College students responded under a multiple differential-reinforcement-of-low-rate 5-s fixed-ratio 8 schedule, with components alternating every 2 min. After 40 programmed minutes of acquisition and 12 min of maintenance, without notice, both schedules changed to extinction for 28 min. During acquisition, between alternations of the multiple schedule, some subjects were asked to develop rules describing the schedule contingencies. Other subjects were given these same rules between alternations, and a third group neither received nor were asked to develop rules. By the end of the acquisition phase, self-generated-rule subjects were more likely to show schedule-typical behavior than were subjects not asked to generate rules. The behavior of those given rules was similar to those asked to generate rules at the end of acquisition, but yoked-rule subjects acquired schedule-typical behavior at a quicker rate. By the end of extinction, during the period corresponding to the previous fixed-ratio interval, all no-rule subjects who had earned points during acquisition and maintenance were responding at a rate of less than 30 responses per minute. Only 3 of the 9 self-generated-rule subjects and 2 of the 5 yoked-rule subjects were similarly responding at this low rate. Results suggest that asking subjects to develop self-rules facilitates acquisition, but can retard extinction. Results also suggest that self-generated rules function similarly to external rules.

The results of many human operant conditioning experiments appear to show that humans are less sensitive than nonhumans to operant consequences, suggesting species discontinuities in basic behavioral processes. A reanalysis of 311 data sets from 25 studies employing variable-interval schedules of reinforcement designed to assess sensitivity to reinforcement corroborates the claim that human behavioral allocation among alternatives often deviates from predictions based on rates of experimentally programmed consequences. Close inspection of the studies in question, however, suggests that methodological issues contribute heavily to the differences noted so far between humans and nonhumans and that an explanation based upon species discontinuities is not tenable.Consequences clearly influence the behavior of nonhuman organisms. The rich operant conditioning literature shows that reinforcing consequences alter the strength of behavior that produces them and forge relations between behavior and antecedent stimuli. These effects hold across a wide range of species, settings, response classes, and types of reinforcers, placing them among the most widely replicated outcomes in the biological and behavioral sciences. As a result, the threeterm operant contingency, which encompasses the relations among antecedent conditions, operant behavior, and reinforcers, has been proposed as the foundation of a broad range of complex capabilities both in nonhuman species (e.g., Donahoe, Burgos, & Palmer, 1993) and, perhaps more speculatively, in humans (e.g., Skinner, 1953Skinner, , 1957.Successful applications to human affairs, based on the core notion that human behavior is sensitive to its consequences, provide reason for optimism about the generality of operant principles. As can be expected ofa successful science, applications have flowed from the laboratory since the earliest days of operant psychology. They include, but are not limited to, animal models of substance abuse and treatment (e

Adolescence is associated with the continued maturation of dopamine neurotransmission and is implicated in the etiology of many psychiatric illnesses. Adolescent exposure to neurotoxicants that distort dopamine neurotransmission, such as methylmercury (MeHg), may modify the effects of chronic d-amphetamine (d-AMP) administration on reversal learning and attentional-set shifting. Male C57Bl/6n mice were randomly assigned to two MeHg-exposure groups (0 ppm and 3 ppm) and two d-AMP-exposure groups (saline and 1 mg/kg/day), producing four treatment groups (n = 10–12/group): Control, MeHg, d-AMP, and MeHg + d-AMP. MeHg exposure (via drinking water) spanned postnatal day 21–59 (the murine adolescent period), and once daily i.p. injections of d-AMP or saline spanned postnatal day 28–42. As adults, mice were trained on a spatial-discrimination-reversal (SDR) task in which the spatial location of a lever press predicted reinforcement. Following two SDRs, a visual-discrimination task (extradimensional shift) was instated in which the presence of a stimulus light above a lever predicted reinforcement. Responding was modeled using a logistic function, which estimated the rate (slope) of a behavioral transition and trials required to complete half a transition (half-max). MeHg, d-AMP, and MeHg + d-AMP exposure increased estimates of half-max on the second reversal. MeHg exposure increased half-max and decreased the slope term following the extradimensional shift, but these effects did not occur following MeHg + d-AMP exposure. MeHg + d-AMP exposure produced more perseverative errors and omissions following a reversal. Adolescent exposure to MeHg can modify the behavioral effects of chronic d-AMP administration.

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The developing fetus is vulnerable to low-level exposure to methylmercury (MeHg), an environmental neurotoxicant, but the consequences of exposure during the adolescent period remain virtually unknown. The current experiments were designed to assess the effects of low-level MeHg exposure during adolescence on delay discounting, preference for small, immediate reinforcers over large, delayed ones, using a mouse model. Thirty-six male C57BL/6n mice were exposed to 0, 0.3, or 3.0 ppm mercury (as MeHg) via drinking water from postnatal day 21 through 59, encompassing the murine adolescent period. As adults, mice lever-pressed for a 0.01-cc droplet of milk solution delivered immediately or four 0.01-cc droplets delivered after a delay. Delays ranged from 1.26 to 70.79 seconds, all presented within a session. A model based on the Generalized Matching Law indicated that sensitivity to reinforcer magnitude was lower for MeHg-exposed mice relative to controls; responding in MeHg-exposed mice was relatively indifferent to the larger reinforcer. Sensitivity to reinforcer delay was reduced (delay discounting was decreased) in the 0.3-ppm group, but not in the 3.0-ppm group, compared to controls. Adolescence is a developmental period during which the brain and behavior may be vulnerable to MeHg exposure. As with gestational exposure, the effects are reflected in the impact of reinforcing stimuli.