Tuesday, July 15, 2008

Devilish clever

Moments into the keynote talk, the teachers and I found ourselves blinded by darkness. As our eyes adjusted, we were told to cover one eye with our hands before the lights were raised again. A little wait for our open eyes to become light-adjusted and then the lights re-dimmed. What would happen to our vision this time? The answer depends on whether adaptation to light levels occurs centrally, in the brain, or locally in each eye. The audience tested this, looking through each eye one at a time and discovering the strange experience of having one eye adapted to the light and one to the dark, thus showing that light adaptation occurs locally. Both eyes open led to a strange, grey, grainy, effect.


A huge video of a waterfall filled the screen. After a minute staring at the cascading water, the video was stopped and the audience experienced the well-known illusion of the water appearing to flow upwards. But what if the flowing water was watched with just one eye (with the other covered), with the paused video then observed through the previously covered eye? The illusion was still experienced, thus showing that in this case, adaptation to motion had occurred centrally, in the brain.

And about expectations

Led Zeppelin's Stairway to Heaven began to fill the lecture room. Then a verse was played backwards (courtesy of Jeff Milner). Could we hear any words in the backward version? None. But then Stafford told us the hidden lyrics: “Oh here's to my Sweet Satan...”. The backward track was played again, and there the words were, bold, impossible to ignore.....Once the expectations for what to hear are in place, they can't be undone. You can't unhear the devilish lyrics once you know about them. This is a powerful demonstration of how our perceptual experiences are based not just on what is served up by our senses, but also on what our brains bring to the table.