Well, in my last post I kind of left my audience hanging in the fact that I discussed the binding problem, but didn’t give any proposed solution. In this post I want to discuss and speculate on a possible answer to the question of how vision is bound together.
Possibly, the most well-known solution is Treisman’s feature-integration theory, which is an attention-based theory of the human visual system. In a nutshell, Treisman has proposed that when you attend to an object, the fact that you are attending to it necessarily integrates all the salient features of the object together aka the features are bound together. Furthermore, he postulates “feature maps” in the parietal lobes of the brain are used to select the features being bound together for any particular object.
His theory can be tested and has been tested in the following way:
Two white digits are briefly presented in the center of a computer screen, one of which is physically large than the other; the subjects’ task is to report the larger of the two digits, a task that requires attention to be directed at the center of the screen. Simultaneously with the digits, two colored letters are briefly presented in the periphery, one of which is always an F or X accompanied by a distractor letter(such as an O). Thus, after reporting on the digits, subjects are asked which of the two target letters occurred(F or X) and, most importantly the color in which that target was presented. If attention is required for binding, one might expect to observe “illusory conjunctions” in this paradigm such that subjects miscombine the features making up the two peripheral letters. And, in fact, that is just what is observed-when a red O and a yellow X are presented, for example, subjects often report seeing a red X more often than would be predicted by chance.(Hunt & Ellis, 2004)
Furthermore, empirical support for Treisman’s theory has been found in patients who have sustained damage to the parietal lobes.
When presented with multiple objects, a patient [who had sustained bi-lateral damage to the parietal lobes] could only report the individual features making up various objects; he was unable to correctly report which features belonged to the same object!(Hunt & Ellis, 2004)
However, I’d like to point out that while there is a lot of empirical support for Treisman’s theory and various other cognitive/neural explanations, there is still an explanatory gap in the following way: as far as I am aware, no theory of vision that attempts to account for the binding problem adequately gives an evolutionary explanation. This is a problem because it seems logical for reasons of parsimony to assume that at some point in our evolutionary history salient features weren’t bound together, so in order to give a satisfactory answer to the binding problem, one must propose some sort of evolutionary pressure explaining how and why they got bound together. I will not go into details in this post, but I speculate that one can get around this “why” problem if one has a wider conceptual framework to substantiate “brain bound” theories such as Treisman’s. Without better conceptual frameworks, these neural theories of perception will necessarily have limited explanatory power, despite being supported by empirical evidence.
Hunt, R., & Ellis, H. (2004). Fundamentals of Cognitive Psychology (Seven ed.): McGraw-Hill Higher Education.