Task difficulty and motor performance in severe subnormality

Three groups of subjects (mentally subnormals, normal adults, and normal children) performed on the pursuit rotor apparatus on two separate occasions. The first involved ten trials with the rotor revolving at 15 rpm, the other ten trials being performed at the more difficult speed of 30 rpm. The results tentatively suggest that IQ, and not MA, is the critical factor involved in the intelligence-complexity interaction in pursuit rotor performance, since the subnormals were most adversely affected by an increase in task difficulty. The implication of this conclusion for the direction of future research is discussed.