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ABSTRACT
According to Milner and Goodale’s dual visual systems (DVS) theory, a division obtains between visual consciousness and motor action, in that the visual system producing conscious vision (the ventral stream) is distinct from the one guiding action (the dorsal stream). That there would be this division is often taken (by Andy Clark and others) to undermine the folk view on how consciousness and action relate. However, even if this division obtains, this leaves open the possibility that conscious ventral information is often transmitted to the unconscious dorsal stream and then used to guide action, a possibility seeming to preserve a significant role for consciousness in action. This article assesses this possibility. In course of doing so, we will review those arguments recently having been made against the DVS view on how visual consciousness and action relate (ones due to, e.g., Briscoe and Schwenkler, or Schenk and McIntosh). What we will find is that, if we properly analyze the data upon which these arguments are based, we are still left with the impression that the DVS view is largely correct; i.e., it is only rarely that visual experience guides action.
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Notes
1. It is interesting to note that the “fine-grained nature” of visual experience that many of these researchers assume is belied to some degree by the poor acuity that we have in peripheral vision, a result of the diminishing numbers of photopic receptors found there.
2. For a review of the debates concerning DVS and the Libet data, and a discussion of how DVS and the Libet data both suggest a “local” form of epiphenomenalism, see Kozuch, Citation2020.
3. For textual evidence for these researchers supporting the formulation appearing just below, see Kozuch, 2015a, esp. 580–81.
4. For textual evidence for this claim, and for an argument that the folk view includes a Directness Clause, see Kozuch, 2015, esp. 580–81.
5. A detailed argument for the idea that this dissociation would falsify Directness, along with an analysis of Directness itself, is found in Kozuch, Citation2015, pp. 580–82. It should be noted, however, that whether this is the case is orthogonal to the aim of this article, which is to evaluate Typicality.
6. Arguments for dorsal representations not being conscious are found in Brogaard, Citation2011a, Citation2011b; see, esp. Kozuch, Citation2015a; one is also found below, in Sect. 6. The strongest argument to the contrary is probably found in Wu, Citation2014a.
7. I am considering representations to be mental states whose function is to indicate the presence of some property (e.g., redness or roundness), and contents to be whatever specific property a representation has as its function to indicate (e.g., redness or roundness; Dretske, Citation1988, Chap. 3; Tye, Citation1995, Chapter 4). Important here is the idea that ontologically distinct representations might have identical contents, as this makes it possible that visual experience might indirectly guide actions (see next footnote).
8. To clarify: The idea here is that there is an instantiation of content C in the conscious ventral stream (call this particular instance “C-v”), one which then causes an instantiation of content C in the dorsal stream (call this instance “C-d”), where C-d is then (directly) used to guide action. So, the contents of the ventral and dorsal streams would be of type-, but not token-, identity. Given this, we can distinguish Typicality from Directness by saying that the former requires just that that the contents driving action and those found in visual experience be type-identical, whereas the latter requires token-identity.
9. But even if it were not part of the folk view, it is still a component of an oft-advocated thesis, i.e., EBC (e.g., Mole, Citation2009; Peacocke, Citation1992; Wallhagen, Citation2007).
10. It is effective, however, against Directness; see Kozuch Citation2015a, esp. pp. 555–8.
11. Thus it turns out that establishing a double dissociation between visual consciousness and action is not necessary (or even useful) for casting doubt on Typicality; this seems to be an interesting way in which the dialectic shifts once the focus is not on evaluating EBC as a whole, but rather just Typicality.
12. Another line of argument that might be used against EBC is to say that conscious ventral representations cannot be used to guide action, since they are “allocentric” (object-centered) representations, whereas what is needed for guiding actions are “egocentric” (viewer-centered) representations (Milner & Goodale, Citation2006, Chapter 4). However, recent developments in the debate obviate the need for a pro-EBC response here, since DVS theorists recently clarified their position as being one in which it is allowed that ventral processing will use both allocentric and egocentric representations (Foley et al., Citation2015).
13. That this is the case quickly becomes evident if one reviews the formal arguments against EBC that Mole and Wu construct. For example, Wu’s argument against EBC uses premises saying that “the visual representation controlling reach represents the disc as size x,” and that the “conscious visual representation controlling report represents the disc as size y, where y does not equal x” (2013:7–8); similarly, Mole construes the argument against EBC to be one claiming that “the system controlling reaching represents the discs as different sizes,” while “it is not the case that the system responsible for conscious awareness represents the discs as different sizes” (2009:997). Note that, in both cases, there is no claim that the representation controlling reaching is veridical.
14. Remember that type-identity is enough for Typicality to be supported, with token-identity being a more appropriate standard in the case of the Directness Clause (see 1.1, esp. fn. 8).
15. For instance, in the Aglioti et al. study, experimenters had subjects indicate how large they perceived a disk to be by using the distance between their thumb and forefinger.
16. Important to note is that this is not because of some kind of “practice effect” that the right-handed effect occurs: Both right- and left-handers express the effect in their right hand.
17. One does not involve visual illusions (Goodale & Milner, Citation2004, p. 92), and the other does not provide instances of an action being fully affected by visual illusions (Carey, Citation2001).
18. Her dorsal lesion being relatively mild can be inferred from her intraparietal sulcus showing normal levels of activity when performing actions.
19. While V3A and V7 are often considered dorsal areas, they provide input to ventral areas as well (Felleman & van Essen, Citation1991).
20. It was recently argued that we cannot know that dorsal representations lack consciousness, since the reports used to indicate this are just as easily explained by dorsal representations simply being inaccessible (Kozuch, Citation2015b; Wu, Citation2020). Unfortunately, addressing “skeptical”-style objections like these go beyond the scope of this article. It can be said, however, that such arguments are applicable to not just the dorsal stream, but to any brain area whose content we suspect might be inaccessible (V1, the thalamus, etc.). This is to say: Such arguments do not uniquely target what I am arguing for her, but rather all arguments aimed at showing a brain area is non-conscious.
21. One might respond to these objections by identifying consciousness with attention (Prinz, Citation2012), but something that we saw above is that this is contentious (see 3.2.2), even more so because crucial support for this identity comes from hemispatial neglect itself (Prinz, Citation2012, Chapter 1).
22. The ventral stream is hypothesized to do things such as provide estimates of the object’s size, weight, distance, and roughness, and to possibly play a role in activating whatever motor coding might already be associated with the object (p. 151).
23. McIntosh and Lashley fabricated oversize versions of familiar objects (e.g., matchboxes), something that caused subjects to use grip apertures too small for the object.
24. In this case, cues involving variance in speed.
25. Something that might be thought to be more promising here would be the idea that conscious ventral representations contribute to types of action that are not yet skilled or performed with automaticity (e.g., Ferretti, Citation2021b), an idea that is in kinship with Briscoe and Schwenkler’s Control Thesis, which holds that conscious ventral information is required for actions that are “complicated, delicate, or unfamiliar” (2015:1438).
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Benjamin Kozuch
Benjamin Kozuch received his doctorate in philosophy from the University of Arizona in 2013, and is now an Associate Professor at the University of Alabama. Much of his research involves using neuroscientific data to evaluate philosophical theories of consciousness, such as those hypothesizing higher-order cognition or attention to be essential for consciousness. He also conducts research regarding visual illusions, and the nature of pain experiences.