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Attentional resolution is a construct that refers to the minimal separation that allows one stimulus to be attended separately from nearby stimuli. The attentional walk task, which requires a series of covert shifts of attention within variably dense arrays of stimuli, was introduced as a method of measuring attentional resolution. Using a cuing task, we show that individual items within arrays that are too dense to support an attentional walk can nonetheless be attended. We note that the precision with which attention can be localized is, in principle, a limitation separate from attentional resolution and conclude that performance in the attentional walk task is better suited for measuring this limitation than for measuring attentional resolution per se. [ABSTRACT FROM AUTHOR]

More than 36000 individuals living in rural Malawi were skin tested with antigens derived from 12 different species of environmental mycobacteria. Most were simultaneously tested with RT23 tuberculin, and all were followed up for both tuberculosis and leprosy incidence. Skin test results indicated widespread sensitivity to the environmental antigens, in particular to Mycobacterium scrofulaceum, M. intracellulare and one strain of M. fortuitum. Individuals with evidence of exposure to ‘fast growers’ (i.e. with induration to antigens from fast growers which exceeded their sensitivity to tuberculin), but not those exposed to ‘slow growers’, were at reduced risk of contracting both tuberculosis and leprosy, compared to individuals whose indurations to the environmental antigen were less than that to tuberculin. This evidence for cross protection from natural exposure to certain environmental mycobacteria may explain geographic distributions of mycobacterial disease and has important implications for the mechanisms and measurement of protection by mycobacterial vaccines.