Addie Johnson

Quick Minds Don't Blink: Electrophysiological Correlates of Individual Differences in Attentional Selection

A well-established phenomenon in the study of attention is the attentional blinka deficit in reporting the second of two targets when it occurs 200500 msec after the first. Although the effect has been shown to be robust in a variety of task conditions, not every individual participant shows the effect. We measured electroencephalographic activity for nonblinkers and blinkers during execution of a task in which two letters had to be detected in an sequential stream of digit distractors. Nonblinkers showed an earlier P3 peak, suggesting that they are quicker to consolidate information than are blinkers. Differences in frontal selection positivity were also found, such that nonblinkers showed a larger difference between target and distractor activation than did blinkers. Nonblinkers seem to extract target information better than blinkers do, allowing them to reject distractors more easily and leaving sufficient resources available to report both targets.

Timing Attention: Cuing Target Onset Interval Attenuates the Attentional Blink

Three experiments tested whether the attentional blink (AB; a deficit in reporting the second of two targets when it occurs 200—500 msec after the first) can be attenuated by providing information about the target onset asynchrony (TOA) of the second target relative to the first. Blocking the TOA did not improve second-target performance relative to a condition in which the TOA varied randomly from trial to trial (Experiment 1). In contrast, explicitly cuing the TOA on a trial-by-trial basis attenuated the AB without a cost to first-target identification (Experiments 2 and 3). The results suggest that temporal cues influence the allocation of attentional resources by adding temporal information to the perceptual description of the second target that can then be used to filter targets from nontargets, resulting in enhanced accuracy.

Probability as certainty : Dichotomous thinking and the misuse of p values

Significance testing is widely used and often criticized. The Task Force on Statistical Inference of the American Psychological Association (TFSI, APA; Wilkinson & TFSI, 1999) addressed the use of significance testing and made recommendations that were incorporated in the fifth edition of the APAPublication Manual (APA, 2001). They emphasized the interpretation of significance testing and the importance of reporting confidence intervals and effect sizes. We examined whether 286Psychonomic Bulletin & Review articles submitted before and after the publication of the TFSI recommendations by APA complied with these recommendations. Interpretation errors when using significance testing were still made frequently, and the new prescriptions were not yet followed on a large scale. Changing the practice of reporting statistics seems doomed to be a slow process.

How important is lateral masking in visual search

Five experiments are presented, providing empirical support of the hypothesis that the sensory phenomenon of lateral masking may explain many well-known visual search phenomena that are commonly assumed to be governed by cognitive attentional mechanisms. Experiment I showed that when the same visual arrays are used in visual search and in lateral masking experiments, the factors (1) number of distractors, (2) distractor density, and (3) search type (conjunction vs disjunction) have the same effect on search times as they have on lateral masking scores. Experiment II showed that when the number of distractors and eccentricity is kept constant in a search task, the effect of reducing density (which reduces the lateral masking potential of distractors on the target) is to strongly reduce the disjunction–conjunction difference. In experiment III, the lateral masking potential of distractors on a target was measured with arrays that typically yield asymmetric search times in visual search studies (a Q among Os vs. an O among Qs). The lateral masking scores showed the same asymmetry. Experiment IV was a visual search study with such asymmetric search arrays in which the number of distractors and eccentricity was kept constant, while manipulating density. Reducing density (i.e., reducing lateral masking) produced a strong reduction of the asymmetry effect. Finally in experiment V, we showed that the data from experiment IV cannot be explained due to a difference between a fine and a coarse grain attentional mechanism. Taken together with eye movement data and error scores from experiment II and with similar findings from the literature, these results suggest that the sensory mechanism of lateral masking could well be a very important (if not the main) factor causing many of the well-known effects that are traditionally attributed to higher level cognitive or attentional mechanisms in visual search.

Dissociable mechanisms underlying individual differences in visual working memory capacity

Individuals scoring relatively high on measures of working memory tend to be more proficient at controlling attention to minimize the effect of distracting information. It is currently unknown whether such superior attention control abilities are mediated by stronger suppression of irrelevant information, enhancement of relevant information, or both. Here we used steady-state visual evoked potentials (SSVEPs) with the Eriksen flanker task to track simultaneously the attention to relevant and irrelevant information by tagging target and distractors with different frequencies. This design allowed us to dissociate attentional biasing of perceptual processing (via SSVEPs) and stimulus processing in the frontal cognitive control network (via time-frequency analyses of EEG data). We show that while preparing for the upcoming stimulus, high- and low-WMC individuals use different strategies: High-WMC individuals show attentional suppression of the irrelevant stimuli, whereas low-WMC individuals demonstrate attentional enhancement of the relevant stimuli. Moreover, behavioral performance was predicted by trial-to-trial fluctuations in strength of distractor-suppression for high-WMC participants. We found no evidence for WMC-related differences in cognitive control network functioning, as measured by midfrontal theta-band power. Taken together, these findings suggest that early suppression of irrelevant information is a key underlying neural mechanism by which superior attention control abilities are implemented.

Colours sometimes count: Awareness and bidirectionality in grapheme–colour synaesthesia

Three experiments were conducted with 10 grapheme–colour synaesthetes and 10 matched controls to investigate (a) whether awareness of the inducer grapheme is necessary for synaesthetic colour induction and (b) whether grapheme–colour synaesthesia may be bidirectional in the sense that not only do graphemes induce colours, but that colours influence the processing of graphemes. Using attentional blink and Stroop paradigms with digit targets, we found that some synaesthetes did report “seeing” synaesthetic colours even when they were not able to report the inducing digit. Moreover, congruency effects (effects of matching the colour of digit presentation with the synaesthetic colour associated with that digit) suggested that grapheme–colour synaesthesia can be bidirectional, at least for some synaesthetes.

Are assumptions of well-known statistical techniques checked, and why (not)?

A valid interpretation of most statistical techniques requires that one or more assumptions be met. In published articles, however, little information tends to be reported on whether the data satisfy the assumptions underlying the statistical techniques used. This could be due to self-selection: Only manuscripts with data fulfilling the assumptions are submitted. Another explanation could be that violations of assumptions are rarely checked for in the first place. We studied whether and how 30 researchers checked fictitious data for violations of assumptions in their own working environment. Participants were asked to analyze the data as they would their own data, for which often used and well-known techniques such as the t-procedure, ANOVA and regression (or non-parametric alternatives) were required. It was found that the assumptions of the techniques were rarely checked, and that if they were, it was regularly by means of a statistical test. Interviews afterward revealed a general lack of knowledge about assumptions, the robustness of the techniques with regards to the assumptions, and how (or whether) assumptions should be checked. These data suggest that checking for violations of assumptions is not a well-considered choice, and that the use of statistics can be described as opportunistic.

Potential impact on HIV incidence of higher HIV testing rates and earlier antiretroviral therapy initiation in MSM.

Background:Increased rates of testing, with early antiretroviral therapy (ART) initiation, represent a key potential HIV-prevention approach. Currently, in MSM in the United Kingdom, it is estimated that 36% are diagnosed by 1 year from infection, and the ART initiation threshold is at CD4+ cell count 350/&mgr;l. We investigated what would be required to reduce HIV incidence in MSM to below 1 per 1000 person-years (i.e. <535 new infections per year) by 2030, and whether this is likely to be cost-effective. Methods:A dynamic, individual-based simulation model was calibrated to multiple data sources on HIV in MSM in the United Kingdom. Outcomes were projected according to future alternative HIV testing and ART initiation scenarios to 2030, considering also potential changes in levels of condomless sex. Results:For ART use to result in an incidence of close to 1/1000 person-years requires the proportion of all HIV-positive MSM with viral suppression to increase from below 60% currently to 90%, assuming no rise in levels of condomless sex. Substantial increases in HIV testing, such that over 90% of men are diagnosed within a year of infection, would increase the proportion of HIV-positive men with viral suppression to 80%, and it would be 90%, if ART is initiated at diagnosis. The scenarios required for such a policy to be cost-effective are presented. Conclusion:This analysis provides targets for the proportion of all HIV-positive MSM with viral suppression required to achieve substantial reductions in HIV incidence.

Rethinking neural efficiency: Effects of controlling for strategy use

A sentence verification task (SVT) was used to test whether differences in neural activation patterns that have been attributed to IQ may actually depend on differential strategy use between IQ groups. Electroencephalograms were recorded from 14 low (89 < IQ < 110) and 14 high (121 < IQ < 142) IQ individuals as they performed the SVT with either a spatial or verbal strategy. Event-related desynchronization in upper alpha (9.5-12.5 Hz) and theta (4-6 Hz) bands showed that different strategies evoked different activation patterns, but these patterns did not differ between groups. However, an IQ-related correlate was found in the preparation interval. Thus, although processing patterns during task performance seem to depend on the strategy used for task execution, preparation for task processing may depend on IQ.

Cultural influences on the measurement of subjective mental workload

Cognitive ergonomics is well entrenched in North American and most European work environments, where systems and products are designed with the capabilities and limitations of the user in mind. A prominent technique for analysing task demands is subjective mental workload measurement. Subjective ratings of mental workload have been shown—in North American and European populations—to be reliable and sensitive to changes in mental workload. However, there is reason to think that cultural differences may affect subjective ratings. This study compared the performance and subjective mental workload ratings of Indonesian (n = 87) and Dutch (n = 88) students in the context of a hybrid memory/visual search task. Performance was comparable for the two groups, but the sensitivity of the subjective workload measures was better in the Dutch than in the Indonesian group. The results are interpreted in light of social axioms and cultural values. Statement of Relevance: Now more than ever ergonomists must think beyond national borders in improving work processes. Globalisation requires that cultural differences be taken into account in developing and applying ergonomic techniques. This paper presents empirical work showing that cultural differences seriously impact the sensitivity of mental workload measures.