Biomedical subjects

Mark Chappell

Publications and source records attributed to Mark Chappell.

7 recordsLinked to original sources

PubMed2006

Dividing attention in the flash-lag illusion.

A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive resources from the flash-lag judgment. The flash-lag illusion was larger, and performance in a detection task was generally poorer, under dual-task conditions than in single-task control conditions. These effects were particularly pronounced when decisions in the two tasks were required simultaneously, as compared to when they could be made sequentially. The results suggest that a time-consuming process is involved in the flash-lag decision, of such a nature that prolonging the process increases the magnitude of the illusion.

Attention↗

PubMed2006

Attention 'capture' by the flash-lag flash.

We report data from eight participants who made alignment judgements between a moving object and a stationary, continuously visible 'landmark'. A reversing object had to overshoot the landmark by a significant amount in order to appear to reverse aligned with it. In addition, an adjacent flash irrelevant to the judgment task reliably increased this illusory 'foreshortening'. This and other results are most simply explained by a model in which the flash causes attentional capture, complemented by processes of temporal integration, or backward inhibition, and object representation. A flash used to probe the perception of a moving object's position disrupts that very perception.

Adolescent↗

PubMed2005

A crucial role of angiotensin converting enzyme 2 (ACE2) in SARS coronavirus-induced lung injury.

During several months of 2003, a newly identified illness termed severe acute respiratory syndrome (SARS) spread rapidly through the world. A new coronavirus (SARS-CoV) was identified as the SARS pathogen, which triggered severe pneumonia and acute, often lethal, lung failure. Moreover, among infected individuals influenza such as the Spanish flu and the emergence of new respiratory disease viruses have caused high lethality resulting from acute lung failure. In cell lines, angiotensin-converting enzyme 2 (ACE2) has been identified as a potential SARS-CoV receptor. The high lethality of SARS-CoV infections, its enormous economic and social impact, fears of renewed outbreaks as well as the potential misuse of such viruses as biologic weapons make it paramount to understand the pathogenesis of SARS-CoV. Here we provide the first genetic proof that ACE2 is a crucial SARS-CoV receptor in vivo. SARS-CoV infections and the Spike protein of the SARS-CoV reduce ACE2 expression. Notably, injection of SARS-CoV Spike into mice worsens acute lung failure in vivo that can be attenuated by blocking the renin-angiotensin pathway. These results provide a molecular explanation why SARS-CoV infections cause severe and often lethal lung failure and suggest a rational therapy for SARS and possibly other respiratory disease viruses.

Analysis of Variance↗

PubMed2004

Events before the flash Do influence the flash-lag magnitude.

The flash-lag effect occurs when a flash abreast of a smoothly moving object is perceived to spatially lag the moving object. The postdiction accounts of this effect assume either that the flash "resets" motion detectors [Science 287 (2000) 2036], or that position information is not computed for moving objects until it is needed [Trends in the Neurosciences 25 (2002) 293], the latter view having also been proposed by Brenner and Smeets [Vision Research 40 (2000) 1645]. According to these accounts, events occurring before the flash should not change the magnitude of the flash-lag effect. In our experiment, pre-exposure of the moving object as a stationary stimulus, for as little as 50 ms before the flash occurred, significantly reduced the flash-lag effect.

Cues↗

PubMed2003

Is there an auditory-visual flash-lag effect?

A flash adjacent to the path of a moving object appears behind the moving object: the 'flash-lag effect'. We sought to test the flash-lag effect with a 'click' instead of a flash: a white triangle horizontally traversed the screen at a constant 12 degrees /s passing through a fixation cross in the presence of a quiet click. The subject judged whether the click occurred before or after the triangle passed through the cross. To be perceived as co-instantaneous events, the click had to be presented 127 ms after the moving triangle reached the cross (a 'click-lead' effect, providing falsification of predictive accounts of the flash-lag effect), as opposed to a standard flash-lag effect condition where a flashed triangle replaced the click and had to appear 60 ms before the moving triangle to appear aligned. With the auditory versus visual processing speed advantage considered, the neural time required to calculate a moving object's position is constant, independent of the modality of the flag.

Acoustic Stimulation↗

PubMed2002

The flash-lag effect and equiluminance.

An object briefly flashed adjacent to the path of another moving object appears to spatially lag the moving object in the direction of its motion: the 'flash-lag effect'. A simple differential lag model account of this effect suggests that it occurs because the moving object activates motion detectors in the faster magnocellular pathway, whereas the flashed object does not. This model was tested by reducing M-pathway involvement using isoluminant stimuli. All four participants, who were university undergraduate students, were exposed to eight conditions, involving all possible combinations of moving and flashing objects coloured either white or green, shown against either a grey or a black background. Green objects were equiluminant with the grey background. The magnitude of the flash-lag effect was found using the method of constant stimuli. No reliable support was found for the hypothesis that equiluminance of the moving object reduces the flash-lag effect. Instead an interaction was found where there was an effect of equiluminance on the flash, but only when the moving object was not equiluminant. Such data is problematic for this and other simple differential lag models of the flash-lag effect.

Adolescent↗

PubMedDate not supplied

Predation intensity does not cause microevolutionary change in maximum speed or aerobic capacity in trinidadian guppies (Poecilia reticulata Peters).

We measured maximal oxygen consumption (VO(2max)) and burst speed in populations of Trinidadian guppies (Poecilia reticulata) from contrasting high- and low-predation habitats but reared in "common garden" conditions. We tested two hypothesis: first, that predation, which causes rapid life-history evolution in guppies, also impacts locomotor physiology, and second, that trade-offs would occur between burst and aerobic performance. VO(2max) was higher than predicted from allometry, and resting VO(2) was lower than predicted. There were small interdrainage differences in male VO(2max), but predation did not affect VO(2max) in either sex. Maximum burst speed was correlated with size; absolute burst speed was higher in females, but size-adjusted speed was greater in males. For both sexes, burst speed conformed to allometric predictions. There were differences in burst speed between drainages in females, but predation regime did not affect burst speed in either sex. We did not find a significant correlation between burst speed and VO(2max), suggesting no trade-off between these traits. These results indicate that predation-mediated evolution of guppy life history does not produce concomitant evolution in aerobic capacity and maximum burst speed. However, other aspects of swimming performance (response latencies or acceleration) might show adaptive divergence in contrasting predation regimes.

Adaptation, Physiological↗