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Up: Architecture levels
The Sensori-Actuator level is the level of primitive motor and
sensory actions, for instance ``move from to
or ``look at
''. At this
level, there are no object representations as there are at the Knowledge
level and the Perceptuo-Motor level. There are no explicit declarative
representations of any kind, only procedural representations (on the
actuator side) and sensor data (on the sensory side). Primitive motor
actions may typically be implemented in a robot control language like VAL,
and some elementary data processing routines may be implemented in a
sensory sub-system, like dedicated vision hardware. At this level, we also
situate reflexes, which we consider to be low-level loops from
sensors to actuators, controlled by simple thresholding devices, operating
independently of higher-level mechanisms, and able to pre-empt the latter.
We see reflexes as primitive mechanisms whose main purpose is prevention of
damage to the hardware, or to put it in anthropomorphic terms, survival of
the organism. As such they take precedence over any other behavior. When
reflexes are triggered, the higher levels are made ``aware'' of this by the
propagation of a signal, but they have no control over the reflex's
execution, which is brief and simple (like a withdrawal reflex seen in
people when they unintentionally stick their hand into a fire).
After the completion of a reflex, the higher levels regain control and must
decide on how to continue or discontinue the activity that was interrupted
by the reflex. Reflex-like processes may also be used to shift the focus of
attention of the Knowledge level.