Sunday, January 31, 2010

Why do we comprehend anything as "all at once" ?

Scientists, testing the reason we sometimes perceive the rotation of a tire (on a car, when its spinning at a certain speed) as going the opposite direction - known as the Wagon-wheel effect - found that "The continuity of our perception is an illusion...The experiment even put a number on our visual frame rate - around 13 frames per second." As there was a specific visual frame rate , the implication was...
...that there is not a single "film roll" in the brain, but many separate streams, each recording a separate piece of information. [In a separate experiment to further examine this] VanRullen examined another neural function, called near-threshold luminance detection. He exposed his subjects to flashes of light barely bright enough to see, and found that the likelihood of them noticing the light depended on the phase of another wave in the front of the brain, which rises and falls about 7 times per second. It turned out that subjects were more likely to detect the flash when the wave was near its trough, and miss it when the wave was near its peak.

So it seems that each separate neural process that governs our perception might be recorded in its own stream of discrete frames. But how might all these streams fit together to give us a consistent picture of the world? Ernst Pöppel, a neuroscientist at the Ludwig Maximilian University in Munich, Germany, suggests all of the separate snapshots from the senses may feed into blocks of information in a higher processing stream. He calls these the "building blocks of consciousness" and reckons they underlie our perception of time (Philosophical Transactions of the Royal Society B, vol 364, p 1887).

It's an appealing idea, since patching together a chronological order of events hitting our senses is no mean feat. Sounds tend to be processed faster than images, so without some sort of grouping system we might, say, hear a vase smashing before we see it happen. Pöppel's building blocks of consciousness would neatly solve this problem: if two events fall into the same building block, they are perceived as simultaneous; if they fall into consecutive buildings blocks, they seem successive. "Perception cannot be continuous because of [the limits of] neural processing," says Pöppel. "A space of 30 to 50 milliseconds is necessary to bring together in one time-window the distributed activity in the neural system."
Pöppel's theory is an interesting one to tie together the discoveries about our processing. Before we had the capability to examine these sorts of questions of cognition (the past few decades?), the historical language used to explore them had been more purely theoretical and philosophical. This shift complicates the responses one can make to a theory such as Pöppel's.

Flash-Flooded Desert in Sinai, Egypt - Click image for LARGE - source: This Fab Trek


  1. The gaps are like what Hume talks about when he says that we can't "see" causality. If you're an empircist or a fool you might jump to the conclusion that causality does not exist. Someone more brilliant, like Bernard Lonergan, will say that human cognition always abstracts intelligibilities from data.

    So, philosophically-speaking, we experience, understand what we have experienced, then judge what we have understood as true or false. That would seem to map onto Pöppel's theory as experience>blocks of information>understanding - data being processed rather than simply comprehended "as is." As with the wheel example, we can be deceived, but then we just need to process more data - not adhere to a minimal account of cognition as only raw experience.

    (Hope that makes sense.)

  2. The only thing I want to know is why does my computer make the you've got mail "bing" a full minute after I see it enter the inbox? geez.
    BTW, Kevin Mitnick has a book out now (you heard he was hired by the Feds, didn't you?)

  3. there's a tree in the water.