Welcome to the Brains Blog’s Symposium series on the Cognitive Science of Philosophy! The aim of the series is to examine the use of methods from the cognitive sciences to generate philosophical insight. Each symposium is comprised of two parts. In the target post, a practitioner describes their use of the method under discussion and explains why they find it philosophically fruitful. A commentator then responds to the target post and discusses the strengths and limitations of the method.
In this symposium, Jorge Morales makes the case for philosophers of perception conducting experiments of their own, with Jonathan Cohen providing commentary on Morales’ empirical work on perspectival shape.
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Philosophy of Perception in the Laboratory
Many arguments in the philosophy of mind hinge on capturing what experiences are like and what they are about. Philosophers’ main method to learn about the nature and contents of mental states has been to introspect them. Our capacity to introspect, however, is often unreliable. To avoid the muddy waters of introspection, philosophers of mind can take two (mutually non-exclusive) approaches to support the empirical claims in their arguments. After all, introspective reports are meant to reveal empirical truths about the mind. The first strategy is to get acquainted with the empirical literature with the goal of finding evidence that is relevant for their philosophical arguments. The second strategy is to run experiments meant to produce the desired evidence (Rose & Danks, 2013). In my research, I have followed both approaches, but here I will argue in favor of directly running philosophy-inspired experiments that take advantage of the full set of methods that psychological research has to offer. In particular, I will focus on testing questions in the philosophy of perception.
There is no doubt that the philosophy of mind has benefited immensely from considering findings from the empirical literature. Rather than trying to introspect what experiences are like, psychological evidence can be leveraged to populate premises with empirical content in philosophical arguments. Merely using available empirical findings, however, has an important limitation: its passive nature. All philosophers can do is hope that the questions they are interested in have been previously addressed. Psychology is a rich field, and there is a lot of relevant research that philosophers can use. However, at least in my experience with consciousness and perception research, it is often the case that there is only neighboring work relevant to the questions we philosophers ask. This might be in part because of the difficulty of studying subjectivity and phenomenology in the laboratory. But there are sociohistorical reasons too. Like any other field, psychology is often concerned with questions that stem from within psychology itself. This is not necessarily because psychologists do not care about philosophical questions about perception (some would, if they knew about them), but because research is to a large extent framework-dependent: some questions only come up while working within a particular tradition or theoretical framework. This entails that particular empirical questions that are important to philosophical debates about conscious experiences may not come up in psychology hallways at all. When this happens, both fields lose. Philosophers are limited to extrapolating results from nearby debates because their (empirical) questions are not being addressed, and psychologists miss the opportunity to test new hypotheses that are often part of a long and theoretically rich tradition. The value of philosophy for science is often laid out in terms of philosophy’s theoretical contributions when reflecting about science (Laplane et al., 2019; Thagard, 2009), but it can also feed questions directly into scientific research programs.
To overcome these limitations, philosophers of mind (and psychologists!) can embrace the strategy of designing and running philosophy-specific experiments themselves. We see this trend in Experimental Philosophy, where philosophers test people’s intuitions about different concepts in moral psychology, epistemology, and language. In psychology and neuroscience, we see significant philosophical influence in areas concerned with morality, modality, memory, imagination, and the neural correlates of consciousness. Surprisingly, however, this kind of direct involvement from philosophers in empirical research has been very limited when concerned with questions about perception. To emphasize, this is not to say that there are not lots of empirical research programs relevant to the philosophy of perception, or that some psychologists have found some inspiration in philosophical work. What seems to be lacking is an explicit effort to address problems that stem from the philosophy of perception with the full toolkit of experimental psychology.
In my research, I use vision science to directly study empirical aspects of philosophical questions about the contents of conscious experiences and what things look to us. I will next discuss a recent example where I used this approach, and then conclude with a reflection about the future of interdisciplinary work.
Look at the golden “coin” in the image below. What shape do you see?
Your answer bears on a centuries-old philosophical debate on the role of subjectivity in perception and on perspectival shapes in particular. At least since Locke and to this day, philosophers have quarreled about the best way to describe the contents of perceptual experiences—for example, of what a rotated “coin” looks like—without finding much consensus. Locke would have said that we only see a flat oval, variously shadowed, not a circle. It is by means of inference that “the judgment, by an habitual custom, alters the appearance [i.e. the oval] into their causes [i.e. the circular coin].” (Locke, 1975, II, ix, 8) Whereas other philosophers think that “the suggestion that pennies look elliptical when seen from most angles is simply not true—they look round” (Smith, 2002, p. 172) and they are “inclined to say it looks just plain circular, in a three-dimensional space—not elliptical at all, in any sense” (Schwitzgebel, 2006, p. 590). And yet others think that our visual experiences are better described by a “dual” character, such that perceptual experience reflects both the true distal properties of objects and their perspectival properties (Noë, 2004) So, which is it? Do we experience the world as it is “out there”? Do we experience the way the world is given to us in sensation and only later “infer” or “judge” what it truly is like? Or is it a mix of both?
Philosophers have arrived at these incompatible positions mostly by resorting to introspection (which sometimes can be reliable (Morales, Forthcoming), but not always), and in some recent cases, by relying on available empirical evidence too. Some—recognizing the importance of designing experiments that directly address philosophical questions—have even suggested possible studies that would help make progress in our understanding of perspectival shapes (Schwenkler & Weksler, 2019). However, philosophers have not really been involved in empirical research that tackle this kind of problems in the philosophy of perception head on.
What about vision scientists? Naturally, they investigate the mechanisms and computations responsible for transforming the retinal images with which visual processing begins into the full-blown 3D representations that characterize our visual perception. In fact, one of the most foundational principles in all vision science is that vision goes beyond the retinal image. This view, popular from Helmholtz and Marr to textbooks, assumes that “perhaps the most fundamental and important fact about our conscious experience of object properties is that they are more closely correlated with the intrinsic properties of the distal stimulus (objects in the environment) than they are with the properties of the proximal stimulus (the image on the retina). This is perhaps so obvious that it is easily overlooked.” (Palmer, 1999, p. 312)
Despite the popularity of this common textbook explanation, as it is well-known in the philosophy of perception, it is far from an established fact that conscious experiences are necessarily closer to the distal stimulus. That is what the whole philosophical debate is about!
This textbook presentation of what our phenomenology is like not only seems to ignore a large philosophical debate, but it also reveals a gap between the questions psychologists seem most interested in asking (e.g. about the mechanisms of shape constancy) and the philosophical questions about what objects look to us.
In a recent project (Morales et al., 2020), my colleagues and I tried to help bridge this gap and directly addressed this philosophical question about appearances using well-established methods in vision science. Importantly, a crucial point of our experiments is that (a) we had this specific philosophical debate in mind when we designed our studies and (b) we made sure we could bypass introspection. Our experiments used “visual search”, a well-established paradigm in vision science that takes advantage of the difficulty of finding an object when it’s next to other object(s) that look similar. For example, think how easy it is to find a red book on a shelf full of green books, and compare it to how hard it is to find that same red book on a shelf full of orange books. So, the logic of our experiments was simple: if rotated circular objects look oval (in some sense), they should make finding true oval objects harder. This means that people should take longer finding the oval in trials like B in the image below, compared to trials like A. And this is true even though the distractor object (on top of pedestal “2” in A and B) is in both cases the exact same circular “coin”. By leveraging visual search, we could link reaction-time differences to the way objects look to subjects. In other words, we could investigate directly a question that has puzzled philosophers since Locke.
Subjects were indeed slower selecting the oval coin when it was next to a rotated circular coin (and hence shared the oval target’s perspectival shape) than when the exact same circular object was seen head on. It is important to note that subjects were very accurate, so they were not slower because they misperceived the shapes. To make sure this result could not be explained by some alternative factor, in eight subsequent experiments we controlled for all sorts of confounds, and every single time we found the same kind of interference. For example, we controlled for low level properties such as size and rotation; we also used moving objects that provided extra visual cues about the shapes of the objects, and we allotted extra time for viewing the stimuli ensuring subjects had all the depth cues they needed to process the shapes correctly and efficiently. We also showed that the effect generalized to other shapes such as trapezoids & squares. Importantly, we found the same effects when we used real 3D objects rather than computer-generated stimuli. After all, the realistic-looking computer-generated images like the ones above only fake 3D properties through clever computer algorithms; in the end, they are flat 2D images presented on a screen. But when selecting a laser-cut 3D oval object like the one below, subjects were slower when the distractor was a rotated circular “coin” than when the distractor was a circular “coin” seen head on. And all this in the real world with real objects!
The results from our experiments suggest that subjects do experience both the true distal shape of objects and their subjective, perspectival shapes. Recall that subjects barely made mistakes selecting the oval, which indicates that mechanisms of shape constancy were effective and allowed subjects to clearly distinguish between true ovals and rotated circles. The reaction time slowdown that we observed over and over again strongly suggests that, despite some philosophical intuitions and cognitive science’s assumptions, our conscious experiences continue to represent perspectival properties even after our visual system resolves the true shape of objects.
Naturally, the results from these experiments cannot settle the debate once and for all. But they do highlight the value of testing empirical questions with philosophical import, and they open an opportunity for further conducting further studies of the same kind. In this case study, we used visual search and reaction times with both computer-generated and real 3D stimuli. But vision science has a vast repertoire of paradigms and measurements that can be used to probe how the visual system works and, importantly, what our experiences are like. The details would depend on the question, but philosophers and psychologists could work with paradigms that manipulate attention, numerosity, color perception, and so on, all while measuring accuracy, false alarms, response trajectories, accuracy/RT trade-offs, and confidence ratings, among many others. When paired with a rich philosophical backdrop, the potential is huge.
As a philosopher, running experiments can be quite fruitful, but it can be daunting too. After all, it takes time, training, and resources to run experiments like the ones vision scientists conduct. However, while this approach does require meaningful interdisciplinary collaborations to be in place, it does not necessarily require that philosophers themselves run the experiments. (This is the route I’ve taken, which is fun and rewarding but it does require time and resources.) Rather, this approach can rely on interdisciplinary teams where philosophical and scientific expertise blend together. Philosophers can become collaborators in psychology teams and help design philosophy-specific experiments that psychologists can then run. Building meaningful, long-term interdisciplinary collaborations also takes time and effort, but the potential benefits for both philosophers of perception (and for vision scientists!) who are willing to build these bridges are worth it.
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Commentary: On the Representation of Proximal Shape
Consider this philosophical chestnut: when you look at a tilted dinner plate, what shape do you see? Answers offered in the literature to this or nearby neighboring questions include:
- ellipticality exclusively (Locke, 1975, II, ix, 8);
- roundness exclusively (Smith 2002, Schwitzgebel 2006, Hopp 2013); and
- both ellipticality and circularity (Peacocke 1983, Noë 2004, Schellenberg 2008, Cohen 2010, 2012).
Morales reports a set of experiments (Morales, Bax, & Firestone, 2020) bearing on this issue. The headline finding here is that visual search for a target oval shape seen head on was impaired by the presence of circular objects rotated in the depth dimension (relative to visual search for ovals seen head on in the presence of circles seen head on). That is (adopting Morales’s terminology), visual search for a target was impaired by the presence of distractors that shared a proximal (/perspectival) shape property, even when target and distractors differed (and participants successfully judged that they differed) in distal shape.
This result shows that our performance on at least one kind of perceptual task is predicted/explained by representations of proximal, rather than distal properties. As such, it provides compelling reason for believing that human psychologies do in fact compute over representations of proximal properties, that such representations are implicated in guiding action and belief, and a fortiori that proximal properties are indeed psychologically represented.
(For an analogous demonstration with respect to color perception–viz., that there is an aspect of perceptual performance predicted/explained by representations of proximal rather than distal color, see Arend & Reeves, 1986, and the experimental literature stemming therefrom. As in the case of Morales et. al.’s experiments on shape perception, it’s hard to see how to make sense of these findings without accepting representations of the relevant proximal properties.)
This is an important result. That said, it leaves some issues unresolved as well. (This is only a clarification; I don’t mean to suggest that Morales thinks otherwise.)
First, if the reported increase in reaction time on visual search for targets matching distractors in proximal shape gives us reason for believing that proximal shape is (/other proximal properties are) psychologically represented, this finding alone says nothing about whether there are, additionally, representations of distal shape (/other distal properties). Now, in the present case, the further observation that participants successfully judged whether targets and distractors matched in distal shape suggests that they are indeed representing distal shape as well. The crucial point, however, is that the evidence for the reality of proximal representation, considered by itself, is agnostic on the distinct question of the reality of distal representation.
Second, while Morales et. al.’s experiments give us reason for believing that proximal shape is psychologically represented, distance remains between the latter conclusion and related but distinct claims that philosophical dispute has often centered on–e.g., that proximal shape is represented perceptually rather than post-perceptually, that it is a property we see rather than make inferences about, that it is represented at a personal rather than subpersonal level, or that it figures in the phenomenal character of our experiences.
I lack space to discuss all of these concerns, but want to remark very briefly on two of the most important.
1. Take the worry about whether the representation of proximal shape is perceptual or post-perceptual. Morales et. al. report a reaction time cost to visual search for a target shape when presented with a distractor matching the target in proximal, but not distal, shape. But because reaction time is a relatively gross measure of all the psychological steps leading up to report (in this case, a keypress), this finding is limited in what it can tell us about the fine-grained structure of the psychological processing. In particular, this result doesn’t tell us whether the reaction time cost (which presumably reflects computation over representations of the target’s and distractor’s proximal shapes) is incurred at a stage of visual processing or some post-perceptual stage on the way to report (cf. classical Stroop interference). Resolving this issue will require not only further empirical investigation, but also a way of thinking about the nature of the perceptual/post-perceptual distinction itself–which is of course hotly contested.
2. A similar point applies to the question about whether proximal shape figures in our phenomenal experience. Morales suggests this is indeed part of his quarry in characterizing his aim as “capturing what experiences are like” (p1). However, once again, though the results offered give us powerful reasons for believing that proximal shape is represented somewhere in our psychologies, they are not by themselves capable of settling whether such representations are accessible to consciousness. This seems important, because philosophers and psychologists who have defended positions like (ii) above (cf. Thouless 1931 on the “phenomenal regression to the real object”) are reasonably read as repudiating proximal shape qua accessible feature of phenomenal experience, rather than qua feature represented within our psychological makeup full stop.
In sum, Morales et. al.’s result strikes me as a significant contribution to our understanding of the psychology of shape perception, though one that invites further inquiry (and funding). As supporters of the cause of full employment for cognitive scientists, surely this is something we can all applaud.
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Arend, L., & Reeves, A. (1986). Simultaneous color constancy. Journal of the Optical Society of America, A, Optics, Image & Science, 3(10), 1743–1751.
Cohen, J. (2010) Perception and computation. Philos. Issues 20, 96–124.
Cohen, J. (2012) Computation and the ambiguity of perception, in Hatfield and Allred (ed), Visual Experience: Sensation, Cognition and Constancy, 160-176. New York: Oxford University Press
Hopp, W. (2013). No Such Look: Problems with the Dual Content Theory, Phenomenology and the Cognitive Sciences 12(4), 813–833.
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