Underpowered samples,false negatives,and unconscious learning

The scientific community has witnessed growing concern about the high rate of false positives and unreliable results within the psychological literature, but the harmful impact of false negatives has been largely ignored. False negatives are particularly concerning in research areas where demonstrating the absence of an effect is crucial, such as studies of unconscious or implicit processing. Research on implicit processes seeks evidence of above-chance performance on some implicit behavioral measure at the same time as chance-level performance (that is, a null result) on an explicit measure of awareness. A systematic review of 73 studies of contextual cuing, a popular implicit learning paradigm, involving 181 statistical analyses of awareness tests, reveals how underpowered studies can lead to failure to reject a false null hypothesis. Among the studies that reported sufficient information, the meta-analytic effect size across awareness tests was d _z = 0.31 (95 % CI 0.24–0.37), showing that participants’ learning in these experiments was conscious. The unusually large number of positive results in this literature cannot be explained by selective publication. Instead, our analyses demonstrate that these tests are typically insensitive and underpowered to detect medium to small, but true, effects in awareness tests. These findings challenge a widespread and theoretically important claim about the extent of unconscious human cognition.     

Ensemble coding remains accurate under object and spatial visual working memory load

A number of studies have provided evidence that the visual system statistically summarizes large amounts of information that would exceed the limitations of attention and working memory (ensemble coding). However the necessity of working memory resources for ensemble coding has not yet been tested directly. In the current study, we used a dual task design to test the effect of object and spatial visual working memory load on size averaging accuracy. In Experiment 1, we tested participants’ accuracy in comparing the mean size of two sets under various levels of object visual working memory load. Although the accuracy of average size judgments depended on the difference in mean size between the two sets, we found no effect of working memory load. In Experiment 2, we tested the same average size judgment while participants were under spatial visual working memory load, again finding no effect of load on averaging accuracy. Overall our results reveal that ensemble coding can proceed unimpeded and highly accurately under both object and spatial visual working memory load, providing further evidence that ensemble coding reflects a basic perceptual process distinct from that of individual object processing.     

Dividing attention across feature dimensions in statistical processing of perceptual groups

Statistical processing has been shown in the perception of several visual dimensions, including size, speed, direction of motion, and orientation. Chong and Treisman (2005) found no decrement when people simultaneously averaged two sets on a single dimension, size. What happens when attention is divided between different dimensions? In two experiments, we investigated judgments of mean size and speed, either within the same objects or in two separate sets. In a third, we examined judgments of mean size and orientation in two different sets. All three experiments suggest a decrement in performance when attention is shared between two dimensions, especially when they are carried by two different sets of objects.     

Amodal completion of unconsciously presented objects

In the visual environment, objects often appear behind occluding surfaces, yet they are automatically and effortlessly perceived as complete. Here, we examined whether visually occluded objects that are presented below the threshold of awareness are amodally completed. We used a priming paradigm in which participants responded to consciously perceived targets that were preceded by unconsciously presented primes. In two experiments, we show that discrimination responses to targets were faster when they were preceded by congruent shapes, regardless of whether these shapes were intact and complete or occluded by a horizontal bar. This priming effect was not produced by a partial match in features, since the occluded primes did not facilitate responses to targets that shared local features (Experiment 1) or contained only the object features that remained visible after occlusion (Experiment 2). These results show that objects presented below the threshold of awareness can be amodally completed and provide compelling evidence that unconscious processing occurs to a greater extent than previously considered.     

Statistical processing: not so implausible after all

Myczek and Simons (2008) have shown that findings attributed to a statistical mode of perceptual processing can, instead, be explained by focused attention to samples of just a few items. Some new findings raise questions about this claim. (1) Participants, given conditions that would require different focused attention strategies, did no worse when the conditions were randomly mixed than when they were blocked. (2) Participants were significantly worse at estimating the mean size when given small samples than when given the whole display. (3) One plausible suggested strategy--comparing the largest item in each display, rather than the mean size--was not, in fact, used. Distributed attention to sets of similar stimuli, enabling a statistical-processing mode, provides a coherent account of these and other phenomena.     

Effects of mental workload and caffeine on catecholamines and blood pressure compared to performance variations

Caffeine is characterised as a central nervous system stimulant, also affecting metabolic and cardiovascular functions. A number of studies have demonstrated an effect of caffeine on the excretion of catecholamines and their metabolites. Urinary epinephrine and norepinephrine have been shown to increase after caffeine administration. Similar trends were observed in our study in adrenaline (ADR) and noradrenaline (NORADR) levels and additionally a dose dependent effect of caffeine. The effect of caffeine on cognitive performance, blood pressure, and catecholamines was tested under resting conditions and under mental workload. Each subject performed the test after oral administration of 1 cup and then 3 cups of coffee. Root mean square error (RMSE) for the tracking task was continuously monitored. Blood pressure was also recorded before and after each stage of the experiment. Catecholamines were collected and measured for three different conditions as: at rest, after mental stress alone, after one dose of caffeine under stress, and after triple dose of caffeine under stress. Comparison of the performance of each stage with the resting conditions revealed statistically significant differences between group of smokers/coffee drinkers compared with the other two groups of non-coffee drinkers/non-smokers and non-smokers/coffee drinkers. There was no statistically significant difference between the last two groups. There was an increase of urine adrenaline with 1 cup of coffee and statistically significant increase of urine noradrenaline. Both catecholamines were significantly increased with triple dose of caffeine. Mental workload increased catecholamines. There was a dose dependent effect of caffeine on catecholamines.