21 January 2006

Combining Aspects of Reality In the Brain

Science Blog reports on research that examines how brains unify multiple sense impressions into a single impression. When a person sees an object, the brain registers the size, shape, contours, textures, colors, etc. in different locations of the CNS. The brain must then assemble this information--quickly now--into an object identification, either consciously or sub-consciously.

For instance, a particular neuron may respond to objects with either a concave fragment at the top or a convex fragment at the bottom. At this point, the neural signals are ambiguous; the brain doesn't know whether the concavity, the convexity or both are present.

Milliseconds later, however, neurons begin to react exclusively to combinations of shape fragments, rather than to individual fragments. In other words, the brain begins to put the pieces together to form larger sections, in the same way that an artisan might fasten discrete shards of stained glass to create a design.

"Humans do a rough categorization of objects very quickly," Connor said. "For instance, in just a tenth of a second, we can recognize whether something we see is an animal or not. Our results show that this immediate, rough impression probably depends on recognizing just one or more individual parts of what we see. Fine discriminations – such as recognizing individual faces – take longer to happen, and our study suggests that this delay depends upon emerging signals for combinations of shape fragments. In a sense, the brain has to construct an internal representation of an object from disparate pieces."

Of course the problem is more complex, involving not only visual features, but odors, sounds, vibration and other touch stimuli, and also underlying emotional states and levels of hunger, fatigue, sleepiness, and distractibility.

Known as the "binding" problem, it is merely one part of the complex study of consciousness.
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