Do alerting signals increase the size of the attentional focus?

Previous research has shown that the presentation of an auditory alerting signal before a visual target increases the interference from flanking distractors. Recently, it has been suggested that this increase in interference may be due to an expansion of the spatial focus of attention. In five experiments, this hypothesis was tested by using a probe technique dedicated to measuring variations in the size of the attentional focus: In the majority of trials, participants performed a letter discrimination task in which their attention was focused on a central target letter. In a randomly intermixed probe task, the size of the attentional focus was measured by letting participants respond to a probe occurring at varying positions. In all experiments, reaction time (RT) to the probe increased from the most central to more lateral probe positions. This V-shaped probe-RT function, however, was not flattened by the presentation of an alerting signal. Overall, this pattern of results is inconsistent with the hypothesis that alerting signals increase the attentional focus. Instead, it is consistent with nonspatial accounts that attribute the increase in interference to an alerting effect on perceptual processing, which then leads to a detrimental effect at the level of response selection.