DISCRIMINATIVE CONTROL (ANIMAL DISCRIMINATION)

Discriminative Control (Animal Discrimination)



Discriminative Control (Animal Discrimination)

Introduction

A growing body of evidence suggests that behavioral variability can come under control of discriminative stimuli (Bhatt 2008). The present experiment further examined discriminative control of variability in a novel way by using the discrimination-reversal paradigm. Eight pigeons responded under a multiple schedule of Vary and Yoke components signaled by different-colored key lights. In the Vary component, 4-response sequences that differed from the previous 10 produced food, while in the Yoke component, any 4-response sequence had a fixed probability of producing food, yoked to the prior Vary component (Huber 2000).

Following stability in this procedure, the key colors signaling the Vary and Yoke components were reversed across four successive conditions. Across the experiment, variability of keypeck sequences was higher in the Vary than in the Yoke component. Across successive reversals, the level of variability in the Vary component adapted more rapidly to the reversed contingencies, while the rate of adaptation in the Yoke component did not change systematically. These results are interpreted in terms of the different contingencies in the Vary and Yoke components (Huber 2003). In addition, the improvement in the rate of adaptation across successive reversals in the Vary component appears consistent with a proactive interference account of discrimination-reversal performance. These results join others in suggesting that variability may be an operant dimension of behavior.

In an experiment rats were trained to discriminate the stimulus properties of amphetamine and saline. Food reinforce was given after lever pressing following intravenous amphetamine infusions but not following saline infusions. Subsequent tests under extinction conditions showed that rats pressed a lever at a high rate following infusions of amphetamine, methamphetamine and cocaine, but at a low rate following saline, ethanol, and epinephrine or sodium pentobarbital (Herrnstein 2006). Similar procedures indicated that rats could also discriminate between ethanol and saline. These findings confirm earlier results indicating that intravenously administered drug can act as discriminative stimuli in controlling operant behavior.

For many years, researchers have sought to understand how nonhuman animals learn to categorize objects (for a review, see Herrnstein, 2000), that is, how nonhuman animals come to treat discreditably different objects or events as members of a common class and respond similarly to them. Researchers have discovered that animals readily categorize objects according to their perceptual similarity (Bhatt, Wasserman, Reynolds, & Knauss, 2008; Herrnstein, Loveland, & Cable, 2006; Lea, Lohmann, & Ryan, 2003). Such perceptual category learning is an important process that allows animals to respond flexibly to a variable environment. Although category learning has been well documented in the nonhuman animal literature, investigators of category learning have encountered a vexing dilemma. One the one hand, researchers who examine category learning often use complex visual stimuli to document the ability of nonhuman animals to form categories that comprise highly heterogeneous members (e.g., Herrnstein et al., 2006; Jitsumori & Yoshihara, 2007); such usage enhances the verisimilitude of the experimental stimuli(Herrnstein 2000).

The results of these studies may be especially interesting because the discriminative stimuli in animals' natural ...