Effects of stimulus duration on audio-visual synchrony perception

The integration of visual and auditory inputs in the human brain occurs only if the components are perceived in temporal proximity, that is, when the intermodal time difference falls within the so-called subjective synchrony range. We used the midpoint of this range to estimate the point of subjective simultaneity (PSS). We measured the PSS for audio-visual (AV) stimuli in a synchrony judgment task, in which subjects had to judge a given AV stimulus using three response categories (audio first, synchronous, video first). The relevant stimulus manipulation was the duration of the auditory and visual components. Results for unimodal auditory and visual stimuli have shown that the perceived onset shifts to relatively later positions with increasing stimulus duration. These unimodal shifts should be reflected in changing PSS values, when AV stimuli with different durations of the auditory and visual components are used. The results for 17 subjects showed indeed a significant shift of the PSS for different duration combinations of the stimulus components. Because the shifts were approximately equal for duration changes in either of the components, no net shift of the PSS was observed as long as the durations of the two components were equal. This result indicates the need to appropriately account for unimodal timing effects when quantifying intermodal synchrony perceptio

Entamoeba lysyl-tRNA Synthetase Contains a Cytokine-Like Domain with Chemokine Activity towards Human Endothelial Cells

Immunological pressure encountered by protozoan parasites drives the selection of strategies to modulate or avoid the immune responses of their hosts. Here we show that the parasite Entamoeba histolytica has evolved a chemokine that mimics the sequence, structure, and function of the human cytokine HsEMAPII (Homo sapiens endothelial monocyte activating polypeptide II). This Entamoeba EMAPII-like polypeptide (EELP) is translated as a domain attached to two different aminoacyl-tRNA synthetases (aaRS) that are overexpressed when parasites are exposed to inflammatory signals. EELP is dispensable for the tRNA aminoacylation activity of the enzymes that harbor it, and it is cleaved from them by Entamoeba proteases to generate a standalone cytokine. Isolated EELP acts as a chemoattractant for human cells, but its cell specificity is different from that of HsEMAPII. We show that cell specificity differences between HsEMAPII and EELP can be swapped by site directed mutagenesis of only two residues in the cytokines' signal sequence. Thus, Entamoeba has evolved a functional mimic of an aaRS-associated human cytokine with modified cell specificity

Recovery of forest-floor vegetation after a wildfire in a Picea mariana forest

We aimed to detect the trajectories of forest-floor vegetation recovery in a Picea mariana forest after a wildfire. Since fire severity in boreal forests is expected to increase because of climate changes, we investigated the effects of ground-surface burn severity, a surrogate for overall fire severity, on the revegetation. We annually monitored vegetation < 1.3 m high in 80 1 m x 1 m quadrats at Poker Flat Research Range (65A degrees 12'N, 147A degrees 46'W, 650 m a.s.l.) near Fairbanks, interior Alaska, where a large wildfire occurred in the summer of 2004, from 2005 to 2009. Sphagnum mosses were predominant on the unburned ground surface. In total, 66 % of the ground surface was burned completely by the wildfire. Total plant cover increased from 48 % in 2005 to 83 % in 2009. The increase was derived mostly by the vegetative reproduction of shrubs on the unburned surface and by the immigration of non-Sphagnum mosses and deciduous trees on the burned surface. Deciduous trees, which had not been established before the wildfire, colonized only on the burned surface and grew faster than P. mariana. Although species richness decreased with increasing slope gradient, these deciduous trees became established even on steep slopes. The wildfire that completely burned the ground surface distorted the revegetation, particularly on steep slopes. The restoration of the Sphagnum surface was a prerequisite after the severe wildfire occurred, although the Sphagnum cover had difficulty returning to predominance in the short term