What is it like to have type-2 blindsight? Drawing inferences from residual function in type-1 blindsight

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Controversy surrounds the question of whether the experience sometimes elicited by visual stimuli in blindsight (type-2 blindsight) is visual in nature or whether it is some sort of non-visual experience. The suggestion that the experience is visual seems, at face value, to make sense. I argue here, however, that the residual abilities found in type-1 blindsight (blindsight in which stimuli elicit no conscious experience) are not aspects of normal vision with consciousness deleted, but are based fragments of visual processes that, in themselves, would not be intelligible as visual experiences. If type-2 blindsight is a conscious manifestation of this residual function then it is not obvious that type-2 blindsight would be phenomenally like vision.

Transcranial magnetic stimulation to visual cortex induces suboptimal introspection

“…However, it has also been suggested that subjective experience of visual stimuli can exist in blindsight patients in the absence of visual phenomenology, or qualia -- sometimes called Type 2 blindsight (Brogaard 2015; Sahraie et al 2010; Kentridge 2015; Foley and Kentridge 2015; Foley 2015; Weiskrantz 1986; Weiskrantz 1996; Cowey and Stoerig 1995). It is unknown how blindsight patients would perform on a criterion-free subjective task such as the present 2IFC paradigm, in which saying “I see nothing” or “I experience nothing” is not an option.…”

Unconscious Perception Reconsidered

“…In terms of direct evidence, Alexander and Cowey () find only evidence of sensory capacities to detect sharp luminance contours and/or stimulus transients in two patients (GY and MS); Azzopardi and Hock () show that motion discrimination in GY is limited to “objectless” first‐order motion energy (i.e., spatiotemporal changes in luminance) as opposed to changes in position or shape; and Kentridge, Heywood, and Weiskrantz () show that DB matches colored stimuli purely on the basis of wavelength and so lacks even the rudiments of color constancy mechanisms (see also Alexander and Cowey , and Kentridge ). None of these capacities implies objective environmental representation.…”

The case for characterising type-2 blindsight as a genuinely visual phenomenon

“…If this is the case, it would seem that a visual pathway, which is performing a role very similar to the one it performs in the normal visual system, mediates type-2 awareness. This is not to say that the visual processing the system can perform has not been seriously degraded both qualitatively and quantitatively (see Section 4 and Kentridge (2015) for more detail on the nature of the residual processing that subserves type-2 blindsight). Rather, the evidence seems to favour the conclusion that the visual system retains some of its normal functioning after damage to V1, and that it is this residual functioning that leads to type-2 awareness.…”

“…On one version, the claim that blindsight is not normal visual awareness is uncontentious: As discussed in the previous section, blindsight subjects' residual processing obviously differs both qualitatively and quantitatively from normal vision, and so it makes sense that their residual visual awareness is radically altered (for more on how radically altered visual processing is in blindsight see Kentridge, 2015). But this weaker claim does not warrant the conclusion that type-2 awareness is not visual, only that it is unlike normal visual awareness.…”

“…Given what we know about the residual processing that subserves blindsight, any visual experience blindsight subjects might have would be very blurry and non-specific: lacking in shape information, colour information, contour information, and other features of the object normally represented in visual experience (see Kentridge, 2015, for a good discussion of the qualitative differences between residual processing that subserves blindsight and normal visual processing). This would lead to any awareness that subjects have being very unusual, explaining why they might judge themselves not to be seeing.…”