Antecedent stimuli can reliably evoke behavior after being correlated with reinforcement. Antecedent stimuli can also reliably inhibit behavior by signaling that there is no chance that reinforcement will occur following a behavior (i.e., extinction). A stimulus that signals extinction is termed s‐delta. Stimuli that signal whether a behavior will be reinforced or not are ubiquitous and very effective in guiding behavior. An “Out of Order” sign on a vending machine tells us that using the machine will not yield us any goodies. In animal behavior, research has found that dogs don’t beg from people who aren’t looking at them (Udell et al. 2011). A person not looking at the dog is effectively an “Out of Order” sign to the dog that means if the dog begs, it is highly unlikely that she will get food. If the person is making eye contact with the dog, it is more likely that food will be given.
One area of training in which “tight” stimulus control is desired is landmine detection. A non‐profit organization called Anti‐Persoonsmijnen Ontmijnende Product Ontwikkeling (APOPO) employed the use of giant pouched rats to help with de‐mining areas of Africa (Poling et al. 2010). The rats are given extensive training on detecting the odor of a landmine and emitting a behavior to indicate that they found an explosive. So that each landmine is identified and removed safely, it is imperative that the explosives have perfect stimulus control over the indicator behavior. That is, the behavior must occur each time a landmine is found, it must never occur when there is no landmine present, it must never occur in response to a different stimulus, and no other behavior should occur in the presence of the landmine (Pryor 1999). Otherwise, it would be a waste of resources to dig for a landmine that isn’t there and would put lives at risk if a landmine is missed.
3.4.3.1 Discrimination and Generalization
After some experience learning a target behavior with one person, a dog might respond to a discriminative stimulus (such as “sit”) from other people. Responding to the same cue from a different person is an instance of generalization. Conversely, if the dog does not respond to a cue by that different person, then the dog is said to discriminate between cues (the cue given by the trainer versus the cue given by the new person). To put it simply, stimulus generalization occurs when an animal responds similarly to different stimuli, whereas stimulus discrimination occurs when an animal responds differently to different stimuli. The extent to which an organism generalizes or discriminates between stimuli is indicative of varying degrees of stimulus control (Cooper et al. 2007).
Animals can learn to discriminate or generalize very subtle features of a stimulus. Nagasawa et al. (2011) demonstrated this aspect of discrimination and generalization with dogs. In their study, dogs were presented two pictures: one of their owner’s smiling face and one of their owner’s neutral face. Touching the smiling picture resulted in a reinforcer, whereas touching the neutral face did not. The dogs learned to choose the smiling picture of their owner most often, meaning that they learned to discriminate between the two pictures. When presented with a smiling and neutral picture of an unfamiliar person, dogs responded similarly in that they chose the smiling face most of the time. The dogs generalized to pictures of novel individuals. Interestingly, though, the dogs were only successful in generalizing their responses to pictures of novel individuals of the same sex as their owner. Since they only learned the discrimination task with one sex, they discriminated between sexes.
The processes of discrimination and generalization are complex; generalization more readily occurs when two stimuli are similar, whereas discrimination readily occurs when two stimuli are very different. In Nagasawa et al.’s (2011) study, the pictures of the smiling face and neutral face were very different, which helped the dogs learn to discriminate between them. The pictures of their owner and another person of the same sex were similar enough that the dogs were able to generalize across those stimuli and choose the smiling face. However, the pictures of their owner and another person of a different sex were distinct enough that generalization did not occur.
3.5 Conclusions
Though learning might seem like a complex topic, understanding the processes that take place when an animal learns helps us to develop tools to modify behavior. Observing changes in an animal’s behavior in response to changes in its environment allows us the opportunity to gain insight into the learning history and make changes to the animal’s behavior. Animals are responding to their environment constantly, and often, the environment responds back in one form or another. This interaction between environment and behavior can be understood through the processes of associative and non‐associative learning.
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