Training Sessions Five through Thirteen: Fixed Ratio Schedules of Reinforcement

Goal: 
To successfully train Tessa to press the bar for an increasing number of required behaviors. In order to reach the final behavior requirement of 20 bar-presses per reinforcement (FR 20), I gradually stretched the ratio from the original FR1 through FR2, FR3, FR5, FR7, FR10, and FR15.

Procedure: 
For each fixed ratio level, Tessa was reinforced for performing the correct number of bar-presses dictated by the FR level. Tessa was not manually reinforced for any behaviors, nor was she encouraged to approach the bar through additional reinforcement. Each session was run for a minimum of twenty minutes. Runtimes for each session are below:

Date	Schedule	Runtime (minutes)
9/25	FR2	23.75
9/26	FR3	21.58
9/27	FR3	22.00
9/28	FR5	21.50
9/29	FR7	22.67
9/30	FR10	28.52
10/01	FR15	21.77
10/02	FR15	24.00
10/04	FR20	29.33
10/05	FR20	22.26

 

Results:
Tessa performed a minimum of 200 bar-presses (FR2) and a maximum of 810 bar-presses (FR10) during her Fixed Ratio Training. FR3 and FR15 schedules were performed over multiple days to ensure Tessa learned the new schedule. As shown in Figure 1, Tessa performed more bar-presses on day 2 of the FR3 and day 2 of the FR15 schedules.

Figure 1: Total number of instrumental behaviors (bar-presses) per training session. Refer to Table 1 for session runtimes. Sessions are listed in the order they were performed.

Discussion:
Tessa made considerable progress through the Fixed Ratio Schedules of Reinforcement during her training. Initially, she became frustrated as the requirements for reinforcement were increased. For example, she began to exhibit escapist behaviors during the first day on FR2 schedules. These behaviors included climbing to the top of the Operant box on all sides, as well as actually climbing to the middle of the top of the Operant box. Although these behaviors were not eliminated, they were mitigated by blocking all exits from the box. You can read about how I reduced these behaviors here.

Although I was able to mitigate some of these troublesome behaviors, Tessa's wide variety of behaviors did affect the efficiency of her training. She was likely to perform a multitude of behaviors between each reinforcement, especially after at least ten minutes of training had elapsed. She would typically receive a reinforcement, then spend at least one minute exploring the rest of the Operant box. She would sniff the front window of the box, climb on all of the walls, and put her nose through any openings in the box. Nevertheless, she developed a better understanding of my expectations as training progressed. She was less likely to spend time exploring as the schedules were increased, which may be simply due to the higher requirements of each schedule. Furthermore, Tessa was likely to become distracted by any activity in the laboratory. This was worst when multiple students were in the lab at one time. In order to alleviate this, I used the rat privacy cover for FR10, FR15, and FR20 schedules.

On average, Tessa became satiated during each training session around 20 minutes of training. This lack of instrumental responses could be attributed to the fact that I ended her earliest shaping sessions after running less than 25 minutes of training. She may have expected to be released from the Operant box, and most importantly she may have assumed she would be released at a specific time and received rat chow in the holding room. The amount of rat chow given on the previous day did not seem to affect her motivation to perform in the Operant box. Likewise, I had difficult maintaining her target weight of 203 grams - however, she did not seem to be any less motivated when she gained weight compared to when she lost weight. You can read more about the schedule of food deprivation here.

Tessa's style of bar-pressing was not the desired style: instead of using her paws to press the bar, she typically pressed the bar with her nose or cheeks while holding a paw on the bar. This shows that the shaping of putting her paws on the bar was shaped successfully, but the behavior of pushing on the bar with her paws may have been overlooked - or possibly replaced by the reinforcement of pressing the bar with her cheeks during the FR schedules. Nevertheless, Dr. Trench once quoted B.F. Skinner as saying "a bar-press is a bar-press is a bar-press," so I did not attempt to change Tessa's style of bar-pressing.

The increase in Tessa's bar-pressing behavior was a function of the schedule she was on at the time: when she was on a higher schedule, she pressed the bar more times than on lower schedules. However, she did not achieve fifty reinforcements for each schedule of reinforcement. I thought fifty reinforcements would be a good goal, but she did not achieve this goal in either of the FR20 sessions. She received a maximum of 90 reinforcements (FR2) and an average of 68 reinforcements across all trials. Figure 2 illustrates the number of reinforcements received during each training session.

Figure 2. Total number of reinforcements per training session. Refer to Table 1 for training runtimes. Schedules are ordered by date they were performed.