From: Patrick Wilken (patrickw@cs.monash.edu.au)
Date: Thu Sep 09 1999 - 18:06:47 MDT
VERDICT IS IN: BRAIN IS SERIAL IMAGE PROCESSOR
By R. Colin Johnson EE Times (09/08/99, 10:48 a.m. EDT)
http://www.eetimes.com/story/technology/advanced/OEG19990908S0001
IOWA CITY, Iowa-Since the emergence of machine vision in the 1960s,
debate has raged over whether a parallel or serial architecture is best.
Researchers modeling visual processes in the brain observed parallelism
in neural structures, but didn't know enough about how visual
information was being represented to resolve the issue. Now University
of Iowa researchers say they've solved this vision research question:
Does the brain operate in parallel or serially?
"We are the first research group to show definitively that the human
brain processes images serially-paying attention to only one object at a
time and shifting rapidly from object to object," said University of
Iowa professor Steven Luck. According to the new insights, the brain
does perform many tasks in parallel, such as muscle coordination for
walking in the park while simultaneously listening to birds chirping.
These are cognitive operations that involve separate processing on
different types of data.
For such diverse tasks it is clear that the brain does operate in
parallel. But when it comes to tasks involving similar data items, the
brain appears to time-division multiplex, that is, focus its attention
on one object at a time so quickly that the conscious mind is not aware
of it. "It's counterintuitive because it seems to our conscious mind
that we are comparing objects simultaneously, but we now think that the
brain's parallelism is similar to a computer's-that is, a computer has
millions upon millions of simultaneously acting transistors, but at the
functional level it is operating serially-one instruction at a time,"
Luck said. The new theory says that the brain operates the same way at
the functional level; it processes information serially, even though the
underlying neural hardware is operating in parallel.
Luck was able to determine whether the brain's processing was parallel
or serial through an experiment he performed in 1994. This experiment
identified a pattern in brain waves known as N2PC, which stands for the
second negative peak (N2) of the posterior contralateral (PC). The N2PC
identifies the location of brain waves as emerging from either the right
or left side of the brain. By arranging the experimental situation, Luck
was able to use N2PC to identify whether a person was processing visual
signals one at a time or simultaneously.
He enlisted the help of graduate student Geoffrey Woodman to perform the
experiment and study the collected data. The experimental setup
presented to subjects a landscape-shaped display of different colored
blocks, most of which were black except for a red block on the left side
and a green block on the right. The subjects were instructed to find the
block with a nick in it and told that it was probably red but could be
green. Those instructions allowed subjects to either process all blocks
in parallel, focus their attention on just the red and green blocks
simultaneously or search for the correct block in the same order each
trial-that is, red, then green, then black.
"It was important that we knew the order in which they paid attention to
the colored objects, because the N2PC works by correlating the brain
waves coming from each side of the brain over many statistical trials,
so we had to always have them search in the same order," Luck said. By
observing the brain activity of the subjects performing the search and
recognizing tasks using N2PC, Luck and Woodman discovered that the brain
turned its attention from one block to the next at intervals of about
1/10th second. "There wasn't a single subject that did the task in
parallel," Luck said.
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Patrick Wilken
Editor: PSYCHE: An International Journal of Research on Consciousness
Board Member: The Association for the Scientific Study of Consciousness
http://psyche.cs.monash.edu.au/ http://assc.caltech.edu/
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