Dr Caster Decides to Perform an Experiment Investigating the Effects

Multiple Choice

Dr. Caster decides to perform an experiment investigating the effects of caffeine and sugar on motor skill performance. He randomly assigns his subjects to one of four groups: high caffeine/high sugar, high caffeine/no sugar, no caffeine/high sugar, no caffeine/no sugar. People in each group are given a soft drink containing the appropriate levels of sugar and caffeine, and then tested on a mirror tracing task. Dr. Caster finds that the people in two of the groups the high caffeine/high sugar and the no caffeine/no sugar) perform at about the same high level, while the other two groups the no caffeine/high sugar and high caffeine/no sugar) perform at about the same poor level. Dr. Caster's results show

A) a main effect of caffeine
B) a main effect of sugar
C) a synergistic interaction
D) an antagonistic interaction