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 Perturbation Experiment as a Way to Study Perception

When you study perception, your goal is to control the flow of information going into the system so that you can measure the resulting behaviour and evaluate how that information is being used. There are two ways to do this, one (sometimes) used by me, one used by, well, everyone else. In this post I'm going to compare and contrast the methods and describe why the perturbation method is what we should all be doing.

The standard method is to present experimentally isolated cues and test whether people can detect those cues. The perturbation experiment presents a 'full cue' environment but selectively interferes with the link between a single variable and the property it might be information about. These two different methods lead to very different ways of thinking and talking about perceptual abilities. 

Affordances are not probabilistic functions

The journal Ecological Psychology is hosting a special issue with papers from a Festschrift for Herb Pick. Karen Adolph and John Franchak have a paper that caught my eye about treating affordances as probabilistic functions, effectively applying standard psychophysical techniques to the study of affordance perception. 

The idea is this: affordance research typically treats affordances as all-or-none, categorical properties. You can either reach that object or you can't; you can either pass through that aperture without turning or you can't. You then measure a bunch of people doing the task as you alter some key parameter (e.g. the distance to the target, or the width of the aperture) and find the critical point, the value of some body-scaled measurement of the parameter where behaviour switches from success to failure. For instance, you might express the aperture width in terms of the shoulder width and look for the common value of this ratio where people switch their behaviour from turning to not turning.