Perception Stored in Single Neurones

Ian Goddard igoddard at erols.mom
Mon Jan 21 10:28:42 EST 2002


Max Planck Institute for Biological Cybernetics

January 17, 2002

Perception is stored in Single Neurones
Tuebingen Max Planck researchers discover
that our perception of diagnostic features 
is controlled by single neurones.               

Perception is something that must be    
learned. As we recognize things in our  
environment we gather experience and this
experience in turn colours our perception. 
This is nothing new, of course. But brain 
researchers are going one step further to 
ask how different kinds of information are 
integrated in the brain and what principles 
govern how perceived objects are represented 
there. Scientists at Tuebingen's Max Planck    
Institute for Biological Cybernetics have
carried out experiments that prove for  
the first time that single nerve cells in
the brain are responsible for controlling
our perception by drawing on prior 
experience. They report their findings in
the latest issue of the journal "nature"
(nature, January 17, 2002).             
Our perception of objects depends on our 
prior experience with them. What most
people would call a bird is "obviously" a
sparrow, sandpiper, or cockatiel for a  
birdwatcher. Expertise sharpens our     
ability to notice details. The more we  
learn about objects and the more familiar
they become, the more details we recognize. 
Thus, we continue to make generalizations, 
but these generalizations get better and 
more accurate all the time.
A research group at the Max Planck
Institute for Biological Cybernetics has
studied what happens in the brain when we
familiarize ourselves with objects. To do
this they first taught rhesus monkeys to
categorize objects according to specific
features. Monkeys are ideal subjects for
such experiments, for they are able to
master a variety of visual categorization
tasks and the organization of their
visual system is strikingly similar to
that of humans.

While the Tübingen monkeys were "working"
the scientists observed the activity of
neurones in a special area of the brain
called the "inferior temporal cortex"
(ITC). Today we know that this area is
responsible for the recognition of
objects. The researchers asked how a
special training program for object
categorization would affect how these
objects are represented in the brain. To
do this they showed the monkeys a series
of line drawings of faces on a computer
monitor. (In another set of experiments
the monkeys learned to recognize fish.)
The faces consisted of an outline of the
head and a total of four variable
features: eye height, eye separation,
nose length and mouth height. Each of
these features could appear in one of
three different variants: the nose, for
example, could be short, medium or long.
The monkeys were trained to distinguish
between two different kinds of faces. In
one category the eyes were low and widely
spaced. In the other category they were
high and narrow. Thus, the two features
"eye separation" and "eye height" served
to define the categories. The other two
features, nose length and mouth height,
varied randomly and were irrelevant for
categorization (cf. Fig. 1).


In these tests the Max Planck scientists
determined that single neurones in a
particular brain region reacted to the
two features "eye height" and "eye
separation." The activity of these
neurones was substantially stronger when
these two "relevant" features fit the
category in question. The other two
features "nose length" and "mouth height"
provoked only an indifferent reaction. In
other words, these specialized neurones
had learned to distinguish between the
two categories. Rather than simply
representing the presence of a specific
object or features, they convey detailed
information about the features that are
diagnostic for the two categories.

The researchers were also able to show
that the monkey brains actually use the
features learned in this experiment to
recognize objects. After training the
animals were able to identify "matching"
faces, i.e. faces with similar features.

The Tübingen group concludes that there
are apparently single neurones that
sharpen our perception when they are
trained to respond to categories. By
making generalizations our brain is able
to encode and interpret what we see
around us.


Prof. Dr. Nikos Logothetis
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tübingen
Tel.: +49 - 70 71 - 6 01 - 6 51
Fax: +49 - 70 71 - 6 01 - 6 52
E-mail: nikos.logothetis at tuebingen.mpg.de

 "To lengthen thy life, lessen thy meals." Ben Franklin


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