Medlab 8 Protocol Summaries

Fixed Ratio (FR):

  • A response is reinforced only after a specified number of responses (default = 1)
    Produces a high, steady rate of responding with only a brief pause after the delivery of the reinforcer

Fixed Interval (FI):

  • The first response is rewarded only after a specified amount of time has elapsed (default = 1 sec)
  • Causes high amounts of responding near the end of the interval, but much slower responding immediately after the delivery of the reinforcer

Variable Ratio (VR): 

  • A response is reinforced after an unpredictable number of responses (mean of 5, ranging from 1 to 20)
  • Gambling and lottery games are good examples of a reward based on a variable ratio schedule
  • Creates a high steady rate of responding

Variable Interval (VI): 

  • A response is rewarded after an unpredictable amount of time has passed (mean of 10 sec, ranging from 0.25 to 39.96 sec)
  • Produces a slow, steady rate of response

Random Ratio (RR): 

  • The random ratio value specifies the probability with which a response will be reinforced
  • 20% chance of reinforcement on each response

Random Interval (RI):

  • Each passing of the interval time has a possibility that the program will move onto the next step. If it doesn’t, the program will go back and time the interval time again, thus obtaining a random interval
  • A “timer” has a 20% chance of timing out every 2 seconds

Chain (CHAIN): 

  • “Chains” two responses together
  • Typically run in test chambers with two standard response levers and stimulus lights
    The stimulus light for the first correct lever turns on, then the animal must press that lever enough times to meet the first user-defined FR value, then the light turns off
  • Then, the stimulus light for the second correct lever turns on, the animal must now press that lever enough times to meet the second FR, then a reinforcement is issued
  • Two part chain where the first FR = 1 and the left lever is the correct lever
  • The second FR = 5 and the right lever is correct

Discrimination (DISC): 

  • Stimulus light breaks the session time into alternating periods of extinction (no light) and fixed ratio (light on)
  • GO/NO-GO The default procedure switches S+ and S- every 30 seconds for the duration of the procedure