to explain how both visual and non-visual sensory information may be filled-in within this dynamic space, creating a unified seamless conscious experience. This neural sensory memory space is likely generated by baseline neural oscillatory activity from the default mode network, other salient networks, brainstem, and reticular activating system. (shrink)

This monograph explains in terms of specified neuronal brain mechanisms and systems, how the human brain does its cognitive work. It elucidates functions such as declarative and episodic learning, imagery, spatial representation, object recognition, semantic processing, narrative comprehension, planning, and motivation. Neurophysiological, psychological, and clinical findings are presented in support of the theoretical model, and a variety of computer simulation tests demonstrate its competence. -/- .

What does it mean to know oneself, and what is the self that one hopes to know? This article outlines the implications of an embodied understanding of persons and some aspects of the “self” that are generally ignored when thinking about our selves. The Cartesian model of body–soul dualism reinforces the idea that there is within us a soul, or self, or mind that is our hidden, inner, and real self. Thus, the path to self-knowledge is introspection. The alternative view (...) is that persons are embodied, embedded, and at times extended. This article emphasizes the bodily, active, contextual, relational, often simulated, and sometimes extended nature of the selves that we are, and that we hope to know. (shrink)

Studies on the syndrome called ‘unilateral visual or spatial neglect’ have been used by philosophers in discussions concerning perceptual phenomenology. Nanay , based on spatial neglects studies, argued that the property of being suitable for action is part of the perceptual phenomenology of neglect patients. In this paper, I argue that the studies on visual neglect conducted thus far do not support Nanay’s thesis that when patients succeed in detecting the neglected object, it’s action properties are part of their perceptual (...) phenomenology; instead, the support the view that the patients consciously see low-level properties such as color and shape. In the first section, I discuss unilateral neglect and extinction. In the second section, I analyze Nanay’s argument. In the third section, I explain why Nanay’s thesis does not follow from the studies on visual neglect. Nanay argues that when neglect patients are cued with an action-property of an object and succeed in perceiving the object in the contralesional side they are phenomenally aware of an action-property of it but they are not phenomenally aware of its low-level properties. Since the patients detect the object, they must be phenomenally aware of some of its properties. Failing to see the low-level properties, the patients should be phenomenally aware is the action-property. Against this, I argue that research on spatial neglect shows that the patients come to see the low-level properties. I also explain why my discussion also supports the more general claim that the studies on neglect and extinction conducted thus far do not establish that the action-properties are part of the patients’ phenomenology. Finally, in section four, I examine a possible objection against my account. My arguments do not entail that the action properties are not part of perceptual phenomenology; only that the neglect studies do not establish this. (shrink)

We describe some of the signs and symptoms of left visuo-spatial neglect. This common, severe and often long-lasting impairment is the most striking consequence of right hemisphere brain damage. Patients seem to (over-)attend to the right with subsequent inability to respond to stimuli in contralesional space. We draw particular attention to how patients themselves experience neglect. Furthermore, we show that the neglect patient's loss of awareness of left space is crucial to an understanding of the condition. Even after left space (...) has been brought into the patient's consciousness (either by local cueing on the left or by an emphasis on global properties of the scene as a whole), this awareness of left space rapidly declines. We suggest that much of the symptomology of left neglect can be interpreted as a disconnection between brain mechanisms that are relatively specialized for local (detail) visual processing and global (panoramic) processing. This failure of communication between functional (subpersonal) mechanisms then has consequences for how perceptual and representational content enters into awareness. Failure of the local contents of left space to be consciously accessed is, in turn, an important aspect of why left neglect is so difficult to remediate. Patients can ''know'' that they have neglect but are cut off from the perceptual awareness that would enable them to overcome their attentional bias to the right. (shrink)

A ‘Radical Simulationist’ account of how folk psychology functions has been developed by Robert Gordon. I argue that Radical Simulationism is false. In its simplest form it is not sufficient to explain our attribution of mental states to subjects whose desires and preferences differ from our own. Modifying the theory to capture these attributions invariably generates innumerable other false attributions. Further, the theory predicts that deficits in mentalizing ought to co-occur with certain deficits in imagining perceptually-based scenarios. I present evidence (...) suggesting that this prediction is false, and outline further possible empirical tests of the theory. (shrink)

This paper argues that humans possess unique cognitive abilities due to the presence of a functional system that exists in the human brain that is absent in the non-human brain. This system, the frontal feedback system, was born in the hominin brain when the great phylogenetic expansion of the prefrontal cortex relative to posterior sensory regions surpassed a critical threshold. Surpassing that threshold effectively reversed the preferred direction of information flow in the highest association regions of the neocortex, producing the (...) frontal feedback system. This reversal was from the caudo-rostral bias characteristic of non-human, or pre-human, brain dynamics to a rostro-caudal bias characteristic of modern human brain dynamics. The frontal feedback system works through frontal motor routines, or action schemes, manipulating the release and reconstruction of stored sensory memories in posterior sensory areas. As an obligatory feature of frontal feedback, a central character, or self, emerges within this cortical network that manifests itself as agent in these reconstructions as well as in the experience of sensory perceptions. Dynamical-systems modeling of cortical interactions is combined in the paper with recent neuroimaging studies of “resting-state” brain activity to bridge the gap between microscopic and macroscopic levels of cortical behavior. This synthesis is used to support the proposal of an information flow reversal occurring in the hominin brain and also to explain how such a reversal generates the wide variety of cognitive and experiential phenomena that many consider to be uniquely human. (shrink)