Blindsight is the term commonly used to describe visually guided behaviour elicited by a stimulus falling within the scotoma (blind area) caused by a lesion of the striate cortex. Such is normally held to be unconscious and to be mediated by subcortical pathways involving the superior colliculus. Blindsight is of considerable theoretical importance since it suggests that destriate man is more like destriate monkey than had been previously believed and also because it supports the classical notion of two visual systems. (...) It is also of potential clinical importance, since it has been claimed recently that systematic practice in blindsight can lead to the recovery of normal visual function in patients with cortical lesions. From a review of the literature it is concluded that all of the phenomena of blindsight can be attributed either to light scatter into unimpaired parts of the visual field or to residual vision resulting from spared striate cortex. The possible contribution f other factors is also considered. It is concluded that blindsight studies have generally failed to control for such nonblindsight interpretations partly because of poor methodology and partly because of difficulties in defining the term. (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)

The phenomenon of `consciousness' is intrinsically related to one's awareness of one's self, of time, and of the physical world. What, then, can be learned about consciousness from people who have suffered brain damage such as amnesia which affects their awareness? This is the question explored by Lawrence Weiskrantz, a distinguished neuropsychologist who has worked with such patients over 30 years. Written in an engaging and accessible style, Consciousness Lost and Found provides a unique perspective on one of the most (...) challenging issues in science today. (shrink)

within-field task as testing proceeded. (In any case, the two-field task is presumably a more difficult one than the one-field task. ...

It is proposed that there are at least two categories of blindsight. One is present in visually guided behaviour in normals as well as in brain-damaged patients, while the other is present only following cortical lesions. It is also proposed that blindsight is blind because residual visual functions are banned from consciousness either when they are subserved by subcortical centres alone or when they are mediated by cortical areas that have never been exclusively associated with such functions before brain injury.

Following lesions to the primary visual cortex, some patients maintain visual capacities within areas of the visual field in which they are defined as clinically blind by static field perimetry. Blindsight describes the ability to discriminate visual stimuli in the absence of awareness of the stimuli in such patients. Some patients exhibit blindsight, but others are aware of the stimuli with which they are presented, a response mode that has been referred to as residual vision. The two response modes are (...) of great interest as they are capable of providing us with information concerning the conscious and unconscious processing of visual signals in humans. However, determining consciousness in these patients is a difficult task and relies on the patient assessing and then reporting on his awareness. In this paper, an experiment is described which is capable of demonstrating conscious visual processing of motion under conditions where the observer is not required to assess his level of awareness. In applying this technique to a human hemianope, GY, it is demonstrated that GY has veridical and conscious perception of visual motion presented to his blind hemifield. Although previously reported, this result can be derived without any reference to GY's commentary on his blind field perception. (shrink)

In the context of this publication on blindsight, I want to address further the brain processes critically responsible for organizing our conscious experience. As in a previous related publication , I am restricting myself to brain and conscious experience, not the fuller topic of ‘consciousness’ as this might be determined by genetic and environmental factors, nor as it is defined in Eastern traditions and in esoteric Western religion and philosophy. For my thoughts on this broader topic the reader is referred (...) to a recent publication prepared for the centennial celebration of Norbert Wiener's birth. That paper is entitled: ‘What is Mind that the Brain May Order It? (shrink)