Page 91 - Introduction to AI Robotics

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3 Biological Foundations of the Reactive Paradigm
use of the word “reactive” in ethology is at odds with the way the word is
used in robotics. In ethology, reactive behavior means learned behaviors or a
skill; in robotics, it connotes a reflexive behavior. If the reader is unaware of
these differences, it may be hard to read either the ethological or AI literature
without being confused.

3.2.1 Reflexive behaviors

Reflexive types of behaviors are particularly interesting, since they imply no
need for any type of cognition: if you sense it, you do it. For a robot, this
would be a hardwired response, eliminating computation and guaranteed to
be fast. Indeed, many kit or hobby robots work off of reflexes, represented
by circuits.
Reflexive behaviors can be further divided into three categories: 10

REFLEXES 1. reflexes: where the response lasts only as long as the stimulus, and the
response is proportional to the intensity of the stimulus.

TAXES 2. taxes: where the response is to move to a particular orientation. Baby tur-
tles exhibit tropotaxis; they are hatched at night and move to the brightest
light. Until recently the brightest light would be the ocean reflecting the
moon, but the intrusion of man has changed that. Owners of beach front
property in Florida now have to turn off their outdoor lights during hatch-
ing season to avoid the lights being a source for tropotaxis. Baby turtles
hatch at night, hidden from shore birds who normally eat them. It had
been a mystery as to how baby turtles knew which way was the ocean
when they hatched. The story goes that a volunteer left a flashlight on the
sand while setting up an experiment intended to show that the baby tur-
tles used magnetic fields to orient themselves. The magnetic field theory
was abandoned after the volunteers noticed the baby turtles heading for
the flashlight! Ants exhibit a particular taxis known as chemotaxis;they
follow trails of pheromones.

FIXED-ACTION 3. fixed-action patterns: where the response continues for a longer duration
PATTERNS than the stimulus. This is helpful for fleeing predators. It is important to
keep in mind that a taxis can be any orientation relative to a stimulus, not
just moving towards.

The above categories are not mutually exclusive. For example, an animal
going over rocks or through a forest with trees to block its view might persist