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3 Biological Foundations of the Reactive Paradigm
Gibson referred to his work as an “ecological approach” because he be-
lieved that perception evolved to support actions, and that it is silly to try
to discuss perception independently of an agent’s environment, and its sur-
vival behaviors. For example, a certain species of bees prefers one special
type of poppy. But for a long time, the scientists couldn’t figure out how the
bees recognized that type of poppy because as color goes, it was indistin-
guishable from another type of poppy that grows in the same area. Smell?
Magnetism? Neither. They looked at the poppy under UV and IR light. In
the non-visible bands that type of poppy stood out from other poppy species.
And indeed, the scientists were able to locate retinal components sensitive
to that bandwidth. The bee and poppy had co-evolved, where the poppy’s
color evolved to a unique bandwidth while at the same time the bee’s retina
was becoming specialized at detecting that color. With a retina “tuned” for
the poppy, the bee didn’t have to do any reasoning about whether there was
a poppy in view, and, if so, was it the right species of poppy. If that color was
present, the poppy was there.
Fishermen have exploited affordances since the beginning of time. A fish-
ing lure attempts to emphasize those aspects of a fish’s desired food, pre-
senting the strongest stimulus possible: if the fish is hungry, the stimulus of
the lure will trigger feeding. As seen in Fig. 3.6, fishing lures often look to a
human almost nothing like the bait they imitate.
What makes Gibson so interesting to roboticists is that an affordance is di-
DIRECT PERCEPTION rectly perceivable. Direct perception means that the sensing process doesn’t
require memory, inference, or interpretation. This means minimal computa-
tion, which usually translates to very rapid execution times (near instanta-
neous) on a computer or robot.
But can an agent actually perceive anything meaningful without some
memory, inference, or interpretation? Well, certainly baby arctic terns don’t
need memory or inference to get food from a parent. And they’re definitely
not interpreting red in the sense of: “oh, there’s a red blob. It’s a small oval,
which is the right shape for Mom, but that other one is a square, so it must
be a graduate ethology student trying to trick me.” For baby arctic terns, it’s
simply: red = food, bigger red = better.
Does this work for humans? Consider walking down the hall and some-
body throws something at you. You will most likely duck. You also probably
ducked without recognizing the object, although later you may determine it
was only a foam ball. The response happens too fast for any reasoning: “Oh
look, something is moving towards me. It must be a ball. Balls are usually
hard. I should duck.” Instead, you probably used a phenomena so basic that