An Example Of A Timing Experiment 131 Procedure and Results

Ten rats were trained on an 82.5-sec fixed-interval schedule of reinforcement for 15 3-h sessions. In this schedule, food was delivered immediately after the first lever response after the fixed interval from the previous delivery of food. The rats were then given five sessions of training on ten different fixed-interval schedules (15, 30, 45, 60, 75, 90, 105, 120, 135, and 150 sec). In each set of five sessions, one rat received each interval. That is, a Latin square design was used. For this example, the analysis will use the last three sessions of each rat from the fixed-interval schedules of 30, 60, and 120 sec.

The mean response rate increased as a function of time since the previous food, as shown in Figure 1.3. In this figure, response rate is shown in absolute units

FIGURE 1.3 Response rate as a function of time since food for fixed-interval reinforcement schedules of 30, 60, and 120 sec. (Unpublished data from our laboratory.)

(responses per minute) and time is also expressed in absolute units (seconds). This temporal gradient increased earlier for the 30-sec FI than for the 60-sec interval, and earlier for the 60-sec interval than for the 120-sec interval. The height of the gradient was positively related to the interval duration, and the response rate immediately after food delivery was greater than the response rate a few seconds later.

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