 For example, Esther Thelen and colleagues found that babies would not make the A-not-B error if they had small weights added to their arms during the first phase of the experiment that were then removed before the second phase of the experiment.This minor change should not impact babies' understanding of object permanence, so the difference that this makes to babies' performance on the A-not-B task cannot be explained by Piagetian theory.Thelen and colleagues also found that various other factors also influenced performance on the A-not-B task (including strength of memory trace, salience of targets, waiting time and stance), and proposed that this could be better explained using a dynamic systems theory approach than using Piagetian theory.