1. An introduction to motivation;Atkinson,1964
2. Distribution of practice and specificity of learning in normals and retardates;Baumeister;American Journal of Mental Deficiency,1967
3. Conflict, arousal, and curiosity;Berlyne,1960
4. Effects of task difficulty on naming performance of aphasic subjects;Brookshire;Journal of Speech & Hearing Research,1972
5. Incentive conditions which influence visual exploration;Butler;Journal of Experimental Psychology,1954