PVT lapses differ according to eyes open, closed, or looking away

Abstract

Study objectives: A lapse during the psychomotor vigilance task (PVT) is usually defined as a response longer than 500 ms; however, it is currently unknown what psychobiological phenomena occur during a lapse. An assessment of what a participant is doing during a lapse may depict varying levels of "disengagement" during these events and provide more insight into the measurement of both a lapse and sleepiness.

Design: Repeated measures.

Setting: Participants underwent extended 30-min PVT sessions twice, at 22:00 and 04:00, under: (i) typical non-distractive laboratory conditions, and (ii) an additional distractive condition.

Participants: Twenty-four healthy young adults (mean age: 23.2 y +/- 2 y; range 21-25 y [12 m; 12 f]) without any sleep or medical problems and without any prior indication of daytime sleepiness.

Interventions: One night of sleep loss. Distraction comprised a TV located at 90 degrees in the visual periphery showing a popular TV program. For the non-distraction condition, the TV was turned off.

Measurements & results: Video data (bird's-eye and frontal view) were used to classify each lapse (> or = 500 ms) as occurring with eyes open (EO), eyes closed (EC), or due to a head turn (HT). EO lapses were more prevalent, with all lapses (EO, EC, and HT) increasing with sleepiness. There was a significant effect of distraction for HT lapses which was exacerbated when sleepy. For lapse duration there was little effect of sleepiness for EO lapses but a significant effect for EC and HT. The 95% confidence intervals for lapse duration and associated behavior showed those lapses greater than 2669 ms were 95% likely to be EC, whereas those 500-549 ms were 95% likely to be EO. Response times of 1217 ms had a 50:50 probability of being EO:EC.

Conclusions: Discriminating the varying causes of lapses whether due to visual inattention (eyes open), microsleep (eyes closed), or distraction (head turn) may provide further insight into levels of disengagement from the PVT and further insight into developing sleepiness.

Figure 1

Frequency of lapses for each condition: A Comparison of eyes open, eyes closed, and head turn lapses. Eyes open lapses were more frequent than all others (P < 0.0005). Eyes open and eyes closed lapses increased when sleepy (P < 0.00005), and lapses caused by distraction (head turn) increased when sleepy which was exacerbated by distraction (P < 0.05).

Figure 2

Mean reaction time of lapses for each condition: A Comparison of eyes open, eyes closed, and head turn lapses. Eyes closed lapses were longer in duration than lapses occurring with the eyes open (P < 0.0005) and head turns (P < 0.002); they also increased when sleepy (P < 0.0005). Eyes open lapses did not increase in duration when sleepy.

Figure 3

Example of relationship between mean RT and likelihood of the eyes being open. All lapses were ranked in duration, with each then expressed as percentage of the preceding 100 for EO, creating a 100-point moving average. Using a least squares function fit, the percent of lapses with eyes open (y) for any given lapse duration (x) is shown. A power law function curve was the best fit for the data (r²=0.99) and the resultant formula gives the percentage probability of the eyes being open (y) for any given lapse duration (x). After 7000 ms, the % probability tails off as all lapses had a < 1% chance of occurring with the eyes open.