EDA – skin sensing | Alan Walks Wales

This is ‘electro-dermal activity’ or what used to be called ‘galvanic skin response’ basically a measure of sweat. It is the same technique as used by a lie detector. When you are under stress, when you get a shock or in general at a heightened level of emotion or activity your skin gets more sweaty and skin resistance decreases.

The sensor used for this was an Affectiva Q wrist-worn device developed originally by Picard’s Affective Computing group in MIT, then commercialised. Unfortunately it is now out of production, but the Q sensor resources page is still available explaining its operation. The device also measures skin temperature and has three-axis accelerometer.

The sensor is placed on the underside of the wrist, the opposite way round to a wrist watch, and the sensors face the skin. I always wore it on my left wrist.

https://alandix.com/AWW-data/AffectivaQ/meta.csv

meta information, one line per file, mostly one day per file

on one occasion there are two files in one day where I accidentally knocked the device off and then had to start it again

fields:

name – file name

url – dropbox url

sampling_rate – always 8 = samples per second

timeset – ignore files where timeset = false, it means I did something wrong!

start_date – \ ___ date and time when recording starts

start_time – /

offset – always +1 I think this means BST rather than GMT

number_of_samples – number of data samples divide by 8 to get duration in seconds

https://alandix.com/AWW-data/AffectivaQ/meta.json

identical data in JSON format

Each EDA file contains 8 lines of header information followed by data starting at line 9:

data columns:

Z-axis – \

Y-axis – > —- accelerometer data … in principle could get paces from this …

X-axis – /

Battery – battery level – ignore

ÔøΩCelsius – skin temperature in degrees

EDA(uS) – EDA in whatever they measure it in!! bigger means more emotion/stress/sweat

Note this is a CSV export from the raw EDA files produced by the Q sensor.

Extract of CSV meta file

name,url,sampling_rate,timeset,start_date,start_time,offset,number_of_samples
2013_04_18_timeUnset_b.csv,https://dl.dropboxusercontent.com/u/5863079/AlanWalksWales/AffectivQ-CSV/2013_04_18_timeUnset_b.csv,8,,000-00-00,00:00:00,+00,304282
2013_04_18_timeUnset.csv,https://dl.dropboxusercontent.com/u/5863079/AlanWalksWales/AffectivQ-CSV/2013_04_18_timeUnset.csv,8,,000-00-00,00:00:00,+00,405610
2013_04_19.csv,https://dl.dropboxusercontent.com/u/5863079/AlanWalksWales/AffectivQ-CSV/2013_04_19.csv,8,1,2013-04-19,10:03:24,+01,330670
2013_04_20.csv,https://dl.dropboxusercontent.com/u/5863079/AlanWalksWales/AffectivQ-CSV/2013_04_20.csv,8,1,2013-04-20,08:56:21,+01,365140
2013_04_21.csv,https://dl.dropboxusercontent.com/u/5863079/AlanWalksWales/AffectivQ-CSV/2013_04_21.csv,8,1,2013-04-21,10:04:17,+01,301553

Extract of EDA data file (CSV export)

Log File Created by Q Live - (c) 2012 Affectiva Inc.
File Version: 1.01
Firmware Version: 1.71
UUID: AQL221200DG
Sampling Rate: 8
Start Time: 2013-05-08 09:16:30 Offset:+01
 Z-axis | Y-axis | X-axis | Battery | �Celsius | EDA(uS)
---------------------------------------------------------
-0.220,0.370,-0.900,-1,22.000,0.032
-0.180,-0.060,-0.850,-1,22.000,0.020
-0.170,-0.040,-0.900,-1,22.000,0.020
-0.160,0.150,-1.340,-1,22.000,0.030
-0.360,0.000,-1.080,-1,22.200,0.034
-0.450,0.530,-0.980,-1,22.000,0.037
0.090,0.440,-0.800,-1,22.000,0.039
-0.320,0.500,-0.850,-1,22.200,0.041
-0.360,0.430,-0.860,-1,22.000,0.041
-0.350,0.640,-0.980,-1,22.200,0.036
-0.410,0.680,-0.730,-1,22.200,0.032
-0.400,0.500,-0.500,-1,22.000,0.032