Judgement of act-outcome contingency: The role of selective attribution

In the first experiment subjects were presented with a number of sets of trials on each of which they could perform a particular action and observe the occurrence of an outcome in the context of a video game. The contingency between the action and outcome was varied across the different sets of trials. When required to judge the effectiveness of the action in controlling the outcome during a set of trials, subjects assigned positive ratings for a positive contingency and negative ratings for a negative contingency. Furthermore, the magnitude of the ratings was related systematically to the strength of the actual contingency. With a fixed probability of an outcome given the action, judgements of positive contingencies decreased as the likelihood that the outcome would occur without the action was raised. Correspondingly, the absolute value of ratings of negative contingencies was increased both by an increment in the probability of the outcome in the absence of the action and by a decrement in the probability of the outcome following the action. A systematic bias was observed, however, in that positive judgements were given under a non-contingent relationship when the outcome frequency was relatively high. However, this bias could be reduced by giving extended exposure to the non-contingent schedule (Experiment 2).

This pattern of contingency judgements can be explained if it is assumed that a process of selective attribution operates, whereby people are less likely to attribute an outcome to some potential target cause if another effective cause is present. Experiments 2 and 3 demonstrated the operation of this process by showing that initially establishing another agent as an effective cause of the outcome subsequently reduced or blocked the extent to which the subjects attributed the outcome to the action.

Finally, we argue that the pattern and bias in contingency judgements based upon interactions with a causal process can be explained in terms of contemporary conditioning models of associative learning.     

The potentiation effect during serial conditioning

The development of suppression in rats to a target conditioned stimulus (CS) was compared in trace and serial conditioning procedures. The interval between the end of the target CS and the shock unconditioned stimulus (US) was filled by a second CS in the serial, but not the trace, procedure. In five experiments the serial procedure produced superior conditioning. This potentiation effect, however, depended critically upon the level of conditioning to the stimulus interpolated between the target CS and the US. When conditioning to the interpolated CS was either reduced by giving independent nonreinforced trials with this CS alone or enhanced by independent reinforced trials, the potentiation effect was abolished. In addition, the insertion of a trace interval between the target and interpolated CSs reduced the effect. However, the magnitude of conditioning to the target CS was unaffected by post-conditioning changes in the conditioned strength of the interpolated CS. These findings are discussed in terms of the contribution of both the association between the CSs themselves, which is inherent in the serial procedure, and that between the target CS and the US.     

More Than Words: Response to Phelan

Studies in Philosophy and Education -     

Auditory and visual serial position functions obey different laws

Rhesus monkeys were tested in serial probe recognition tasks with either travel slide pictures or natural sounds. Tests with four-item lists produced serial position functions that were essentially opposite in shape for the two modalities and changed in opposite ways with retention interval. For visual memory, the primacy effect grew and the recency effect dissipated with retention interval. Capuchin monkeys, humans, and pigeons showed similar results. For auditory memory with rhesus monkeys, the recency effect grew and the primacy effect dissipated with retention interval. These results taken together, along with results from rehearsal tests of monkeys and humans, implicate two passive memory processes with different time courses. Interference among items within auditory lists was manipulated by varying the time between items and categories of items. Interference across lists was manipulated by varying the item pool size and, hence, item repetitions. Changes in the auditory serial position functions indicated that proactive and retroactive interference may have been instrumental in these dynamically changing serial position functions. Implications for theories and models of memory are discussed.     

Evidence for Free Radical-Mediated Reduction of Lymphocytic 5′-Ectonucleotidase During Stress

Previously we showed that stress and depression could result in a 50% lowering of lymphocytic 5-ectonucleotidase (NT) which could be resolved by a diet high in antioxidants. This study suggested that high levels of free radicals mediated by stress/depression may be involved in lowering NT activities. The aim of the present study was to assess whether oxygen radicals could directly affect NT and whether excess free radicals generated in stress/depression may affect tissue ascorbate stores. Exam-stressed students and depressed patients were compared respectively to these students at low stress and depressed patients on high antioxidant intakes. In this study, NT correlated positively with tissue ascorbate stores. A range of antioxidants were tested as possible inhibitors of oxy radical interaction with NT using nitroblue tetrazolium reduction to for-mazan with superoxide anion. At physiological plasma concentrations, ascorbate inhibited this reduction but dehydroascorbate, tocopherol, retinol, selenium, urate, and reduced glutathione were ineffective. Superoxide anion directly reduced lymphocytic NT activity and this effect was reversed by either 100 molar ascorbate in vitro or a high antioxidant intake in vivo. In conclusion, the low NT activities and ascorbate stores found in stressed/depressed people appear to be mediated by higher levels of free radicals reported in these subjects. These conclusions are consistent with published reports of (1) normal NT levels in melancholic patients on high antioxidant diets; (2) heightened inflammatory reponses during stress/depression; (3) low serum levels of zinc in depressed patients.     

Moore Inferences

André Gallois (in The World Without, the Mind Within , Cambridge UP, 1996) maintains that the following schema expresses a warranted form of inference:
p
——————
I believe that p .
I argue that these 'Moore inferences' are not warranted.     

Effect of stimulus frequency on subjective vibrotactile magnitude functions

Subjective magnitude functions were determined by the method of magnitude estimation at 60 and 250 Hz at the fingertip and thenar eminence, both with and without a rigid surface surrounding the contactor. When the surround was in place, the slopes of the curves were independent of stimulus frequency. The slopes became frequency dependent when the surround was removed—the lower frequency produced a steeper slope at both body sites. An explanation of the effect is suggested. It involves the frequency characteristics and spatial sensitivity of the receptors.

     

Effects of alcohol and marijuana on dynamic visual acuity: I. Threshold measurements

Alcohol and marijuana produce significant dose-related reductions in dynamic visual acuity. Ten subjects participated in a double-blind experiment involving three dose levels of each drug (including placebo). The reduction of DVA produced by alcohol (1.0 ml 95% ethanol/kg body weight) was greater than for marijuana (15 mg Δ-9-tetrahydrocannabinol), and we suggest that this difference was produced by differential oculomotor effects of the two drugs. We have speculated that reduction in DVA under alcohol may be a contributing factor in alcohol-related traffic accidents.     

Obedience as a function of experimenter competence

The purpose of this study was to investigate obedience to an E’s commands as a function of E competency. Based upon Orne’s (1962, 1969) discussion of the demand characteristics inherent in the typical aggression study, it was hypothesized that E incompetence would decrease S obedience. Competence was manipulated by: (1) presenting some Ss with a nervous and inexperienced E, and (2)“accidentally” killing the victim (a rat) midway through the experiment. Thirty-two undergraduate female Ss participated in the experiment—supposedly a study on the physiological effects of stress. Obedi6nce was operationalized as the difference, in simple reaction time, between trials on which Ss were told that their response might result in shock to the rat and trials on which they were told that their response might save the rat from shock. Significant differences in obedience were obtained between competent and incompetent E conditions, and a significant “kill” effect was found in the competent E conditidn. The results of this study suggested that the extreme acts of obedience observed in the laboratory (e.g., Milgram, 1963) occur only when E is perceived as competent. This finding imposes limits on the generalizability of laboratory studies of obedience.