Latency effects in orientation popout

AbstractA target that differs in orientation from neighboring lines and “pops out” has been found to evoke larger responses in cortical V1 cells than lines in the uniform texture surround which do not popout (e.g., Journal of Neurophysiology 67 (1992) 961). If this is more than a coincidence of observations, physiological properties of contextual modulation should be reflected in the perception of salience. In particular, as the differential suppression from texture surround has been reported to be delayed, target salience may be affected by the history of surrounding lines, i.e. by their orientation before the target was presented. This was tested using a feature flicker paradigm in which target and background lines changed their orientations (Experiment 2). All subjects (N=4) indicated a benefit in target detection when target orientation was not previously present in the surround. A control experiment showed that this effect was not caused by the purely temporal aspects of asynchronous stimulus presentation (Experiment 3). To distinguish this effect from other sources of delayed processing, Experiment 1 compared the performance in target detection and target identification tasks, for single-lines and popout targets. All subjects required longer stimulus presentation time to identify the orientation of a single line than to detect the line itself, indicating that orientation coding needs longer processing than encoding stimulus onset. However, most subjects needed even longer presentations to detect popout, suggesting that the processing of orientation contrast adds to this delay. In an appendix, putative response variations of V1 cells to asynchronous flicker are computed

Norovirus acute gastroenteritis among US and European travellers to areas of moderate to high risk of travellers' diarrhoea: a prospective cohort study

BACKGROUND Acute gastroenteritis (AGE) is a major medical condition for travellers worldwide, particularly travellers to low- and middle-income countries. Norovirus (NoV) is the most common cause of viral AGE in older children and adults, but data on prevalence and impact among travellers is limited. METHODS Prospective, multi-site, observational cohort study conducted 2015-2017, among adult international travellers from the US and Europe to areas of moderate to high risk of travel-acquired AGE. Participants provided self-collected pre-travel stool samples and self-reported AGE symptoms while travelling. Post-travel stool samples were requested from symptomatic subjects and a sample of asymptomatic travellers within 14days of return. Samples were tested for NoV by RT-qPCR, genotyped if positive, and tested for other common enteric pathogens by Luminex xTAG GPP. RESULTS Of the 1109 participants included, 437 (39.4%) developed AGE symptoms resulting in an overall AGE incidence of 24.7 per 100 person-weeks (95% CI: 22.4; 27.1). Twenty NoV-positive AGE cases (5.2% of those tested) were identified at an incidence of 1.1 per 100 person-weeks (95% CI: 0.7; 1.7). NoV-positive samples belonged mostly to genogroup GII (18, 85.7%); None of the 13 samples sequenced belonged to genotype GII.4. Clinical severity of AGE was higher for NoV-positive than for NoV-negative cases (mean modified Vesikari Score 6.8 vs 4.9) with more cases classified as severe or moderate (25% vs 6.8%). Eighty percent of NoV-positive participants (vs. 38.9% in NoV-negative) reported at least moderate impact on travel plans. CONCLUSIONS AGE is a prevalent disease among travellers with a small proportion associated with NoV. Post-travel stool sample collection timing might have influenced the low number of NoV cases detected; however, NoV infections resulted in high clinical severity and impact on travel plans. These results may contribute to targeted vaccine development and the design of future studies on NoV epidemiology

Distance versus hemifield costs in the identification of cued double targets

The paradigm of cued visual selection was used to measure the identification speed of single targets and target pairs in large item arrays. Four target categories were tested: oblique lines (orientation, Exp.1 and 5a), vertical bars with the upper and lower halves slightly displaced (Vernier's, Exp.2), T letters at four orientations (T's, Exp.3), and red or green oblique lines (conjunctions, Exp.4 and 5). In all experiments, performance with double targets in various distances from another was compared with that for single targets at the same presentation time. Despite reported differences in the need of attention for their discrimination, all four target types revealed similar performance characteristics in the task. The identification of double targets was strongly disturbed at near target distances (2.5 deg), slightly disturbed at medium distances (6.5 deg), and not or only little disturbed at far target distances (12 deg). Also the identification of individual targets in target pairs was usually worse than that of single targets, except at far distances. In later analysis, target pairs were also distinguished whether they had been located in same or different visual hemifields. It turned out that all near target pairs were located in same, all far target pairs in different hemifields. To disentangle hemifield from distance variations, a new set of target positions was tested (Exp.5), in which near and far distances occurred both within and across hemifields. The results revealed a clear predominance of hemifield effects. The identification of target pairs presented in same hemifields was notably worse than the identification of target pairs presented in different hemifields. Distance variations had almost no effect. In an aside finding, the study collected further evidence for an independent feature processing in conjunctions; the color of colored lines was always faster identified than their orientation (Exp.4)