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)

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)

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)

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)

Abstract. A rhesus monkey, Helen, from whom the striate cortex was almost totally removed, was studied intensively over a period of 8 years. During this time she regained an effective, though limited, degree of visually guided behaviour. The evidence suggests that while Helen suffered a permanent loss of `focal vision she retained (initially unexpressed) the capacity for `ambient vision.

: 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)

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.

This volume is the result of the third Appalachian Conference on Behavioral Neurodynamics which focused on the problem of scale in conscious experience.

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 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)

This book, a member of the Series in Affective Science, is a unique interdisciplinary sequence of articles on the cognitive neuroscience of emotion by some of ...

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)

Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to general cognition. This paper sets out some of the arguments for both sides (arguments from computer vision, neuroscience, Psychophysics, perceptual learning and other areas of vision science) and defends the position that an important part of visual perception, which may be called early vision or just vision, (...) is prohibited from accessing relevant expectations, knowledge and utilities - in other words it is cognitively impenetrable. That part of vision is complex and articulated and provides a representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat different outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain conceptual and methodological issues, including the use of signal detection theory and event-related potentials to assess cognitive penetration of vision. A distinction is made among several stages in visual processing. These include, in addition to the inflexible early-vision stage, a pre-perceptual attention allocation stage and a post-perceptual evaluation, memory-accessing, and inference stage which provide several different highly constrained ways in which cognition can affect the outcome of visual perception. The paper discusses arguments that have been presented in both computer vision and psychology showing that vision is "intelligent" and involves elements of problem solving". It is suggested that these cases do not show cognitive penetration, but rather they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been compiled into the visual system. The paper also examines a number of examples where instructions and "hints" are alleged to affect. (shrink)

INTRODUCTION Beyond Dissociations Reassembling the mind-brain after all? Yves Rossetti Antti Revonsuo "Comme des banes de poissons de meme espece, ...

GY, an extensively studied human hemianope, is aware of salient visual events in his cortically blind field but does not call this ''vision.'' To learn whether he has low-level conscious visual sensations or whether instead he has gained conscious knowledge about, or access to, visual information that does not produce a conscious phenomenal sensation, we attempted to image process a stimulus s presented to the impaired field so that when the transformed stimulus T(s) was presented to the normal hemifield it (...) would cause a sensation similar to that caused by s in the impaired field. While degradation of contrast, spatio-temporal filtering, contrast reversal, and addition of smear and random blobs all failed to match the response to a flashed bar sf, moving textures of low contrast were accepted to match the response to a moving contrast-defined bar, sm. Orientation and motion direction discrimination of the perceptually matched stimuli [sm and T(sm)] was closely similar. We suggest that the existence of a satisfactory match indicates that GY has phenomenal vision. (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)

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