Working memory encoding delays top-down attention to visual cortex

The encoding of information from one event into working memory can delay high-level, central decision-making processes for subsequent events [e.g., Jolicoeur, P., & Dell'Acqua, R. The demonstration of short-term consolidation. Cognitive Psychology, 36, 138-202, 1998, doi:10.1006/cogp.1998.0684]. Working memory, however, is also believed to interfere with the deployment of top-down attention [de Fockert, J. W., Rees, G., Frith, C.D., &Lavie, N. The role ofworking memory in visual selective attention. Science, 291, 1803-1806, 2001, doi:10.1126/science.1056496]. It is, therefore, possible that, in addition to delaying central processes, the engagement of working memory encoding (WME) also postpones perceptual processing as well. Here, we tested this hypothesis with time-resolved fMRI by assessing whether WME serially postpones the action of top-down attention on low-level sensory signals. In three experiments, participants viewed a skeletal rapid serial visual presentation sequence that contained two target items (T1 and T2) separated by either a short (550 msec) or long (1450 msec) SOA. During single-target runs, participants attended and responded only to T1, whereas in dual-target runs, participants attended and responded to both targets. To determine whether T1 processing delayed top-down attentional enhancement of T2, we examined T2 BOLD response in visual cortex by subtracting the single-task waveforms from the dualtask waveforms for each SOA. When the WME demands of T1 were high (Experiments 1 and 3), T2 BOLD response was delayed at the short SOA relative to the long SOA. This was not the case when T1 encoding demands were low (Experiment 2). We conclude that encoding of a stimulus into working memory delays the deployment of attention to subsequent target representations in visual cortex

Age-Related Changes in Perirhinal Cortex Sensitivity to Configuration and Part Familiarity and Connectivity to Visual Cortex

The perirhinal cortex (PRC) is a medial temporal lobe (MTL) structure known to be involved in assessing whether an object is familiar (i.e., meaningful) or novel. Recent evidence shows that the PRC is sensitive to the familiarity of both whole object configurations and their parts, and suggests the PRC may modulate part familiarity responses in V2. Here, using functional magnetic resonance imaging (fMRI), we investigated age-related decline in the PRC’s sensitivity to part/configuration familiarity and assessed its functional connectivity to visual cortex in young and older adults. Participants categorized peripherally presented silhouettes as familiar (“real-world”) or novel. Part/configuration familiarity was manipulated via three silhouette configurations: Familiar (parts/configurations familiar), Control Novel (parts/configurations novel), and Part-Rearranged Novel (parts familiar, configurations novel). “Real-world” judgments were less accurate than “novel” judgments, although accuracy did not differ between age groups. The fMRI data revealed differential neural activity, however: In young adults, a linear pattern of activation was observed in left hemisphere (LH) PRC, with Familiar > Control Novel > Part-Rearranged Novel. Older adults did not show this pattern, indicating age-related decline in the PRC’s sensitivity to part/configuration familiarity. A functional connectivity analysis revealed a significant coupling between the PRC and V2 in the LH in young adults only. Older adults showed a linear pattern of activation in the temporopolar cortex (TPC), but no evidence of TPC-V2 connectivity. This is the first study to demonstrate age-related decline in the PRC’s representations of part/configuration familiarity and its covariance with visual cortex

On the Seasonal Occurrence and Abundance of the Zika Virus Vector Mosquito Aedes Aegypti in the Contiguous United States

Introduction: An ongoing Zika virus pandemic in Latin America and the Caribbean has raised concerns that travel-related introduction of Zika virus could initiate local transmission in the United States (U.S.) by its primary vector, the mosquito Aedes aegypti. Methods: We employed meteorologically driven models for 2006-2015 to simulate the potential seasonal abundance of adult Aedes aegypti for fifty cities within or near the margins of its known U.S. range. Mosquito abundance results were analyzed alongside travel and socioeconomic factors that are proxies of viral introduction and vulnerability to human-vector contact. Results: Meteorological conditions are largely unsuitable for Aedes aegypti over the U.S. during winter months (December-March), except in southern Florida and south Texas where comparatively warm conditions can sustain low-to-moderate potential mosquito abundance. Meteorological conditions are suitable for Aedes aegypti across all fifty cities during peak summer months (July-September), though the mosquito has not been documented in all cities. Simulations indicate the highest mosquito abundance occurs in the Southeast and south Texas where locally acquired cases of Aedes-transmitted viruses have been reported previously. Cities in southern Florida and south Texas are at the nexus of high seasonal suitability for Aedes aegypti and strong potential for travel-related virus introduction. Higher poverty rates in cities along the U.S.-Mexico border may correlate with factors that increase human exposure to Aedes aegypti. Discussion: Our results can inform baseline risk for local Zika virus transmission in the U.S. and the optimal timing of vector control activities, and underscore the need for enhanced surveillance for Aedes mosquitoes and Aedes-transmitted viruses

Competition explains limited attention and perceptual resources: implications for perceptual load and dilution theories

Both perceptual load theory and dilution theory purport to explain when and why task-irrelevant information, or so-called distractors are processed. Central to both explanations is the notion of limited resources, although the theories differ in the precise way in which those limitations affect distractor processing. We have recently proposed a neurally plausible explanation of limited resources in which neural competition among stimuli hinders their representation in the brain. This view of limited capacity can also explain distractor processing, whereby the competitive interactions and bias imposed to resolve the competition determine the extent to which a distractor is processed. This idea is compatible with aspects of both perceptual load and dilution models of distractor processing, but also serves to highlight their differences. Here we review the evidence in favor of a biased competition view of limited resources and relate these ideas to both classic perceptual load theory and dilution theory

The Perirhinal Cortex Modulates V2 Activity in Response to the Agreement Between Part Familiarity and Configuration Familiarity

Research has demonstrated that the perirhinal cortex (PRC) represents complex object-level feature configurations, and participates in familiarity versus novelty discrimination. Barense et al. [(in press) Cerebral Cortex, 22:11, doi:10.1093/cercor/bhr347] postulated that, in addition, the PRC modulates part familiarity responses in lower-level visual areas. We used fMRI to measure activation in the PRC and V2 in response to silhouettes presented peripherally while participants maintained central fixation and performed an object recognition task. There were three types of silhouettes: Familiar Configurations portrayed real-world objects; Part-Rearranged Novel Configurations created by spatially rearranging the parts of the familiar configurations; and Control Novel Configurations in which both the configuration and the ensemble of parts comprising it were novel. For right visual field (RVF) presentation, BOLD responses revealed a significant linear trend in bilateral BA 35 of the PRC (highest activation for Familiar Configurations, lowest for Part-Rearranged Novel Configurations, with Control Novel Configurations in between). For left visual field (LVF) presentation, a significant linear trend was found in a different area (bilateral BA 38, temporal pole) in the opposite direction (Part-Rearranged Novel Configurations highest, Familiar Configurations lowest). These data confirm that the PRC is sensitive to the agreement in familiarity between the configuration level and the part level. As predicted, V2 activation mimicked that of the PRC: for RVF presentation, activity in V2 was significantly higher in the left hemisphere for Familiar Configurations than for Part-Rearranged Novel Configurations, and for LVF presentation, the opposite effect was found in right hemisphere V2. We attribute these patterns in V2 to feedback from the PRC because receptive fields in V2 encompass parts but not configurations. These results reveal two new aspects of PRC function: (1) it is sensitive to the congruency between the familiarity of object configurations and the parts comprising those configurations and (2) it likely modulates familiarity responses in visual area V2.Grant sponsor: NSF; Grant number: BCS 0960529 (to M.A.P.); Grant CIHR; Grant number: MOP-115148 (to M.D.B.); Grant sponsor: McKnight Brain Research Foundation Grant sponsor: NSERC Discovery Grant (to M.D.B.