Albino rats can reliably distinguish between the odors of stressed and unstressed rats. Five animals learned to interrupt an ongoing response when air from the cages of stressed rats was introduced into the test compartment, and to continue responding when air from unstressed rats was introduced. The discrimination does not seem to depend on recognition of odors of individual rats.

The present experiment is concerned with resistance to extinction after a schedule of partial reinforcement as compared with continuous or 100 per cent reinforcement. In this case the partial reinforcement was effected according to a fixed time schedule or periodically.A number of different ways are available for reinforcing responses only part of the time. Pavlov (8) introduced the procedure of presenting reinforcement on alternate trials, then on every third trial, and finally on every fourth presentation of the CS. Skinner (10) later extensively examined a partial reinforcement procedure which he called reinforcement at a fixed ratio. It consists of presenting the reinforcing stimulus after a prescribed number of responses.A second method of fractionating reinforcement was reported by Skinner in 1933 ( 10). This consists of periodic reinforcement or reinforcement according to a fixed time schedule. That is, a response after a specified interval is followed by presentation of the reinforcing stimulus with intervening responses going unreinforced. Thus a rat depressing a lever may receive a pellet of food when it responds after a two minute interval has lapsed. Clock time is the critical variable in this procedure. Rate of responding is inversely related to the length of the time interval where the latter is varied from one to 12 minutes (10).The consequences of these two procedures-periodic reinforcement and reinforcement at a fixed ratio-are grossly different (10). In conditioning, the rate of responding decreases as the time interval in periodic reinforcement increases and the rate of responding curves are smooth. With fixed ratio reinforcement the rate of responding in conditioning is somewhat higher at the larger ratios with all rate curves exhibiting a typical scalloped effect produced by reduced rates of responding immediately following presentation of reinforcement. More rapid responding is differentially strengthened in the fixed ratio case. In periodic reinforcement, on the other hand, very prolonged exposure results in reduced rates of responding which Skinner (10) has interpreted as the formation of a temporal discrimination. The effects of the two techniques seem to be greatly different in extinction. After fixed ratio reinforcement, rate of responding is extremely high and the extinction curves break sharply. (Whether this is a fatigue phenomenon has not been investigated.) In extinction following this procedure, if responses are to come out, they appear rapidly. In extinction after periodic reinforcement, Skinner (10) has suggested that the rate is lower than after continuous reinforcement although the ultimate level attained in terms of number of responses may be higher. The present study is concerned with this issue.A third way of presenting reinforcement for only part of the responses is the procedure more recently developed by Skinner (11) of aperiodic reinforcement or reinforcement according to a random or irregular time schedule. This technique circumvents the ultimate

No abstract

No abstract

No abstract