Interactions between endogenous and exogenous attention during vigilance

Abstract

The ability to remain vigilant over long periods of time is critical for many everyday tasks, but controlled studies of visual sustained attention show that performance declines over time when observers are required to respond to rare stimulus events (targets) occurring in a sequence of standard stimulus events (nontargets). When target discrimination is perceptually difficult, this vigilance decrement manifests as a decline in perceptual sensitivity. We examined whether sudden-onset stimuli could act as exogenous attentional cues to improve sensitivity during a traditional sustained attention task. Sudden-onset cues presented immediately before each stimulus attenuated the sensitivity decrement, but only when stimulus timing (the interstimulus interval [ISI]) was constant. When stimulus timing was variable, exogenous cues increased overall sensitivity but did not prevent performance decline. Finally, independent of the effects of sudden onsets, a constant ISI improved vigilance performance. Our results demonstrate that exogenous attention enhances perceptual sensitivity during vigilance performance, but that this effect is dependent on observers' being able to predict the timing of stimulus events. Such a result indicates a strong interaction between endogenous and exogenous attention during vigilance. We relate our findings to a resource model of vigilance, as well as to theories of endogenous and exogenous attention over short time periods.

Figure 1

Stimuli and timing for the transient display version of the sustained attention task. Sequence of events is shown for one non-target trial (long line stimulus) and one target trial (short line stimulus). The transient mask appeared before and after every line (both targets and non-targets) as depicted. In the stable display version, the mask was presented continuously throughout the entire 1850 ms inter-event interval (e.g., in place of the sole fixation square shown in the figure). Stimuli are shown in white for illustrative clarity, but were presented in light grey during the tasks; the fixation square was presented in red in Experiment 1 and yellow in Experiment 2. In Experiment 2, the inter-event interval varied randomly across trials (M = 1850, range = 1350–2350 ms). The fixation square was continuously visible at the center of the screen during all tasks.

Figure 2

Changes in perceptual sensitivity (A′) as a function of time on task in Experiment 1. A′ plotted over four contiguous 8-minute blocks (240 trials each) for each display version (stable and transient).

Figure 3

Changes in perceptual sensitivity (A′) as a function of time on task in Experiment 2. A′ plotted over four contiguous 8-minute blocks (240 trials each) for each display version (stable and transient).

Figure 4

Changes in reaction time to targets as a function of time on task in Experiment 2. Reaction time plotted over four contiguous 8-minute blocks.

Figure 5

Changes in perceptual sensitivity (A′) as a function of time on task in Experiments 1 and 2 for the transient display version. A′ plotted over four contiguous 8-minute blocks (240 trials each) for constant (Experiment 1; N = 16) and variable (Experiment 2; N = 20) inter-event interval conditions.