Аннотация
Hierarchy plays a key role in human motor control and learning. We
can generate a variety of structured motor sequences such as writing
or speech and learn to combine elemental actions in novel orders.
We previously proposed the Modular Selection and Identification for
Control (MOSAIC) model to explain the remarkable ability animals
show in motor learning, adaptation and behavioral switching. In this
paper, we extend this to a hierarchical MOSAIC (HMOSAIC). Each layer
of HMOSAIC consists of a MOSAIC, which is a set of paired control
and predictive models. The higher-level MOSAIC receives two inputs:
an abstract (symbolic) desired trajectory and posterior probabilities
of its subordinate level, which represent which modules are playing
a crucial role in the lower level under the current behavioral situation.
The higher control model generates, as a motor command, prior probabilities
for the lower-level modules, and therefore prioritizes which lower-level
modules should be selected. In contrast, the higher predictive model
learns to estimate the posterior probability at the next time step.
The outputs from controllers as well as the learning of both predictors
and controllers are weighted by the precision of the prediction.
We first show that this bidirectional architecture provides a general
framework capable of hierarchical motor learning that is chunking
of movement patterns. Then, we discuss the similarities between the
HMOSAIC architecture and the closed cerebro?cerebellar loop circuits
recently found by Middleton and Strick (Trends in Neuroscience 21
(1998) 367). In our view, modules in one layer are involved with
similar functions and assumed to be implemented by one of the cerebro?cerebellar
loop circuits. These layers are then connected to each other by the
bidirectional information flows within the cerebral cortex.
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