Pupillary fluctuation amplitude before target presentation reflects short-term vigilance level in Psychomotor Vigilance Tasks

Abstract

Our daily activities require vigilance. Therefore, it is useful to externally monitor and predict our vigilance level using a straightforward method. It is known that the vigilance level is linked to pupillary fluctuations via Locus Coeruleus and Norepinephrine (LC-NE) system. However, previous methods of estimating long-term vigilance require monitoring pupillary fluctuations at rest over a long period. We developed a method of predicting the short-term vigilance level by monitoring pupillary fluctuation for a shorter period consisting of several seconds. The LC activity also fluctuates at a timescale of seconds. Therefore, we hypothesized that the short-term vigilance level could be estimated using pupillary fluctuations in a short period and quantified their amplitude as the Micro-Pupillary Unrest Index (M-PUI). We found an intra-individual trial-by-trial positive correlation between Reaction Time (RT) reflecting the short-term vigilance level and M-PUI in the period immediately before the target onset in a Psychomotor Vigilance Task (PVT). This relationship was most evident when the fluctuation was smoothed by a Hanning window of approximately 50 to 100 ms (including cases of down-sampled data at 100 and 50 Hz), and M-PUI was calculated in the period up to one or two seconds before the target onset. These results suggest that M-PUI can monitor and predict fluctuating levels of vigilance. M-PUI is also useful for examining pupillary fluctuations in a short period for elucidating the psychophysiological mechanisms of short-term vigilance.

Pupillary fluctuation amplitude preceding target presentation is linked to the variable foreperiod effect on reaction time in Psychomotor Vigilance Tasks

“…A better index for estimating temporal attention in the medium-term variable FP is the pupillary fluctuation amplitude before target presentation, or the Micro-Pupillary Unrest Index (M-PUI) [ 35 ]. We have recently proposed the M-PUI, a quantitative index of pupilar diameter fluctuation degree over a shorter timescale [ 35 ], which was inspired by the better-known “Pupillary Unrest Index (PUI)” of pupillary unrest over a longer timescale [ 36 ].…”

“…A better index for estimating temporal attention in the medium-term variable FP is the pupillary fluctuation amplitude before target presentation, or the Micro-Pupillary Unrest Index (M-PUI) [ 35 ]. We have recently proposed the M-PUI, a quantitative index of pupilar diameter fluctuation degree over a shorter timescale [ 35 ], which was inspired by the better-known “Pupillary Unrest Index (PUI)” of pupillary unrest over a longer timescale [ 36 ]. In our previous paper, we reported a within-individual trial-by-trial positive correlation between M-PUI and RT (i.e., the M-PUI’s reflection of short-term vigilance levels) using the PVT with the medium-term variable FP [ 35 ].…”

“…We have recently proposed the M-PUI, a quantitative index of pupilar diameter fluctuation degree over a shorter timescale [ 35 ], which was inspired by the better-known “Pupillary Unrest Index (PUI)” of pupillary unrest over a longer timescale [ 36 ]. In our previous paper, we reported a within-individual trial-by-trial positive correlation between M-PUI and RT (i.e., the M-PUI’s reflection of short-term vigilance levels) using the PVT with the medium-term variable FP [ 35 ]. That is, we found that a participant’s M-PUI in long RT trials was significantly larger than that in short RT trials without considering the FP length.…”

“…That is, we found that a participant’s M-PUI in long RT trials was significantly larger than that in short RT trials without considering the FP length. However, from the perspective of medium-term variable FP studies, this trial-by-trial positive correlation could have been mediated by both FP and SE effects, only the FP effect, only the SE effect, or none of these effects [ 35 ]. Notably, the positive correlation disappeared when the M-PUI calculation period was more than a few seconds away from the time immediately before the target presentation, suggesting that the real-time M-PUI reflects RT with a temporal resolution of a few seconds.…”

“…Table 1 ). Similarly, we suggested the theoretical possibility that M-PUI might capture the locus-coeruleus norepinephrine (LC-NE) system’s preparatory state for the target detection’s phasic enhancement [ 35 ]. These previous findings and theoretical possibilities suggest that M-PUI might reflect temporal attention in preparation for a target, i.e., the FP or SE effect [ 35 ].…”