The sound of one hand clapping.

The 'non-sensory' feelings of familiarity, rightness and tip-of-the-tongue postulated in the target article all find a natural explanation within existing models, including Gray's (1995) comparator model, of the way in which top-down and bottom-up processing interact to select the contents of consciousness. 1. No Qualia -No Problem Much current research aims to increase the precision with which one can describe the three-way set of correlations that underlie the problem of consciousness: between functions, neural states and conscious experiences. Clearly, description of these correlations requires adequate description of each of the three dimensions that go into them. In this respect, the phenomenology of conscious experience has long lagged behind its two partners. By drawing attention to a relatively neglected aspect of conscious experience, Sensation's Ghost (SG) makes an important contribution to remedying this situation, and for that reason I warmly applaud. However, no matter how sophisticated these correlations become, they will not by themselves answer the question: how does consciousness fit into the rest of the natural world? As always, we are unlikely to find an answer to this question until we have properly understood the question itself. For this reason much of the intense discussion of the Hard Problem of consciousness over the last couple of decades has been directed to formulating it in a way that strips it down to its essentials. This is why there has been so much concentration on the nature of full-blown qualia: that is, what we see, hear, touch, taste etc when we interact consciously with the external world (or, properly speaking, with what our brains construct so well as a simulated external world that we take it to be real; Velmans, 2000). If there were no qualia, there would be no Hard Problem of consciousness, indeed no problem of consciousness at all. There are no doubt many other problems about conscious experience, including the one that SG flags up. But it is a reasonable assumption that, if we once get a serious handle on how the brain creates qualia (I choose my words carefully, in full knowledge that many philosophers and some scientists will object strongly to them), these other problems will fall fairly easily into place. That is why there is such a concentration upon qualia it is not simply a matter of research myopia. Now, of course, this assumption may be wrong. Mangan, indeed, makes exactly the opposite one: that it will be better to start with 'less obtrusive aspects of our phenomenology' (p. 1). Who knows? He may be right. It is only after you know the solution to a problem that you can be sure of the best way to approach it. In the absence of qualia there would be, not only no problem of consciousness, but no mind/body problem either. We could then just get on with the accumulation of data to firm up the set of correlations between functions and brain states in the reasonable belief that this alone will provide all we need to know about the way the brain does the job of mind. For there is no conceptual difficulty in understanding how the brain can do the job of mind; and there are already a host of empirical demonstrations of how it actually does it (in neuroscience) or might do it (in psychology or computer science). Turning to the specifics of SG, among other things there is no problem in understanding in principle how the brain might compute non-conscious familiarity or rightness. That there are 'feelings' of familiarity and rightness, in the sense that people are able to report them (which is still, but not I hope for ever, the best available empirical hall-mark of conscious experience) is beyond dispute. Also beyond dispute is that familiarity and rightness cannot be conceptually the same as one another. As Mangan points out, one can tell the difference readily enough between two equally familiar words, only one of which is right for the current gap in a stream of discourse; just as one can tell of two words, both with the right semantics for the gap, that one is more familiar than the other. Examples of this kind can be multiplied readily. But it does not follow from this conceptual difference that the brain uses radically different machinery to compute the two types of 'feeling'. Indeed, I shall try to show below that it uses essentially the same machinery for both. I also find persuasive Mangan's argument that these 'feelings' are conscious, though they are not full-blown qualia. It is for this reason that I have put the scare quotes round 'feeling'. Whatever 'familiarity' and 'rightness' are, they are not like the full-blown feeling of being tickled, having an itch, or stroking velvet. What they seem to lack is the vivid qualities that are normally called 'sensory' (it is hard to capture, however, whether this is a difference in kind or degree). So, let us by all means go along with Mangan in calling them 'non-sensory experiences'. But we then still need a terminology that distinguishes these experiences from qualia. The phrase 'non-sensory qualia', also used by Mangan, is for me a step too far in obscuring this distinction; for we should then always need, I suppose, to talk about 'full-blown qualia', or something like that, for what are at present qualia tout court. To avoid this, I shall in the rest of this commentary use 'NSE' as an acronym for 'non-sensory experiences'. While I find Mangan's overall argument in favour of the concept of NSE persuasive, some of its aspects are troubling. Thus, there is an assertion (p. 5) that 'any experience that occurs in more than one sensory mode is non-sensory.' This is clearly false. As one among many possible examples, the well-known ventriloquist's illusion (one hears a voice coming from what one sees as moving lips, even though it is in fact coming from somewhere else) shows that the qualia that go to make up 'hearing someone speak' are a combination of experiences in two sensory modalities but it is certainly not a 'nonsensory' experience. Another troubling aspect is the flirtation with the rightly discarded notion of sense-data or 'naked sensations' (p. 5). Thus Mangan writes (loc. cit.) that NSE can be thought of as 'the contents in consciousness which, when added to and merged with sensations, create perceptions.' Oddly, for an avowedly phenomenological approach, this is surely and simply phenomenologically wrong. Not that the phenomenology here is simple it rarely is (one of the many reasons why, while one should never neglect phenomenology, the aim must be to transcend it with a theoretically viable and experimentally testable account of consciousness). My take on the phenomenology is itself complex and not easily summarised (I expand upon it in a forthcoming book). The following is a tenuously brief overview. A first division is into those qualia that are endowed with meaning, that is, in the philosophical sense of the term (Searle, 1983) are 'intentional', and those that are not. This division corresponds, at least roughly, to the distinction between those contents of consciousness that make up the perceived external world, and those that make up the perceived inner body (the perceived external body is part of the external world). The brain, of course, constructs both the perceived external world and the perceived inner body, but it does so using largely different structures (Damasio, 2000) and largely different sensory channels (vision, audition, touch, olfaction and gustation for the former; visceral, nociceptive and feedback from the autonomic nervous system for the latter). So far as I can judge from my own phenomenology, contents of consciousness of the former type are almost invariably intentional, but those of the latter type usually not. (Compare the feeling of nausea, which just is that feeling, with seeing a car's number plate, which cannot be seen other than as a series of meaningful letters and numbers.) There are, to be sure, exceptions to these generalisations. The qualia that normally go to construct the external world can occur in almost total isolation from meaning. This is the case after certain kinds of brain pathology, producing the agnosias, and more tellingly for at least some normal forms of musical experience. It is much harder for me to identify cases of the reverse dissociation -meaning without qualia. An anonymous reviewer of this commentary offers as an example the concept of the square root of -1. Sadly, I am too poor a mathematician to verify the assertion that this can be apprehended as a 'naked concept', without any visualisation of the symbol i or square root signs. My personal phenomenology tells me that, in the case of the meaningful qualia that make up the external world, the relevant experience is always integrated: qualia come saturated with meaningful interpretation. It is not possible in experience to separate these from one another. But we are perhaps here up against the limits of unaided introspection. It is of course possible conceptually to separate NSE, such as familiarity or rightness, from the qualia with which they are from time to time allied; and it is possible in principle to devise machinery that puts them together into the alliance. In the remainder of this commentary, I shall focus on a specific way in which this can be done. 2. The Comparator Model The 'comparator' model I shall present is largely my own, but it shares with several other contemporary models features relevant to the position set forth in SG. Mangan states that his 'overall concern is to link non-sensory experiences to non-conscious processes that evaluate context information in the modern sense' (p. 6). The aim of the comparator model is to account for the selection of the contents of consciousness. Thus, for Mangan, there are three elements: (1) contextual non-conscious processes, (2) NSE and (3) qualia. The comparator model explicitly links the first and third of these. But, as I shall now show, it also provides a natural account of NSE, and it does this without addition or modification. The comparator model was initially developed in order to account for a wide range of empirical data relating to the neuropsychology of anxiety (Gray, 1982a, b; Gray and McNaughton, 2000). Subsequently, it was employed in an account of the positive psychotic symptoms of acute schizophrenia (Gray et al., 1991; Gray, 1998), and this led in turn to an application to the selection of the contents of consciousness (Gray, 1995, plus commentaries and response). The essential computational function discharged by the comparator is to compare, nonconsciously and quite generally, information currently received via all thalamocortical sensory pathways (up to the level of neocortical analysis) with a prediction as to what that information should be. The prediction is based jointly upon previous stimulusstimulus and response-stimulus regularities (stored as memories) under circumstances similar to those operating now; the circumstances 'operating now' are themselves defined by the output of the comparator at the preceding comparison process. In addition, the comparator takes account of the subject's ongoing motor program, as what the world will be like in the next moment depends upon what the subject is doing in this one. These processes occur on a time base of the order of 100 ms from the termination of one process of comparison to termination of the next. The output from the comparison process selects a series of items in the neocortical description of the sensory world in the light of their novelty/familiarity and predictedness/unpredictedness (these concepts are not identical to one another, in just the same way that Mangan's familiarity and rightness are not identical concepts). The selection is biassed towards items which are novel, either because they occur despite not being expected or because they fail to occur despite being expected; and towards items which are goals or sub-goals for an ongoing motor program. The selected items are reactivated by feedback from the comparator system to those areas of the sensory neocortex (visual, auditory, somatosensory etc) in which they have just been non-consciously analysed. It is this reactivation by feedback from the comparator that selects these items for entry into consciousness. (I have no serious idea how such an 'entry into consciousness' actually occurs, but then neither does anyone else; this is the nub of the Hard Problem. Also, this brief account, based as it is upon my 1995 paper, needs supplementation to account for the fact that the items towards which conscious experience is biased unpredicted events and predicted goals fit into a much more extensive framework making up the constructed external world; I deal with this in a