Judgement bias in predicting the success of one's own basketball free throws but not those of others.

Skilled basketball players are supposed to hit more often from the free throw distance than would be predicted by their shooting performances at adjacent distances. This is dubbed an especial skill. In the current study, we examined whether especial skills in free throw performance in basketball map onto especial skills in visually judging the success of basketball free throws. In addition, we tested whether this effect would be present in those who predict their own shots but absent in those who judge shots performed by another person. Eight skilled basketball players were coupled with eight equally skilled players, and performed 150 set shots from five different distances (including the free throw distance) while the yoked partner observed the shots. At the moment of ball release, the performers' and the observers' vision were synchronously occluded using liquid-crystal occlusion goggles, and both independently judged whether the shot was successful or not. Results did not replicate an especial skill effect in shooting performance. Based on signal detection theory (SDT) measures (d' and criterion c), results also revealed no especial skill for visually discriminating successful from unsuccessful shots at the foul line when compared to other distances. However, players showed an especial skill judgement bias towards judging balls 'in' at the foul line, but not at other distances. Importantly, this bias was only present in those who judged the success of their own shots, but not in those who judged the shots performed by someone else.