Course: Visual Perception and the Brain
School: Duke via Coursera (free)
Instructor: Dale Purves
The purpose of the course is to consider how what we see is generated by the visual system.
Thus the objectives of the course are:
– To introduce you to some fascinating perceptual phenomenology
– To make you think about how this phenomenology can be explained
– To make you consider what possible explanations imply about brain function.
[Addendum: This course has been converted to the new Coursera platform; content may have changed, and the experience is likely to be different]
A course about the science behind optical illusions? What could be more fun?
By coincidence, we were in the Color unit on the day #TheDress went Twittercrazy (The Guardian‘s article used the same illustration chosen as the header of the course). Except… since this is one of those “release all the material on day 1 and take as you will” courses, I’d long completed that unit. Nevertheless, I joined in, commenting on the discussion board that Coursera was missing out on a marketing opportunity by not tweeting about the course while the hashtag was trending; they did, a bit later, but forgot the hashtag, and, unforgivably, misspelled the professor’s name. As I understand it, the whole issue was nonsense anyway: several different copies of the photo were circulating, and a lot of it had to do with color balancing in processing as well as lighting during the photography itself. But it was fun anyway.
Prof. Purves was emphatic during the first week of class, however: what we call optical illusions are not “illusions.” They are, in fact, the way our visual system has evolved to give us a perception of reality that is survival-based. We see optical illusions, the dress, and everything else, that way – even when we don’t realize it – because our visual pathways can’t handle anything beyond a photon stimulating a cell in the fovea, so at least three factors – illumination, reflectance, transmittance – are conflated and lost forever to our perception. It’s the genius of evolution that we’ve been able to “see” well enough to survive this long, so that we’re here to fight about whether the dress is white and gold or blue and black .
The things you come across in MOOCs. By the way, you can take a look at the prof’s website to see many of the concepts covered in this course – and then some. I, for instance, still don’t believe these two tables have the same dimensions, merely rotated 90°. A quick screen clip, some playing around with Word shapes, and… yeah, they really are.
The first week introduced the foundational concept of the course, the “inverse problem” – the difficulty of recreating reality from that conflation that gets transmitted as a single stimulus – then, after a couple of weeks on the structure of the primary visual system and various ways of conceptualizing our ability to see, repeatedly went back to that inverse problem as we looked at our perception of lightness and brightness, color, depth, geometry, and motion. They all came back to that inverse problem, and a similar way of getting around it as an adaptive trait. It’s an idea I came to wonder a great deal about – can we perceive anything the way it is?
A fascinating idea – lots of the ideas in this course were thought-provoking – yetI found it to be one of the drier courses I’ve taken, complicated by twisted syntax and some of the most “academic” discourse I’ve encountered in any MOOC. Take this description of the Bayes Theorem: “And it’s a statement of conditional probabilities, the left hand side of this equation being equivalent to the right and the left hand side of the equation expresses the probability of A given B, where A is in vision, an image or a stimulus, and B, would be the underlying state of the world. This is called the posterior probability, this left hand side of the equation. And it is given by the probability of B given A, that is what’s the probability of the state of the world given the image, were multiplied by the probability of, of the image in the first place, and that’s generally normalized by the probability of underlying states of the world.” I’m glad I’d run into this before in a more comprehensible form, or I would’ve wept.
Staff presence was limited to operational issues. In fact, a “warning” greeted us at the start of class – it wasn’t called a warning, but I’m not sure what else it could be called: “The TAs will also attempt to directly respond to some posts in order to facilitate discussion or address certain problems. Please be aware that the TAs are neither professional experts in computer science, biology or life science.” I suppose it’s just as well they didn’t actually attempt to facilitate discussion, although logistical issues were addressed – questions on written assignment requirements, problems with exam submissions, etc.
Some of us (including classmates from the concurrent Plato course – more good timing) used the message boards to bandy about more philosophical approaches to the material, dipping into epistemology. At one point, that disintegrated into a pissing match so I backed off. That happens sometimes. It happens more often when a course isn’t well-monitored. As I keep saying, every MOOC is different. Some MOOCs show ownership; others, don’t. It’s kind of a shame, because Dr. Purves obviously had great depth of knowledge about, and passion for, his field. Some of that came across, but it could’ve been a knock-your-socks off experience, and it wasn’t.
Grading was based on quizzes – they were timed, but generously so, and multiple attempts were permitted – and a final peer assessed paper that could be viewed as optional, depending on one’s goals; some students are quite fond of Certificates of Achievement, with or without Distinction, and as there was no Distinction here, and a Certificate could be earned by acing the quizzes, it was possible to skip the paper. However, I found it beneficial; I could pull my thoughts together in an organized way and put the Inverse Problem and the concept of survival-based perception into my own words and tell a story. I’ll also get to see other papers, which is a huge benefit of doing any Peer Assessment (only a tiny fraction of students show up on the message boards, and it’s always fun to see what others are thinking).
I signed up for this course because of the Philosophy and the Sciences course I took last Fall; it was a natural continuation of the science portion. It’s material worth learning, and I find the point of view fascinating (I’ve used it in other courses already), even if the packaging was a little disappointing.