I construe the debate about cognitive penetration (CP) in the following way: are there causal relations between cognition and perception, such that the processing of the later is systematically sensitive to the content of the former? Framing the debate in this way imparts some pragmatic commitments. We need to make clear what distinguishes perception from cognition, and what resources each brings to the table. And we need to clarify what kind of causal relationship exists, and whether it is strong enough to be considered “systematic.”
I think that current debates about cognitive penetration have failed to be clear enough on these vital pragmatic considerations, and have become muddled as a result. My view is that once we understand perception and cognition aright, we should recognize as an empirical fact that there are causal relationships between them—however, these relations are general, diffuse, and probabilistic, rather than specific, targeted, and determinate. Many supporters of CP certainly seem to have the latter kind of relationship in mind, and it is not clear that the former kind supports the consequences for epistemology and cognitive architecture that these supporters suppose. My primary goal, then, rather than denying cognitive penetration per se, is to de-fuse it (Burnston, 2016, 2017a, in prep).
The view of perception, I believe, that informs most debates about CP, is that perception consists in a set of strictly bottom-up, mutually encapsulated feature detectors, perhaps along with some basic mechanisms for binding these features into distinct “proto” objects (Clark, 2004). Anything categorical, anything that involves inter-featural (to say nothing of intermodal) association, anything that involves top-down influence, or assumptions about the nature of the world, and anything that is learned or involves memory, must strictly be due to cognition.
To those of this theoretical persuasion, evidence for effects of some subset of these types in perception is prima facie evidence for CP. Arguments in favor of CP move from the supposed presence of these effects, along with arguments that they are not due to either pre-perceptual attentional shifts or post-perceptual judgments, to the conclusion that CP occurs.
On reflection, however, this is a somewhat odd, or at least non-obvious move. We start out from a presupposition that perception cannot involve X. Then we observe evidence that perception does in fact involve X. In response, instead of modifying our view of perception, we insist that only some other faculty, like cognition, must intervene and do for perception that for which it, on its own, lacks. My arguments in this debate are meant to undermine this kind of intuition by showing that, given a better understanding of perception, not only is positing CP not required, it is also (in its stronger forms anyway) simply unlikely.
Consider the following example, the Cornsweet illusion (also called the Craik‑O’Brien-Cornsweet illusion).
In this kind of stimulus, subjects almost universally perceive the patch on the left as darker than the patch on the right, despite the fact that they have the exact same luminance, aside from the dark-to-light gradient on the left of the center line (the “Cornsweet edge”) and the light-to-dark gradient on the right. The standard view of the illusion in perceptual science is that perception assumes that the object is extended towards the perceiver in depth, with light coming from the left, such that the panel on the left would be more brightly illuminated, and the patch on the right more dimly illuminated. Thus, in order for the left panel to produce the same luminance value at the retina as the right panel, it must in fact be darker, and the visual system represents it so: such effects are the result of “an extraordinarily powerful strategy of vision” (Purves, Shimpi, & Lotto, 1999, p. 8549).
Why construe the strategy as visual? There are a number of related considerations. First, the phenomenon involves fine-grained associations between particular features (luminance, discontinuity, and contrast, in particular configurations) that vary systematically and continuously with the amount of evidence for the interpretation. If one increases the depth-interpretation by foreshortening or “bowing” the figure, the effect is enhanced, and with further modulation one can get quite pronounced effects. It is unclear at best when we would have come by such fine-grained beliefs about these stimuli. Moreover, the effects are mandatory, and operate insensitively to changes in our occurrent beliefs. Fodor is (still) right, in my view, that this kind of manditoriness supports a perceptual reading.
According to Jonathan Cohen and me (Burnston & Cohen, 2012, 2015), current perceptual science reveals effects like this to be the norm, at all levels of perception. If this “integrative” view of perception is true, then embodying assumptions in complex associations is no evidence for CP—in fact it is part-and-parcel of what perception does.
What about categorical perception? Consider the following example from Gureckis and Goldstone (2008), of what is commonly referred to as a morphspace.
According to current views (Gauthier & Tarr, 2016; Goldstone & Hendrickson, 2010), categorical perception involves higher-order associations between correlated low-level features. So, recognizing a particular category of faces (for instance, an individual’s face, a gender, or a race) involves being able to notice correlations between a number of low-level facial features such as lightness, nose or eye shape, etc., as well as their spatial configurations (e.g., the distance between the eyes or between the nose and the upper lip). A wide range of perceptual categories have been shown to operate similarly.
Interestingly, forming a category can morph these spaces, to group exemplars together along the relevant dimensions. In Gureckis and Goldstone’s example, once subjects learn to discriminate A from B faces (defined by the arbitrary center line), novel examples of A faces will be judged to be more alike each other along diagnostic dimension A than they were prior to learning. Despite these effects being categorical, I suggest that they are strongly analogous to the cases above—they involve featural associations that are fine-grained (a dimension is “morphed” a particular amount during the course of learning) and mandatory (it is hard not to see, e.g., your brother’s face as your brother) in a similar way to those above. Moreover, subjects are often simply bad at describing their perceptual categories. In studies such as Gureckis and Goldstone’s, subjects have trouble saying much about the dimensional associations that inform their percepts. As such, and given the resources of the integrative view, a way is opened to seeing these categorical effects as occurring within perception.
If being associative, assumption-involving, or categorical doesn’t distinguish a perceptual from a cognitive representation, what does? While there are issues cashing out the distinction in detail, I suggest that the best way to mark the perception/cognition distinction is in terms of representational form. Cognitive representations are discrete and language-like, while perceptual representations represent structural dimensions of their referents—these might include shape dimensions (tilt, slant, orientation, curvature, etc.), the dimensions that define the phenomenal color space, or higher-order dimensions such as the ones in the face case above. The form distinction captures the kinds of considerations I’ve advanced here, as well as being compatible with wide range of related ways of drawing the distinction in philosophy and cognitive science.
With these distinctions in place, we can talk about the kinds of cases that proponents of CP take as evidence. On Macpherson’s example, Delk and Fillenbaum’s studies purporting to show that “heart” shapes are perceived as a more saturated red than non-heart shapes. Let’s put aside for a moment the prevalent methodological critiques of these kinds of studies (Firestone & Scholl, 2016). Even so, there is no reason to read the effect as one of cognitive penetration. Simply the belief “hearts are red,” according to the form distinction, does not represent the structural properties of the color space, and thus has no resources to inform perception to modify itself any particular way. Of course, one might posit a more specific belief—say, that this particular heart is a particular shade of red—but this belief would have to be based on perceptual evidence about the stimulus. If perception couldn’t represent this stimulus as this shade on its own, we wouldn’t come by the belief. Moreover, on the integrative view this is the kind of thing perception does anyway. Hence, there is no reason to see the percept as being the result of cognitive intervention.
In categorical contexts, one strong motivation for cognitive penetration is the idea that perceptual categories are learned, and often this learning is informed by prior beliefs and instructions (Churchland, 1988; Siegel, 2013; Stokes, 2014). There are problems with these views, however, both empirical and conceptual. The empirical problem is that learning can occur without any cognitive influence whatsoever. Perceivers can become attuned to diagnostic dimensions for entirely novel categories simply by viewing exemplars (Folstein, Gauthier, & Palmeri, 2010). Here, subjects have no prior beliefs or instructions for how to perceive the stimulus, but perceptual learning occurs anyway. In many cases, however, even when beliefs are employed in learning a category, it’s obvious that the belief does not encode any content that is useful for informing the specific percept. In Goldstone and Gureckis’ case above, subjects were shown exemplar faces and told “this is an A” or “this is a B”. But this indexical belief does not describe anything about the category they actually learn.
One might expect that more detailed instructions or prior beliefs can inform more detailed categories—for instance Siegel’s suggestion that novitiate arborists be told to look at the shape of leaves in order to distinguish (say) pines from birches. However, this runs directly into the conceptual problem. Suppose that pine leaves are pointy while birch leaves are broad. Learners already know what pointy and broad things look like. If these beliefs are all that’s required, then subjects don’t need to learn anything perceptually in order to make the discrimination. However, if the beliefs are not sufficient to make the discrimination—either because it is a very fine-grained discrimination of shape, or because pine versus birch perceptions in fact require the kind of higher-order dimensional structure discussed above—then their content does not describe what perception learns when subjects do learn to make the distinction perceptually. In either case, there is a gap between the content of the belief and the content of the learned perception—a gap that is supported by studies of perceptual learning and expertise (for further discussion, see Burnston, 2017a, in prep). So, while beliefs might be important causal precursors to perceptual learning, they do not penetrate the learning process.
So, the situation is this: we have seen that, on the integrative view and the form distinction, cognition does not have the resources to determine the kind of perceptual effects that are of interest in debates about CP. In both synchronic and diachronic cases, perception can do much of the heavy lifting itself, thus rendering CP unnecessary to explain the effects. A final advantage of this viewpoint, especially the form distinction, is that it brings particular forms of evidence to bear on the debate—particularly evidence about what happens when processing of lexical/amodal symbols does in fact interact with processing of modal ones. The details are too much to go through here, but I argue that the key to understanding the relationship between perception and cognition is to give up the notion that there are ever direct relationships between the tokening of a particular cognitive content and a specific perceptual outcome (Burnston, 2016, 2017b). Instead, I suggest that tokening a cognitive concept biases perception towards a wide range of possible outcomes. Here, rather than determinate casual relationships, we should expect highly probabilistic, highly general, and highly flexible interactions, where cognition does not force perception to act a certain way, but can shift the baseline probability that we’ll perceive something consistent with the cognitive content. This brings priming, attentional, and modulatory effects under a single rubric, but not one on which cognition tinkers with the internal workings of specific perceptual processes to determine how they work in a given instance. I thus call it the “external effect” view of the cognition-perception interface.
Now it is open to the defender of cognitive penetration to define this diffuse interaction as an instance of penetration—penetration is a theoretical term one may define as one likes. I think, however, that this notion is not what most cognitive penetration theorists have in mind, and it does not obviously carry any of the supposed consequences for modularity, theoretical neutrality, or the epistemic role of perception that proponents of CP assume (Burnston, 2017a; cf. Lyons, 2011). The kind of view I’ve offered captures, in the best available empirical and pragmatic way, the range of phenomena at issue, and does so very differently than standard discussions of penetration.
Burnston, D. C. (2016). Cognitive penetration and the cognition–perception interface. Synthese, 1–24. DOI: doi:10.1007/s11229-016‑1116‑y
Burnston, D. C. (2017a). Is aesthetic experience evidence for cognitive penetration? New Ideas in Psychology. DOI: https://doi.org/10.1016/j.newideapsych.2017.03.012
Burnston, D. C. (2017b). Interface problems in the explanation of action. Philosophical Explorations, 20 (2), 242–258. DOI: http://dx.doi.org/10.1080/13869795.2017.1312504
Burnston, D. C. (In preparation). There is no diachronic cognitive penetration.
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 Different theorists stress different properties. Macpherson (2012) stresses effects being categorical and associational, Nanay (2014) and Churchland (1988) their being top-down. Raftopoulos (2009) cites the role of memory in categorical effects and Stokes (2014) and Siegel (2013) the importance of learning in such contexts.
 This kind of reading of intra-perceptual processing is extremely common across a range of theorists and perspectives in perceptual psychology (e.g., Pylyshyn, 1999; Rock, 1983; Yuille & Kersten, 2006).
 This view also rejects the attempt to make these effects cognitive by defining them as tacit beliefs. The problem with tacit beliefs is that they simply dictate that anything corresponding to a category or inference must be cognitive, which is exactly what’s under discussion here. The move thus doesn’t add anything to the debate.
 This requires assuming a “specificity” condition on the content of a purported penetrating belief—namely that a candidate penetrator must have the content that perception learns to represent. I argue in more detail elsewhere that giving this condition up trivializes the penetration thesis (Burnston, in prep).