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Jerry Fodor has consistently cited the persistence of illusions–-especially the Müller-Lyer illusion–-as a principal form of evidence for the informational encapsulation of modular input systems. Fodor proposed that these modules’ stereotypical deliverances about how the world appears could serve as a theory-neutral observational foundation for (scientific) knowledge. For a variety of reasons Fodor rejected Paul Churchland's putative counter-examples to these mental modules’ cognitive impenetrability. Fodor's discussions suggest that demonstrating modules’ cognitive penetrability would hinge on showing that because subjects either (a) acquire some explicit theory or (b) gain wider perceptual experience, they would, in the synchronic case, very quickly cease to experience the illusion or, at any rate, experience a mitigated version of it. Diachronic penetration, by contrast, would involve processes that deliver one of these outcomes over a decidedly longer period. Marshall Segall, Donald Campbell, and Melville Herskovits’ (1966) research across seventeen cultures shows that culturally influenced differences in visual experience during the first two decades of life substantially affect how people experience the Müller-Lyer stimuli. In some of the societies most people were virtually immune to the illusion. Such findings call Fodor's showcase evidence for the cognitive impenetrability of the visual input system into question and, thereby, threaten to block the path to the theory-neutral, observational consensus that he scouts.
Acknowledgements
We wish to express our gratitude to two anonymous referees and to Cees van Leeuwen for their helpful comments on an earlier version of this paper.
Notes
Notes
[1] So, e.g., Daniel Dennett's Consciousness Explained (1991) includes an appendix for scientists as well as one for philosophers.
[2] See, e.g., papers citing empirical findings that seem to pose problems for Dennett's (1991) proposals about the character of consciousness such as Churchland and Ramachandran (1993 and McCauley (1993).
[3] Although this paper and the subsequent exchange with Paul Churchland that we discuss appeared in various issues of Philosophy of Science, we shall cite the page numbers for passages from these various papers in what we presume are more readily available versions in Fodor's A Theory of Content and Other Essays (1990) and in Churchland's A Neurocomputational Perspective (1989).
[4] Thus it is not too surprising that his pioneering attention to mental modules’ specifications notwithstanding, Fodor (2000) has proven unsympathetic to the recent proliferation of modular analyses. To him it seems modularity run amok.
[5] It is important to note, however, that Fodorian modules can have access to information other than that provided by their inputs. Fodor allows that input systems may contain information about their proprietary domain from the outset and that top-down processing within a module on the basis of such information can occur (1983, pp. 76–77).
[6] See, e.g., the brief discussion in the next section concerning (Churchland's citation of) the famous studies with inverting lenses.
[7] See, e.g., the brief discussion in the next section concerning relevant research by ecological realists inspired by Gibson's approach to perception.
[8] Again, see the brief discussion of the inverting lens experiments in the next section.
[9] One way to handle this apparent impasse might be to note that Fodor and Churchland's comments invoke items (viz., descriptions as opposed to the semantic properties of expressions) at different analytical grains. (Thanks to Charles Nussbaum for bringing this point to our attention.)
[10] In we listed the locations and countries given by Segall et al. (1966), and have not updated the names of the countries.
[11] Wapner and Werner (1957) used stimuli that differed slightly from those Segall et al. (1966) used, and the PSE values indicate a stronger effect.
[12] Segall et al. (1966, ch. 7) discuss how variations in the details of the Müller-Lyer stimuli influence the magnitude of the illusory effect. The modifications in question are not a problem for interpreting the results, because exactly the same stimuli were used in every society, including Evanston.
[13] As we have seen, though, Churchland insists that no one ever meant to suggest that this illusion or any others were synchronically penetrable.