Supplementary materials for Cognitive Rhythms: Unobtrusive and Continuous Sensing of Alertness Using a Mobile Phone
This repository contains supplementary materials for Cognitive Rhythms: Unobtrusive and Continuous Sensing of Alertness Using a Mobile Phone. UbiComp, 2016. DOI: 10.1145/2971648.2971712
To assess alertness, we used the Psychomotor Vigilance Test (PVT) which is a reaction time test. In this test, the user responds to a visual stimulus shown at random intervals. Various statistical summaries of response time have been shown to be indicative of alertness.
In our paper, we operationalize alertness as relative response time(RRT). The steps of computing RRT from PVT response time are as follows:
- The first step involves removing false starts — cases where users responded (wrongly) before the stimulus has been shown.
- Since a PVT session includes multiple visual stimuli tests,
we calculate the median response time (
MRTs,p) for each session
- We then remove outlier sessions with
MRTs,p falling outside (mean ± 2.5 × SD) for each participant.
- Next, we take the mean
MRTs,p across all of participant
p’s sessions to establish an individual baseline for participant
- Finally, we compute the RRT of a given session as its percentage deviation
p’s individual baseline. That is, given a PVT session
sfor a participant
pwith a median reaction time for that session of
MRTs,p, the corresponding RRT is calculated as:
Here, MMRTp is the mean
MRT averaged across all
N sessions from