In contrast, when the tone frequency was randomized while maintaining the 15 Hz modulation rate, dramatic plasticity of A1 temporal responses occurred without any map reorganization. Thus, variability of one feature can profoundly impact plasticity of another. Determining which features of a stimulus are behaviorally important is a difficult problem that has been largely ignored in the plasticity literature. It would not only be inefficient to simultaneously adjust the cortical tuning for every stimulus feature, it would create representations that did not generalize well. There is no evidence that primary sensory cortex has specific information about task goals, so the cortex probably uses information contained in the input itself to make an educated guess about how to improve performance.
Variability shapes behavioral generalization functions in humans and animals.
This result further substantiates the hypothesis that NB activity marks important stimuli and allows simple cortical rules to improve the representation of features likely to be useful based on the statistics of input. These studies represent my initial investigations of the principles of cortical self-organization using NB stimulation. I have three major goals for my continuing research. The first is to develop a general theory of cortical plasticity by extending my investigations of the plasticity rules that operate in relation to simple features for which auditory cortex neurons are tuned. These features include duration, intensity, bandwidth, FM direction and rate.