EXPRESS: The Role of Contingency and Correlation in the Stroop Task

Facilitation (faster responses to Congruent trials compared to Neutral trials) in the Stroop task has been a difficult effect for models of cognitive control to explain. The current research investigated the role of word-response contingency, word-colour correlation, and proportion congruency in producing Stroop effects. Contingency and correlation refers to the probability of specific word-response and word-colour pairings that are implicitly learnt while performing the task. Pairs that have a higher probability of occurring are responded to faster, a finding that challenges top-down attention control accounts of Stroop task performance. However studies that try to experimentally control for contingency and correlation typically do so by increasing the proportion of incongruent trials in the task, which cognitive control accounts posit affects interference control via the top-down biasing of attention. The present research focused on whether facilitation is also affected by contingency and correlation while additionally looking at the effect of proportion congruency. This was done in two experiments that compared the typical design of Stroop task experiments (i.e., having equal proportions of Congruent and Incongruent trials but also contingency and correlational biases) to: a) a design that had unequal congruency proportions but no contingency or correlation (Experiment 1), and b) a design where the correlation is biased but proportion congruency and contingency were not (Experiment 2). Results did not support the hypotheses that contingency or correlation affected facilitation. Interference was almost halved in the alternative design of Experiment 2, demonstrating an effect of contingency learning in typical measures of Stroop interference.

Hierarchical reasoning by neural circuits in the frontal cortex

Humans process information hierarchically. In the presence of hierarchies, sources of failures are ambiguous. Humans resolve this ambiguity by assessing their confidence after one or more attempts. To understand the neural basis of this reasoning strategy, we recorded from dorsomedial frontal cortex (DMFC) and anterior cingulate cortex (ACC) of monkeys in a task in which negative outcomes were caused either by misjudging the stimulus or by a covert switch between two stimulus-response contingency rules. We found that both areas harbored a representation of evidence supporting a rule switch. Additional perturbation experiments revealed that ACC functioned downstream of DMFC and was directly and specifically involved in inferring covert rule switches. These results‏ reveal the computational principles of hierarchical reasoning, as implemented by cortical circuits.

Response Rates Are Governed More by Time Cues Than Contingency

Classical conditioning is normally thought to strengthen associations between stimuli, and instrumental conditioning is thought to select responses. This difference has been used to account for the usual result that instrumental conditioning produces higher response rates than classical conditioning. The present experiment suggests that the comparison of instrumental and classical tasks has overlooked temporal cues that are often confounded with response contingency, and that the time cues exert a critical influence on response rate. When the two tasks are equated for temporal cues, the response rate of rats is similar in classical and instrumental tasks.

Australia's Fixed-Wing Aerial Dispersant Capability

ABSTRACT Since January 1997, Australia has had in place a fixed-wing aerial dispersant capability (FWADC) designed to provide the country with a cost-effective aerial dispersant delivery system. The FWADC is managed by the Australian Maritime Safety Authority (AMSA) and is funded jointly by AMSA and the Australian Institute of Petroleum (AIP) through its subsidiary, the Australian Marine Oil Spill Centre (AMOSC). The FWADC is based on the concept of using single-engine turbine-powered agricultural aircraft with a payload capacity of between 1,850 and 3,100 Liters of dispersant, depending on aircraft type. At a cost of AUD$400,000 per annum, Australia has access to a minimum of two primary aircraft, 24 hours every day of the year. Additional aircraft complement the two primary aircraft on an “aircraft of opportunity” basis. This paper addresses the background to the development and implementation of Australia's fixed-wing aerial dispersant capability and its integration into Australia's national oil spill response contingency arrangements. It also provides an overview of AMSA's role in managing the capability and providing training for aircraft operators and support crews in aerial dispersant-related operations.