The attraction effect in motor planning decisions

In motor lotteries the probability of success is inherent in a person’s ability to make a speeded pointing movement. By contrast, in traditional economic lotteries, the probability of success is explicitly stated. Decision making with economic lotteries has revealed many violations of rational decision making models. However, with motor lotteries people’s performance is often near optimal, and is well described by statistical decision theory. We report the results of an experiment testing whether motor planning decisions exhibit the attraction effect, a well-known axiomatic violation of some rational decision models. The effect occurs when changing the composition of a choice set alters preferences between its members. We provide the first demonstration that people do exhibit the attraction effect when choosing between motor lotteries. We also found that people exhibited a similar sized attraction effect in motor and traditional economic paradigms. People’s near-optimal performance with motor lotteries is characterized by the efficiency of their decisions. In attraction effect experiments performance is instead characterized by the violation of an axiom. We discuss the extent that axiomatic and efficiency measures can provide insight in assessing the rationality of decision making.