Crossmodal attention alters auditory contrast sensitivity

We examined the influence of covert, endogenous, crossmodal attention on auditory contrast sensitivity in a two-interval forced-choice dual-task paradigm. Attending to a visual stimulus has been found to alter the visual contrast response function via a mechanism of contrast gain for sustained visual attention, or a combination of response gain and contrast gain for transient visual attention (Ling and Carrasco, 2006). We examined if and how auditory contrast sensitivity varied as a function of attentional load, the difficulty of a competing visual task, and how such effects compared to those found for the influences of attention on visual processing. In our paradigm, subjects listened to two sequential white noise stimuli, one of which was amplitude modulated. Subjects reported which interval contained the amplitude modulated auditory stimulus. At the same time a sequence of 5 letters was presented, in an rsvp stream at central fixation, for each interval. Subjects judged which interval contained the visual target. For a given block of trials, subjects judged which interval contained white letters (easy visual task) or, in a separate block of trials, which interval had more target letters ‘A’ (difficult visual task). We found that auditory thresholds were lower for the easy compared to the difficult visual task and that the shift in the auditory contrast response function was reminiscent of a contrast gain mechanism for visual contrast. Importantly, we found that the effects of crossmodal attention on the auditory contrast response function diminished with practice.