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3.4 Perception in Behaviors
in an agent; the interesting aspect of the cycle is where perception and cog-
nition come in. The agent may have to act to acquire more perception or to
accomplish a task. Also, the agent may or may not need to “plan” an action
on each update.

3.4.2 Two functions of perception
Perception in behavior serves two functions. First, as we saw with IRMs,
RELEASE it serves to release a behavior. However, releasing a behavior isn’t necessar-
ily the same as the second function: perceiving the information needed to
accomplish the behavior. For example, consider an animal in a forest fire.
The fire activates the fleeing. But the fleeing behavior needs to extract in-
GUIDE formation about open spaces to run through obstacles in order to guide the
behavior. A frightened deer might bolt right past a hunter without appar-
ently noticing.
In both roles as a releaser and as a guide for behavior, perception fil-
ters the incoming stimulus for the task at hand. This is often referred to
as action-oriented perception by roboticists, when they wish to distinguish
their perceptual approach from the more hierarchical global models style of
perception. Many animals have evolved specialized detectors which sim-
plify perception for their behaviors. Some frogs which sit in water all day
with just half their eyes poking up have a split retina: the lower half is good
for seeing in water, the upper half in air.

3.4.3 Gibson: Ecological approach

The central tenet of Gibson’s approach is that “... the world is its own best
representation.” Gibson’s work is especially interesting because it comple-
ments the role of perception in IRM and is consistent with the action-per-
ception cycle. Gibson postulated (and proved) the existence of affordances.
AFFORDANCES Affordances are perceivable potentialities of the environment for an action. For ex-
ample, to a baby arctic tern, the color red is perceivable and represents the po-
tential for feeding. So an affordance can be a more formal way of defining the
external stimulus in IRM. But like IRMs, an affordance is only a potential—
it doesn’t count until all the other conditions are satisfied (the baby tern is
hungry). An affordance can also be the percept that guides the behavior. The
presence of red to a hungry baby arctic tern releases the feeding behavior.
But the feeding behavior consists of pecking at the red object. So in this case,
red is also the percept being used to guide the action, as well as release it.