While I was tooling around for the previous blog piece based on a PNAS article, I stumbled on to a supplement contained in the same September 13 issue that has the pretty image above on the cover. Pure gold! It contains papers from a colloquium on the quantification of behavior, and they were so good I gave you the link to all of them. But the one that’ll interest you most is the seventh one down, entitled Understanding Vision in Wholly Empirical Terms, authored by Purves, Wojtach, and Lotto.
Here is one set of images from the paper, supporting their premise that context shapes perception. The figures in “A” are an example of a perceived difference in luminance based on simultaneous brightness contrast of the figure against its background. Also known as irradiation, it’s a subject I published an article almost 30 years ago, but Purves and Lotto have far eclipsed what I did with the concept. Figure “B” is just one of many compelling examples that Doctors Purves and Lotto provide, and is taken from a book that they co-authored, titled: Why We See What We Do, detailing their empirical theory of vision.
I recall buying the book and being impressed with it, but I forgot how good it was, though not without some controversy at the time. Dr. Purves has quite an academic pedigree, with his BA from Yale, an MD from Harvard, a postdoc in neuobiology and biophysics, and now Director of the Neuorscience and Behavioral Disorders program at Duke. As is Oliver Sacks, I’m a bit partial to Purves because of his preoccupation with auditory processing and visual processing. Purves’ laboratory website has a wealth of information about his work. You can also get a taste for some of his lab’s work on visual behavior from Dr. Lotto’s 2009 TED talk:
Purves and Lotto have a new edition of their book, in which they present evidence for their empirical theory of vision even more forcefully. Of particular interest is their topics in Chapter 5:
5. Seeing Distance and Depth
- Approaches to Rationalizing Visual Space
- Monocular Perception of Distance
- Monocular Distance Percepts Elicited by Stimuli with Minimal Context
- Depth Perception Arising from Binocular Information
- Binocular Fusion and Rivalry
- Sherrington’s Experiment
- An Empirical Explanation of Fusion and Rivalry
- Conventional Explanations of Binocular Depth Perception
- Problems Explaining Stereoscopy in Terms of Retinal Disparity
- Random Dot Stereograms
- Advantages of Stereopsis on an Empirical Basis
…. and Chapter 7:
7. Making Sense of the Visual System in Empirical Terms
- The Receptive Field Properties of Visual Neurons
- Problems Linking Receptive Field Properties to Perception
- The Empirical Alternative
- Mechanism Underlying Visual Perception
- How the Links between Images and Behavior Are Established
- Understanding the Organization of the Visual System in These Terms
And to top it off, a primer on visual system structure and function as an appendix.
The essential premise in the paper by Purves, Wojtach, and Lotto is that retinal stimuli trigger neuronal activity in circuits that have been fully determined by accumulated species and individual experience, with the behavioral success (or failure) arising from interactions with the environment over time. My only beef with their paper is that it trivializes the role of Bayesian inference or probability, which I feel still plays a strong role in vision and visual behavior.
– Leonard J. Press, O.D., FCOVD, FAAO