The function of the SSAA
Using the files exported from E4 Connect, the SSAA extracts Heart Rate (HR), Heart Rate Variability (HRV) (time-domain methods, frequency-domain methods, non-linear domain methods) and Electrodermal Activity (EDA) relative to time interval parameters specified by the researcher. The user interface is therefore able to be tailored to meet a range of analytical conditions focused on either the micro analysis of arousal in time specific segments such as every few seconds during a foreign language spoken presentation, or relative to longer macro periods of analysis such as across an entire classroom period or activity. For the HRV time-domain, the beat-to-beat interval (NNMean) can be calculated up to once per 0.015625 (1/64) second while for the EDA mean (EDAMean) it is possible to capture data once per 0.25 (1/4) second. For HR, the mean value of the HR (HRMean) and the standard deviation of the HR (HRSD) are calculated. For the HRV time-domain, the mean value of the beat-to-beat interval (NNMean) and the standard deviation of the beat-to-beat interval (NNSD) are calculated. For the HRV frequency-domain, very low frequency (VLF), low frequency (LF), high frequency (HF), and the ratio of LF and HF (LF/HF) are calculated. For the HRV non-linear domain, SD1 and SD2 Poincaré Plots are calculated as follows:
As X = {RR1, RR2, ..., RR(n - 1)}, and Y = {RR2, RR3, ..., RRn},
PP SD1: The standard deviation of '(X - Y) / Sqrt(2)' in the condition range using the duration column of IBI.csv.
PP SD2: The standard deviation of '(X + Y) / Sqrt(2)' in the condition range using the duration column of IBI.csv.
For the EDA analysis, the mean value of the EDA (EDAMean) and the standard deviation of the EDA (EDASD) are calculated. The SSAA exports the results relative to each experimental time interval as a single tabulated .csv file using the columns shown below. It also exports visualizations in the form of Lomb-Scargle Periodograms and Poincaré Plots for each analysis interval parameter specified.
Results of this study indicate the potential of the Empatica E4 as a practical and valid tool for research on HR and HRV under non-movement conditions.
(Schuurmans et al. 2020: 2)
Journal of Medical Systems
https://doi.org/10.1007/s10916-020-01648-w
Alterations in the physiological signals are not easily controlled by the subject, thus, these entitle a more authentic insight into the subject emotional experience.
(Bota et al. 2020: 2)
Sensors
https://doi.org/10.3390/s20174723
What are the data properties?
The SSAA makes use of the data collected, processed and exported by the Empatica E4 which is downloaded from E4 Connect as a .zip file containing raw data relative to six primary physiological indicators:
Accelerometer (file: ACC.csv):
Data from 3-axis acceleometer sensor in the range [-2g, 2g] (sampled at 32 Hz)
(More information available HERE)
Blood Volume Pulse (file: BVP.csv):
Data from photoplethysmograph (PPG) (sampled at 64 Hz)
(More information available HERE)
Electrodermal Activity (file: EDA.csv):
Data from the electrodermal activity sensor in μS (sampled at 4 Hz)
(More information available HERE)
Inter Beat Interval (file: IBI.csv):
Inter beat intervals (intermittent output with 1/64 second resolution)
(More information available HERE)
Skin Temperature (file: TEMP.csv):
Data from temperature sensor in degrees on the Celsius (°C) scale (sampled at 4 Hz)
(More information available HERE)
Heart Rate (file: HR.csv): This file contains the average heart rate values, computed in spans of 10 seconds (More information available HERE)
Source:
Empatica (2021) Data export and formatting from E4 connect
Example SSAA Output:
Individual Student Data L2 Five-Minute Presentation (60-second analytical intervals)
Funded by the Japan Society for the Promotion of Science
Kakenhi Grant-in-Aid for Scientific Research (No: 19K00765)