It is important to distinguish between learning (including conditioning) and performance. The phenomena of cognitive maps and of latent learning both demonstrate that something may be learned but not shown until later. Factors that influence learning. Several factors may affect learning. Learning generally increases with increased amount of practice or training. Practice alone, however, is not enough. Classical conditioning requires an unconditioned stimulus (UCS); operant conditioning requires reinforcement (positive or negative). Within limits, the amount of reward can affect learning, although the relationship between the two is complex, and the subject has been studied extensively. Surprisingly, an increase in reward can sometimes cause a decrease in response. Delay of reward is also much studied. In general, only a short time should elapse between a response and its reinforcement. In partial reinforcement, a subject is not rewarded every time for making a response. In general, partial reinforcement leads to a greater persistence in behavior than does continuous reinforcement. (Slot‐machine players can attest to this fact.) Interstimulus time, the time between presentations of a given stimulus, can also be important in both classical and operant conditioning. Optimal conditions can be determined for a particular situation. Factors that influence performance. Since learning is a relatively permanent change in behavior that occurs as a result of experience, experimenters must be certain that factors other than learning have not influenced the responses being studied and be alert to what those factors might be. Several factors that influence performance but not necessarily learning include the following. Variations in level of motivation can influence performance. For example, if two rats have been through the same conditioning process but one of them is denied food until it is very hungry, that rat may press a bar that produces a food pellet with more vigor than the less‐hungry rat. The vigor of the response, in this case, does not reflect different degrees of learning—both rats have learned the bar‐pressing response—but rather different levels of motivation. Stimulus intensity may influence performance as well. But while a more intense CS might produce a stronger conditioned response (CR), the increased vigor of the response does not necessarily, and in general does not, indicate greater learning. If extreme effort must be used in a response, for example in pressing a weighted bar, fatigue may affect a subject's performance. Intertrial intervals have also been shown to affect performance. Too many trials too quickly can result in decreased performance simply because of fatigue or boredom.