Attention and prepulse inhibition: the effects of task-relevant, irrelevant, and no-task conditions

We investigated whether attentional modulation of prepulse inhibition (PPI) is due to increased protection of processing of attended lead stimuli, decreased protection of processing of ignored lead stimuli, or a combination of both processes. Task and no-task trials, pre-cued by red and blue dots on a computer screen, were randomly intermixed. College student participants were instructed to do a tone duration judgment task on trials preceded by one color (task condition) and to do nothing on trials preceded by the other color (no-task condition). On task condition trials participants were instructed to count the number of longer duration tones of a particular pitch (attended condition) and to ignore tones of a different pitch (ignored condition). White noise startle stimuli were presented at 60 ms and 120 ms lead intervals on some trials in each condition. Additional startle stimuli were presented during the inter-trial intervals to measure baseline (unmodified) startle response. PPI in the attended condition was reliably greater than that in both the ignored and no-task conditions. PPI did not differ between the ignored and no-task conditions. The results are consistent with the conclusion that attentional modulation of PPI is due to increased protection of attended stimuli and not to decreased protection of ignored stimuli. Possible reasons for robust attentional modulation at the 60 ms lead interval as well as the usual 120 ms lead interval are discussed.