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PSYC 2210
Tony Neild

Chapter 10 Stimulus Control and Concept Formation stimulus control: the relationship between stimuli and the behaviours that follow them; behaviours can be controlled by the stimuli that precede them generalization: a subjects tendency to respond to novel stimuli in much the same way that it has previously responded to similar, familiar stimuli Generalization gradients generalization gradient: a graphic representation of generalization in which the x-axis plots some dimension along which the test stimuli are varied and the y axis shows the strength of conditioned responding to the different stimuli Ways to obtain generalization gradient use probe trials in which are occasionally inserted among reinforced trials with the training stimulus ex: other colours are briefly presented to measure the pigeons responding but no reinforcer is given the advantage of embedding probe trials among reinforced trials with the training stimulus is that the procedure can continue indefinitely without the threat of extinction until sufficient data are collected disadvantage: subject may begin to form discrimination Another method is : to start with the same training phase ex: pigeon learns to respond to yellow key light then follow with a series of extinction trials with both the yellow light and other colours the trick is to obtain enough trials with each stimulus before responding extinguishing , which can often be accomplished by keeping the durations of extinction trials short What causes Generalization Gradients? Pavlov's answer was that generalization is an automatic by-product of the conditioning process he believed that generalization is an inherent property of the nervous system cannot be so easily dismissed ; generalization gradients are innate Lashley and Wade: some explicit discrimination training along the dimension in question is necessary before the typical peaked generalization gradient is obtained; without discrimination training, generalization gradient would be flat and the subject would respond just as strongly to all novel test stimuli as to the training stimulus; depend on learning experiences How Experience Affects the Shape of Generalization Gradients Jenken's and Harrison 1960 2 groups of pigeons, VI schedule 1000Hz tone 3 pigeons received non differential training: every trial was the same- the key light was lit, the 1000hz was on, Vi schedule 5 other pigeons received presence-absence training, which included 2 types of trials 1) trials with 1000hz tone 2) trials without the tone, during which the key light was lit as usual but no reinforcer after training: extinction trials, different trials included different tone frequencies, or no tone at all non differential training produced generalization gradients that were basically flat; response rates were roughly the same at al tone frequencies presence-absence training produced typical generalization gradients with sharp peaks at 1000hz S+ a discriminative stimulus for reinforcement, S- a discriminative stimulus for the absence of reinforcement intradimensional training: a type of discrimination training in which responses in the presence of one stimulus are reinforced, but responses in the presence of a different stimulus from the same physical continuum are not reinforced in summary: generalization gradients are dependent on experiences with non differential training, tone frequency exerted no control over responding after presence-absence training, tone frequency exerted modest control and typical generalization gradients were obtained intradimensional training very sharply peaked gradients were obtained no special training needed for generalization gradients to appear How sensory Deprivation Affects the Shape of Generalization Gradients necessary to prevent the possibility of discrimination learning along the dimension in question from the moment a subject is born Peterson: raising 4 ducklings in an environment that was illuminated with yellow monochromatic light 589 nanometers all objects appeared yellow regardless of their actual colour after training the ducklings to peck at a yellow key got water reinforcement, conducted generalization test with key lights of different colours produced flat generalization gradients, indicating the colour exerted no control over their behaviour this shows that stimulus control by wavelength of light can occur even when a subject has had no previous exposure to more than one colour Is Stimulus Control Absolute or Relational> simultaneous discrimination procedure: 2 stimuli are presented together and the subject must choose between them absolute theory of stimulus control: the animal has learned about the two stimuli separately; ex: learned that animal has learned that light grey colour produces food and dark grey does not relational theory of stimulus control: the animal has learned something about the relationship between the 2 stimuli; ex: learned that the lighter grey is associated with food Transposition and Peak Shift (Koehler)transposition: the subject has transferred the relational rule to a new pair of stimuli trained chickens on simultaneous discrimination task several trials in which the two stimuli were 1) the light grey card that has previously served as the S+ and 2) a card with a lighter grey (Hanson) peak shift: a shift in the generalization gradient in a direction away from the S+ - after discrimination training with a reinforced stimulus and an unreinforced stimulus, a shift in the peak of generalization gradient from the reinforced stimulus in a direction away from the unreinforced stimulus - shows that it is often impossible to predict how a subject will respond in the presence of one stimulus simply by knowing the reinforcement schedule associated with that stimulus successive discrimination procedure: generalization gradients are usually obtained by presenting the various stimuli one at a time Spence's Theory of Excitatory and Inhibitory Gradients (absolute theory) proposed that in intradimensional training, an excitatory generalization gradient develops around the S- associative strength: the ability of each stimulus to elicit a response Spence proposed that the net associative strength of any stimulus can be determined by subtracting its inhibitory strength from its excitatory strength The Intermediate- Size Problem Gonzalez, Gentry and Bitterman conducted an experiment on intermediate size problem with chimpanzees stimuli: nine squares of different sizes smallest square area of 9 inches and largest with area of 27 inches during the training, the chimpanzees were alway presented with squares 1 5 and 9 on test trials, chimpanzees were presented with different sets of three squares and they were reinforced no matter which square they chose chimps usually chose the square of intermediate size on test trials the chimps behaved as thought they were responding to the relationships among the stimuli, not their absolute sizes Evaluating the Two Theories adaptation level theory: subjects tend to adapt to the range of stimuli that are presented, and this adaptation is reflected in where the peak of generalization gradient ap
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