Abstract
The study of the contrast between fundamental aspects of spatial and temporal awareness offers a good opportunity to bring to light the relation between philosophical and scientific theories of consciousness. In this paper we critically examine important work by Rick Grush on spatial and temporal experience, and we show that while there is a valid claim for the relevant neuroscientific model to be one that supports Gareth Evans's stance on "behavioral space", there is not at present any scientific model that offers comparable support for philosophical theories of temporal experience, despite some claims by Grush that might suggest the contrary. Moreover, we argue that careful attention to the spatial case allows us to locate the point at which even relatively successful cases of neuroscientific modeling and explanation are left wanting when their aim is to show that phenomenal features of experience are a function of the representational structures produced by our neural information-processing machinery: an aim widely shared by the predominant programmatic stance in current neuroscience research.
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Notes
For the purposes of this paper, it will not be necessary to be more specific as to what exactly the center is, in relation to which objects are located egocentrically. Thus, the word "egocentric" is here meant to have a generic meaning covering the more specific eye-centered, head-centered, and torso-centered frames of reference (or combinations thereof) which appear in the neuroscientific literature.
In "Molyneux's Question". Evans also addressed the issue of spatial experience in his posthumous book The Varieties of Reference. For present purposes, it will suffice to refer to the paper.
Some celebrated neurophysiological findings concerning certain deficits and their relations to the so-called ventral and dorsal pathways in the brain (Milner and Goodale 1995/2006) have been used to question the claim that visual experience represents spatial properties of objects around the perceiver using an egocentric frame of reference. Those findings have also cast doubt on the claim that there is a constitutive link between the spatial contents of the perceiver’s visual experience and that person’s bodily actions. While we insist that nothing relevant hinges on the actual truth of the theories and models that are presented or mentioned in the course of arguing for the claims of this paper, we also realize that the discussion is likely to be of more interest if such theories and models are not known to be obsolete. Fortunately, we can refer here to Briscoe (2009), where such questioning and doubt is mostly dispelled. The most damaging criticism might seem to come from maintaining the “two visual systems—ventral/dorsal—hypothesis”, according to which visually guided action uses an egocentric frame, while conscious visual awareness uses an allocentric frame; which of course is contrary to Evans’s theoretical stance. Briscoe argues—convincingly, we believe—that there are alternative hypotheses, compatible with Evans’s stance, which give a better explanation of the neurophysiological findings (pp. 441–444). Finally, Briscoe disputes (also successfully, to our mind) the general claim that action requires a different “computational format” from that used in visual experience (compare Clark 2001).
This description follows the explanation in Heil (1987), as does Grush's. There are more modern versions, but they are not relevant for present purposes.
His motivation for preferring this unusual term to the much more frequently used term "content" to mark the difference between the two kinds of users is that the latter term is associated with the idea of having information about something, and, as we have seen, the having of information is common to both groups of subjects. In contrast, he says, "'phenomenology' and its various cognates are very loaded" and—he adds—he does not "want to get mired in an argument as to whether there are 'spatial' qualia, for example" (Grush 2007, p. 390).
Additional support for a claim about these differences may emerge from considering different ways in which such subjects could imagine an obstacle or an opening.
For a particularly clear exposition of the basis function model, using minimal mathematical apparatus, see Grush (2009, pp. 331–337). The exposition that follows is limited to the visual case.
The description of the model in which the basis functions are Gaussian-sigmoid functions is called "Pouget's model" by Grush (it corresponds to the original work by Pouget and collaborators). He uses "basis function model" for the generalized case where the functions do not need to be exactly of that form. For our purposes, the terminological distinction is unnecessary, and the model described can simply be taken as paradigmatic of the generalized category, characterized by BFM1 and BFM2.
Although Pouget and his collaborators are very clear that they mean the basis function model to apply to audition as well, they do not provide much detail concerning the application of the model to this case. In fact, Pouget et al. (2002) is devoted to the problem of multisensory integration of spatial representations. Given that in each of the three characters that intervene in the comparison of spatial navigation performance (to wit, normal sighted user, highly proficient user of the sonic guide and unskilled user) only one modality—either visual or auditory—is relevant, the issue of multisensory integration does not need to be brought up here.
The connection between the basis function model and Evans’s views on egocentric location has been a major topic in Grush’s writings. Here, we closely follow the discussion in Grush (2007), especially pp. 394–397. For the sake of brevity, we skip certain details, or merely leave them implicit. The most important of these may be Grush’s distinction between two kinds of dispositions, which is not found explicitly in Evans (see op. cit., p. 393). Furthermore, as we discuss in Sect. 1 above, in his formulation (p. 397), Grush uses the term "purport", while here we have maintained Evans's "content". If we bear in mind that "content" does not simply mean having information about, we see no good reason to use Grush’s unfamiliar term here. Finally, Grush says that the convergence at stake is "nearly unprecedented", which is not relevant for present purposes.
The notion of physical (e.g., neural) or information-processing machinery underpinning a property, relation, structure or process described at the personal level at which philosophical and folk-psychological hypotheses and theories operate is articulated in Davies (2000). In Fernández-Prat (2008) one of us developed Davies's position to an extent. In the cases analyzed by Davies, there are inferences "of a relatively a priori character" from the personal to the subpersonal level. In fact, in the present case, it could be argued that such inferences lead from Evans's dispositional account to the existence of some sort of information-processing structure that locates objects in such a way that their egocentric location makes the subject ready for immediate action, instead of giving their location by spatial coordinates. Naturally, the actual existence of neural structures which implement such information-processing models is entirely a matter of empirical investigation. In Davies's analysis, when the underpinning relation can be established, the information-process models and the hypothesis about their physical implementations confer some sort of support on the personal level theories. We will thus say that the scientific models or theories underwrite the personal level analysis. It is important here that such a relation falls short of a reductive explanatory relation. The difference will become crucial in the last section.
Geldard and Sherrick (1972) reports the original study of this phenomenon.
There has been neurobiological evidence of the existence of estimation in the brain since Duhamel, Colby and Goldberg found that the work of neurons in the parietal cortex of the monkey can lead to the anticipation of internal stimulation as a function of the eye's saccade efference copies (see Duhamel et al. 1992). Inspiration for Grush's work came partly from such work, which would also show that emulation is also neurobiologically possible (see Grush 2009, pp. 324–325). For his explanation of temporal illusion based on models that implement the emulative hypothesis see, especially, Grush (2005). Grush frequently talks of such models as "neuroscientific models", even if they are properly abstract models for which very little neurophysiological detail is given (compare Grush 2006, p. 446). The use of the adjective is somewhat more adequate in the case of a model that involves a synthesis with the basis function model, such as that to be mentioned below. In any case, we will follow Grush here in his use of the adjective "neuroscientific" in this somewhat relaxed sense.
We will see presently that Grush has modified his position, and just how. We think, however, that it is still instructive to study his original stance in order to understand better what it is that should be taken into account in assessing a theory of temporal experience.
We will use the Grush's term "underwrite" in what follows, taking it as an informal version of Davies "underpin", which was explained in fn. 11. As advanced there, we also use "underwrite" for the relation between two theories or models when one describes the information processing—or the neural implementation thereof—that underpins or underwrites the properties, dispositions or processes described by theories at the personal level.
Husserl's analysis, of which the tripartite structure is only a part, is the best known version of the "retentionalist" approach to temporal consciousness (see Dainton 2017a, §6). The negative conclusion eventually to be reached here may well apply not only to other types of analysis within the same group, but also to the extensionalist approach, widely regarded as its main rival. See fn. 18 for more on this.
We are indebted to one of our anonymous referees for pressing us on this point.
Grush (2006) criticizes in detail proposals by van Gelder, Varela and Lloyd concerning how to "bridge" the Husserlian analysis of the temporal aspects of experience and computational neuroscience. The gist of Grush's criticism is that such proposals simply assume that there is a direct connection between the vehicles of temporal representation and their contents, "a matter of isomorphism or iconicity or any other similarly simple coding scheme" (p. 441). We fully concur with Grush here. To the best of our knowledge, there have not been comparable attempts to construct a bridge between a personal-level analysis of the temporal aspects of perceptual experience and a subpersonal, information-processing approach, taking either retentionalist approaches other than Husserl's or extensionalist analysis as a basis. Concerning the latter analysis, Dainton, one of the main advocates of extensionalism, in his recent work Dainton (2017a; b) does not give any indication of a "bridge" between this view and information-processing models, neural or otherwise. The so-called "Overlap Model"—the version of extensionalism Dainton favors—neither is, nor hints at an information-processing model. Dainton roughly makes the point that one cannot infer the phenomenal properties of temporal experience from neural information-processing models of the data structures of the brain. So, even if the latter exhibited retentional features, this would be no threat to extensionalist views of the former. We fully agree with this general point but of course nothing about information-processing models underwriting, or in any way supporting, extensionalist views can be inferred from it. Furthermore, in the only case known to us where some progress in bridging a philosophical theory with neuroscientific theorizing in the temporal case may be claimed, the philosophical theory is explicitly meant to question the widespread acceptance of a basic division of theories of time experience into retentionalist and extensionalist (see Lee 2014).
The claim that experience—or a certain type of experience—has an A-ish character, or that it has a B-ish character, can be articulated in a number of ways. Grush (2016) is content with a rough, intuitive rendering, and we follow that here. For insightful recent representatives of the two views see, respectively, Crowther and Soteriou (2017), and Hoerl (2009).
On pp. 8–10, Grush not only claims that for very short intervals (less than 200 ms) "[n]o point … is singled out as a now bracketed by past and future" (p. 8), but he further argues that what is needed in order to coordinate perception and action is not a representation of a “now” instant, but just what B-ish content delivers, be it simultaneity or temporal precedence: "what is important is that my hand gets to the location below the vase earlier than (and maybe a specific temporal amount earlier than) the vase itself, so that I can catch it before it breaks on the floor" (p. 10).
And even here, we should keep in mind the fact that, in Grush's sense, what is "retained" can undergo drastic modification, in contrast to the Husserlian sense of the term (see Grush 2006, p. 448).
This more ambitious aim seems to be a general one throughout Grush's work on information-processing models of consciousness. Grush does not explicitly differentiate between a less ambitious aim and a more ambitious one; indeed, he may reject the difference. In any case, the fact that it is unmarked in his writings helps its being overlooked.
To illustrate, a systematic approach should take into account the "lining up particular phenomena in a continuous series based on the order of their similarities: for instance, ordering a series of greys from white to black where the order follows their 'given' and 'natural' affinity of gradation"; or the way in which, "by looking at several reds … the universal that they have in common [is recognized] on the basis of their likeness"; or also the recognition "that every variant of red is in conflict with every variant of green" (Albertazzi 2013, p. 4).
We thus subscribe here to the other element of Davies's (2000) stance between the subpersonal and the personal: interaction without reduction.
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Acknowledgements
Thanks to Naomi Eilan and Hemdat Lerman for comments on a first version of the paper and the anonymous reviewers from Synthese. We also thank María José Frápolli and Víctor Martín Verdejo for comments on material of the last section presented at the IX Conference of the Spanish Society for Logic, Methodology and Philosophy of Science (Madrid, 15-11-2018). This work was supported by the Ministerio de Economía, Industria y Competitividad, Gobierno de España (FFI2015-63892-P) and the Ministerio de Ciencia e Innovación (Government of Spain) and the European Union under Grant PID2019-105728GB-100 (MINECO/FEDER, EU).
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Fernández-Prat, O., Quesada, D. Philosophy and cognitive science on spatial and temporal experience. Synthese 199, 9089–9108 (2021). https://doi.org/10.1007/s11229-021-03195-4
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DOI: https://doi.org/10.1007/s11229-021-03195-4