Perception Example

Figure 3-4: Sense Perception

Finally, we move onto Figure 3-4, concerning sense perception. This material is explained more elaborately in Section 3.4. The term “affirmation of existence” cannot be explained here, it is explained in Section 3.3.1. Despite these precautions, this example gives a good initial idea of how the view works.

One might wonder how the mind as a cognitive model of its body’s causal

Idea of Body

Understanding of Body’s Causal Structure Idea of Brain Signature Nature of External Body

Updates Human Body

Body’s Causal Structure Signature Pattern in Brain

Mode of

Perceived as Existing through Idea of Signature Causes Affirms Existence of Affirms Existence of

operation perceives external bodies and second, how those perceptions are distinguished from the body model itself.

First, the body model is an understanding of the invariant causal structure of the body, but that does not in and of itself tell anything about the environment in which the body is. Therefore, the understanding of the body’s operation as a whole is distinguished from the states of the physiological system (or affections of the body as Spinoza calls them).

Now, the mind as an understanding of its body perceives other bodies precisely because it “knows how” the body operates. The visual system (eyes, nerves, and the brain) is a part of the body. When that part of the body is affected with a sensory trace from another body, the body model cognizes the presence of the other body from based on its understanding what a certain change in the body entails for the body’s operation.

Sensory images are changes in the patterns of activity within the brain which is the operational nexus of the whole body. The brain’s job is to orient the eyes and the head to track the other body that is seen, but also to prepare the body for, say, catching that other body if it happens to be a mosquito. The brain does all of that by first forming a kind of signature of the mosquito in the brain structure.

The idea of the brain signature of the mosquito updates the mind’s internal body model. Because the mind is an understanding of the body’s causal structure, it can read off the nature of the mosquito from the idea of mosquito signature in the brain. That new idea is the sensory perception of the mosquito. The perception of is not an idea of the

signature (or trace) its effects on the visual system. Therefore, my sensory perception of the mosquito is really an idea-of-mosquito-as-it-affects-my-body.

Spinoza does not comment exactly how accurate that sensory perception of the mosquito is. Instead, he emphasizes that we get a cognitive grasp only to the nature of the mosquito only to the extent our body’s structure is receptive to the nature of the mosquito. Any errors in sensory perception are due to the limitations of the filters and sensors that are in place in the human physiology.66

The sensory images do not exist as mental items which are inspected by a mental homunculus. Rather, the ideas of images are modifications of the body model. The changes in the brain state which are sensitive to signals from external bodies change the body’s behavior. The ideas of those changes in the brain are changes (or updates) in the body model. They are only informative for the mind because the mind is a model of the operation of the body. The mind uses sensory ideas only to infer the next state of the body model, whereas in the traditional account of the mind sensory ideas are material from which the mental agent can abstract information for the purposes of deciding where to move the body. In this way, a sensory idea is just a mode of body cognition, a cognitive map that extends the body model so that more intricate and far reaching ideas of actions

66 _{See 2p35s. Spinoza writes: “[...] when we gaze at the sun, we see it as some two hundred feet distant from}

us. The error does not consist in simply seeing the sun in this way but in the fact that while we do so we are not aware of the true distance and the cause of our seeing it so. For although we may later become aware that the sun is more than six hundred times the diameter of the earth distant from us, we shall nevertheless continue to see it as close at hand. For it is not our ignorance of its true distance that causes

us to see the sun to be so near; it is that the affection of our body involves the essence of the sun only to the extent that the body is affected by it.” (My emphasis)

can be inferred from the causal structure of the body.

Finally, one should wonder what the relationship of the mind as a model of its body is to our conscious, explicit thinking, e.g. when I’m diagnosing a broken bicycle. My diagnostic thought employs a model of the causal operation of the bicycle, which I use to understand what the bicycle does. Does this mean that my mind is equally a cognitive model of my body as it is of the bicycle?

The body model constitutes the essence of the mind, whereas the thoughts about the bicycle are perceptions of the mind. Their difference is that the body model is a principle of inferring from perceptions of what happens to the body to what the body does. Even though the diagnostic model of the bicycle reproduces the behavior of that body, that perceptual model is only derivative or secondary. In the process of being a cognitive model of its body’s operation, the mind comes to perceive the external world as it alters and affects the physiology of its body.

3.2 The Mind as a Cognitive Model of the Causal Structure of its Body