Resolution of outcome-induced response conflict by humans after extended training

Studies of incongruent discrimination learning, where the outcome event of one response acts as the discriminative stimulus for the opposite response, suggest that humans rely on habitual stimulus–response (S–R) associations when outcome–response (O–R) associations would cause response conflict. Here, two experiments were conducted to investigate the robustness of this habitual strategy. In Experiment 1, we found that extensive instrumental discrimination training supported learning about the incongruent R → O contingencies, as assessed by an outcome devaluation test. Differential representations of the stimulus and the (associatively retrieved) outcome may have allowed for goal-directed incongruent performance. Experiment 2 failed to provide evidence for this possibility; direct presentation as well as associative retrieval of the incongruent events (by Pavlovian stimuli) activated the response that was associated with each event in its role of stimulus as opposed to outcome. We did find that participants successfully acquired explicit knowledge of the incongruent contingencies, which raises the possibility that propositional encoding allowed them to overcome the response conflict caused by O–R associations. Alternative associative and propositional accounts of successful goal-directed incongruent performance with extensive training will be discussed.     

Relationship Between Muscle Fiber Type and Reactive Balance: A Preliminary Study

The authors’ objective was to quantify the relationship between type II muscle fiber composition and recovery latency from controlled perturbations. Thirty healthy adults performed a Thorstensson test to indirectly determine muscle fiber composition of the knee extensors. On a subsequent day, reactive balance was measured by assessing latency time required to accommodate three controlled perturbations via computerized dynamic posturography. The proportion of type II fibers had a negative correlation with latency caused by a large backward perturbation (r = –.62, p = .001). These data may indicate a higher percentage of type II fibers in the knee extensors are associated with better reactive balance. Further investigation is warranted, in particular as it pertains to populations at risk for balance impairment.     

The role of the instrumental contingency in the motivational control of performance

In four experiments we investigated an irrelevant incentive effect based upon a transition from hunger to thirst. Hungry rats were trained to lever press either for sucrose solution or for food pellets before performance was tested in extinction while they were thirsty. Reinforcer-specific motivational control was found in the first experiment in that the animals pressed the lever more on tests following training with the sucrose solution rather than with food pellets. Moreover, this effect was seen only when testing was conducted following water, but not following food deprivation. The outcome of the remaining experiments suggests that this motivational control is not mediated by the instrumental contingency between lever pressing and the sucrose reinforcer during training. In these studies lever pressing and chain pulling were reinforced concurrently, one with sucrose and the other with food pellets, in order to equate the noninstrumental functions of the incentives. Following this training, lever pressing in extinction under thirst was unaffected by the type of incentive used as its reinforcer during training.     

Correlates of household smoking bans in low-income families of children with and without asthma

Exposure to secondhand smoke (SHS) harms all children's health, especially children with asthma. Yet, children with asthma are as likely to live with smokers as healthy children. Household smoking bans are being advocated to reduce children's harm from SHS. To measure the effect of household smoking bans on child SHS exposure and to examine correlates of strict smoking bans in a low-income, diverse sample, 91 children with asthma were matched to 91 healthy children. All had at least one smoker living in their homes. Nicotine dosimeters, child cotinine assays, and maternal reports quantified child SHS exposures. Maternal reports of household smoking rules, behaviors, and beliefs, and other family characteristics were also gathered. The presence of a strict household smoking ban vastly reduced children's SHS exposures and was associated with fewer cigarettes smoked by the mother and by other family members, the belief that SHS was a personal health risk, having children with asthma, and living in a single-family home. Many children are exposed to high levels of SHS at home. Strict household smoking bans greatly decrease, but do not eliminate children's SHS exposure. Even in disadvantaged families, mutable factors were associated with strict smoking bans. Increased dissemination and use of established public health strategies are needed to reduce children's SHS exposures.     

Cognitive demands of error processing

This study used a dual-task methodology to assess attention demands associated with error processing during an anticipation-timing task. A difference was predicted in attention demands during feedback on trials with correct responses and errors. This was addressed by requiring participants to respond to a probe reaction-time stimulus after augmented feedback presentation. 16 participants (8 men, 8 women) completed two phases, the reaction time task only and the anticipation-timing task with the probe RT task. False feedback indicating error and a financial reward manipulation were used to increase relevance of errors. Data supported the hypothesis that error processing is associated with higher cognitive demands than processing feedback denoting a correct response. Individuals responded with quicker probe reaction times during presentation of feedback on correct trials than on error trials. These results are discussed with respect to the cognitive processes which might occur during error processing and their role in motor learning.     

Attention and expectation in human predictive learning: the role of uncertainty

Three localized, visual pattern stimuli were trained as predictive signals of auditory outcomes. One signal partially predicted an aversive noise in Experiment 1 and a neutral tone in Experiment 2, whereas the other signals consistently predicted either the occurrence or absence of the noise. The expectation of the noise was measured during each signal presentation, and only participants for whom this expectation demonstrated contingency knowledge showed differential attention to the signals. Importantly, when attention was measured by visual fixations, the contingency-aware group attended more to the partially predictive signal than to the consistent predictors in both experiments. This profile of visual attention supports the Pearce and Hall (1980) theory of the role of attention in associative learning.