Posts tagged ‘perception’

November 27, 2010

my first dead vole: synchrony, structure, snow.

by Jacob Lee

I want to first thank Carl, John, and Asher for giving me the opportunity to join Dead Voles as its fourth member! I am looking forward to a future of exciting exchanges and world domination! I have been a little shy about starting- a funny feeling in someone with a relatively visible amateur online presence. What should I write about? What if everyone thinks its boring? What if its a just a dead vole? Oh wait

Lately I have been working on a little problem. I wanted some way to say that two configurations in some space are structurally identical but in a way which abstracts from any particular way that space happens to be structured. I do not say independent of how that space is structured, since the underlying structure of a space is what gives any configuration of locations its form.*

Anyway, while I was pondering these things, and doing a little background googling, I came across something completely different, the fascinating work by Sang-Hun LeeĀ  and Randolph Blake on how the perception of spatial structure can be induced by temporal synchrony.

Picture an old black and white analog television filled with static, what is often described as ‘snow’. Each pixel on the screen changes its luminescence by some random amount at random intervals. It is unstructured chaos. Such a sequence cannot be compressed without loss, because it does not have any regular structures.

Temporal Synchrony and Random Luminescence

Temporal Synchrony and Random Luminescence Source:

ImagineĀ  synchronizing a block of pixels’ random changes in luminescence, and voila! you see the block of pixels as a distinct visual object! It must be emphasized that the synchronized changes happen at random intervals, and each pixel’s change in luminescence in the synchronized block was individually random. You can see an animation here.

Lee and Blake do a bit more with this than I have described. actually did was a little more complicated and involved. Check it out (PDF).

It reminds me of the fact that staring at that old television set filled with static, if you try you can see any shape or scene that you desire. Perhaps the brain is selectively picking up random synchronizations in the visual field. Lookie lookie! Its a couple dancing! Lookie lookie! It’s a coyote chasing a rabbit! Lookie lookie, its Jacob’s first dead vole!

*We might specify that two spatial configurations are equivalent if there is some kind of structure preserving map between them: in particular, you define a set of invariant transformations of the space. Which of these aspects need to be invariant depends on the space at hand. For example, a linear transformation of a geometric figure, like a triangle, in a Cartesian plane preserves shape, size, orientation. Jerry Seligman uses a similar approach to derive the equivalence class of situations in his paper Physical Situations and Information Flow.


Seligman, Jerry. 1991. Physical situations and information flow. In Situation theory and its applications, ed. Jon Barwise, Jean Mark Gawron, Gordon Plotkin, and Syun Tutiya, 2:257-292. CSLI Lecture Notes 26. Stanford, CA, USA: Center for the Study of Language and Information (CSLI).