Click on the thumbnail to enlarge.	Discrimination Training
	Discrimination training involves reinforcing a behavior (e.g., pecking) in the presence of one stimulus but not others.  In the picture to the left, a chicken was presented with two note cards; one card contained a red circle, while the other card contained a blue circle.  A peck on the red circle was reinforced, while a peck on the blue circle was not reinforced.  Eventually, the chicken only pecked the red circle.  The Baileys also used note cards with different shapes (e.g., circles v. squares) to demonstrate discrimination training involving geometric figures.  With discrimination training, animals like chickens are said to be able to "tell the difference" between shapes (like circles or squares) or colors (like red or blue), as long as the animal has the appropriate sensory apparatus, like color vision.

Click on the thumbnail to enlarge.	Discriminative Stimulus
	The discriminative stimulus is the cue (stimulus) that is present when the behavior is reinforced.  The animal learns to exhibit the behavior in the presence of the discriminative stimulus.  In the example above, the red circle was the discriminative stimulus (sometimes abbreviated SD, pronounced "S-Dee".)  In the case of note cards with squares and circles, if the Baileys had reinforced pecking a square rather than a circle, the SD would have been the square.  (To complicate the matter, animal trainers like to call the SD the "hot stimulus," because behaving in the presence of that stimulus will get the animal a reinforcer.)  Further, the animal does not have to interact with the discriminative stimulus - for example, in the post-card vending chicken, a light signals the availability of reinforcement, but the chicken does not have to interact with the light and only has to pull a loop. Refer to the picture to the left.  The staff of ABE often used "targets" to help control the behavior of animals.  In many demonstrations, the animals were taught to touch the target with their noses.  These targets were "hot" stimuli and, therefore, discriminative stimuli.  In short, discriminative stimuli occur before the behavior and are said to control the behavior (refer back to the three-term contingncy).
Click on the thumbnail to enlarge.	S-delta
	The S-delta (SD) is the stimulus in the presence of which the behavior is not reinforced.  At first during discrimination training, the animal often responds in the presence of stimuli that are similar to the SD.  These similar stimuli are S-deltas.  Eventually, responding to the S-delta will be extinguished.  (Animal trainers call the S-delta the "cold stimulus.") Let's take the example of pecking a red circle.  The trainer makes two cards, one with a red circle and one with blue circle.  The chicken is reinforced for pecking the red circle, but not blue circle. (At first, the chicken might peck both circles, but if pecking is only reinforced in the presence of the red circle, pecking will eventually occur only in the presence of that circle.)  The blue circle would be an S-delta.