Stoerig and Cowey’s work is widely regarded as showing that monkeys with lesions in the primary visual cortex have blindsight. However, Mole and Kelly persuasively argue that the experimental results are compatible with an alternative hypothesis positing only a deficit in attention and perceptual working memory. I describe a revised procedure which can distinguish these hypotheses, and offer reasons for thinking that the blindsight hypothesis provides a superior explanation. The study of blindsight might contribute towards a general (...) investigation into animal consciousness, though there is a problem when it comes to showing how a non-verbal animal can indicate whether or not it is perceiving consciously. Perhaps whether there is something that it is like to be a given animal depends on whether it exhibits the cognitive profile of conscious vision as opposed to non-conscious “natural blindsight.”. (shrink)
Blindsight is the ability of patients with an impaired visual cortex to perform visually in their blind field without acknowledging that performance. This ability has been interpreted as a sign of the absence of phenomenal consciousness, and neuroscientific studies have extensively studied cases of it. Different proposals separate visual form recognition from motion perception, and attempt to show that either the former or the latter is solely responsible for blindsight performance. However, a review of current experimental evidence shows (...) that a poor performance (on both form and motion) is accompanied by poor awareness. Blindsight cases do not influence the qualia debate, because they denote a severe visual performance deficit, and not because of a purportedly non-phenomenal nature of consciousness. (shrink)
In a recent response paper to Brogaard (2011a), Morten Overgaard and Thor Grünbaum argue that my case for the claim that blindsight subjects are not visually conscious of the stimuli they correctly identify rests on a mistaken necessary criterion for determining whether a conscious experience is visual or non-visual. Here I elaborate on the earlier argu- ment while conceding that the question of whether blindsight subjects are visually con- scious of the visual stimuli they correctly identify largely is (...) an empirical question. I conclude by sketching a method for testing whether blindsight subjects have visual con- sciousness of stimuli presented to them in their blind field. (shrink)
Newell and Shanks (2012) argue that an explanation for blindsight need not appeal to unconscious brain processes, citing research indicating that the condition merely reflects degraded visual experience. We reply that other evidence suggests that blindsighters’ predictive behavior under forced choice reflects cognitive access to low-level visual information that does not correlate with visual consciousness. Thus, while we grant that visual consciousness may be required for full visual experience, we argue that it may not be needed for decision making (...) and judgment. (shrink)
Some patients with damaged striate cortex have blindsight-the ability to discriminate unseen stimuli in their clinically blind visual field defects when forced-choice procedures are used. Blindsight implies a sharp dissociation between visual performance and visual awareness, but signal detection theory indicates that it might be indistinguishable from the behavior of normal subjects near the lower limit of conscious vision, where the dissociations could arise trivially from using different response criteria during clinical and forced-choice tests. We tested the latter (...) possibility with a hemianopic subject during yes-no and forced-choice detection of static and moving targets. His response criterion differed significantly between yes-no and forced-choice responding, and the difference was sufficient to produce a blindsight-like dissociation with bias-sensitive measures of performance. When measured independently of bias, his sensitivity to static targets was greater in the forced-choice than in the yes-no task (unlike normal control subjects), but his sensitivity to moving targets did not differ. Differences in response criterion could therefore account for dissociations between yes-no and forced-choice detection of motion, but not of static pattern. The results explain why patients with blindsight are apparently more often ''aware'' of moving stimuli than of static stimuli. However, they also imply that blindsight is unlike normal vision near threshold, and that pattern- and motion-detection in blindsight may depend on different sets of neural mechanisms during yes-no and forced-choice tests. (shrink)
Blindsight, the ability to blindly discriminate wavelength and other aspects of stimuli in a blind field, sometimes occurs in people with lesions to striate (V1) cortex. There is currently no consensus on whether qualitative color information of the sort that is normally computed by double opponent cells in striate cortex is indeed computed in blindsight but doesn?t reach awareness, perhaps owing to abnormal neuron responsiveness in striate or extra-striate cortical areas, or is not computed at all. The existence (...) of primesight, the experience of colored afterimages in blindsight, has been taken to suggest that qualitative color information is computed either in pre-striate or striate cortical areas but is not broadcast to working memory. I argue here that a recent study in which color phosphenes were induced in a blindsighter using bilateral transcranial magnetic stimulation indicates that computations necessary for conscious color vision are lost in blindsight. Owing to this loss, the neural responsiveness in extrastriate cortical areas is abnormal and hence is unable to give rise to color awareness. Blindsight is thus degraded vision in which the computations necessary for conscious color vision have been lost. (shrink)
: The work of Alan Cowey and Petra Stoerig is often taken to have shown that, following lesions analogous to those that cause blindsight in humans, there is blindsight in monkeys. The present paper reveals a problem in Cowey and Stoerig ’ s case for blindsight in monkeys. The problem is that Cowey and Stoerig ’ s results would only provide good evidence for blindsight if there is no difference between their two experimental paradigms with regard (...) to the sorts of stimuli that are likely to come to consciousness. We show that the paradigms could differ in this respect, given the connections that have been shown to exist between working memory, perceptual load, attention, and consciousness. (shrink)
The work of Alan Cowey and Petra Stoerig is often taken to have shown that, following lesions analogous to those that cause blindsight in humans, there is blindsight in monkeys. The present paper reveals a problem in Cowey and Stoerig's case for blindsight in monkeys. The problem is that Cowey and Stoerig's results would only provide good evidence for blindsight if there is no difference between their two experimental paradigms with regard to the sorts of stimuli (...) that are likely to come to consciousness. We show that the paradigms could differ in this respect, given the connections that have been shown to exist between working memory, perceptual load, attention, and consciousness. (shrink)
The neural substrate of early visual processing in the macaque is used as a framework to discuss recent progress towards a precise anatomical localization and understanding of the functional implications of the syndromes of blindsight, achromatopsia and akinetopsia in humans. This review is mainly concerned with how these syndromes support the principles of organization of the visual system into parallel pathways and the functional hierarchy of visual mechanisms.
The evidence of blindsight is occasionally used to argue that we can see things, and thus have perceptual belief, without the distinctive visual awareness accompanying normal sight; thereby displacing phenomenality as a component of the concept of vision. I maintain that arguments to this end typically rely on misconceptions about blindsight and almost always ignore associated visual (or visuomotor) pathologies relevant to the lessons of such cases. More specifically, I conclude, first, that the phenomena very likely do not (...) result from dissociations within a single system, but from the interaction of evolutionarily distinct, if interacting, systems; second, that a closer study of spared motor abilities indicates that verbal responses of patients result not from degraded vision but from proprioception; and, finally, above chance verbal responses, being forced guesses, are not tentative beliefs and cannot become beliefs just by training patients to have more confidence in their responses. (shrink)
Cortical color blindness, or cerebral achromatopsia, has been likened by some authors to ''blindsight'' for color or an instance of ''covert'' processing of color. Recently, it has been shown that, although such patients are unable to identify or discriminate hue differences, they nevertheless show a striking ability to process wavelength differences, which can result in preserved sensitivity to chromatic contrast and motion in equiluminant displays. Moreover, visually evoked cortical potentials can still be elicited in response to chromatic stimuli. We (...) suggest that these demonstrations reveal intact residual processes rather than the operation of covert processes, where proficient performance is accompanied by a denial of phenomenal awareness. We sought evidence for such covert processes by conducting appropriate tests on achromatopsic subject M.S. An ''indirect'' test entailing measurement of reaction times for letter identification failed to reveal covert color processes. In contrast, in a forced choice oddity task for color, M.S. was unable to verbally indicate the position of the different color, but was surprisingly adept at making an appropriate eye movement to its location. This ''direct'' test thus revealed the possible covert use of chromatic differences. (shrink)
The filling-in process proposed as a cover up for the existence of the blind spot has some conceptual similarities to blindsight. The perceptual operation of a hypothetical mechanism responsible for filling in represents a logical paradox. The apparent indeterminacy of the percept in the optic-disc region can be tested experimentally by viewing the grating test pattern below.
Blindsight is classically defined as residual visual capacity, e.g., to detect and identify visual stimuli, in the total absence of perceptual awareness following lesions to V1. However, whereas most experiments have investigated what blindsight patients can and cannot do, the literature contains several, often contradictory, remarks about remaining visual experience. This review examines closer these remarks as well as experiments that directly approach the nature of possibly spared visual experiences in blindsight.
Blindsight is an unusual condition where the sufferer can respond to visual stimuli, while lacking any conscious feeling of having seen the stimuli. It occurs after a particular form of brain injury. The first edition of 'Blindsight', by one of the pioneers in the field - Lawrence Weiskrantz, reported studies of a patient with this condition. It was an important, much cited publication. In the past twenty years, further work has been done in this area, and this new (...) edition brings the book up to date. Retaining the original text, but adding substantial new chapters and colour illustrations, the first section of the book summarizes findings on DB since the last published account in 1986. The second part includes information on other new research that has occurred since the last edition. As well as giving an account of research over a number of years into a particular case of blindsight, it provides a discussion of the historical and neurological background, a review of cases reported by other investigators, and a number of theoretical and practical issues and implications. -/- The book will be valuable for cognitive psychologists and cognitive neuroscientists, as well as philosophers of mind. (shrink)
In three macaque monkeys with unilateral removal of primary visual cortex and in one unoperated monkey, we measured reaction times to a visual target that was presented at a lateral eccentricity of 20o in the normal, left, visual hemifield. When an additional stimulus was presented at the corresponding position in the right hemifield (hemianopic in three of the monkeys), it significantly slowed the reaction time to the left target if it preceded it by delays from 100-500 msec. The most effective (...) delay depended on the particular experimental paradigm and perhaps on the experience of the monkey with the task. The results show that reaction times to seen targets in the normal hemifield of monkeys are influenced by the presentation of ''unseen'' targets in the anopic hemifield, as in some patients with cortically blind visual field defects. (shrink)
Blindsight and vision for action seem to be exemplars of unconscious visual processes. However, researchers have recently argued that blindsight is not really a kind of uncon- scious vision but is rather severely degraded conscious vision. Morten Overgaard and col- leagues have recently developed new methods for measuring the visibility of visual stimuli. Studies using these methods show that reported clarity of visual stimuli correlates with accuracy in both normal individuals and blindsight patients. Vision for action has (...) also come under scrutiny. Recent findings seem to show that information processed by the dor- sal stream for online action contributes to visual awareness. Some interpret these results as showing that some dorsal stream processes are conscious visual processes (e.g., Gallese, 2007; Jacob & Jeannerod, 2003). The aim of this paper is to provide new support for the more traditional view that blindsight and vision for action are genuinely unconscious per- ceptual processes. I argue that individuals with blindsight do not have access to the kind of purely qualitative color and size information which normal individuals do. So, even though people with blindsight have a kind of cognitive consciousness, visual information process- ing in blindsight patients is not associated with a distinctly visual phenomenology. I argue further that while dorsal stream processing seems to contribute to visual awareness, only information processed by the early dorsal stream (V1, V2, and V3) is broadcast to working memory. Information processed by later parts of the dorsal stream (the parietal lobe) never reaches working memory and hence does not correlate with phenomenal awareness. I con- clude that both blindsight and vision for action are genuinely unconscious visual processes. (shrink)
Discrimination of forms defined solely by color and discrimination of hue are dissociated in cerebral achromatopsia. Both must be based on potentially explicit information derived from differentially color-sensitive photoreceptors, yet only one gives rise to phenomenal experience of color. By analogy, visual information may be used to form explicit representations for action without giving rise to any phenomenal experience other than that of making the action.
Perception enables us to think demonstrative thoughts about the world around us, but what must perception be like in order to play this role? Does perception enable demonstrative thought only if it is conscious? This paper examines three accounts of the role of consciousness in demonstrative thought, which agree that consciousness is essential for demonstrative thought, but disagree about why it is. First, I consider and reject the accounts proposed by Gareth Evans in The Varieties of Reference and by John (...) Campbell in Reference and Consciousness before offering an alternative proposal of my own. My proposal is that consciousness plays an essential epistemic role in explaining the capacity for demonstrative thought about an object by enabling the subject to form immediately justified beliefs about the object. (shrink)
Open-minded people should endorse dogmatism because of its explanatory power. Dogmatism holds that, in the absence of defeaters, a seeming that P necessarily provides non-inferential justification for P. I show that dogmatism provides an intuitive explanation of four issues concerning non-inferential justification. It is particularly impressive that dogmatism can explain these issues because prominent epistemologists have argued that it can’t address at least two of them. Prominent epistemologists also object that dogmatism is absurdly permissive because it allows a seeming to (...) provide justification even if the seeming was caused in some apparently inappropriate way. I conclude by disarming this objection. (shrink)
This chapter argues that attention is a distinctive mode of consciousness, which plays an essential functional role in making information accessible for use in the rational control of thought and action. The main line of argument can be stated quite simply. Attention is what makes information fully accessible for use in the rational control of thought and action. But what makes information fully accessible for use in the rational control of thought and action is a distinctive mode of consciousness. Therefore, (...) attention is a distinctive mode of consciousness. In a slogan: attention is rational-access consciousness. (shrink)
Subliminal perception (SP) is today considered a well-supported theory stating that perception can occur without conscious awareness and have a significant impact on later behaviour and thought. In this article, we first present and discuss different approaches to the study of SP. In doing this, we claim that most approaches are based on a dichotomic measure of awareness. Drawing upon recent advances and discussions in the study of introspection and phenomenological psychology, we argue for both the possibility and necessity of (...) using an elaborated measure of subjective states. In the second part of the article, we present findings where these considerations are implemented in an empirical study. The results and implications are discussed in detail, both with reference to SP, and in relation to the more general problem of using elaborate introspective reports as data in relation to studies of cognition. (shrink)
Our Own Minds presents an account of the nature and development of self-consciousness. Bogdan describes the mind of the infant as outward looking, turning in on itself only at a relatively late stage of development. This it does as a response to the increasingly sophisticated sociocultural pressures it faces throughout infancy and early childhood. The book is difficult to follow (about which, more later) but the main line of argument is this: to begin with, infants are attuned to their physical (...) and sociocultural environment, employing an early form of intuitive psychology, a practical capacity to interact with conspecifics, referred to by Bogdan as 'naïve psychology' (129). However, infants are faced with a series of sociocultural tasks (109-12), the implementation of which requires them to develop various executive capacities (105-9) which 'install' a form of self-consciousness, dubbed by Bogdan 'extrovert self-consciousness' (99-100). The increasingly demanding nature of these sociocultural tasks has the consequence that, around the age of 4, intuitive psychology undergoes a shift, becoming 'commonsense psychology' (129-30). This enables children to represent others' propositional attitudes and to think 'offline' (129-30). These new abilities and associated executive capacities, in their turn, 'install' a new form of self-consciousness, 'introvert self-consciousness' (159). Whilst the child's intuitive psychology and self-consciousness continue to develop until adolescence (33), this is where the book's central argument ends. (shrink)
Consciousness is a mongrel concept: there are a number of very different "consciousnesses." Phenomenal consciousness is experience; the phenomenally conscious aspect of a state is what it is like to be in that state. The mark of access-consciousness, by contrast, is availability for use in reasoning and rationally guiding speech and action. These concepts are often partly or totally conflated, with bad results. This target article uses as an example a form of reasoning about a function of "consciousness" based on (...) the phenomenon of blindsight. Some information about stimuli in the blind field is represented in the brains of blindsight patients, as shown by their correct "guesses," but they cannot harness this information in the service of action, and this is said to show that a function of phenomenal consciousness is somehow to enable information represented in the brain to guide action. But stimuli in the blind field are BOTH access-unconscious and phenomenally unconscious. The fallacy is: an obvious function of the machinery of access-consciousness is illicitly transferred to phenomenal consciousness. (shrink)
This paper explores the idea that many “simple minded” invertebrates are “natural zombies” in that they utilize their senses in intelligent ways, but without phenomenal awareness. The discussion considers how “first-order” representationalist theories of consciousness meet the explanatory challenge posed by blindsight. It would be an advantage of first-order representationalism, over higher-order versions, if it does not rule out consciousness in most non-human animals. However, it is argued that a first-order representationalism which adequately accounts for blindsight also implies (...) that most non-mammals are not conscious. The example of the honey bee is used to illuminate these claims. Although there is some reason to think that bees have simple beliefs and desires, nevertheless, their visually-mediated cognizing is comparable to that of an animal with blindsight. There is also reason to think that the study of blindsight can also help determine how consciousness is distributed in the animal world. (shrink)
