Common sense says that visual agnosia is impossible. It ought not exist. If an object like a safety pin or a bar of white soap is in full view, you see it, and you know what a "safety pin" or a "bar of soap" is, then you cannot fail to recognize what you see. If you identify the safety pin as "something silver and shiny like a watch or a nail clipper," or you identify the bar of white soap as (...) "a piece of paper," then common sense would dictate that either you fail to see the object, or your knowledge is somehow deficient. But visual agnosics, who make such responses, clearly do--in some sense--"see" the objects in question. Often they can, for example, make accurate and recognizable drawings of what they see. Some lack measurable visual field defects; they have a full visual field. And they clearly know what a "safety pin" or a "bar of soap" is: if allowed to touch the object, or its use is pantomimed, correct identification is immediate. "I see it now," they may say. We get a failure specifically in visual recognition, even though sufficient sensory functions and cognitive functions are demonstrably intact. Such is the mystery of visual agnosia. (shrink)
The HIT framework accepts a number of assumptions that are widely held as plausible or even well established in the literature on category-specific agnosia. We point out that a number of these elementary conjectures, now almost taken for granted, have received little in the way of convincing empirical support.
In general, the idea is that what makes a mental state conscious is that it is the object of some kind of higher-order representation (HOR). A mental state M becomes conscious when there is a HOR of M. A HOR is a “meta-psychological” state, i.e. a mental state directed at another mental state. So, for example, my desire to do a good powerpoint presentation becomes conscious when I am (non-inferentially) “aware” of the desire. Intuitively, it seems that conscious states, as (...) opposed to unconscious ones, are mental states that I am “aware of” in some sense. (shrink)
The cortical visual mechanisms involved in processing spatial relationships remain subject to debate. According to one current view, the ''dorsal stream'' of visual areas, emanating from primary visual cortex and culminating in the posterior parietal cortex, mediates this aspect of visual processing. More recently, others have argued that while the dorsal stream provides egocentric coding of visual location for motor control, the separate ''ventral'' stream is needed for allocentric spatial coding. We have assessed the visual form agnosic patient DF, whose (...) lesion mainly affects the ventral stream, on a prehension task requiring allocentric spatial coding. She was presented with transparent circular disks. Each disk had circular holes cut in it. DF was asked to reach out and grasp the disk by placing her fingers through the holes. The disks either had three holes (for forefinger, middle finger, and thumb) or two holes (for forefinger and thumb). The distance between the forefinger and thumb holes, and the orientation of the line formed by them, were independently varied. DF was quite unable to adjust her grip aperture or her hand orientation in the three-hole task. Although she was able to orient her hand appropriately for the two-hole disks, she still remained unable to adjust her grip aperture to the distance between the holes. These findings are consistent with the idea that allocentric processing of spatial information requires a functioning ventral stream, even when the information is being used to guide a motor response. (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)
Although Wayne Wu correctly identifies a flaw in the way in which my 2009 article frames the debate about ‘zombie action’, he fails in his attempts to strengthen the case for thinking that our actions are under less conscious control than we usually imagine. His argument, like the arguments that my earlier paper addressed, can be blocked by allowing that an embodied demonstrative concept can contribute contents to a visual experience.
I critically examine Adams and Garrison’s proposed necessary condition for the mark of the cognitive (Adams and Garrison in Minds Mach 23(3):339–352, 2013). After a brief presentation of their position, I argue not only that their proposal is in need of additional support, but also that it is too restrictive.
The proposed model holds that, at its most fundamental level, visual awareness is quantized. That is to say that visual awareness arises as individual bits of awareness through the action of neural circuits with hundreds to thousands of neurons in at least the human striate cortex. Circuits with specific topologies will reproducibly result in visual awareness that correspond to basic aspects of vision like color, motion and depth. These quanta of awareness (qualia) are produced by the feedforward sweep that occurs (...) through the geniculocortical pathway but are not integrated into a conscious experience until recurrent processing from centers like V4 or V5 select the appropriate qualia being produced in V1 to create a percept. The model proposed here has the potential to shift the focus of the search for visual awareness to the level of microcircuits and these likely exist across the kingdom Animalia. Thus establishing qualia as the fundamental nature of visual awareness will not only provide a deeper understanding of awareness, but also allow for a more quantitative understanding of the evolution of visual awareness throughout the animal kingdom. (shrink)
I respond to three arguments aimed at establishing that natural kind properties occur in the experiential content of visual experience: the argument from phenomenal difference, the argument from mandatory seeing, and the argument from associative agnosia. I conclude with a simple argument against the view that natural kind properties occur in the experiential content of visual experience.
David Milner and Melvyn Goodale, and the many psychologists and philosophers who have been influenced by their work, claim that ‘the visual system that gives us our visual experience of the world is not the same system that guides our movements in the world’. The arguments that have been offered for this surprising claim place considerable weight on two sources of evidence — visual form agnosia and the reaching behaviour of normal subjects when picking up objects that induce visual illusions. (...) The present article shows that, if we are careful to consider the possibility that a demonstrative gesture can contribute content to a conscious experience, then neither source of evidence is compelling. (shrink)
This paper concentrates on the basic properties of ''consciousness'' that temporal coding is postulated to relate to. A description of phenomenal consciousness based on what introspection tells us about its contents is offered. This includes a consideration of the effect of various brain lesions that result in cortical blindness, apperceptive and associative agnosia, and blindsight, together with an account of the manner in which sight is regained after cortical injuries. I then discuss two therories of perception-Direct Realism and the Representative (...) Theory. This includes a discussion of the concept of the body-image, phantom limbs, the alleged projection of sensations, the ontological status of phenomenal space, the homunculus argument, the validity of topographic coding, the difference between the stimulus field and the visual field, and two theories of brain-mind relationship-the Identity Theory and the Bohr-Heisenberg theory of brain-mind complementarity. Finally I suggest that the binocular rivalry obtained in the case of the stroboscopic patterns that result from intermittent photic stimulation of one eye, when used in animal expeiments with unit recording, offers a good experimental method of investigating the binding problem. (shrink)
Over recent years, there has been a resurgence of interest in arguments favouring intellectualism—the view that Ryle’s epistemic distinction is invalid because knowing how is in fact nothing but a species of knowing that. The aim of this paper is to challenge intellectualism by introducing empirical evidence supporting a form of knowing how that resists such a reduction. In presenting a form of visuomotor pathology known as visual agnosia, I argue that certain actions performed by patient DF can be distinguished (...) from a mere physical ability because they are (1) intentional and (2) knowledge-based; yet these actions fail to satisfy the criteria for propositional knowledge. It is therefore my contention that there exists a form of intentional action that not only constitutes a genuine claim to knowledge but, in being irreducible to knowing that, resists the intellectualist argument for exhaustive epistemic reduction. (shrink)
Psychogenic depersonalization is an altered mental state consisting of an unusual discontinuity in the phenomenological perception of personal being; the individual is engulfed by feelings of unreality, self-detachment and unfamiliarity in which the self is felt to lack subjective perspective and the intuitive feeling of personal embodiment. A new sub-feature of depersonalization is delineated. 'Prosthesis' consists in the thought that the thinker is a 'mere thing'. It is a subjectively realized sense of the specific and objective 'thingness' of the particular (...) object thought about. I show that prosthesis is an important cognitive feature of depersonalization, and may be psychologically connected with the tendency of depersonalized individuals to report 'philosophical' types of thinking. Indeed, several philosophical issues concerning the identity of the self appear to have been enhanced by prosthesis experiences. Thus, far more efficient than William James's experimental attempts to uncover philosophical truths under the influence of nitrous oxide intoxication, prosthesis may be a safe and recommended experience for philosophers. The history of depersonalization theories is presented from Krishaber to Freud, and the main approaches to prosthesis criticized. Finally, a fresh approach to psychogenic depersonalization is outlined on the basis of certain cognitive similarities with visual agnosia. This paper may be understood as continuing the Jamesian tradition 'experimental abnormal psychology', that is, of examining extraordinary mental states with an eye to their philosophical implications. (shrink)