Visual Pathways

For almost half a century dual-stream advocates have vigorously defended the view that there are two functionally specialized cortical streams of visual processing originating in the primary visual cortex: a ventral, perception-related ‘conscious’ stream and a dorsal, action-related ‘unconscious’ stream. They furthermore maintain that the perceptual and memory systems in the ventral stream are relatively shielded from the action system in the dorsal stream. In recent years, this view has come under scrutiny. Evidence points to two overlapping action pathways: a (...) dorso-dorsal pathway that calculates features of the object to be acted on, and a ventro-dorsal pathway that transmits stored information about skilled object use from the ventral stream to the dorso-dorsal pathway. This evidence suggests that stored information may exert significantly more influence on visually guided action than hitherto assumed. I argue that this, in turn, supports the notion of skilled automatic action that is nonetheless agential. My focus here will be on actions influenced by implicit biases (stereotypes/prejudices). Action that is biased in this way, I argue, is in an important sense intentional and agential. (shrink)

In its classical form, epiphenomenalism is the view that conscious mental events have no physical effects: while physical events cause mental events, the opposite is never true. Unlike classical epiphenomenalism, contemporary forms do not hold that conscious men­ tal states always lack causal efficacy, only that they are epiphenomenal relative to certain kinds of action, ones we pre-theoretically would have thought consciousness to causally contribute to. Two of these contemporary, empirically based challenges to the efficacy of the mental are the (...) focus of this chapter. The first, originating in research by Libet, has been interpreted as showing that the neural events initiating voluntary actions precede our conscious willing of them, meaning the conscious will cannot be what causes them. The second challenge, originating in studies by Milner and Goodale, consist of instances in which the content of visual consciousness and motor action dissociate, casting doubt on the intuitive view that visual consciousness guides visually based motor action. (shrink)

What’s presented in our normal waking perceptual visual experiences feels present to us, while what we “see” in pictures and imagine does not. What about dreams? Does what we “see” in a dream feel present? Jennifer Windt has argued for an affirmative answer, for all dreams. But the dreams which flow from the brain’s registration of myoclonic twitches present a challenge to this answer. During these dreams motion-guiding vision is shut off, and, as Mohan Matthen has argued, motion-guiding vision seems (...) to be a key mechanism underlying the feeling of presence. I propose that the feeling of presence in fact involves two components: the feeling of immersion, and the feeling of availability for action. I suggest that only the feeling of availability for action derives from motion-guiding vision, and, hence, hypothesize that body-driven dreams lack this component to the feeling of presence. Finally, the distinction between these two varieties of presence has implications for measures of presence in virtual environments, as these measures can diverge over which of the two varieties they track. (shrink)

Empirical work and philosophical analysis have led to widespread acceptance that vision for action, served by the cortical dorsal stream, is unconscious. I argue that the empirical argument for this claim is unsound. That argument relies on subjects’ introspective reports. Yet on biological grounds, in light of the theory of primate cortical vision, introspection has no access to dorsal stream mediated visual states. It is thus wrongly assumed that introspective reports speak to absent phenomenology in the dorsal stream. In light (...) of this, I consider a different conception of consciousness’s relation to agency in terms of access. While theoretical reasons suggest that the inaccessibility of the dorsal stream to conceptual report is evidence that it is unconscious, this position begs important questions. I propose a broader notion of access in respect of the guidance of intentional agency and not, narrowly, conceptual report (Note: this paper contradicts my earlier paper, "The Case for Zombie Agency"). (shrink)

According to Hubert Dreyfus’s famous claim that expertise is fundamentally “mindless,” experts in any domain perform most effectively when their activity is automatic and unmediated by concepts or cognitive processes like attention and memory. While several scholars have recently challenged the plausibility of Dreyfus’s “mindless” account of expertise for explaining a wide range of expert activities, there has been little consideration of the one form of expertise which might be most amenable to Dreyfus’s account – namely, perceptual expertise. Indeed, Dreyfus’s (...) account of expert coping is ultimately an account of perceptual expertise, in that an expert’s intuitive situational responses are thought to rely on a sophisticated repertoire of perceptual skills. In this paper, I examine the feedforward model of sensory processing that Dreyfus uses to illustrate the perceptual underpinnings of expert action, and consider its resonance with psychological research that characterizes perceptual expertise as being automatic, holistic, pre-attentive, and non-cognitive in nature. However, citing competing empirical research, I argue instead that Dreyfus’s model of perceptual expertise cannot adequately explain the integral roles of attention, memory, and conceptual knowledge in expert object recognition. I conclude that the Dreyfusian model of perceptual expertise fails – the perceptual repertoire of skills that grounds expert object recognition is not operative in isolation from the expert’s conceptual repertoire. (shrink)

Back when researchers thought about the various forms that color vision could take, the focus was primarily on the retinal mechanisms. Since that time, research on human color vision has shifted from an interest in retinal mechanisms to cortical color processing. This has allowed color research to provide insight into questions that are not limited to early vision but extend to cognition. Direct cortical connections from higher-level areas to lower-level areas have been found throughout the brain. One of the classic (...) questions in cognitive science is whether perception is influenced, and if so to what extent, by cognition and whether a clear distinction can be drawn between perception and cognition. Since perception is seen as providing justification for our beliefs about properties in the external world, these questions also have metaphysical and epistemological significance. The aim of this paper is to highlight some of the areas where research on color perception can shed new light on questions in the cognitive sciences. A further aim of the paper is to raise some questions about color research that are in dire need of further reflection and investigation. (shrink)

The question of whether cognition can influence perception has a long history in neuroscience and philosophy. Here, we outline a novel approach to this issue, arguing that it should be viewed within the framework of top-down information-processing. This approach leads to a reversal of the standard explanatory order of the cognitive penetration debate: we suggest studying top-down processing at various levels without preconceptions of perception or cognition. Once a clear picture has emerged about which processes have influences on those at (...) lower levels, we can re-address the extent to which they should be considered perceptual or cognitive. Using top-down processing within the visual system as a model for higher-level influences, we argue that the current evidence indicates clear constraints on top-down influences at all stages of information processing; it does, however, not support the notion of a boundary between specific types of information-processing as proposed by the cognitive impenetrability hypothesis. (shrink)

In this book, Michael Madary examines visual experience, drawing on both phenomenological and empirical methods of investigation. He finds that these two approaches—careful, philosophical description of experience and the science of vision—independently converge on the same result: Visual perception is an ongoing process of anticipation and fulfillment. Madary first makes the case for the descriptive premise, arguing that the phenomenology of vision is best described as on ongoing process of anticipation and fulfillment. He discusses visual experience as being perspectival, temporal, (...) and indeterminate; considers the possibility of surprise when appearances do not change as we expect; and considers the content of visual anticipation. Madary then makes the case for the empirical premise, showing that there are strong empirical reasons to model vision using the general form of anticipation and fulfillment. He presents a range of evidence from perceptual psychology and neuroscience, and reinterprets evidence for the two-visual-systems hypothesis. Finally, he considers the relationship between visual perception and social cognition. An appendix discusses Husserlian phenomenology as it relates to the argument of the book. Madary argues that the fact that there is a convergence of historically distinct methodologies itself is an argument that supports his findings. With Visual Phenomenology, he creates an exchange between the humanities and the sciences that takes both methods of investigation seriously. (shrink)

Perceptual processes, in particular modular processes, have long been understood as being mandatory. But exactly what mandatoriness amounts to is left to intuition. This paper identifies a crucial ambiguity in the notion of mandatoriness. Discussions of mandatory processes have run together notions of automaticity and ballisticity. Teasing apart these notions creates an important tool for the modularist's toolbox. Different putatively modular processes appear to differ in their kinds of mandatoriness. Separating out the automatic from the ballistic can help the modularist (...) diagnose and explain away some putative counterexamples to multimodal and central modules, thereby helping us to better evaluate the evidentiary status of modularity theory. (shrink)

Milner and Goodale's influential account of the primate cortical visual streams involves a division of consciousness between them, for it is the ventral stream that has the responsibility for visual consciousness. Hence, the dorsal visual stream is a ‘zombie’ stream. In this article, I argue that certain information carried by the dorsal stream likely plays a central role in the egocentric spatial content of experience, especially the experience of visual spatial constancy. Thus, the dorsal stream contributes to a pervasive feature (...) of consciousness. (shrink)

The aim of this paper is to argue that action-guiding vision is not cognitively impenetrable and arguments that suggest otherwise rely on an unjustified identification between actionguiding vision and dorsal vision – a functional and an anatomical way of describing the mind. The examination of these arguments show the importance of making a distinction between the functional and the anatomical level when addressing the problem of cognitive penetrability.

In response to Mole 2009, I present an argument for zombie action. The crucial question is not whether but rather to what extent we are zombie agents. I argue that current evidence supports only minimal zombie agency.

This paper examines Milner and Goodale’s hypothesis about the two visual streams and raises the questions of whether properties in egocentric space (commonly associated with the vision-for-action, or "dorsal," stream) can be part of the phenomenal content of perceptual experience, or only properties in allocentric space (commonly associated with the vision-for-perception, or "ventral," stream) can play this role, and how (if at all) properties in egocentric space differ from properties in allocentric space. These questions are reminiscent of issues raised by (...) Christopher Peacocke's "equal-sized trees" case: if you are looking at equal-sized trees on the side of a road, the trees will phenomenally look to you to be equally tall. But it is also true that a tree will take up more of the space in your visual field the closer it is to you. So, the equal-sized trees will also phenomenally look to you to have different heights. Your (visual) perceptual experience is not illusory. That is, the trees veridically look to you to have the same height, and they also veridically look to you to have different heights. Call the sort of issue raised here the "problem of dual looks." I provide a solution to the problem of dual looks that helps shed light on whether properties in egocentric space can be part of the phenomenal content of perceptual experience, and how (if at all) properties in egocentric space differ from properties in allocentric space. (shrink)

The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching , pointing and perceptual judgment responses to masked Müller–Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length (...) at brief durations remained sensitive to veridical stimulus length , but not the illusion , which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception or action responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric- and slower allocentric information pick up, respectively. (shrink)

This article is about a sidebar in James Gibson's last book, The ecological approach to visual perception. In this sidebar, Gibson, the founder of the ecological perspective of perception and action, argued that to perceive an affordance is not to classify an object. Although this sidebar has received scant attention, it is of great significance both historically and for recent discussions about specificity, direct perception, and the functions of the dorsal and ventral streams. It is argued that Gibson's acknowledgment of (...) Wittgenstein's ideas of classification suggests a limited scope of his theory of direct perception?it cannot account for the classification of objects. The implications for both the specification debate and theorizing about the brain's dorsal and ventral pathways are explored. Based on a recent ecological conception of information and direct perception, we ultimately argue that both affordance perception and classification are direct. (shrink)

Today many philosophers of mind accept that the two cortical streams of visual processing in humans can be distinguished in terms of conscious experience. The ventral stream is thought to produce representations that may become conscious, and the dorsal stream is thought to handle unconscious vision for action. Despite a vast literature on the topic of the two streams, there is currently no account of the way in which the relevant empirical evidence could fit with basic Husserlian phenomenology of vision. (...) Here I offer such an account. In this article, I show how the empirical evidence ought to be understood in a way that is informed by phenomenology. The differences in the two streams are better described as differences in spatial and temporal processing. Rather than simply “unconscious,” the dorsal stream can be better described as making a special contribution to what Husserl identified as the visual horizon. (shrink)

I aim to give a new account of picture perception: of the way our visual system functions when we see something in a picture. My argument relies on the functional distinction between the ventral and dorsal visual subsystems. I propose that it is constitutive of picture perception that our ventral subsystem attributes properties to the depicted scene, whereas our dorsal subsystem attributes properties to the picture surface. This duality elucidates Richard Wollheim’s concept of the “twofoldness” of our experience of pictures: (...) the “visual awareness not only of what is represented but also of the surface qualities of the representation.” I argue for the following four claims: (a) the depicted scene is represented by ventral perception, (b) the depicted scene is not represented by dorsal perception, (c) the picture surface is represented by dorsal perception, and (d) the picture surface is not necessarily represented by ventral perception. (shrink)

Neuropsychological findings used to motivate the "two visual systems" hypothesis have been taken to endanger a pair of widely accepted claims about spatial representation in conscious visual experience. The first is the claim that visual experience represents 3-D space around the perceiver using an egocentric frame of reference. The second is the claim that there is a constitutive link between the spatial contents of visual experience and the perceiver's bodily actions. In this paper, I review and assess three main sources (...) of evidence for the two visual systems hypothesis. I argue that the best interpretation of the evidence is in fact consistent with both claims. I conclude with some brief remarks on the relation between visual consciousness and rational agency. (shrink)

The purpose of this paper is to defend what I call the action-oriented coding theory (ACT) of spatially contentful visual experience. Integral to ACT is the view that conscious visual experience and visually guided action make use of a common subject-relative or 'egocentric' frame of reference. Proponents of the influential two visual systems hypothesis (TVSH), however, have maintained on empirical grounds that this view is false (Milner & Goodale, 1995/2006; Clark, 1999; 2001; Campbell, 2002; Jacob & Jeannerod, 2003; Goodale & (...) Milner, 2004). One main source of evidence for TVSH comes from behavioral studies of the comparative effects of size-contrast illusions on visual awareness and visuo- motor action. This paper shows that not only is the evidence from illusion studies inconclusive, there is a better, ACT-friendly interpretation of the evidence that avoids serious theoretical difficulties faced by TVSH. (shrink)

I aim to give a new account of picture perception: of the way our visual system functions when we see something in a picture. My argument relies on the functional distinction between the ventral and dorsal visual subsystems. I propose that it is constitutive of picture perception that our ventral subsystem attributes properties to the scene, whereas our dorsal subsystem attributes properties to the surface. Keywords: picture perception; dorsal subsystem;.

Reflection on the fine-grained information required for visual guidance of action has suggested that visual content is non-conceptual. I argue that in a common type of visually guided action, namely the use of manipulable artefacts, vision has conceptual content. Specifically, I show that these actions require visual attention and that concepts are involved in directing attention. In acting with artefacts, there is a way of doing it right as determined by the artefact’s conventional use. Attention must reflect our understanding of (...) the function and appropriate ways to use these artefacts, understanding that requires possession of the relevant concept. As a result, we attend to the artefact’s relevant functional properties. In these cases, attention is structured by concepts. This discussion has a bearing on the dual visual stream hypothesis. While it is often held that the two visual streams are functionally independent, the argument of this essay is that the constraints on attention suggest a functional interaction between them. (shrink)

This book has three principle aims: to show that neither vision nor mental imagery involves the creation or inspection of picture-like mental representations; to defend the claim that our visual processes are, in significant part, cognitively impenetrable; and to develop a theory of “visual indexes”. In what follows, I assess Pylyshyn’s success in realising each of these aims in turn. I focus primarily on his arguments against “picture theories” of vision and mental imagery, to which approximately half the book is (...) devoted. I argue that Pylyshyn adopts an unnecessarily restricted interpretation of what it would be for mental representations to be picture-like, and that this leads him prematurely to reject the possibility of explaining the introspective evidence concerning the nature of mental imagery. (shrink)

Vision, more than any other sense, dominates our mental life. Our visual experience is just so rich, so detailed, that we can hardly distinguish that experience from the world itself. Even when we just think about the world and don't look at it directly, we can't help but 'imagine' what it looks like. We think of 'seeing' as being a conscious activity--we direct our eyes, we choose what we look at, we register what we are seeing. The series of events (...) described in this book radically altered this attitude towards vision. This book describes one of the most extraordinary neurological cases of recent years--one that profoundly changed scientific views on consciousness. It is the story of Dee Fletcher--a woman recently blinded--who became the subject of a series of scientific studies. As events unfolded, Milner and Goodale found that Dee wasn't in fact blind--she just didn't know that she could see. Taking us on a journey into the unconscious brain, the two scientists who made this incredible discovery tell the amazing story of their work, and the surprising conclusion they were forced to reach. Written to be accessible to students and popular science readers, this book is a fascinating illustration of the power of the 'unconscious' mind. (shrink)

Which roles are played by subcortical pathways in models of cortical streams for visual processing? Through their thalamic relays, magnocellular (M) and parvocellular (P) projecting ganglion cells send complementary signals to V1, where their outputs are combined in several different ways. The synergic role of M and P cells in vision can be understood by estimating cell response entropy in all domains of interest.

Since the publication of my "Are Theories of Imagery Theories of Imagination? An _Active Perception_ Approach to Conscious Mental Content,", a good deal of published material has appeared or has come to my attention that either provides additional support for the Perceptual Activity Theory PA theory) of mental imagery presented in ATOITOI, or that throws further doubt on the rival theories that are criticized there. Other relevant evidence was not mentioned in ATOITOI because I lacked the space for a proper (...) explanation of its relevance. I hope eventually to write and publish a new account of " PA " theory, that will make use of much of this material. In the meantime this page provides citations to the "new" support, and discussion sections that briefly explain the relevance of the cited material. Quite apart from presenting new lines of supporting evidence and argument, I hope this page will help to clarify many aspects of. (shrink)

The Grand Illusion, the experience of a rich phenomenal visual world supported by a poor internal representation of that world, is echoed by petit illusions of the same sort. We can be aware of several aspects of an object or pattern, even when they are inconsistent with one another, because different neurological mechanisms code the various aspects separately. They are bound not by an internal linkage, but by the structure of the world itself. Illusions exploit this principle by introducing inconsistencies (...) into normally consistent patterns of stimulation. (shrink)

Spatial neglect is a disorder of space-related behaviour. It is characterized by failure to explore the side of space contralateral to a brain lesion, or to react or respond to stimuli or subjects located on this side. Research on spatial neglect and related disorders has developed rapidly inrecent years. These advances have been made as a result of neuropsychological studies of patients with brain damage, behavioural studies of animal models, as well as through functional neurophysiological experiments and functional neuroimaging.The Cognitive (...) and Neural Bases of Spatial Neglect provides an overview of this wide-ranging field of scientific endeavour, providing a cohesive synthesis of the most recent observations and results. As well as being a fascinating clinical phenomenon, the study of spatial neglect helps us tounderstand normal mechanisms of directing and maintaining spatial attention and is relevant to the contemporary search for the cerebral correlates of conscious experience, voluntary action and the nature of personal identity itself.The book is divided into seven sections covering the anatomical and neurophysiological bases of the disorder, frameworks of neglect, perceptual and motor factors, the relation to attention, the cognitive processes involved, and strategies for rehabilitation.Chapters have been written by a team of the leading international experts in this field.This will be essential reading for neuropsychologists, neurologists, neurophysiologists, cognitive neuroscientists and psychologists. (shrink)

Can we learn without consciousness? When the eminent neuropsychologist, Lawrence Weiskrantz first coined the term 'blindsight' to describe a condition whereby a patient could demonstrate that they were aware of some object, yet insist that they were completely unaware of its existence, the response from some in the scientific community was one of extreme skepticism. Even now, there are those who question the existence of unconscious learning, and the topic remains one of the most actively researched and debated in psychology. (...) In recent years evidence for unconscious processing across a range of sensory modalities have come from studies of vision, audition, memory, emotion, and action. Never before have these studies of unconscious processing in the different senses been brought together into a single volume. In a book dedicated to Lawrence Weiskrantz, some of the leading psychologists and cognitive neuroscientists of the day explain what we know about unconscious processing in the different senses. Including contributions from, amongst others, David Milner, Jon Driver, Alan Cowey, and Ray Dolan, the book presents a state of the art account of what we now know about 'the unconscious'. The book will provide a fascinating account for students and researchers in psychology, cognitive neuroscience, and philosophy. (shrink)

O'Regan & Noë run into some difficulty in trying to reconcile their “seeing as acting” proposal with the perception and action account of the functions of the two streams of visual projections in the primate cerebral cortex. I suggest that part of the problem is their reluctance to acknowledge that the mechanisms in the ventral stream may play a more critical role in visual awareness and qualia than mechanisms in the dorsal stream.