[Decision strategy as a function of uncertainty of the result: I. Latency of the decision]

Until now, the decision strategy used by human beings faced with a dichotomous situation was studied considering that speed of reaction was the main dependent variable. It was found that, in a two choice reaction time (CRT) task, subjects used a very conservative decision strategy. That is, when compared with events of 0.5 probability, only those events with a probability of no less than 0.9 caused a significant decrease in CRT. In real sport situations however, the tennis player can not only increase his speed of response but can also change his position on the court in order to defend more appropriately the area of the court which appears more likely to be attacked. Two experiments were conducted in order to verify this hypothesis. In both experiments, a two CRT task was used; the independent variables being: (a) event probability and (b) time allotted to complete the appropriate response (TA). Results indicate that as soon as the probability of an attack reached 0.7, subjects started initiating defensive responses closer to the most probable area of attack. It thus appears that subjects were not as conservative as that reported in studies where CRT measures only were considered. On the other hand, subjects used a strategy which enabled them to reduce their total response time without increasing choice errors. In fact it seems that, when facing event uncertainty, the main concern of the human being is to keep his error rate as low as possible even if this is not the best strategy to use.