Retroalimentación y reajuste del plan diseñado

In this section I consider the proposal that visual attention makes information spontaneously accessible for use in the control of thought and action. The motivation for this view of the explanatory role of attention comes from the observation that blindseers need to be prompted to make guesses about objects in their blind field. As we saw in Chapter 1, GY is able to detect the presence of a target displayed to his blind field; he is able to do this well

78

above chance and his response time is faster following a valid than a

misleading cue. In those experiments, the presentation of the target stimulus was signalled to GY by an auditory tone, which was also his cue to

respond.91 This marks a substantial difference between GY’s ability to detect objects in his blind field and the ability of normally sighted people (and, presumably, GY when he uses his intact hemifield). When we open our eyes we are confronted by the world: our thoughts about the objects we see and our actions with respect to those objects generally need no prompting. It is very tempting to conclude, therefore, that the distinctive way in which visual attention explains visually based object-directed thoughts and actions is by prompting them. When I am visually attending to an object, in addition to the selection and enhancement of processing of the object by my visual system, I am aware of it. Being aware of it in this way – attentively aware of it, so to speak – seems to explain why I don’t need to be prompted to think about it, or act with respect to it. This suggests that the explanatory role of visual attention to an object is to make visual information from that object

spontaneously accessible for the purpose of thought about the object, and action with respect to it.

Ned Block (e.g. Block (1995)) has argued, in effect, that the inference to an explanatory role for visual attention from the inability of subjects with

blindsight to prompt themselves is not valid. In §2.1 I look at his argument, which makes use of the hypothetical condition of ‘super blindsight’. I question the coherence of super blindsight as described by Block. I conclude that

79

Block is right to question the validity of the inference, but that because of the questionable coherence of super blindsight, the issue is one which needs to be resolved by looking at actual cases. In §2.2 I look at empirical evidence from both a monkey and a human that seems to support the existence of a partial kind of ‘super’ blindsight. Both demonstrate spontaneous visually based object-directed actions in the absence of visual awareness. In §2.3 I outline an influential hypothesis, David Milner and Melvyn Goodale’s two visual systems hypothesis, that purports to explain how this partial super blindsight is possible. The empirical evidence from ‘partial super blindsight’ along with the evidence Milner and Goodale draw on for their hypothesis strongly indicates that visual attention to an object is not necessary for visual information from it to be spontaneously accessible for the purpose of action with respect to it. This presents a choice. Either visual attention is no longer treated as a unitary, conscious phenomenon and the defence of the pre- theoretical conception of attention as sufficient for awareness is given up, or a different explanatory role for attention is found. Sections 3-5 of this chapter all consider explanatory roles for attention conceived as a unitary, conscious phenomenon.

2.1 Blindsight and Super Blindsight

When we talk of paying attention to things we see, part of what we mean is that we are aware of the things we are paying attention to. I cannot pay attention to the magician’s card trick while remaining completely unaware of it. Robert Kentridge and others have challenged this conception of attention,

80

arguing that GY’s visual abilities demonstrate that attending to an object is not sufficient for being aware of it. I have responded that a recognisable and quite typical way of talking about attending to things we see – what I have called visual attention – points to a conception of visual attention that plays an explanatory role for us: visual attention explains, for example, how I know what I am looking at. If visual attention plays an explanatory role that cannot be played by the visual selection and enhancement the blindseer is capable of, we have the basis of a defence of the sufficiency of visual attention for visual awareness. The challenge is to identify what this explanatory role is, and why it cannot be played by the visual selection and enhancement the blindseer is capable of. A promising first step in identifying the explanatory role of visual attention is to compare the abilities of blindseers and the normally sighted. Blindseers, it appears, are unable to make reports about objects in their blind field unless they are prompted to do so. Accordingly, the proposal we are considering here is that visual attention is necessary for us to be able to spontaneously access visual information in the service of object-directed thought and action.

The strategy behind this proposal faces a challenge brought by Ned Block. Block (Block (1995)) has argued against drawing conclusions about the function of consciousness from the deficits exhibited by blindseers. According to Block, blindseers lack not only visual awareness, but also a functionally defined kind of consciousness. Block argues for a distinction between what he calls phenomenal consciousness and access

81

“… experience. P-conscious properties are experiential ones. P-conscious states are

experiential, that is, a state is P-conscious if it has experiential properties. The totality of

the experiential properties of a state are ‘what it is like’ to have it.”92

The state of being visually aware of an object is an example of a

phenomenally conscious state. It is noteworthy that phenomenally conscious properties are not to be identified with any cognitive, intentional or functional properties.93

We correctly attribute an access conscious (or ‘A-conscious’) state to a subject when a representation of the content of the state is

“… poised for use as a premise in reasoning,… poised for rational control in action, and…

poised for rational control of speech.”94

On Block’s analysis, blindseers lack visual representations of objects

presented to their blind fields that are P-conscious, but those representations are also not A-conscious, and their inability to spontaneously report the presence of the objects is due to the lack of access consciousness. Block’s main aim in his (1995) is to demonstrate how one kind of argument about the function of what he calls phenomenal consciousness is invalid. The kind of

92 _{Block (1995) p. 230.} 93 _{Block (1995) p. 230.}

94 _{Block (1995) p. 231. Block allows that a state may be access conscious even if it is not}

poised for the rational control of speech. Block also allows for the possibility that a

phenomenally conscious state may not be access conscious, and therefore not reportable (pp. 232-233, p. 234).

82

argument he is targeting infers from the fact that the blindseer’s lack of visual awareness is accompanied by an inability to spontaneously report the

presence of objects in his blind field that a function of visual awareness is to make visual information accessible for spontaneous report. This argument is invalid, Block maintains, because there could be (and Block thinks there is) something else missing in blindsight, and it is the lack of this further

component of normal functioning (‘access consciousness’) that is responsible for the blindseer’s inability to spontaneously report objects presented to their blind field.

To support his case, Block considers the hypothetical possibility of super

blindsight. The super blindseer can prompt himself to make guesses about what is in his blind field in such a way that

“Visual information from his blind field simply pops into his thoughts in the way that

solutions to problems we’ve been worrying about pop into our thoughts, or in the way some people just know the time or which way is North without having any perceptual

experience of it.”95

Visual information is access conscious for the super blindseer without being phenomenally conscious. The super blindseer is able to spontaneously report the presence of objects in his blind field. To accept super blindsight as a coherent possibility is to accept that we can conceive of access

consciousness in the absence of phenomenal consciousness. If we can

83

conceive of access consciousness in the absence of phenomenal consciousness, phenomenal consciousness – and therefore visual

awareness – cannot be conceptually necessary for the availability of visual information for spontaneous response. Yet it seems very plausible that visual awareness is necessary for spontaneous, visually based thoughts and

actions. According to the pre-theoretical conception I have described, it is

because I am aware of (and attending to) the magician’s hands that I come to know how he does his trick. The surprising abilities of subjects with blindsight appear to challenge this view. Blindseers can acquire visually based information about their environment in the absence of any awareness. However, in the experiments with GY described in the last chapter, the unconscious visual information he acquired was not available to him for spontaneous responses. A modified view therefore suggested itself: visual awareness is necessary for visually based information to be used

spontaneously. If the super blindseer can do everything his normally sighted counterpart can do, even this modified view is incorrect.

So it is a pressing question to ask whether super blindsight as envisaged by Block is a coherent possibility. The sketch Block provides suggests the super blindseer prompts himself to guess about what is in his blind field, following which answers ‘simply pop into his head’. What the sketch does not make clear is exactly how the super blindseer’s self-prompting is supposed to work. In actual cases of blindsight (even the remarkable discrimination and identification abilities demonstrated by DB96), the blindseer has to be

84

prompted by the experimenters to respond when a stimulus is presented to his blind field.97 Perhaps we can we fill out Block’s sketch by trying to imagine how super blindsight might work.

Suppose a super blindseer is sat in front of a blank monitor screen, and his task is to press a button when he thinks something is presented on the screen. He doesn’t have to identify it, just press the button as soon as he thinks it appears. He may become quite good at this if the stimulus is presented in the first few seconds, or minutes. But what if there is a much longer delay? In the controlled environment of a laboratory, with clear instructions explaining his task, this might be feasible. But in a natural

environment, with unpredictable eventualities, how does the super blindseer know when to prompt himself, or in which direction to look? And how does he interpret his ‘guesses’? As he watches an empty bus stop, let us suppose he detects a woman walking up to it. He prompts himself again, and again detects a woman at the bus stop. Is it the same woman? He may detect the same properties again, but given the discrete, periodic nature of his visual information about the world, mistaking one thing for another very similar one will always be more of a possibility for him than for a normal subject. More generally, it seems he is prone to missing events that occur, as it were, ‘in between prompts’. Perhaps there is some way of augmenting his abilities to deal with this, but it seems like we will have to attribute yet more ill-defined

97 _{In Trevethan et al. (2007) DB’s almost incredible identification of 25 of 28 animal outlines}

so faint (2% contrast) that normally sighted control subjects could at most identify 2 is described as ‘spontaneous’ (p. 2097). To clarify, what Trevethan et al. mean is that DB was not choosing from a list, though he was given some indication of the kind of thing (‘animals’, ‘modes of transport’ or both) to expect. All the tests carried out on DB reported in the paper were forced response tests, meaning DB was prompted to respond. My use of

85

abilities to him for it to be plausible that his self-prompting will enable him to function like a normally sighted person.

There are other ways in which the super blindseer’s lack of visual awareness will affect what he can do on the basis of unconscious visual information. As I have characterised the relationship between visual awareness and attention, people who enjoy normal vision are, on occasion, prompted to attend to something because of their visual awareness of it. I may be looking for a particular book among a pile of books, and shift my attention over each of the books in turn to determine if it is the right one. I know which direction to shift my attention in, because I am aware of all the books in the pile and I know which ones I have just looked at. How does the super blindseer know which direction to shift his attention in? Our visual environment is typically quite complex, and often includes moving objects (e.g. people, other animals, and vehicles). If the super blindseer shifts his visual ‘selection’ from one object to another, he will no longer be receiving any visual information about the first object, and could therefore lose track of it. In contrast, I can continue to be aware of objects I am not attending to, including moving objects. My characterisation of the relationship between visual attention and visual awareness on which these claims rely is defended in chapter 4. But I think even without these questions about the coherence of super blindsight, we should be sceptical.

How could a periodic source of information, derived from someone repeatedly prompting themselves to guess what is in their environment,

86

provide the sort of continuous flow of information visual experience can provide us with? I suppose someone could insist that super blindsight could provide a continuous flow of information, but the nature of this information, and the way the super blindseer manages it, then become mysterious. How could someone who has learned to prompt himself do so both voluntarily and continuously? And if he receives continuous information, what form would this information take? Would it be like a running commentary on the objects in his line of sight? How, without some sort of guidance, would he be able to voluntarily focus his visual attention on particular objects? I cannot myself make much sense of how any of this this would work.

If the super blindseer does not receive a continuous flow of visual

information, his visual abilities would appear to be functionally (and not just phenomenally) different. To borrow John McDowell’s memorable phrase, when we open our eyes we are ‘saddled with content’.98 The super blindseer is not saddled with content; he has to pull out information a piece at a time, and it is arguable that for that reason the kind of visual information he has access to is qualitatively different. Suppose someone with normal vision was to look at an event proceeding, such as an object moving, or changing colour. If she attended to the object without blinking or looking away, she would see the object moving, or changing colour. Put in the same position, the super blindseer would only detect different stages of the event. Arguably, this is not just a difference in quantity of information, it is also a difference in the kind of information. A subject with normal vision is able to perceive the

98 _{McDowell (1994/1996) p. 10 “… experience is passive. In experience one finds oneself}

87

continuous progress of events. The super blindseer is only able to detect discrete states of the world.

There may well be ingenious ways of adding to Block’s sketch, and answering the questions about super blindsight I have raised. But the

important point, I think, is this. Super blindsight was introduced by Block as a device to help us understand the possibility of access consciousness without phenomenal consciousness. Instead, it has raised more questions than it has answered. As a way of illustrating a conceptual possibility, it has not

delivered.

Block is, however, right to conclude that the concurrent absence of visual awareness and the ability to spontaneously report the presence of objects does not of itself prove that the lack of the first causes the lack of the second. It is logically possible that the absence of the ability to spontaneously report is unrelated to the absence of visual awareness, or that a third factor is responsible for the absence of both. This possibility notwithstanding, it remains very plausible that visual awareness of objects has some role to play in prompting object-directed thoughts and actions. When we speak of being distracted by something we see, what we mean is that something we see captures our attention, and we start thinking about it because we are conscious of it. It isn’t obvious how a person could be distracted by something she was not aware of. Block’s sketch of super blindsight is inconclusive, since it simply doesn’t provide enough information for us to envisage it working. What we need to decide whether spontaneous visually

88

based object-directed thoughts and actions are possible in the absence of visual awareness of those objects is an actual case of super blindsight. Interestingly, it turns out that there are actual cases, albeit in a limited kind of way.

In §2.2 below, I consider two cases that could be described as ‘partial super blindsight’. The first case is of a monkey named Helen whose visual cortex (the area damaged in subjects with blindsight) was removed. The

psychologist Nicholas Humphrey, who studied Helen closely over a long period of time, not only provides a clear description of her ‘super blindsight’ like abilities, but also offers what I think are intriguing pointers to

understanding what her abilities are missing. The second case is of a human blindseer, TN, with bilateral blindsight (i.e. a complete lack of visual