Operant Conditioning – Chapter 8 Theories of Learning October 14, 2005 Class #23

Discriminative Stimulus (SD ) A stimulus in the presence of which responses are reinforced and in the absence of which they are not reinforced… Basically, its a signal that a response will be followed by a reinforcer It signals the availability of the reinforcer thus increasing the probability it will occur The behavior then is considered to be under stimulus control See next slide…

Stimulus Control Having stimulus control means that the probability of the behavior varies depending upon the stimuli present Our behavior often comes under stimulus control without our awareness A person that contributes to charity generously while in church, but watches every penny spent while at work SD  R  SR ??  ??  ??

Stimulus Control: Generalization Generalization is when responses to one stimulus occur to other, usually similar stimuli Generally, as the training and test stimuli become more different responding will decline, producing what is called a generalization gradient

Generalization Gradient Guttman & Kalish (1956) Pigeons were reinforced for pecking a 580 nm lit key (orange-yellow) on a VI schedule A test session was then given where many different colored key lights were presented in extinction

Stimulus Generalization as a Measure of Stimulus Control Training S+ Pigeons were trained to peck in the presence of a colored light of 580 nm wavelength and then tested in the presence of other colors. Guttman & Kalish (1956)

Stimulus Generalization: Applied Rincover & Koegel (1975) were attempting to train autistic children to imitate One child, Joey, learned to touch his head when the Experimenter said “do this” and touched his own head; unfortunately, it took 300 trials A generalization test in a different location and with a different experimenter, resulted in 0% correct responses It turned out that the first Experimenter had frequently held Joey’s hands in his lap before each trial began Another generalization test was conducted and this time the new experimenter held Joey’s hands first, then said “do this” & touched his head: resulted in 60% correct responding A third test was conducted and the experimenter just held Joey’s hands in his lap: 100% correct responding What gained stimulus control???

Stimulus Control: Discrimination A better procedure for training Joey would have been to use discrimination training… Discrimination training involves presenting at least 2 stimuli but reinforcing only one of them Discrimination is differential responding to multiple stimuli A discriminative stimulus for extinction (S∆) is a stimulus that signals the absence of reinforcement

Stimulus Control: Discrimination Azrin & Hayes (1984) used discrimination training to increase males’ sensitivity to cues signaling females’ level of interest in males Subjects were shown 24 film clips of couples conversing; half were positive instances of female interest and half were negative instances Subjects were reinforced for correctly identifying whether each slide involved female interest or not The male subjects increased their correct responses by over 50% as a result of the training

Stimulus Control: The Peak Shift Effect The peak shift effect is when the peak of a generalization gradient shifts away from the S∆ following discrimination training

Hanson (1959) Procedure Several groups of pigeons pecking different colored key lights The control group was trained with just one stimulus, a 550 nm key light, reinforced on a VI schedule The experimental groups were given successive discrimination training with 2 key lights, the 550 nm light was always the SD, and different groups had a different wavelength as the S∆

Hanson (1959): The experimental group had a 590 S∆

“Mr. Shallow” example… “Mr. Shallow” identifies women on just one quality – introversion vs. extroversion He has just broken up with Jackie who is an introvert (he said she’s boring) Jackie is the discriminative stimulus for extinction (S∆) here Earlier in his life, “Mr. Shallow” had an exciting relationship with Liz who was a pure extrovert Liz is the Discriminative Stimulus (SD ) here

“Mr. Shallow” example… “Mr. Shallow” moves to a new city and starts hitting the singles bars seeking a new partner According to the peak shift, what type of woman will he be trying to “hook up” with???

Stimulus Control: Multiple Schedules A multiple schedule is a complex schedule of reinforcement It is like a chained schedule except that each link is reinforced A multiple schedule consists of 2 or more simple schedules presented in sequence, each resulting in reinforcement and each having a distinctive SD

Stimulus Control: Behavioral Contrast Behavioral contrast is a change in a reinforcer’s effectiveness caused by previous experience with other reinforcers The change may be due to the schedule of reinforcement or the magnitude of the reinforcer Positive contrast occurs when the previous reinforcer was less valued (current reinforcer’s effectiveness is increased) Negative contrast occurs when the previous reinforcer was valued more (current reinforcer’s effectiveness is decreased)

Crespi (1942)

Stimulus Control: Behavioral Contrast If presented a signal that indicates a change in rate or magnitude of reinforcement is about to begin, anticipatory contrast will often occur Anticipatory contrast is a change in behavior (increase or decrease) in inverse anticipation of an upcoming change in reinforcement (decrease or increase)

Seems to be the case with us to right from the start… Kobre and Lipsitt (1972) Participants Newborns Procedure Artificial nipple that either gave reinforcer of sucrose or water Results Support contrast effect

Stimulus Control: Fading & Errorless Discrimination Learning Errorless Discrimination Learning involves setting up the discrimination training procedure in such a way that the organism learns the discrimination without making mistakes Do all shaping (pretraining) with the SD only, which is always associated with reinforcement Fade in the S∆ gradually (start with a weak version and work up to the final strength of the stimulus)

Stimulus Control: Fading & Errorless Discrimination Learning There are fewer adverse side effects (e.g., frustration) during learning when using an errorless discrimination procedure However, organisms are less flexible when the discrimination changes if they were trained with an errorless procedure versus the standard approach Therefore, you should only use the procedure for factual information where the response requirements are unlikely to change

Haupt et al. (1975) Participant 9 year-old girl with math difficulties Procedure Correct answers were gradually faded out

Stimulus Control: Additional Applications Training animals for public performance Targeting Eliminating problem behaviors in animals Training in and/or eliminating human behaviors Improving study habits Reducing insomnia

Credits: www.radford.edu/~pjackson/ExtinctIC.ppt