Abstract
Purpose :
Daily tasks, like driving, require constant visual monitoring and quick responses to critical moments, such as changing traffic lights. Although focusing on one task usually reduces attention to concurrent activities, detecting and responding to targets enhances perception and memory. The attentional boost effect, linked to the transient release of norepinephrine (NE) from the locus coeruleus (LC) during target detection, raises questions about whether LC activity is triggered by target detection, the response, or both. This study uses pupil dilation as a proxy for LC activation to investigate the connection between the LC-NE system and the attentional boost effect.
Methods :
Participants viewed a rapid letter series, including a pre-specified target letter 33% of the time, a diverse range of nontarget letters 33% of the time, and blank trials with a fixation cross in the remaining instances. In Experiment 1 (N=24), participants pressed the spacebar upon detecting the target letter, withholding responses to nontarget and blank trials. In Experiment 2 (N=24), they pressed the spacebar upon detecting any of the 19 nontarget letters, withholding responses to target and blank trials. Pupil diameter on target, nontarget, and blank trials was measured relative to baseline levels.
Results :
In Experiment 1, participants responding to targets showed significantly larger pupil dilation on target trials than on nontarget and blank trials (ps < .001). No significant difference emerged between nontarget and blank trials (p = .329). This dilation may be attributed to target detection, response, or both. Experiment 2 aimed to clarify these possibilities: responding to nontarget trials resulted in significant pupil dilation compared to blank trials (p < .001), indicating the response alone can drive LC activity. Additionally, a smaller but still significant pupil dilation was observed on target trials compared to blank trials (p < .001), despite no response on target trials, suggesting target detection alone also drives LC activity.
Conclusions :
The findings support the hypothesis that the LC-NE system tracks both the perceptual goal of finding a visual target and the response goal of acting on a relevant moment. The LC-NE response aligns with behavioral findings showing that both target detection and response enhance the perception and memory of concurrent background stimuli.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.