Science News - February 12, 2011

since there would be nothing to predict
anyway.”
Evolutionary forces and learned
expectations jointly produce streak-
seeking minds, proposes psychologist
Andreas Wilke of Clarkson University
in Potsdam, N. Y. In the distant past and
in the present moment, in stands of trees
dotting a savanna and in shopping malls
punctuating an urban sprawl, desirable
stuff clusters together.

A gambler’s dilemma

In support of the idea that human thinking — not just brain activity but also how the brain reads the environment—is attuned to streaks, Scheibehenne and his colleagues have found that volunteers prefer betting on the next symbol to appear on a computerized slot machine if they have seen one or both of its two symbols (cherries and a peach, for example) come up several consecutive times on a regular basis, rather than in a random succession that includes a few clusters here and there. That makes sense for gamblers, since a streaky machine is more predictable than a random one.

In contrast, bettors trying to decide whether cherries or a peach would turn up next tended to do poorly and to give up on machines with symbols that frequently alternate, apparently overlooking the predictable back-and-forth pattern, the scientists report in an upcoming Evolution and Human Behavior.

Betting patterns of the 238 participants in the slot machine study— who were vying for $50 awards given to the top two gamblers — signaled an intuitive preference for streaky sequences, says Scheibehenne. Slot machines elicited a foraging strategy used by animals that seek food distributed in patches, whether icons were programmed to appear randomly or regularly in long strings.

Foraging for slot machine successes in this way worked best on streaky machines and worst on alternating machines.

Finding clumps of anything depends on a simple rule of thumb: Keep searching in the same place after a successful choice, such as finding a berry in a bush, and move to another spot after a failed attempt or two. For alternating sequences, the opposite approach works better: Look elsewhere after a correct choice and stay put after an error, because the situation will reverse quickly.

For random sequences anything goes, because all strategies do equally poorly.

In Scheibehenne’s study, volunteers saw two slot machines on a computer screen. Participants didn’t know which machine generated a random sequence of icons and which one produced a sequence that alternated icons or clustered them together to varying extents. Overall, players continued to bet on streaky machines

70 percent of the time after making winning choices. And players used the patch-finding strategy on about half of their alternating-machine bets and a bit more often than that when wagering on random machines.

“Participants may have had a general tendency to use the appropriate choice strategy for streaky environments as a default strategy in all cases, which could explain their inferior performance on alternating sequences,” Scheibehenne says.

Consistent with that possibility,
participants made progressively more
losing bets on slightly and moderately
alternating sequences over 250 trials,
appearing to become increasingly con-
fused, rather than learning to predict
back-and-forth swings.
These findings build on evidence of
hot-hand thinking across cultures that
was reported in 2009 by Wilke and
anthropologist Clark Barrett of the
University of California, Los Angeles.
Wilke and Barrett developed a com-
puter game that simulates a search for
fruit trees in a forest and for modern
resources such as parking spaces. In
100 trials, each player decides whether
to stay in the same spot or
move to a new spot to find
what they want. In each case,
resources are randomly dis-
tributed.

Among 32 UCLA students and 32 Shuar hunter-gatherers living in an In another exercise, the students and hunter-gatherers tried to predict 100 random coin flips. Half the students, who knew about the concept of randomness, usually assumed incorrectly that getting heads meant that the next flip would yield another heads, and getting tails would lead to another tails. So did nearly all Shuar.

“This supports the idea that hot-hand thinking is an evolved default, which, in cases of true randomness, must be learned out of,” Wilke says.

In stands
of trees
and in
shopping
malls,
desirable
stuff clusters
together.

Hunting and gathering Even in a video game where players roam huge domes searching for chests that contain glowing green spheres, a foraging tactic that evolution has honed for finding patches of berries and other

Picking winners in a new study, volunteers predicted whether cherries or a peach would next appear on a slot machine programmed to frequently alternate the symbols (top) or to deliver them in clusters (bottom). people appeared to expect streaks in both cases. source: