These three habits could be said to be arranged in a hierarchy according to thier strength. The same principal can apply to human learning. For example, in the Stroop test, reading is a stronger habit than color naming. If we call reading the Stroop test the correct response, the Stroop is a much easier task than if we call color naming the correct response. Thus easy tasks are those that are defined as having the dominant habit as the correct response.
Difficult tasks have a subordinant habit as the correct response.
Don't start to write your intros yet. In stimulus generalization studies, Mednick could only find results consistent with the theory when using naive subjects. Veterans of psych research studies did not behave according to the theory. S-S also found that MAS effects were more likely to occur when using naive Ss, dim rooms, and conditions that made subjects uneasy. So the anxiety theory was revised using other aspects of Hull-Spence theory.