Scientific American Mind-June/July 2007

garding whether they have perceived
something and then must wager either
a small or a large amount of money on
their degree of confi dence in this decision.
If the person’s decision proves
correct, she wins this money; otherwise,
she loses it. The optimal strategy
is to bet high whenever she feels that
she is not merely guessing. The experimenters
apply this wagering technique
to three examples of nonconscious
processing.
The fi rst experiment involves patient
G.Y., who has “blindsight” from
a car accident that damaged areas of
his brain involved in visual processing.
This condition leaves him with the
nonconscious ability to locate a light
or report the direction in which a colored
bar on a computer screen is moving,
although he denies having any
visual experience of that bar; he insists
that he is simply guessing. G.Y. can indicate
the presence or absence of a
faint, small grating correctly in 70
percent of all trials, far above chance
(50 percent). Yet he fails to convert
this superior performance into money
when wagering; he places a high bet
on only about half (48 percent) of his
correct choices. When G.Y. is consciously
aware of the stimulus, he wagers
high—much as you or I would.
His wagering thus seems to mirror
his conscious awareness of the stimulus
(that is, his belief that he saw it)
rather than his actual (unconscious)
detection of the stimulus, suggesting
that wagering may provide a means to
measure awareness.
The second experiment involves an
artifi cial grammar task in which participants
learn a small number of short
letter strings. They are then told that
the strings obeyed a simple rule (of the
kind, for example, that every “x” is
followed by an “a”). But they are not
told what the rule is. When shown a
new string, subjects can more often
than not determine correctly whether
the new string follows the unknown
rule. Yet only rarely can they articulate
why they believe a string does or
does not obey the rule. The overall
rate of correct classifi cation (81 percent)
is far better than chance. Yet
subjects do not convert performance
into money. High wagers follow a correct
choice 45 percent of the time and
follow a false choice 32 percent of the
time. In short, the study participants
are usually right about whether the
string follows the rule, but they lack
enough confi dence to bet on it.
Winning Hands
In the fi nal experiment, called the
Iowa gambling task, subjects pick the
top card from one of four decks. Each
card wins or loses the person a certain
amount of money. Unbeknownst to
the participants, two of the four decks
have a net positive yield and two have
a negative yield. They must place a
low or high wager on the chosen card
before it is revealed and lose or win
accordingly. In the test, the subjects
turn scores of cards over, one by one,
each time fi nding out whether they
win or lose. They almost always fi gure
out which decks are winners and
start to pull cards mostly from those
decks—but they usually turn over at
least 30 cards on those decks before
they gain the confi dence to bet aggressively
on the results. That is, subjects
only start to make money long after
their own behavior should have revealed
that they knew which decks
were winners.
To explore this hesitation, Persaud
and his colleagues used a variant of
this experiment in which they queried
the subjects every tenth trial regarding
everything they knew about the game
and the decks. When the subjects thus
examined their knowledge of the
game, the gap between the onsets of
positive deck selection and advantageous
betting disappeared, suggesting
that the act of introspection alters
subjects’ awareness. Examining their
knowledge made them more aware of
what they knew. This fi nding indicates
( The experimenters apply this wagering technique to three )
examples of nonconscious processing.
(Further Reading)
that if subjects learn to trust their gut
instincts—and bet on knowledge they
are not yet aware of—they can do better,
a demonstration of the utility of
the leitmotif of Western philosophy,
“Know thyself.”
The wagering techniques used by
Persaud, McLeod and Cowey rely on
people’s instinct for reaping a profi t.
Compared with forcing subjects to
become aware of their own consciousness—and
in the process perturbing
the very phenomenon one wishes to
measure—wagering provides a more
subtle way to assess awareness. This
is an exciting and revealing new way
to study awareness and consciousness.
From such small steps comes progress
in answering the age-old question
of how consciousness arises from
experience. M
CHRISTOF KOCH is professor of biology and
engineering at the California Institute of Technology
and serves on Scientifi c American
Mind’s board of advisers. KERSTIN PREU-
SCHOFF is a postdoctoral scholar in decision
theory and neuroscience at Caltech.
◆ The Quest for Consciousness: A Neurobiological Approach. Christof Koch. Roberts
& Company Publishers, 2004.
◆ Post-Decision Wagering Objectively Measures Awareness. Navindra Persaud, Peter McLeod
and Alan Cowey in Nature Neuroscience, Vol. 10, pages 257–261; January 2007.
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