From: malcolm@interval.com (Malcolm Slaney)
Date: Tue, 21 Feb 1995 17:30:38 -0800
Subject: Coding of Signals in the Brain
Message-Id: <v02110101ab703f43163a@[192.203.7.70]>

Three of the big unanswered questions in neurophysiology are
        How is information encoded in the brain?
        How is the information used to make a decision?
        How do we learn?
These questions are especially critical for us auditory people.
Information coding was the subject of many late night arguments at ARO.
We'll talk about decision making this week at CCRMA, and next week we'll
talk about plasticity.

We can't answer the encoding question, but we can start looking at how
information is combined to make a decision.  Dan Salzman and Bill Newsome
have been looking at this problem in the visual system of a monkey.  They
have found cells that respond to visual orientation.  They can also
electrically manipulate these cells and get an identical response.  But
what happens if you apply both visual and electrical stimulation?  Does the
average of the two directions win, or do the cells pick the largest?

Dan Salzman has been studying this problem here at Stanford and has agreed
to come describe his work.  The experiments are conceptially simple and the
results are interesting.

        Who:    Dan Salzman (Stanford Neurobiology)
        What:   Winner take-all vs. Averaging
        When:   Thursday February 23, 1995 at 11AM
        Where:  CCRMA Library (Top Floor of the Knoll at Stanford)
        Why:    Decision making is important to understanding audition...

Next week, Josh Gold (Stanford Neurobiology) will be reviewing a paper on
plasticity of frequency representation.

See you at CCRMA.  Bring your question and see some excellent
neurophysiology experiments!

-- Malcolm



TITLE:           Neural mechanisms for forming a perceptual decision.
AUTHOR:          Salzman, C. Daniel  (Stanford U School of Medicine, Dept of
                   Neurobiology, CA, US)
                 Newsome, William T.
PUBLICATION:     Science.  1994 Apr Vol 264(5156) 231-237.  (ISSN 00368075)
ABSTRACT:  Cognitive and behavioral responses to environmental stimuli depend
   on an evaluation of sensory signals within the cerebral cortex. The
   mechanism by which this occurs in a specific visual task was investigated
   with a combination of physiological and psychophysical techniques. Monkeys
   discriminated among 8 possible directions of motion while 2 directional
   signals were manipulated in the middle temporal area of dorsal extrastriate
   cortex. Ss tended to cast decisions in favor of one or the other signal,
   indicating that the signals exerted independent effects on performance and
   that an interactive mechanism such as vector averaging of the 2 signals was
   not operative.




TITLE:           Cortical microstimulation influences perceptual judgements of
                   motion direction.
AUTHOR:          Salzman, C. Daniel  (Stanford U School of Medicine, CA, US)
                 Britten, Kenneth H.
                 Newsome, William T.
PUBLICATION:     Nature.  1990 Jul Vol 346(6280) 174-177.  (ISSN 00280836)
ABSTRACT:  Measured the effect on psychophysical performance of modifying the
   firing rates of physiologically characterized neurons. Three rhesus monkeys
   were required to report the direction of motion in a visual display while
   receiving electrical stimulation to clusters of directionally selective
   neurons in the middle temporal visual area, an extrastriate area that plays
   a prominent role in the analysis of visual motion information.
   Microstimulation biased Ss' judgments toward the direction of motion encoded
   by the stimulated neurons. This result indicates that physiological
   properties measured at the neuronal level can be causally related to a
   specific aspect of perceptual performance.