Wednesday night, I headed to the beautiful Bell House in the Gowanus section of Brooklyn for the monthly Secret Science Club lecture by NYU Neuroscientist David Carmel. Dr Carmel's field is the role of the brain in visual perception, and his lecture was accompanied by many displays illustrating the topics he addressed. Before the lecture, attendees were supplied with small slips of paper displaying the classic blind spot demonstration, and "glasses" with a red and a green gel, much like classic 3-D glasses (not to be confused with X-Ray Spex).
Humans tend to recognize patterns, and often impose aninterpretation on objects which isn't supported by further observation.
The "blind spot" phenomenon was explained- the optic nerve connects to the retina in a region that lacks the cells that "receive" incoming light. The blind spot test allows one to "locate" one's blind spot, but an unusual thing occurs- the brain "fills in" the missing details, in the test, one perceives a blank white space in the white background, if one were to draw a line on the paper through the two test images, one would perceive a continuation of the line where the "missing" image should be.
After a brief discussion of "metacognition", basically one's abilitity to know what one knows, and the ability of one to recall images briefly flashed on a screen, Dr Carmel presented a bunch of bistable images, which are basically unchanging stimuli which can be perceived in various ways. A classic bistable image is the Necker Cube. Dr Carmel also displayed the ambiguous duck/rabbit (sounds like an ingredient in a McGravitasian recipe), the vase/face image and the young woman/old crone image. Notably, one cannot perceive both images simultaneously.
The most mind-blowing part of the lecture was a demonstration of the selective attention test, which must be seen to be believed. Sadly, I fall within the 50% or so percent of the population which gets blindsided by the test. It's truly humbling. The sequel is not quite so bad.
Dr Carmel then went on to demonstrate binocular rivalry, instructing the audience to use the two-toned "glasses" to "separate" the two images in this composite- as one looked at the image with glasses, one would alternate between seeing the face and the building. I am ashamed to admit that I asked a n00b question, about the ability of color blind persons to perceive the two images, forgetting that they would experience the binocular rivalry, with the two images appearing gray. I sure hope a colour vision specialist doesn't read this, because I really didn't drink enough Ommegang to justify the lapse.
Dr Carmel went on to discuss the portions of the brain involved in perception, focusing on the use of transcranial magnetic stimulation to monitor brain activity. Here's a nice, brief overview of TMS... Dr Carmel showed a video of himself receiving TMS, and having one of his hands moving without his volition (a waggish bastard in the audience asked him if TMS had been weaponized for use in crowd suppression... not yet, at any rate). While the primary visual cortex is located at the rear of the brain, there are other portions of the brain which are involved in perception. Dr Carmel studied the role of the right parietal lobe in perception of and found that TMS affected the duration of "dominance" in binocular rivalry. At the same time, one of his colleagues found that TMS decreased the duration of "dominance". They were able to reconcile these seemingly contradictory findings by ascertaining that they had been stimulating slightly different regions of the parietal lobe. One portion of the parietal lobe plays a role in maintaining an interpretation of visual stimuli, while another plays a role in changing our perception of something based on changes in the perceived stimuli.
The lecture ended with a summation- we perceive the world with our brains. Perception is a balancing act- we make choices as to how we interpret the visual stimuli we receive. All told, it was yet another brilliant lecture, and the accompanying video presentations really knocked it out of the park- I'm still a little freaked out about the selective attention test.
Sorry about the delay, folks, but I had to chase down links to a lot of the images which were featured in the lecture (and ya know, I almost forgot one of the best examples of bistable imagery.