Esprits atypiques: les sciences cognitives de la différence et des potentialités

Cognitio 2015

Colloque jeunes chercheuses et chercheurs en sciences cognitives

Montréal, 8, 9, et 10 juin 2015

What can schizophrenia teach us about the cognitive penetration of visual experience?

Dimitria Gatzia.

The influence of perception on cognition (whether it involves doxastic or non-doxastic states) is fairly uncontroversial in philosophy and psychology. It is widely accepted that our perceptual experiences generate certain cognitive states such as beliefs, desires, or intentions. For example, your visual experience of a traffic light being red while driving can generate the belief that you must bring your car into a full stop. Cognition, by contrast, has traditionally treated as having little, if any, influence on perception, as being cognitively impenetrable (Fodor, 1983; Pylyshyn, 1984).

The Cognitive Impenetrability Hypothesis (CIH) can be understood either as a causal or a semantic thesis. According to the causal thesis, cognitive states do not cause chances in the phenomenal character of visual experience (Siegel, 2005, 2012). For example, your belief that the ripe banana in front of you is green does not cause changes in the phenomenal character of your visual experience, meaning it does not cause you to experience it as green. According to the semantic thesis, not only is there no causal connection between cognitive states and the phenomenal character of visual experience, but there is also no “semantic coherence” between them (Pylyshyn, 1984, 1999; Macpherson, 2012). Semantic coherence requires that cognitive states stand in an inference-supporting relation to visual experience (Pylyshyn, 1999: 343). For example, suppose that your belief that the ripe banana in front of you is green causes you to experience it as green. In this case, your visual experience has roughly the same content as your belief—they are semantically coherent. It is this semantic coherence that allows you to infer that it is green.

Although I have previously addressed the question of cognitive penetration as it relates to the phenomenology of color experience (see Brogaard and Gatzia, In press), here I am interested in its relation to early vision (defined both functionally and anatomically). Philosophers who have defended the cognitive impenetrability of early vision have argued that although top-down processes (cognition-driven) influence bottom-up processes (stimulus-driven), such influences do not constitute cases of cognitive penetration since these top-down processes are not cognitive in nature (Raftopoulos, 2001; Pylyshyn 1999).

In this paper, I address the question of whether cognitive states, particularly beliefs, knowledge, or memory penetrate early vision. Learning about normal brain function often involves examining aberrant conditions. Studies on the visual system of patients with schizophrenia can shed some light to the debate of cognitive penetration. For example, some such studies show that the reason patients with schizophrenia are not susceptible to hollow-mask illusion is that (contrary to normal subjects who exhibit a strengthening of top-down processes) their visual systems are less constrained by top-down processes, relying more on visual bottom-up processing (Dima et al., 2009). The hollow-mask illusion is similar to the Müller-Lyer illusion, which is widely thought to provide intuitive support for the CIH. The reason being that the illusion persists even after one comes to believe that the lines are of equal length. The hollow-mask illusion also provides intuitive support for the CIH since it too persists after one comes to believe that the mask is hollow. However, I argue that findings pertaining to the insusceptibility of patients with schizophrenia to the hollow-mask illusion provide much needed empirical evidence for the veracity of the CIH. Further, I argue that these findings can shed some light to the purported modular architecture of the mind (Fodor, 1993) as well as the supposed epistemic roles of perception (Siegel, 2012; Brogaard and Gatzia, In press).