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Phenomenal and Access Consciousness Ned Block and Cynthia MacDonald CONSCIOUSNESS AND COGNITIVE ACCESS NED BLOCK This article concerns the interplay between two issues that involve both philosophy and neuroscience: whether the content of phenomenal consciousness is ‘rich’ or ‘sparse’, whether phenomenal consciousness goes beyond cognitive access, and how it would be possible for there to be evidence one way or the other. I Introduction. I will begin with an illustration that raises the issue of whether phenomenal consciousness could be so divorced from cognitive access that a subject can have an experience that he does not and cannot think about. Then I will mention a puzzle about whether there could be evidence one way or the other on that issue, and suggest a solution to the puzzle. The issue of sparse versus rich experiences will be introduced and connected to the puzzle, then some empirical evidence will be described that casts some light on the issue.1 II An Illustration. Nancy Kanwisher (2001) and her colleagues (Tong, Nakayama, Vaughan and Kanwisher 1998) have found impressively robust correlations between the experience of faces and activation at the bottom of the temporal lobe, usually in the subject’s right hemisphere in what they call the ‘fusiform face area’. One method that has been used to investigate the neural basis of face perception exploits a phenomenon known as ‘binocular rivalry’ (see Koch 2004, ch. 16). If a face-stimulus is presented to one eye and a house stimulus to the other, the subject experiences a face for a few sec1 Most of the material presented here derives from Block (2007a, 2007b, forthcoming). ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.x290 NED BLOCK onds, then a house, then a face, etc. If the visual processing areas of the brain are examined while the face/house perceptual alternation is ongoing, much stronger alternations in sync with the percept are found in the fusiform face area than in other areas. The fusiform face area lights up when subjects are experiencing seeing a face and not when subjects are experiencing seeing a house, despite the fact that the stimuli are unchanging. The fusiform face area also lights up when subjects imagine faces (O’Craven and Kanwisher 2000). No one would suppose that activation of the fusiform face area all by itself is sufficient for face-experience. I have never heard anyone advocate the view that if a fusiform face area were kept alive in a bottle, that activation of it would determine face-experience, or any experience at all (Kanwisher 2001). The total neural basis of a state with phenomenal character C is—all by itself—sufficient for the instantiation of C. The core neural basis of a state with phenomenal character C is the part of the total neural basis that distinguishes states with C from states with other phenomenal characters, for example, the experience as of a face from the experience as of a house. (The core neural basis is similar to what Semir Zeki (Zeki 2001; Zeki and Bartels 1999) has called an essential node.) So activation of the fusiform face area is a candidate for the core neural basis—not the total neural basis—for experience as of a face (see Block 2005; Chalmers 2000; Shoemaker 1981). There is some evidence that a total neural basis of a kind of experience is the core neural basis of that kind of experience plus active reverberations involving that core neural basis and the upper brain stem including the thalamus. (The most convincing evidence is that disabling the thalamus seems the common core of what different general anesthetics do (Alkire and Miller 2005). But for some doubts, see Alkire 2008; Tononi and Koch 2008.) Here is the illustration I have been leading up to. There is a type of brain injury which causes a syndrome known as ‘visuo-spatial extinction’. If the patient sees a single object on either side, the patient can identify it, but if there are objects on both sides, the patient can identify only the one on the right and claims not to see the one on the left (Aimola Davies 2004). (With competition from the right, the subject cannot attend to the left.) However as Geraint Rees has shown in two fMRI studies of one patient (known as ‘GK’), when GK claims not to see a face on the left, his fusiform face area (on the right—which is fed by the left side of space) lights up almost as ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.xPHENOMENAL AND ACCESS CONSCIOUSNESS 291 much as—and in overlapping areas involving the fusiform face area—when he reports seeing the face (Driver and Vuilleumier 2001; Rees et al. 2000, 2002). III The Self. Should we conclude that the fusiform face area is not the whole of the core neural basis for the experience as of a face? Or that activation of the fusiform face area is the core neural basis for the experience as of a face but that some other aspect of the total neural basis is missing in GK? However, another possibility is that GK genuinely has face experience that he doesn’t know about and cannot know about. Wait—is that really a possibility? Does it even make sense to suppose that a subject could have an experience that he doesn’t and can’t know about? What would make it his experience? The last question about GK can be answered by thinking about his visual field. What is the visual field? If you look straight ahead and hold a rod out to the side and slowly move it forward, you will be able to see it at roughly 100° from straight ahead. If you do the same coming down from the top, you will see it at roughly 60°, and if you do it from the bottom, you will see it at roughly 75°. This is a rough way of measuring the visual field. For more precision, the visual field is measured with gratings. Subjects are asked whether at a given eccentricity the grating looks like a grating or like a uniform grey field. The shape of the visual field in normal people is oval, elongated to the right and left, and slightly larger on the bottom. The Humphrey Field Analyser HFA-II-I can measure your visual field in as little as two minutes. The United Kingdom has a minimum visual field requirement for driving (60° to the side, 20° above and below); US states vary widely in their requirements (Peli and Peli 2002). Of course one can measure something without knowing what it is. But it will be too much of a digression to go further into that issue now. The point I wish to make is that it is known that visuo-spatial extinction arises from a difficulty attending to one side of space when there is a competing target of attention on the other side of space. Some may say that GK’s lack of attention to the left prevents him from having any experience of a face stimulus on the left, but another possibility is that GK’s lack of attention to the left ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.x292 NED BLOCK prevents his genuine experience of a face on the left from reaching the machinery of cognitive access. On that hypothesis, we can understand the face experience as his experience by noting that it is in his visual field. One could meaningfully ask, for example, whether it is the same half of his visual field in the vertical dimension as his experience on the right, or which is closer to the periphery, the one on the left or the one on the right. In what follows, I will assume it is meaningful to suppose that GK has an experience that he does not and cannot know about, turning to the question of whether it would be possible to empirically investigate that meaningful possibility. IV The Methodological Puzzle. How could the issue be investigated? A natural methodology is to find the neural basis of face experience in clear cases and apply it to problem cases where for some reason there is no cognitive accessibility of the experience. However, in order to apply this methodology to the case of GK, one would first have to ask the question as to whether the activation of the fusiform face area (the core neural basis) plus its connections to the upper brain stem is sufficient for consciousness (i.e. is a total neural basis), or whether the total neural basis of face experience includes the frontal activation that underlies the cognitive access that itself underlies our ability to report our experience. But that question raises the issue of whether there can be face experience without cognitive accessibility, the very issue that we started with. So it looks as if the obvious methodology eats its own tail. Another variant of the problem: how can we find out whether there can be conscious experience without the cognitive accessibility required for reporting conscious experience, since any evidence would have to derive from reports that themselves derive from that cognitive access? Note that the problem cannot be solved by stipulating a definition of ‘conscious’. Whatever definition one offered of this and other terms, the puzzle could be put in still other terms: for example, there would still be the question of whether what it is like to have that experience includes whatever cognitive processes underlie our ability to report the experience. ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.xPHENOMENAL AND ACCESS CONSCIOUSNESS 293 The problem does not arise in the study of, for example, water. On the basis of the study of the nature of accessible water, we can know the properties of inaccessible water, for example, in environments outside our light cone—that is, environments that are too far away in space and time for signals travelling at the speed of light to reach us. We have no problem in extrapolating from the observed to the unobserved and even unobservable in the case of water because we are antecedently certain that our cognitive access to water molecules is not part of the constitutive scientific nature of water itself. In homing in on a core neural basis of phenomenal consciousness, we have a choice about whether or not to include within the core neural basis the aspects of those neurological states that underlie reportability. If we do, then unreportable phenomenally conscious states are ruled out; if we do not, unreportable phenomenally conscious states are allowed. Few scientifically minded people in the twenty-first century would suppose that water molecules are partly constituted by our cognitive access to them (Boghossian 2006), but few would be sure whether phenomenal consciousness is or is not partly constituted by cognitive access to it. It is this asymmetry that is at the root of the Methodological Puzzle of phenomenal consciousness. V The Solution. The solution to the Methodological Puzzle is the method of inference to the best explanation, that is, the approach of looking for the framework that makes the most sense of all the data, not just reports (Harman 1965; Peirce 1903, vol. v, p. 171). The reader may feel that I have already canvassed inference to the best explanation and that it did not help. Recall that I mentioned that the best explanation of all the data about observed water can give us knowledge of unobserved—even unobservable—water. I said that this approach does not apply straightforwardly to consciousness. We are antecedently certain that our access to information about water molecules is not part of the natural kind that underlies water molecules themselves. But we are not certain (antecedently or otherwise) about whether our cognitive access to our own consciousness is partly constitutive of the consciousness. Without antecedent knowledge of this—according to the reasoning that ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.x294 NED BLOCK leads to the Methodological Puzzle—we cannot know whether whatever makes a phenomenal state cognitively inaccessible also renders it non-phenomenal. Here is the fallacy in that argument: the best theory of all the data may be one that lumps consciousness together with water molecules as something whose constitutive nature does not include cognitive access to it. To hold otherwise is to suppose—mistakenly—that there are antecedent views—or uncertainties, in this case—that are not up for grabs. Perhaps an analogy will help. It might seem, offhand, that it is impossible to know the extent of errors of measurement, for any measurement of errors of measurement would have to be derived from measurement itself. But we can build models of the sources of measurement error and test them, and if necessary we can build models of the error in the first-level models, and so on, stopping when we get a good predictive fit. For example, the diameter of the moon can be measured repeatedly by a number of different techniques, the results of which will inevitably vary about a mean. But perhaps the diameter of the moon is itself varying? That can be investigated by simultaneously building models of sources of variation in the diameter itself (for example, the temperature of the moon) and models of error in the various methods of measurement. Those models contain assumptions which can themselves be further tested. The puzzle of how it is possible to use measurement itself to understand errors of measurement is not a deep puzzle. As soon as one sees the answer, the problem of principle falls away. I do not believe that the same is true for the Methodological Puzzle. One reason is the famous ‘explanatory gap’ (Levine 1983; Nagel 1974). There may be reasonable doubt whether the method of inference to the best explanation can apply in the face of the explanatory gap. A second point is that with the demise of verificationism (Uebel 2006), few would think that the nature of a physical magnitude such as length or mass is constitutively tied to our measurement procedures. The mass of the moon is what it is independently of our methods of ascertaining what it is. But verificationism in the case of consciousness is much more tempting—see Dan Dennett’s ‘first person operationism’ (Dennett 1991) for a case in point. ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.xPHENOMENAL AND ACCESS CONSCIOUSNESS 295 VI Rich versus Sparse Experience. As I explained at the outset, this paper concerns the interplay between two issues, the Methodological Puzzle just canvassed and the issue of ‘rich’ versus ‘sparse’ conscious contents, the source of which, in current controversies, is a phenomen-on called ‘change blindness’. As illustrated in figure 1, a drawing or photograph is presented briefly to subjects, followed by a blank, followed sometimes by an identical photograph but other times by a similar but not identical photograph, followed by another blank. Then the cycle starts over. Figure 1. The ‘change blindness’ paradigm. A picture is presented briefly, then a blank screen, then another picture which may or may not differ in some respect from the first one, then another blank, then the cycle starts over. The result is that subjects are surprisingly unable to tell what changes between the two pictures, even after watching the cycle many times. I am grateful to Ron Rensink for redrawing this figure and for permission to use it. You can experience something of the phenomenon if you look at figures 2 and 3 without looking at them side by side. When the two photographs differ, they usually differ in one object that changes colour, shape or position or appears or disappears. The surprising result is that subjects are often unaware of the difference between the two pictures, even when the changed region takes up a good deal of the photographic real estate. Even with fifty repetitions of ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.x296 NED BLOCK the same change over and over again, people are often unaware of the change. It is widely agreed that the phenomenon is an attentional one. The items that change without detection have been shown to be items that the subjects do not attend to. But the controversial question is whether the explanation of the surprising inability of subjects to notice the change is due to inattentional blindness or inattentional inaccessibility. Figure 2. Compare this with figure 3 without looking at the two figures side by side. There is a difference between the two pictures that can be hard to be aware of, a fact that motivates the appellation (a misnomer in my view) ‘change blindness’. I am grateful to Ron Rensink for supplying this figure. The idea of the inattentional blindness view of the phenomenon is that subjects do not actually see the features that change (Noë 2004, O’Regan and Noë 2001). By contrast, the inattentional inaccessibility view (Block 2001) says that subjects may see the features that change, but fail to notice the difference, because although much of the detail in each picture is phenomenally registered, it is not conceptualized at a level that allows cognitive access to the difference. As Fred Dretske (2004) has noted, the difference between the two stimuli in a change blindness experiment can be one object that appears or disappears, and one can be aware of that object that consti©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.xPHENOMENAL AND ACCESS CONSCIOUSNESS 297 tutes the difference without noticing that there is a difference. As will be explained below, there appears to be a limit in ‘working memory’ of about four items. (The existence of such a limit is not part of the dispute between the proponents of inattentional blindness and inattentional inaccessibility.) Proponents of inattentional blindness typically take this limit to show that despite the appearance of a rich visual world, one only sees about four items at a time, and thus that conscious experience is surprisingly ‘sparse’. The impression that one takes in many more things is supposed to derive from a ‘refrigerator light illusion’ in which subjects mistake the easy accessibility of all sorts of detail for actually seeing that detail (O’Regan and Noë 2001). (The analogy invokes a fool who thinks that the refrigerator light is always on because it is on when he looks.) Dehaene and his colleagues put the point as follows: The change blindness paradigm demonstrates this ‘discrepancy between what we see and what we think we see’ (Simons and Ambinder 2005). In this paradigm, viewers who claim to perceive an entire visual scene fail to notice when an important element of the scene changes. This suggests that, at any given time, very little of the scene is actually consciously processed. Interestingly, changes that attract attention or occur at an attended location are immediately detected. Thus, the illusion of seeing may arise because viewers know that they can, at will, orient attention to any location and obtain conscious information from it. (Dehaene et al. 2006, p. 210) The upshot is a disagreement about whether perceptual consciousness is ‘rich’ or ‘sparse’. The advocates of ‘sparse’ visual experience argue that the limits of working memory are the limits of experience, whereas the advocates of rich experience can allow that experience ‘overflows’ cognitive accessibility. Now we can get a glimpse of the relevance of the sparse/rich issue to the Methodological Puzzle. The argument of this paper is that we already have some evidence for the ‘rich’ view, and the upshot is that the capacity of the perceptual consciousness system is much larger than the capacity of the ‘working memory’ system that underlies the cognitive access that itself underlies reportability. And this difference in capacity shows that consciousness and cognitive access are to some extent based in different systems with different properties. I have mentioned the results about working memory, but I will now address that issue in more detail. ©2008 The Aristotelian Society Proceedings of the Aristotelian Society, Vol. cviii, Part 3 doi: 10.1111/j.1467-9264.2008.00247.x298 NED BLOCK Figure 3. Compare this with figure 2 without looking at the two figures side by side. There is a difference that can be hard to see. I am grateful to Ron Rensink for supplying this figure. VII Working Memory. At a neural level, we can distinguish between memory that is coded in the active firing of neurons—and ceases when that neuronal firing ceases—and structural memory that depends on changes in the neural hardware itself, for example, change in strength of synapses. The active memory—which is active in the sense that it has to be actively maintained—is sometimes described as ‘short term’—a misdescription, since it lasts as long as active firing lasts, which need not be a short time if the subject is actively rehearsing. The term ‘working memory’ is used differently by different people (Cowan 2007), but in th