Lecture 11: Doctrines of Sensations and Unconscious Inferences (Turvey, 2019, Lectures on Perception)

This Lecture is about Helmholtz, and his theory of sensations being integrated into perceptual experience via unconscious inference. Everything in here should look very familiar to anyone who has ever taken a Sensation and Perception class, because modern theories of indirect perception are literally versions of this account. (I'll note as well that, while there are embodied and ecological interpretations of the free energy principle (e.g. Bruineberg et al, 2018), one common interpretation is that it is an implementation of Helmholtz's unconscious inference; e.g. Friston and Kiebel 2009; Hohwy, 2013). 

Unconscious inference is a firmly Cartesian programme. It is about using the physiological measurements of things like light, and inferring their underlying causes (i.e. what is happening in the world to be perceived). Unsurprisingly, it is going to run into the same main problem, namely unrepayable loans of intelligence. 

The doctrine of sensations comes from two related doctrines; that of elemental receptors and that of specific nerve energies. 

The Doctrine of Elemental Receptors

Each sensory system is based in sets of elemental receptors. Vision begins with the activity of photoreceptors; hearing begins the activity of auditory receptors; and so on. These interact with physical energy, and transduce it into nervous system energy. This is how the first grade of sense works (Lecture 6). The raw material of perception is this physical energy (in sound waves, features such as the amplitude and frequency), and these are turned into psychological equivalents (loudness and pitch, respectively). These physical properties do not contain all the features of perceptual experience (things like surfaces, or meaningful events) and so these features must be inferred and added into experience. 

The Doctrine of Specific Nerve Energies

The next question is how is the first grade of sense developed into the second sense, where these physical properties lead to some kind of awareness (Lecture 6). The proposed solution is specific nerve energies; visual cell stimulation leads to visual experience, even if that stimulation wasn't caused by light. Auditory receptor simulation leads to auditory experience, and so on. Turvey notes this doesn't really explain anything, and leaves a gap about things like the qualia of experience (the blueness of something, for example). This is a physiological implementation of Kant's ideas (Lecture 9).

The Doctrine of Sensations

Based on these first two doctrines, the basis for perception becomes the specific output of nerves in response to elemental receptors interacting with physical energy; sensations. Sensations are (pg. 166)

1. punctate (discrete entities)
2. momentary
3. integrable (can be combined via association or inference)
4. immutable 
5. irreducible
6. anatomically specific
7. mental correlates of energy variables
8. signs (meaningless symbols)
9. private
10. necessary for perception

In effect, sensations are as letters of an alphabet to language, or genes to biology; a limited set of discrete elements that can be combined in an indefinitely large number of ways. This process of combination, for Helmholtz, is unconscious and immune to conscious knowledge; for example, the computation of the size of something based on the sensations on the retina is not affected even if you 'know' something is off - this is why illusions occur. 

Turvey doesn't specifically note this, but this is the basic framework for sensation-based study of perception, where the key method is psychophysics: experiments designed to establish the relationship between physical variables and their psychological counterparts. He discusses an example of this type of research (how the experience of something as black or white varies with surface reflectance). This example reveals some common problems. First, there is no clear single correlation between values of reflectance with experience of lightness (the proposed link between the first and second grades of sense is not working the way this theory expects). Second, lightness actually seems to vary in non-obvious ways (he describes an effect that shows 'white' is how we experience the highest luminance in a specific context, so as the context changes we experience the surface differently even though it is still physically the same). Reflectance seems to be impredicative (Lecture 3). 

Finally, Turvey discusses a key problem with this theory. It assumes that the raw material of visual perception is the detection of light. But light, per se, is actually invisible! We do not see light - if we did, visual experience would be of the dense ambient fog of light that surrounds us. But we see through this to the surfaces and events in the world. (Another example is a spotlight in a dark room: from the side, you cannot see the spotlight, only the surfaces it is reflecting off; dust, the wall, etc). He notes a Gibsonian distinction, between the energy of stimulation (e.g. light) and the order in stimulation (i.e. information-L).