The poggendorff illusion with subjective contours

Gregory (1972) has claimed that the Poggendorff misalignment effect occurs when the collinear obliques are separated by subjective rather than real contours. He used two figures to demonstrate this variant of the illusion. Two experiments to test the claim are reported. The first showed that apparent misalignment in one of the two original figures is no greater than that with two obliques alone (the oblique line effect), but misalignment in the other is greater than with two oblique lines and than with a control without subjective contours. The second experiment showed that apparent misalignment in the second figure was less than in two control figures without subjective contours. Since this reduced effect was probably due to the nature of the intersection between the oblique and a semi-circular element, the role of subjective contours remains unsettled.     

The interaction between response effects during the acquisition of response priming

In three experiments we investigated the role of associative learning in the acquisition of response priming by effect stimuli, by examining their interaction during response-effect learning. Having replicated the ability of visual effect stimuli to prime their associated responses, we paired a response with a compound consisting of visual and auditory effects before assessing the ability of the auditory effect stimulus to prime the response. This priming was reduced if the visual stimulus had been pre-trained as an effect of the response. By contrast, priming by the visual effect stimulus was potentiated when the auditory effect had been pre-trained. We interpret these interactions in terms of contemporary associative learning theory derived from studies of conditioning.     

Re-examination of the role of within-compound associations in the retrospective revaluation of causal judgements

We investigated blocking and retrospective revaluation of causal judgements using a scenario in which food cues acted as potential causes of an allergic reaction as the outcome. In the blocking contingency,the treatment cues were either paired or unpaired with the outcome prior to a second stage in which sequential compounds of treatment and target cues were paired with the outcome. The order of this compound and treatment training was reversed in retrospective revaluation contingencies. When the interstimulus interval between the treatment and target cues was unfilled on compound trials (Experiments 1 and 3), both blocking and retrospective revaluation were observed in that the target cue trained in compound with the paired treatment cue attracted lower causal ratings than the target cue trained in compound with the unpaired treatment cue. By contrast, performing a mental arithmetic task using numerals presented during the interstimulus interval had no effect on the magnitude of blocking but rendered retrospective revaluation unreliable (Experiments 2 and 3). These results provide further support for accounts of revaluation based upon within-compound associations.     

The role of drug expectancy in the control of human drug seeking

Human drug seeking may be goal directed in the sense that it is mediated by a mental representation of the drug or habitual in the sense that it is elicited by drug-paired cues directly. To test these 2 accounts, the authors assessed whether a drug-paired stimulus (S+) would transfer control to an independently trained drug-seeking response. Smokers were trained on an instrumental discrimination that established a tobacco S+ in Experiment 1 and a tobacco and a money S+ in Experiment 2 that elicited an expectancy of their respective outcomes. Participants then learned 2 new instrumental responses, 1 for each outcome, in the absence of these stimuli. Finally, in the transfer test, each S+ was found to augment performance of the new instrumental response that was trained with the same outcome. This outcome-specific transfer effect indicates that drug-paired stimuli controlled human drug seeking via a representation or expectation of the drug rather than through a direct stimulus-response association.     

Free-operant acquisition with delayed reinforcement

The acquisition of free-operant lever pressing by hungry rats was investigated under a schedule in which the first lever press in each second programmed a reinforcer delivery after a fixed delay. In two studies acquisition was observed under programmed delays ranging between 0 and 32 sec, although animals trained with a delay of 64 sec pressed no more than yoked, non-contingent controls. In the final study an attempt was made to enhance sensitivity to the instrumental contingency under a 64-sec delay by exposing the animals to the operant chamber in the absence of the lever prior to each training session. Only animals receiving such exposure pressed significantly more than their non-contingent controls.     

Context Conditioning and Free operant Acquisition under Delayed Reinforcement

Three experiments examined the effect of context conditioning on the acquisition of freeoperant lever pressing by hungry rats when the presentation of the food reinforcer was delayed for 32 sec. The first study replicated the preexposure effect reported by Dickinson, Watt, and Griffiths (1992): Exposure to the contextual cues with the lever withdrawn prior to each instrumental training session enhanced acquisition, an effect that was attenuated by the presentation of non-contingent reinforcement during the preexposure periods. Signalling the non-contingent reinforcers during the preexposure periods with a brief auditory stimulus enhanced acquisition in a second study, suggesting that the non-contingent reinforcement interferes with acquisition through context conditioning. The final study confirmed this conclusion using a within-subject procedure in which pressing different levers was reinforced in two contexts, one of which was also associated with non-contingent reinforcers.     

No effects of transcranial direct current stimulation on visual evoked potential and peak gamma frequency

Cognitive Processing - Evidence suggests that the visual evoked potential (VEP) and gamma oscillations elicited by visual stimuli reflect the balance of excitatory and inhibitory (E-I) cortical...