This study compared the effects of (+/-)3,4-methylenedioxymethamphetamine, d-amphetamine, and cocaine on performance of rats in a delayed matching-to-sample procedure using a variety of indices of performance to determine the mechanism by which working memory task impairments arise. All 3 drugs produced an overall delay-independent decrease in accuracy rather than a delay-dependent increase in the rate of forgetting. This impairment arose as a result of current-trial choice responses being progressively more affected by responses made in the immediately preceding trial as drug dose increased. Therefore, all 3 drugs produced qualitatively similar disruptions in memory task performance best characterized as an impairment arising from proactive sources of interference.

Three experiments using multiple schedules of reinforcement explored the implications of resistanceto-change findings for the response-reinforcer relation described by the law of effect, using both steadystate responding and responding recorded in the first few sessions of conditions. In Experiment 1, when response-independent reinforcement was increased during a third component, response rate in Components 1 and 2 decreased. This response-rate reduction was proportionately greater in a component in which reinforcer magnitude was small (2-s access to wheat) than in the component in which it was large (6-s access to wheat). However, when reinforcer rates in the two components were varied together in Experiments 2 and 3, response-rate change was the same regardless of the magnitude of reinforcers used in the two components, so that sensitivity of response rates to reinforcer rates (Experiment 2) and of response-rate ratios to reinforcer-rate ratios (Experiment 3) was unaffected by the magnitude of the reinforcers. Therefore, the principles determining resistance to change, described by behavioral momentum theory, seem not to apply when the source of behavior change is the variation of reinforcement contingencies that maintain the behavior. The use of extinction as a manipulation to study resistance to change is questioned.Key words: resistance to change, quantitative law of effect, generalized matching law, sensitivity to reinforcement, behavioral momentum, multiple schedules, key peck, pigeons There are two main conceptions of response strength in schedule-control research, each deriving from a different style of experimental behavior analysis. One identifies response strength with the rate or probability of a response, and derives from research conducted in a tradition dominated by the law of effect. This type of work is characterized by studies in which the schedules maintaining responding are varied over conditions, and resulting changes in response rate are related to changes in the rate of the "strengthening" variable, reinforcement. Quantitative analysis indicates a hyperbolic relation between response rate and reinforcer rate, which is thought to depend on the availability of extraneous reinforcers obtained for behavior other than the target response (see e.g., de Villiers & Herrnstein, 1976;Herrnstein, 1970Herrnstein, , 1974. Thus, "strong" behavior is identified with a high response rate and is observed when high frequencies of reinforcement maintain the response. A feature of this research is that it analyzes steady-state behavior-that is, the level at which the re- sponse occurs after prolonged exposure to each schedule.A second area of study, and one enjoying a resurgence of interest, is research dealing with behavioral resistance to change. Resistance is measured using changes in the rate of a response following an alteration of the environmental context for that response; here, strong behavior is identified with high resistance. Early studies considered resistance to extinction. For example, Hear...

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2Using cognitive control to ignore distractions is essential for successfully achieving our goals. In emotionallyneutral contexts, motivation can reduce interference from irrelevant stimuli by enhancing cognitive control.However, attention is commonly biased towards emotional stimuli, making them potent distractors. Can motivation aid control of emotional distractions, and does it do so similarly for positive and negative stimuli?Here, we examined how task motivation influences control of distraction from positive, negative, and neutral scenes. Participants completed a simple perceptual task while attempting to ignore task-irrelevant images. One group received monetary reward for fast and accurate task performance; another (control) group did not.Overall, both negative (mutilation) and positive (erotic) images caused greater slowing of responses than neutral images of people, but emotional distraction was reduced with reward. Crucially, despite the different motivational directions associated with negative and positive stimuli, reward reduced negative and positive distraction equally. Our findings suggest that motivation may encourage the use of a sustained proactive control strategy that can effectively reduce the impact of emotional distraction.

Evidence suggests that acute exposure to (+/-)3,4-methylenedioxymethamphetamine (MDMA) produces qualitatively similar effects on recognition task performance as other stimulant-type drugs. The current study examined whether there was a similar neurochemical basis to these memory effects by examining the effects of a D1 receptor antagonist (SCH23390) and D2 antagonist (eticlopride) on MDMA- or cocaine-induced impairments in delayed matching-to-sample performance in rats. At low doses it was shown that eticlopride was ineffective in antagonizing either MDMA or cocaine's effects, and at higher doses exacerbated their effects. In contrast, the D1 receptor antagonist SCH23390 was only able to significantly attenuate the disruption caused by MDMA, but not cocaine's effects. Therefore, although present evidence suggests that the effect of acute MDMA on memory-task performance may be related to its effects at D1 receptor sites, there may be differences between MDMA and cocaine in the precise neurochemical pathways involved despite their having similar cognitive effects.

It has long been observed that patients with Parkinson's disease (PD) can sometimes react and move quickly in response to an external stimulus in a way that they cannot when required to initiate the movement themselves. This curious phenomenon has sometimes been called 'paradoxical kinesis'. The present study was an attempt to demonstrate this phenomenon in patients with PD using an objective and quantifiable experimental procedure. A reaction time task was used in which participants had to press one of two computer keys, either left or right, to save a cartoon person on a computer screen from being run over by a motor car. In one condition, trials started after a traffic light appeared on the computer screen and then changed from red to green. In a second condition, the participants had to first press a third response key which resulted in the traffic light appearing on screen and changing from red to green. Participants also received both these conditions with the addition of a visual cue, an arrow, which told them in advance which direction to respond in (i.e., left or right key) on each trial. The purpose of the visual cue was to separate the effects of motor planning from motor activation. Healthy controls reacted quickest when they initiated trials themselves whereas the PD group were quicker to respond when trials were externally generated. Both groups were quicker under the visual cue condition. The results are discussed in terms of recent research which has suggested that two separate neural systems may be involved in externally generated or stereotyped actions and motor responses which require self-generated or nonroutine decision making.

Despite the prevalence of problem gamblers and the ethical issues involved in studying gambling behavior with humans, few animal models of gambling have been developed. When designing an animal model it is necessary to determine if behavior in the paradigm is similar to human gambling. In human studies, response latencies following winning trials and near win trials are greater than those following clear losses. Weatherly and Derenne (Anal Gambl Behav 1:79-89, 2007) investigated whether this pattern was found with rats working in an animal analogue of slot machine gambling. They found a similar pattern of response latencies but the subjects' behavior did not come under control of the visual stimuli signalling the different outcomes. The animal model of slot machine gambling we used addressed procedural issues in Weatherly and Derenne's model and examined whether reinforcer magnitude and the presence of near win trials influenced response latency and resistance to extinction. Response latencies of the six female Norway Hooded rats varied as a function of reinforcer magnitude and the presence of near-win trials. These results are consistent with prior research and with the idea that near win trials serve as conditional reinforcers.