Steady-state performance of a subject under a schedule was developed and is shown in Fig. 1. The schedule was mult FR30 FI300s, which is technical shorthand for the following schedule: A stimulus, A, starts: When the subject has made 30 responses, a reinforcer is presented (FR30). Then, a stimulus starts again. If it is A, then FR30 is in effect again. If, however, it is a different stimulus, B, then the first response after 300 sec has elapsed leads to the reinforcer. FR and FI components continue in an irregular sequence (Fig. 1), with each component accompanied by its distinctive stimulus. In Fig. 1, each of the four upward-sloping continuous lines shows a complete session. The sessions are spaced some days apart. The record is

Figure 1 Effects of three different doses of phenobarbital in the same subject. Ordinate is cumulative number of responses in session. For description see text (reproduced with permission from Annals of the New York Academy of Sciences 65, p. 272, Fig. 5, 1956).

made by an ink pen on paper moving from left to right. Each response moves the pen one step up the paper. Results today are not obtained, of course, by measuring a record with a ruler, any more than astronomers hand measure star positions on a photograph. The computer presents results as desired. But graphic displays are still useful in communicating information, and some workers still find the cumulative record a useful real-time monitor.

The leftmost line in Fig. 1 shows the control performance. The remaining three records show the performance of the same subject after doses of 5.7, 10, and 17 mg of phenobarbital, from left to right. (Phenobarbital was widely prescribed in low doses during the first half of the 20th century for its calming effect).

The subject was a pigeon, a frequently studied subject at the time, on a restricted diet; during the session, operation of a key led intermittently to brief food deliveries, the reinforcer. Each session comprised five FR30 segments and five FI 300s segments, each concluded by food delivery. The two distinctive stimuli were visual, different colored lights, consistently accompanying the FR components and the FI components. The sequence of components was the same in all sessions: FR30, FI300 sec, FR30, FI300 sec, FI300 sec, FR30, FR30, FR30, FI300 sec, and FI300 sec. The sessions thus lasted about 30 min. In the first record, labeled "O" (a control session), the FR components appear as two horizontally (i.e., timewise) closely spaced hatch marks with a high constant rate of responding (steep slope). The FI components, in contrast, show low or absent responding at the beginning of the interval, followed by a period of acceleration (short here) to a rate less than that under FR that is then sustained until the interval ends and the reinforcer ensues.

The effects of phenobarbital are major and obvious. Following 5.7 mg, the total number of responses in the session increased to about 1500 (averaging more than 1 per second) compared to about 750 in the control session. Responding under FR is not visibly changed, although the rate is actually somewhat increased. The initial pause in the intervals is markedly attenuated by the phenobarbital so that responding approaches a constant rate through the interval. It should be noted that the 5.7-mg dose is already higher than the usual daily dosage that was given to ambulant patients: The effects, however, are also greater than were sought therapeutically.

Following 10 mg of phenobarbital, FR responding is still not visibly affected, but responding under FI is reduced and almost abolished in the fourth interval. Following 17 mg, responding under FI is abolished, but one FR is completed, albeit at an abnormally low rate of responding.

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