Block argues, by the method of inference to the best explanation (IBE), for the thesis that cognitive accessibility is not part of the constitutive nature of phenomenal consciousness. He claims his view provides the best explanation of the apparent respect in which phenomenology overflows cognitive access and that it meshes with the neural data, which he takes to show that the machinery underlying cognitive access is distinct from that underlying phenomenal consciousness.
As with any case of IBE, the plausibility of Block's argument will depend on both the data it aims to explain and the range of alternative explanations available. Challenges may be raised in both respects, especially if one allows for the possibility that phenomenal consciousness may admit of degrees rather than being an all or nothing matter. If so, critical cases in which phenomenal consciousness apparently occurs in the absence of some types of cognitive access may be better regarded as cases in which a lesser degree of phenomenal consciousness involves a lesser degree of cognitive access. We need not suppose, for example, that when we have phenomenal visual experience of a scene we phenomenally represent all of its features. Phenomenal consciousness may be partial and incomplete in ways that correlate with our partial cognitive access.
Does phenomenology in fact overflow cognitive access? In experiments such as those by Sperling (Reference Sperling1960) and Landman et al. (Reference Landman, Spekreijse and Lamme2003), subjects often report having experienced more features than they can identify, categorize, or detect changes in. However, such reports do not necessarily show that phenomenal consciousness exceeds cognitive access. Though the subjects in the Sperling experiments cannot cognitively identify many of the specific letters that were briefly presented to them, they do have cognitive access to the fact that they were presented with an array of 12 characters. Their cognitive access is limited, but so too may be their phenomenal consciousness of those letters. If one holds a “movie screen of the mind” model of phenomenal consciousness, it may seem impossible that there could be letters that are phenomenally present as letters without being present as specific letter shapes. But such a model is at best problematic, and if one rejects it, then there seems no reason why the characters of which the subjects are aware could not be indeterminate in ways that exactly match their limited cognitive access to those features.
Moreover, the subjects' reports of what they experienced under such marginal conditions may be more problematic than Block contends. He rejects the idea that they might be hyperillusions – cases in which how it seems that it seems, is not how it really seems. He says he knows of no such illusions. However, the well-known color marker demonstration (Dennett Reference Dennett1991) would seem to be just that. We have the firm belief that our phenomenal experience of the entire visual field is colored; that is how it seems to us. But if we hold fixation to the front and hold a marker whose color we do not know at arms length to the side, we cannot discern its color. If it is gradually moved toward the front, we cannot see its color until it is far toward the center of our field of vision, though we can detect its motion almost as soon as it begins to move – which reflects the fact that the retina lacks cones at the periphery but not motion detectors. Nor is the illusion easily dispelled, as Block says is generally true of cognitive illusions. Despite participating in the marker demonstration, one still experiences the illusion (hyperillusion) that one's whole visual field is phenomenally colored.
The possibility that phenomenal consciousness may admit of degrees also enlarges the space of alternatives against which Block's view must be compared in assessing his IBE argument. He contrasts his position mainly with what he calls metaphysical and epistemological correlationism, but these views, like his own, do not consider the possibility that phenomenal consciousness may be partial, indeterminate, and admitting of degrees. If one allows for that possibility, then there are other hypotheses one might consider about whether cognitive access is sometimes a constitutive element of phenomenal consciousness.
If the neural substrate of phenomenal consciousness involves interactions among multiple brain regions, and the specific regions vary for different experiences – two ideas Block endorses in general – then could it not be the case that sometimes those regions most active in providing cognitive access are among the relevant constitutive elements? The suggestion is not merely hypothetical. As Block acknowledges, phenomenal consciousness involves some sort of awareness. Indeed, it involves the awareness or experience of objects present to the self – that is, objects experienced from the perspective of the self. There need not involve a commitment to any traditional substantial notion of the self. The self and the self-perspective may well be virtual structures. As I look at my desk the phenomenal content of my experience is that a blue mug is present here and now before me. In light of the integrative role played by the machinery of cognitive access, it seems plausible to regard it as constituting part of the substrate of my phenomenal consciousness of that mug as an object in my world, rather than merely a cause of my experience.
Perhaps in marginal and attenuated cases, we may have phenomenal experiences of isolated properties or features, and in such cases perhaps all the constitutive elements of our phenomenal consciousness lie outside the structures that support cognitive access. But those would be cases in which we are phenomenally conscious to a lesser degree than is typical. In more normal cases of full-blown phenomenal consciousness, we experience colors, shapes, and motions as properties of objects present to us as part of our world. And in those cases, it seems plausible to treat the regions that present those objects to us, that give us access to those objects, as parts of the substrate of such phenomenal consciousness.
