Page 312 - Deep Learning

The Formation of Belief 295

We are not conscious of any distinction between forming a percept and decid-
ing that it is true; seeing and believing do indeed appear subjectively as a single
mental event. The distinction becomes noticeable only when we are faced with
some anomaly or illusion. For example, the Ames room is a weirdly propor-
tioned room that tricks an observer into seeing a person as changing in size
8
when he walks from one side of the room to the other. The observer does
not, of course, believe that the person is changing, so in this case seeing is not
believing. The acts of encoding (perception in the narrow sense) and assigning
a truth value are forced apart by this deliberately contrived illusion. in all but
a small number of such cases we automatically and unconsciously trust our
visual system. our attitude to our ears is similar. if we hear a sound, we believe
that it has some physical source and we instantaneously form beliefs about its
location and nature. if it sounds like the neighbor’s dog barking, then we are
disposed to believe that it is the neighbor’s dog.
Unlike perception, language comprehension is not obviously also believ-
ing. Doubting our eyes or ears is difficult, but doubting a writer or speaker
comes easily. nevertheless, everyday human interaction would not work
if everybody doubted everything everybody said. in the normal course of
events, we tend to believe rather than disbelieve. This habit starts early: Many
of our beliefs are imposed on us by our parents while we are still too young
to conduct an independent evaluation. in discourse as well as vision, belief is
the default and doubt is the exception; as long as new information does not
contradict prior beliefs, it is typically accepted as true. This Principle of Truth
as Default is the reason that April fool jokes work, rumors spread and fiscal
markets experience periods of irrational exuberance.
it follows that in the normal case, a belief base grows monotonically,
through additions and extensions but with no changes in the content or truth
value of any prior belief. everyone undergoes multiple events of this sort every
day; indeed, the phrase “you learn something new every day” has achieved
proverb status. i refer to this case as routine belief formation. The two prin-
ciples of Ubiquitous Encoding and Truth as Default plus the standard psycho-
logical principles of perception, language and memory that can be found in
psychology textbooks are sufficient to understand routine, monotonic belief
formation.
The matter stands quite differently when a person receives information
that contradicts one or more of his beliefs. The cognitive processes triggered
by new but contradictory information cannot be limited to the monotonic
processes of encoding its content and accepting it as true. To maintain coher-
ence in his belief system, the person also has to resolve the contradiction.