Figure 7. Behavioral Logic for Operant Training and Discrimination Testing.

All diagrams use 0.5-s intervals here for clarity; the actual sampling rate was 16 Hz.

(A) Lever press response training. Animals that waited D seconds without emitting a lever press would elicit an audio prompt that signaled the start of a trial. The first lever press response in the following T = 6 s was rewarded with a drop of water. At the end of the trial, any remaining water was withdrawn. D was increased from 0.25 s to 4 s.

(B) Nose poke training. D was first increased from 4 to 60 s to decrease the frequency of trial initiated by waiting. Trials could alternatively be initiated if an animal placed its nose in the nose poke for N seconds. As this behavior was established, N was increased from 0.063 s to 1.5 s.

(C) Stimulus training. All trials in this stage were initiated by a 1.5-s nose poke. Each trial was randomly assigned as either S+ or S−, and the start of the trial was signaled by the descent of the corresponding stimulus pin. The pin remained in the vibrissa field until nose fixation was broken or until the trial ended. In S+ trials, the first lever press response after the start of the trial resulted in a reward. If no response occurred within P seconds, an audio prompt sounded. P was increased from 0.125 s to 6 s. Lever presses were ignored in S− trials.

(D) Stimulus discrimination testing. The audio prompt was eliminated from S+ trials. The number of lever press responses, L, required to obtain a reward in S+ trials was increased until a difference between S+ and S− responses was apparent. This value was typically L = 5 or 6; the example here illustrates L = 2. The structure of S− trials was unchanged.