2013年8月22日木曜日

Ant colonies outperform individuals when a sensory discrimination task is difficult but not when it is easy

Takao Sasaki, Boris Granovskiy, Richard P. Mann, David J. T. Sumpter, and Stephen C. Pratt
PNAS August 20, 2013 vol. 110 no. 34 13769-13773

アリの集団は、単独個体と比べて、より良い意思決定ができるのか(より良い営巣地を見つける)?
課題が難しい(二つに営巣地の候補が似ている)場合、集団の方がより良い意思決定ができる。
一方、課題が簡単(より優れた営巣地が明らかに分かる)な場合は単独個体の意思決定の方が優れている。

“Collective intelligence” and “wisdom of crowds” refer to situations in which groups achieve more accurate perception and better decisions than solitary agents. Whether groups outperform individuals should depend on the kind of task and its difficulty, but the nature of this relationship remains unknown. Here we show that colonies of Temnothorax ants outperform individuals for a difficult perception task but that individuals do better than groups when the task is easy. Subjects were required to choose the better of two nest sites as the quality difference was varied. For small differences, colonies were more likely than isolated ants to choose the better site, but this relationship was reversed for large differences. We explain these results using a mathematical model, which shows that positive feedback between group members effectively integrates information and sharpens the discrimination of fine differences. When the task is easier the same positive feedback can lock the colony into a suboptimal choice. These results suggest the conditions under which crowds do or do not become wise.

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