Acute and chronic effects of methsuximide and mephenytoin on the delayed-matching-to-sample performance of pigeons.

Acute and chronic effects of methsuximide and mephenytoin were examined in pigeons performing under a delayed-matching-to-sample procedure. Acute administrations of methsuximide (25-175 mg/kg) and mephenytoin (40-160 mg/kg) produced generally dose-dependent decreases in accuracy. At the two highest doses, methsuximide decreased rate of responding to the sample stimulus; mephenytoin did so only at the highest dose. At low doses, both methsuximide and mephenytoin increased response rate over control. After 20 sessions of daily exposure to methsuximide (100 mg/kg) or mephenytoin (80 mg/kg), tolerance developed to the accuracy-decreasing effects of both drugs.

Effects of methsuximide and mephenytoin on the responding of pigeons under a fixed-consecutive-number schedule with and without an external discriminative stimulus.

The effects of the antiepilepsy drugs methsuximide and mephenytoin were examined in pigeons responding under a fixed-consecutive-number (FCN) schedule with and without an added external discriminative stimulus. On this schedule, food was delivered whenever subjects responded between 8 and 12 times on one response key (work key), and then responded once on a second response key (reinforcement key). Under one variant of the FCN schedule (FCN 8-SD), an external discriminative stimulus signalled completion of the response requirement on the work key; no such stimulus change occurred under the other (FCN 8) schedule. The two FCN schedules (with an without stimulus change) alternated at 5-min intervals within each session for all subjects. Methsuximide (25-200 mg/kg) and mephenytoin (40-160 mg/kg) produced generally dose-dependent decreases in percentage of reinforced response runs and rate of responding. The magnitudes of these effects were comparable under both variants of the FCN schedule.

Discriminative stimulus properties of ethosuximide in the pigeon.

After initial exposure to 80 mg/kg, pigeons trained on a two-key drug discrimination procedure rapidly learned to discriminate 120 mg/kg ethosuximide from saline. When 40-160 mg/kg doses of ethosuximide were administered during generalization tests, the percentage of responses directed to the ethosuximide-appropriate key varied directly with dose. Time-effect determinations revealed that the discriminable properties of ethosuximide were evident as early as 15 min after, and as late as 2 h after, intramuscular injection. The discriminative stimulus properties of ethosuximide failed to generalize to the anticonvulsant compounds clonazepam (0.5-4 mg/kg), methsuximide (25-200 mg/kg), and phenytoin (5-15 mg/kg). Generalization was apparent with certain doses of primidone (250, 300 mg/kg) and mephenytoin (80, 160, 240 mg/kg). The concomitant administration of pentylenetetrazol (5, 10, 20 mg/kg) partially blocked the discriminable properties of the training dose of ethosuximide.

Failure of the partial inverse benzodiazepine agonist Ro15-4513 to block the lethal effects of ethanol in rats.

The partial inverse benzodiazepine agonist Ro15-4513 has been found to antagonize some of the behavioral and physiological effects of low to moderate doses of ethanol. In the present study, pretreating rats with Ro15-4513 (1, 3, 10, and 30 mg/kg) at doses equal to or greater than those used in prior investigations failed to block the lethal effects of intraperitoneal injections of ethanol at a dose of 5.4 g/kg. These results suggest that the lethal actions of ethanol may involve a mechanism that is not blocked by Ro15-4513, which is known to selectively antagonize ethanol-stimulated chloride uptake via the GABA-coupled chloride ion channel.

Discriminative stimulus properties of phenytoin in the pigeon: determination via a cumulative dosing procedure.

Pigeons were trained in a cumulative dosing procedure to emit one response in the presence of 15 mg/kg phenytoin and another response in the absence of phenytoin. After reliable discrimination was established, generalization tests with other anticonvulsant drugs were conducted. Ethosuximide (20-120 mg/kg) and methsuximide (25-100 mg/kg) engendered very little phenytoin-appropriate responding. Clonazepam (0.125-1 mg/kg) engendered more phenytoin-appropriate responding, but less than the training dose of phenytoin. Similar results were obtained when these drugs were administered in conventional single dose per session generalization tests. When tested in that fashion, mephenytoin (80 and 160 mg/kg) engendered some phenytoin-appropriate responding, but less than the training dose of phenytoin. Administering 10 mg/kg pentylenetetrazol in combination with 5, 10, 15, and 20 mg/kg cumulative doses of phenytoin reduced phenytoin-appropriate responding relative to levels obtained with these doses of phenytoin alone.

Effects of Ro 15-4513 on schedule-controlled responding of pigeons.

The partial inverse benzodiazepine agonist Ro 15-4513 has been found to antagonize some of the behavioral and physiological effects of ethanol, but relatively little is known about the behavioral effects of the drug alone. In the present study, pigeons responding under a multiple fixed-ratio 25 interresponse-time-greater-than-6-sec schedule of food delivery were exposed acutely and chronically to Ro 15-4513. Acute administrations of the drug (1.0, 1.8, 3.2, and 5.4 mg/kg) reduced response rates under the fixed-ratio component at some doses, although two birds were more sensitive to the drug than the third subject. Response rates under the interresponse-time-greater-than-6-sec component were not affected by acute administrations of Ro 15-4513. When 5.4 mg/kg Ro 15-4513 was administered prior to 15 consecutive sessions, tolerance developed to the rate-reducing effects of the drug under the fixed-ratio component. These findings, in contrast to those of early investigations in which gross measures of behavior were employed, suggest that Ro 15-4513 is behaviorally active at relatively low doses.

Effects of mephenytoin on schedule-controlled responding in the pigeon.

Acute and chronic effects of mephenytoin (30-360 mg/kg) were examined in pigeons responding under a multiple fixed-ratio 50 fixed-interval 90-sec schedule of food delivery. The highest dose administered acutely (240 mg/kg) produced substantial reductions in rate of responding under both components of the multiple schedule; the effects of other doses were small and inconsistent. With chronic exposure tolerance appeared to develop to the rate-decreasing effects of the drug.

Effects of methsuximide on schedule-controlled responding in the pigeon.

Acute and chronic effects of methsuximide (25, 50, 75, and 100 mg/kg), a succinimide with anticonvulsant properties, were examined in pigeons responding under a multiple fixed-ratio 50 fixed-interval 90-sec schedule of food delivery. The clearest acute effect of methsuximide was a substantial reduction in response rates under both components of the multiple schedule when the drug was administered at 100 mg/kg. Detailed analysis of the temporal distribution of responding under the fixed-interval failed to reveal rate-dependent drug effects. Tolerance appeared to develop to the effects of methsuximide when the drug was administered chronically.

Pentylenetetrazol-induced seizures in pigeons and the effects of ethosuximide thereon.

Previous research has shown that ethosuximide in high enough doses disrupts operant responding in pigeons. Whether or not these same doses protect against seizure activity in this species has not been determined. In the present study a system for scoring pentylenetetrazol-induced seizures in pigeons was developed and the effects of ethosuximide on such seizures were evaluated. Pentylenetetrazol at 15, 27 and 47 mg/kg reliably induced seizures in Experiment 1. In Experiment 2 six doses of ethosuximide were tested for their seizure-controlling effectiveness. Doses of 20, 40, 80, 160 and 320 mg/kg ethosuximide had little effect on seizures induced by 27 mg/kg pentylenetetrazol; 640 mg/kg significantly reduced but did not completely eliminate seizures. This dose (640 mg/kg) is several times higher than the doses found to disrupt operant behavior in our previous studies.

Effects of d-amphetamine and ethosuximide on responding under delayed-matching-to-sample procedures with differential and nondifferential outcomes.

Pigeons were exposed to delayed-matching-to-sample (DMTS) procedures in which food or a flash of the feeder light followed correct responses. When these consequences were correlated with a particular stimulus (e.g., food followed matching responses to red and a flash of the feeder light followed matching responses to green), accuracy was higher (i.e., stimulus control was greater) than when discriminative stimuli and consequences were not correlated. Although stimulus control in the absence of drug appeared to be weaker under the uncorrelated procedure, neither d-amphetamine (0.5-3.0 mg/kg) in Experiment 1 nor ethosuximide (40-160 mg/kg) in Experiment 2 disrupted accuracy to a greater extent under that procedure. These results, like those of a prior investigation, suggest that drug effects are similar under DMTS procedures regardless of whether correlated or uncorrelated outcomes are arranged.

Determinants of pausing under variable-ratio schedules: Reinforcer magnitude, ratio size, and schedule configuration.

Pigeons pecked a key under two-component multiple variable-ratio schedules that offered 8-s or 2-s access to grain. Phase 1 assessed the effects of differences in reinforcer magnitude on postreinforcement pausing, as a function of ratio size. In Phase 2, postreinforcement pausing and the first five interresponse times in each ratio were measured as a function of differences in reinforcer magnitude under equal variable-ratio schedules consisting of different configurations of individual ratios. Rates were also calculated exclusive of postreinforcement pause times in both phases. The results from Phase 1 showed that as ratio size increased, the differences in pausing educed by unequal reinforcer magnitudes also increased. The results of Phase 2 showed that the effects of reinforcer magnitude on pausing and IRT durations were a function of schedule configuration. Under one configuration, in which the smallest ratio was a fixed-ratio 1, pauses were unaffected by magnitude but the first five interresponse times were affected. Under the other configuration, in which the smallest ratio was a fixed-ratio 7, pauses were affected by reinforcer magnitude but the first five interresponse times were not. The effect of each configuration seemed to be determined by the value of the smallest individual ratio. Rates calculated exclusive of postreinforcement pause times were, in general, directly related to reinforcer magnitude, and the relation was shown to be a function of schedule configuration.

Pausing under variable-ratio schedules: Interaction of reinforcer magnitude, variable-ratio size, and lowest ratio.

Pigeons pecked a key under two-component multiple variable-ratio schedules that offered 8-s or 2-s access to grain. Postreinforcement pausing and the rates of responding following the pause (run rates) in each component were measured as a function of variable-ratio size and the size of the lowest ratio in the configuration of ratios comprising each schedule. In one group of subjects, variable-ratio size was varied while the size of the lowest ratio was held constant. In a second group, the size of the lowest ratio was varied while variable-ratio size was held constant. For all subjects, the mean duration of postreinforcement pausing increased in the 2-s component but not in the 8-s component. Postreinforcement pauses increased with increases in variable-ratio size (Group 1) and with increases in the lowest ratio (Group 2). In both groups, run rates were slightly higher in the 8-s component than in the 2-s component. Run rates decreased slightly as variable-ratio size increased, but were unaffected by increases in the size of the lowest ratio. These results suggest that variable-ratio size, the size of the lowest ratio, and reinforcer magnitude interact to determine the duration of postreinforcement pauses.

Performance of children under a multiple random-ratio random-interval schedule of reinforcement.

Three children, aged 1.5, 2.5, and 4.5 years, pressed telegraph keys under a two-component multiple random-ratio random-interval schedule of reinforcement. In the first condition, responses on the left key were reinforced under a random-interval schedule and responses on the right key were reinforced under a random-ratio schedule. In the second condition, the schedule components were reversed. In the third condition, the original arrangement was reinstated. For all subjects, rates of responding were higher in the random-ratio component despite higher rates of reinforcement in the random-interval component. The average interreinforcement interval of the random-interval component was increased in the fourth condition, resulting in more similar rates of reinforcement for both schedule components, and then returned to its original value in the fifth condition. In both conditions, all subjects continued to exhibit higher rates of responding in the ratio component than in the interval component. Although these observations are consistent with results from studies with pigeons, it is argued that the response-rate differences between the interval and ratio schedule components are sufficient to demonstrate schedule sensitivity.

Separating discriminative and function-altering effects of verbal stimuli.

Ever since Skinner's first discussion of rule-governed behavior, behavior analysts have continued to define rules, either explicitly or implicitly, as verbal discriminative stimuli. Consequently, it is not difficult to find, in the literature on rule-governed behavior, references to stimulus control, antecedent control, or to rules occasioning behavior. However, some verbal stimuli have effects on behavior that are not easily described as discriminative. Such stimuli don't evoke behavior as discriminative stimuli, but rather alter the functions of other stimuli in a manner analogous to operant and respondent conditioning. Hence, this type of control has been called function altering. Any known stimulus function (e.g., evocative, or [conditioned] reinforcing or punishing functions) can apparently be altered by such function-altering stimuli. Describing these stimuli as discriminative stimuli obscures their possible function-altering effects and consequently may retard inquiry into them. This paper encourages behavior analysts to begin separating the discriminative and function-altering effects of verbal stimuli and suggests that by doing so, behavior analysts may better understand what may be most unique about these stimuli. Results from several experiments, especially those in which children served as subjects, are analyzed. Finally, some speculations are offered concerning the genesis of function-altering stimuli.

Function-altering effects of contingency-specifying stimuli.

Contingengy-specifying stimuli (CSSs) can function differently than discriminative stimuli. Rather than evoking behavior due to a history of discrimination training, they alter the function of other stimuli and, therefore, the behavioral relations involving those stimuli. CSSs can alter the evocative function of discriminative stimuli, establishing operations, and conditional stimuli, as well as the efficacy of reinforcing and punishing stimuli and of stimuli that can function in second-order respondent conditioning. The concept of function-altering CSSs has implications for such areas of interest as stimulus equivalence, the terminology involving "rules" and "rule-governed behavior," and the way in which behavior analysts view the effects of such basic processes as reinforcement and punishment.

Rules: Function-altering contingency-specifying stimuli.

Behavior analysts have traditionally defined rules as discriminative stimuli. Three problems with this interpretation are discussed. First, because the effects of rules are often delayed, and the effects of discriminative stimuli are immediate, classifying rules as discriminative stimuli violates the definitional requirements of the latter. Second, when rules are defined as discriminative stimuli, other truly unique effects of rules may be obscured. Finally, both rules and contingencies develop new behavioral relations; however, when rules are interpreted as discriminative stimuli, their effects are not readily compared with those of contingencies. As an alternative, we suggest that rules be interpreted as function-altering contingency-specifying stimuli. Implications of this function-altering interpretation for terminology and research strategy are discussed.

A descriptive taxonomy of environmental operations and its implications for behavior analysis.

Environmental operations may be classified according to whether they have evocative or function-altering effects. Evocative events, such as the presentation of unconditioned and conditioned stimuli, establishing operations, and discriminative stimuli, serve to increase, decrease, or maintain the momentary frequency of behavior. Function-altering operations, such as operant and respondent conditioning, the correlation of stimuli, and the presentation of certain verbal stimuli, serve to increase, decrease, or maintain the evocative and function-altering (e.g., reinforcing or punishing) functions of other events. This paper expands upon the functional taxonomy of environmental events described by Michael (1993a). The resulting classification scheme should permit behavior analysts to more easily respond to similarities and differences between functional environmental events. This paper discusses implications of the suggested taxonomy for how behavior analysts talk about motivational variables, discriminative stimuli, the operant unit of analysis, and the distinction between operant and respondent conditioning.

Intelligence: Real or artificial?

Throughout the history of the artificial intelligence movement, researchers have strived to create computers that could simulate general human intelligence. This paper argues that workers in artificial intelligence have failed to achieve this goal because they adopted the wrong model of human behavior and intelligence, namely a cognitive essentialist model with origins in the traditional philosophies of natural intelligence. An analysis of the word "intelligence" suggests that it originally referred to behavior-environment relations and not to inferred internal structures and processes. It is concluded that if workers in artificial intelligence are to succeed in their general goal, then they must design machines that are adaptive, that is, that can learn. Thus, artificial intelligence researchers must discard their essentialist model of natural intelligence and adopt a selectionist model instead. Such a strategic change should lead them to the science of behavior analysis.

A reply to behavior analysts writing about rules and rule-governed behavior.

Verbal stimuli called "rules" or "instructions" continue to be interpreted as discriminative stimuli despite recent arguments against this practice. Instead, it might more fruitful for behavior analysts to focus on "contingency-specifying stimuli" which are function-altering. Moreover, rather than having a special term, "rule," for verbal stimuli whose only function is discriminative, perhaps behavior analysts should reserve the term, if at all, only for these function-altering contingency-specifying stimuli.