Abstract
Is vision informationally encapsulated from cognition or is it cognitively penetrated? I shall argue that intentions penetrate vision in the experience of visual spatial constancy: the world appears to be spatially stable despite our frequent eye movements. I explicate the nature of this experience and critically examine and extend current neurobiological accounts of spatial constancy, emphasizing the central role of motor signals in computing such constancy. I then provide a stringent condition for failure of informational encapsulation that emphasizes a computational condition for cognitive penetration: cognition must serve as an informational resource for visual computation. This requires proposals regarding semantic information transfer, a crucial issue in any model of informational encapsulation. I then argue that intention provides an informational resource for computation of visual spatial constancy. Hence, intention penetrates vision.
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Notes
I shall tend to use the broader “corollary discharge”. Proprioception provides another useful signal, but it is judged to be too slow for spatial constancy mechanisms.
Fodor provided other criteria for modularity, and in many places offers weaker formulations of both modularity and informational encapsulation. However, the statements just noted are explicit and occur both in the 1983 and 2001 books. This clarity will aid discussion in what follows. A referee helpfully emphasizes to me that Fodor has other motivations supporting encapsulation, such as aiding the speed of computations or the enhancing the objectivity of perceptual representations.
On terminology: “Informational encapsulation” is understood as a relation between X and Y and thus, it is possible for X to be encapsulated in relation to Y but not to Z (cf. Fodor 1983, p. 69). I shall generally speak of X as encapsulated relative to Y or, when encapsulation fails, X as penetrated by Y. Correlatively, we have to relativize modularity: X can be modular relative to Y but not to Z.
Cf. Austen’s Clark’s (Clark 1996, p. 480) notion of the visual field as “the field of view at time t […], the mereological sum—the scattered totality—of physical phenomena seen at time t. The field of view is a large three dimensional physical phenomenon”.
It is worth emphasizing the Bruce Bridgeman has argued (1991) that in fact, the eye is stable during the eye press, due to compensating oculomotor response when we push on the eye.
This is a plausible necessary condition on neurobiological explanations of consciousness. Whether it is sufficient is, of course, very controversial.
Cf. Peacocke (1992) on scenario content. The following discussion simplifies matters by discussing only two-dimensional representations and ignores the third dimension, distance. This does not affect the argument.
Milner and Goodale’s (1995) account of the human cortical visual streams suggests that dorsal stream representations are unconscious while the Hierarchical theory implies that the dorsal stream contributes to consciousness. There is at least one reported lesion likely restricted to the dorsal stream (visual area MST) affecting spatial constancy (Haarmeier et al. 1997): when the patient follows a moving object only by moving the eye, the background that normally looks spatially constant appears to him to move.
I leave open whether Macpherson’s indirect mechanism satisfies the Computation Condition. My task is to explicate that condition.
A referee has pointed out to me out that the original discussion of encapsulation concerned visual systems not visual experiences. There has been a shift back and forth in recent discussion. (1–3) and FIC can be restated to emphasize systems rather than experiences. For example, the crucial Computation Condition can be written: The influence of Y in the visual system’s computations outputting representation p is intelligible due to those visual computations using information in Y in its computation.
Milner and Goodale (1995) have argued that the dorsal cortical visual stream directly controls visually-guided movement.
A referee notes a likely rejoinder: intentions are proprietary inputs to the motor system that get the process up and running, but play no role after initiation. That intentions are persisting states rather than discrete events suggests that they don’t serve the role of providing an input to the motor system as opposed to an informational store (akin to memory) that can be drawn upon once motor processing is triggered. In contrast, visual stimulation at the retina is an event that provides an input triggering visual processing, but intentions do not function in that way. They are not triggers for but constraints on processing. Moreover, on current motor control models, the intended state, or motor representations based on it, is constantly reinvoked during motor processing in comparator mechanisms: the motor system makes a prediction from corollary discharge based on the initial motor command, compares this with the intended state, and then issues new motor commands to correct any error. This corrective command is again compared with the intended state, generating further corrections and so on until the correct movement is completed. So, information from intention is recurrently used in motor computations. The central issue is to show that the corollary discharge signal does carry information from intention to the visual system. This is the task of the next section.
I want to emphasize semantic information versus the mathematical notion of information in Shannon information theory. As Shannon emphasized, the issue in his theory is not in the first instance semantic information but mutual information (measured in bits). The Computation Condition concerns semantic information (content).
Cf. Dretske’s (1981, p. 57) Xerox Principle: “If A carries the information that B, and B carries the information that C, then A carries the information that C”.
One point to note: clause (iii) in the antecedent needs a bit of finessing to allow that r can be a degraded version of p and q a degraded version of r, with each subsequent content preserving a part (but lesser part) of the original command.
One might think that the relevant motor representations specify muscle contractions. There is, however, also evidence of motor representations of more abstract actions as well. Consider the controversial mirror neurons that are bimodal: they fire when the primate perceives as certain kind of action and also executes that action (Rizzolatti et al. 2001).
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Acknowledgments
I am grateful to Fiona Macpherson for hosting a conference on cognitive penetration where these ideas were initially put forward. Fiona and Dustin Stokes pushed me further at the conference and also through their writings on this topic. I am grateful also for conversations with participants at the conference. I thank an anonymous referee for the journal who helpfully steered this paper in a more readable and focused direction. Various scientists also helped: Bruce Bridgeman, whose work on spatial constancy is central, answered several of my questions over email and later, members of the Brain Group at CMU gave helpful feedback, keeping my appeal to neuroscience in line. I’m especially grateful to Dan Burnston, Jonathan Cohen, Carl Olson, Carol Colby, and Nathan Hall for their input.
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Wu, W. Visual spatial constancy and modularity: Does intention penetrate vision?. Philos Stud 165, 647–669 (2013). https://doi.org/10.1007/s11098-012-9971-y
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DOI: https://doi.org/10.1007/s11098-012-9971-y