Effects of stimulus variation on the reinforcing capability of nonpreferred stimuli

We examined the effects of stimulus (reinforcer) variation in several different contexts. In Study 1, we identified high-quality (HQ) and low-quality (LQ) stimuli based on results of a paired-stimulus assessment and examined their effects when available under concurrent-reinforcement schedules for 8 participants. No participants showed preference for the LQ stimuli when compared singly or in a varied arrangement to the HQ stimulus. In Study 2, we identified nonpreferred (NP) stimuli based on results of a single-stimulus assessment and examined their effects when available under single-reinforcement schedules for 3 participants. Results of Study 2 were mixed. One participant's data indicated that the varied presentation of NP stimuli produced a modest improvement in performance over that observed when the stimuli were presented singly. By contrast, a second participant's data showed no facilitative effect for the varied delivery of NP stimuli and that the inclusion of an HQ stimulus in the varied arrangement obscured the reinforcing effects of the HQ stimulus. The 3rd participant's data showed no effect for the varied delivery of NP stimuli but an apparent facilitative effect when an HQ stimulus was included in the varied arrangement, which was attributable solely to the presence of the HQ stimulus.     

Concurrent-schedule performance in transition: changeover delays and signaled reinforcer ratios

Six pigeons were trained in experimental sessions that arranged six or seven components with various concurrent-schedule reinforcer ratios associated with each. The order of the components was determined randomly without replacement. Components lasted until the pigeons had received 10 reinforcers, and were separated by 10-s blackout periods. The component reinforcer ratios arranged in most conditions were 27:1, 9:1, 3:1, 1:1, 1:3, 1:9 and 1:27; in others, there were only six components, three of 27:1 and three of 1:27. In some conditions, each reinforcement ratio was signaled by a different red-yellow flash frequency, with the frequency perfectly correlated with the reinforcer ratio. Additionally, a changeover delay was arranged in some conditions, and no changeover delay in others. When component reinforcer ratios were signaled, sensitivity to reinforcement values increased from around 0.40 before the first reinforcer in a component to around 0.80 before the 10th reinforcer. When reinforcer ratios were not signaled, sensitivities typically increased from zero to around 0.40. Sensitivity to reinforcement was around 0.20 lower in no-changeover-delay conditions than in changeover-delay conditions, but increased in the former after exposure to changeover delays. Local analyses showed that preference was extreme towards the reinforced alternative for the first 25 s after reinforcement in changeover-delay conditions regardless of whether components were signaled or not. In no-changeover-delay conditions, preference following reinforcers was either absent, or, following exposure to changeover delays, small. Reinforcers have both local and long-term effects on preference. The former, but not the latter, is strongly affected by the presence of a changeover delay. Stimulus control may be more closely associated with longer-term, more molar, reinforcer effects.     

Uncontrollability, depression, and the construction of mental models.

Three studies examined mental model generation after preexposure to uncontrollability and in a depressive state. The purpose of the experiments was to test the implications of the cognitive exhaustion model, applying an explicit conceptualization of social mental models and a process-tracing method developed by U. von Hecker (1997). An experimental situation was created for observation of consecutive, rule-based construction steps as a function of input diagnosticity, and for the quality assessment of constructed mental models. The findings show that participants preexposed to uncontrollability, as well as depressed students, were able, as were controls, to identify rule-relevant information needed for model construction. However, they were less able than control participants to engage in a more cognitively demanding and generative step of processing (i.e., in integrating the pieces of input information into a coherent mental model of sentiment relations).     

Memory improvement by post-trial injection of lidocaine into the tuberomammillary nucleus, the source of neuronal histamine.

Brain histamine is exclusively contained within and released from neurons whose cell bodies are clustered in the tuberomammillary nucleus (TM) of the posterior hypothalamus. This experiment examined the effects of a transient inactivation of the TM on inhibitory avoidance learning. Rats with chronically implanted cannulae were tested on a 1-trial step-through avoidance task. Immediately following training, the rats received unilateral intra-TM infusions (0.5 microl) of lidocaine (5 or 20 microg). Control groups included vehicle-injected rats and a group given an injection of 20 microg lidocaine 5 h after training. When tested 24 h later, rats treated with 20 microg lidocaine exhibited longer step-through latencies than vehicle-treated controls, indicative of superior learning of the task. The failure of the delayed post-trial injection of lidocaine to significantly influence step-through latencies indicates that the compound influenced learning by modulating memory storage processes rather than by acting on performance variables during retrieval of the task. Thus, inactivation of the TM by lidocaine can exert facilitatory effects on mnemonic processing, which might be related to a temporary reduction of histaminergic activity during the early phase of memory consolidation.     

Illusory volumes from conformation

The purpose of this paper is to offer demonstrations of 'illusory volumes' in the spirit of the illusory flat surfaces described by Kanizsa. These demonstrations of illusory volumes exploit a new cue to the recovery of surface curvature from ambiguous images: conformation. In assuming conformation, the visual system assumes that the surface of a volume conforms to the curvature of its neighboring, underlying, or supporting surface, in the absence of image cues to the contrary. Demonstrations that exploit the assumption of conformation provide several insights into the nature of the inferential processing that underlies contour, surface, and volume formation. In particular, these demonstrations imply that the visual system does not calculate local surface curvature, illusory contours, or occlusion relationships before it analyzes global surface relationships.     

Effects of different accessibility of reinforcement schedules on choice in humans

Based on the delay-reduction hypothesis, a less profitable schedule should be rejected if its duration exceeds the mean delay to reinforcement. It should be accepted if its duration is shorter than the mean delay. This was tested for humans, using a successive-choice schedule. The accessibility of the less profitable (variable-interval 18 s) schedule was varied by changing the duration (in terms of a fixed interval) of the waiting-time component preceding its presentation. Forty-eight students were randomly assigned to three groups. In Phase 1, the duration of the less profitable schedule equaled the mean delay to reinforcement in all groups. In Phase 2, waiting time preceding the less profitable schedule was reduced in Group 1 and increased in Group 2. Thus, the schedule was correlated either with a relative delay increase (Group 1) or a delay reduction (Group 2). In Group 3, conditions remained unchanged. As predicted, acceptance of the less profitable schedule decreased in Group 1 and increased in Group 2. The increased acceptance in Group 2 was accompanied by a decreased acceptance of the more profitable (variable-interval 3 s) schedule, resembling a pattern of negative contrast. Response rates were higher under the component preceding (a) the more profitable schedule in Group 1 and (b) the less profitable schedule in Group 2. Implications for the modification of human choice behavior are discussed.     

Detection, genetic counseling and phenotype prevention of Duchenne muscular dystrophy

Literature data and the own ascertainment of Duchenne muscular dystrophy cases concentrated on the Leipzig county confirm the necessity of early diagnosis and of central registration, search for female carries and genetic counselling. A newborn screening is supported provided that its organization will be practicable. About 12% of Duchenne cases are secondary affections of brothers. It should be possible to prevent one third of all cases by means of counselling also of the female relatives of the mothers. The repeated estimation of serum creatinkinase activity, completed by electromyography, has the greatest practical importance for the identification of heterozygous carriers. For the genetic counselling of definite carriers and women at risk it is possible only to recommend intrauterine sex prediction and the selective abortion of male fetuses.     

Type specificity of alcoholism. 1. Introduction and review of the literature

It was the aim of this empirical investigation to find out etiologically effective factors of gamma- and delta-alcoholism and condusions for prognosis and prevention. While for gamma-alcoholics an addicted attitude is typical during misuse, for delta-types it is a disposition in the vegetative-somatic range. The prognosis of delta-addicts after attendance and following intensive care is better than that of gamma-alcoholics. During a research period of 3 years a significant increase of delta-types was observed. This trend is explainable only sociologically by the development of drinking patterns in the direction of permissive-functionally disturbed culture. Hence, prevention is possible only by changing drinking patterns.     

Noradrenaline loss and the disruption of between-CS stimulus generalisation effects in aversion learning

In stimulus blocking the previous conditioning to one stimulus, A, followed by conditioning to the compound stimulus, AB, results in less conditioning to the other stimulus, B. Three experiments were performed to study the effect of the prior pairing of a stimulus A (noisy bottle) with lithium chloride followed by stimulus AB (saccharin plus noisy bottle) and lithium chloride pairings upon the strength of the aversion to the target stimuls B (saccharin) in NA-depleted and control rats. The results obtained were not in keeping with a "blocking" explanation since enhancement, rather than blocking, of the saccharin aversion was obtained, and confirm several recent demonstrations of the "anti-blocking" effect from investigations using the conditioned suppression procedure. DSP4 treatment attenuated the aversion-enhancement ("anti-blocking") effects in all three experiments. The possibility that DSP4-induced noradrenaline depletions may cause some disruption of between-CS associations leading to a lesser higher order conditioning or stimulus generalisation is discussed and the present findings do add further evidence to the conclusion that noradrenaline is intimately involved in attentional processes.