Philosophy, Perception and NeuroscienceJohn SmythiesCenter for Brain and Cognition, University of California San Diego, La Jolla. California and Institute of Neurology, University College, London.  smythies@psy.ucsd.edu

Perception 38(5) 638-651 (2009)This paper presents the results of some recent experiments in neuroscience and perceptual science* that reveal the role of virtual reality in normal visual perception, and the use of television technology by the visual brain. This involves particularly the cholinergic system in the forebrain. This research throws new light on the nature of perception and the relation of phenomenal consciousness and its brain. It is directly relevant to criticisms by certain analytical philosophers of aspects of neuroscience relating to these matters. In particular I pay attention to their support for Direct Realism.

Introduction.

A number of recent experiments in visual neuroscience have profound implications for neurophilosophy, news of which has not filtered through as yet to the main body of philosophers. [start * ] Before presenting this evidence some clarification of terms is indicated. It is important to distinguish between several different Realist theories of perception in philosophy—two species of Direct Realism (Naive and Critical), Physiological Realism, Phenomenal Realism and Color Realism, to name the most prominent. Most discussion in this area has been based on the supposition that perception is a unified process. However, evidence from clinical neurology suggests that this is not so. Rather phenomenology and epistemology are based on activity in two different brain areas. In associative agnosia the patient can see objects perfectly well—her phenomenology is intact. She can pick up objects on a table and does not bump into things when she moves about. But she cannot recognize objects and does not realize what they are used for. Her epistemology is impaired. A patient with blindsight, in contrast, cannot see objects. She cannot pick up objects from the table and bumps into things when she moves around. But, when asked to “guess” what the object is out there, she is frequently correct, and can tell you how to use it. She can also correctly name colors. In the allied but distinct condition of aphasia, a patient can see and recognize objects, but just cannot find the name for them. Blindsight is mediated by direct connections between the lateral geniculate body and the higher visual cortex that bypass the primary visual cortex area 17. Thus epistemology and phenomenology have a profoundly different cerebral basis and their philosophical relationship needs to be re-evaluated in this context.

Realism

On this basis the various realist theories can be categorized as follows:—

Naive Realism. This states that both components of perception—phenomenal and epistemological—are direct. That is to say that (1) phenomenological objects seen are identical with physical objects seen (or at least with their surfaces (Stroll 1988) or at least part of the time) and (2) no process of inference is used when we ordinarily look at external objects and obtain information about them. Perception, in this view, has perfect fidelity. In contrast, in the old sense-datum theory we are supposed to infer the properties of the external physical objects we look at by inferences based on our experience of the