Abstract
Both the focus of sustained attention and an individual's readiness to shift attention among spatial locations fluctuate over time. However, the interaction of these ongoing changes in attentional states remains unknown. In the current study, participants completed a modified gradual continuous performance task during which they monitored one of two lateralized streams of black and white images for the appearance of frequent target stimuli, withholding responses to foils. Periodically, a visual cue signaled participants to either maintain fixation at the current stream or to make a saccade to the opposing stream, and participants made a parity categorization for a digit appearing at the cued location. Trial-by-trial variation in pupil size, an indicator of arousal, accounted for both fluctuations in sustained attention and shift readiness but fluctuations in sustained attention were not associated with general modulations of shift readiness. Furthermore, we manipulated the frequency of gaze shift cues over time and observed that unexpected shift cues were most disruptive when participants lacked sustained focus, yielding a greater cost in saccade latencies than when the efficacy of sustained attention was high. Our results suggest that ongoing changes in sustained attention occur independently from gaze shifting readiness but carry consequences for learned saccade preparation.