MAMEM SSVEP Database

Abstract

Released by the Information Technologies Institute (CERTH-ITI) and powered by MAMEM HORIZON 2020, the MSSVEP database contains EEG recordings of 11 subjects under the stimulation of flickering lights, used to study the steady state visually evoked potentials. The data is divided into three sets in which the experimental procedures and capturing devices differ.

Experimental Procedures

Each of the 11 subjects (8 males and 3 females), aged between 24 and 39 years old, performed up to five sessions of each of the three different experiments.

Experiment 1

Subjects were exposed to non-overlapping flickering lights from five magenta boxes with frequencies [6.66Hz, 7.5Hz, 8.57Hz 10Hz and 12Hz]. 256 channel EEG recordings were captured.

Each session of the experimental procedure consisted of the following:

1. 100 seconds of rest.
2. An adaptation period in which the subject is exposed to eight 5 second windows of flickering from a magenta box. Each flickering window is of a single isolated frequency, randomly chosen from the above set, specified in the FREQUENCIES1.txt file under 'adaptation'. The individual flickering windows are separated by 5 seconds of rest.
3. 30 seconds of rest.
4. For each of the frequencies from the above set in ascending order, also specified in FREQUENCIES1.txt under 'main trials':
   • Three 5 second windows of flickering at the chosen frequency, separated by 5 seconds of rest.
   • 30 seconds of rest.
   This gives a total of 15 flickering windows, or 23 including the adaptation period.

The order of chosen frequencies is the same for each session, although there are small-moderate variations in the actual frequencies of each individual window. The .freq annotations list the different frequencies at a higher level of precision.

*Note: Each 'session' in experiment 1 includes an adaptation period, unlike experiment 2 and 3 where each subject undergoes only one adaptation period before their first 'session'.

Experiment 2

Subjects were exposed to flickering lights from five violet boxes with frequencies [6.66Hz, 7.5Hz, 8.57Hz, 10Hz, and 12Hz] simultaneously. Prior to and during each flicking window, one of the boxes is marked by a yellow arrow indicating the box to be focused on by the subject. 256 channel EEG recordings were captured.

Each subject underwent a single adaptation period before the first of their 5 sessions (unlike experiment 1 in which each session began with its own adaptation period). In the adaptation period, the subject is exposed to ten 5-second flickering windows from the five boxes simultaneously, with the target frequencies specified in the FREQUENCIES2.txt file under 'adaptation'. The flickering windows are separated by 5 seconds of rest, and the 100s adaptation period precedes the first session by 30 seconds.

Each session consisted of the following:

1. For the series of frequencies specified in the FREQUENCIES2.txt file under 'sessions':
   • A 5 second window with all boxes flickering and the subject focusing on the specified frequency's marked box, followed by 5 seconds of rest.
   • This gives a total of 25 flickering windows for each session (not including the first adaptation period).
2. Five minutes of rest before the next session (not including the 5th session).

The order of chosen frequencies is the same for each session, although there are small-moderate variations in the actual frequencies of each individual window.

*Note: Each 'session' in experiment 1 includes an adaptation period, unlike experiment 2 and 3 where each subject undergoes only one adaptation period before their first 'session'.

Experiment 3

Subjects were exposed to flickering lights from five magenta boxes with frequencies [6.66Hz, 7.5Hz, 8.57Hz 10Hz and 12Hz] simultaneously. Prior to and during each flicking window, one of the boxes is marked by a yellow arrow indicating the box to be focused on by the subject. The Emotiv EPOC 14 channel wireless EEG headset was used to capture the subjects' signals.

Each subject underwent a single adaptation period before the first of their 5 sessions (unlike experiment 1 in which each session began with its own adaptation period). In the adaptation period, the subject is exposed to ten 5-second flickering windows from the five boxes simultaneously, with the target frequencies specified in the FREQUENCIES3.txt file under 'adaptation'. The flickering windows are separated by 5 seconds of rest, and the 100s adaptation period precedes the first session by 30 seconds.

Each session consisted of the following:

1. For the series of frequencies specified in the FREQUENCIES3.txt file under 'sessions':
   • A 5 second window with all boxes flickering and the subject focusing on the specified frequency's marked box, followed by 5 seconds of rest. Between the 12th and 13th flickering window, there is a 30s resting period.
   • This gives a total of 25 flickering windows for each session (not including the first adaptation period).
2. Five minutes of rest before the next session (not including the 5th session).

The order of chosen frequencies is the same for each session, although there are small-moderate variations in the actual frequencies of each individual window.

*Note: Each 'session' in experiment 1 includes an adaptation period, unlike experiment 2 and 3 where each subject undergoes only one adaptation period before their first 'session'.

Files

Experiment 1 Waveforms and Annotations

File names are in the form S0NNn, where NN is the subject number and n is the session letter for that subject. Each session lasts in the order of several minutes and is sampled at 250Hz.

Each session has the following files:

• A waveform file of the EEG signals (.dat) along with its header file (.hea). If the channel corresponds to an international 10-20 channel then it is labeled as such. Otherwise, it is just labeled 'EEG'.
• An annotation file (.flash) containing the locations of each individual flash.
• An annotation file (.win) containing the locations of the beginning and end of each 5 second flickering window. The annotations are labeled as '(' for start and ')' for stop, along with auxiliary strings indicating the frequency of each flashing windows.

The FREQUENCIES1.txt file contains the approximate frequencies of the flickering windows, equal for each session, adaptation, and subject. Note that the .win annotations list the different frequencies at a higher level of precision.

Experiment 2 Waveforms and Annotations

File names are in the form T0NNn, where NN is the subject number and n is a - e for the session letter or x for the adaptation period. Each session lasts in the order of several minutes and is sampled at 250Hz.

Each session and adaptation period has the following files:

• A waveform file of the EEG signals (.dat) along with its header file (.hea). If the channel corresponds to an international 10-20 channel then it is labeled as such. Otherwise, it is just labeled 'EEG'.
• An annotation file (.flash) containing the locations of each individual flash.
• An annotation file (.win) containing the locations of the beginning and end of each 5 second flickering window. The annotations are labeled as '(' for start and ')' for stop, along with auxiliary strings indicating the focal frequency of the flashing windows.

The FREQUENCIES2.txt file indicates the approximate marked frequencies of the flickering windows, equal for each session, adaptation, and subject. These values are equal to those contained in the .win annotations.

Experiment 3 Waveforms and Annotations

File names are in the form U0NNn, where NN is the subject number and n is a - e for the session letter or x for the adaptation period. In addition, session file names end with either i or ii, corresponding to the first 12 or second 13 windows of the session respectively. Each session lasts in the order of several minutes and is sampled at 128Hz.

Each session half and adaptation period has the following files:

• A waveform file of the EEG signals (.dat) along with its header file (.hea).
• An annotation file (.win) containing the locations of the beginning and end of each 5 second flickering window. The annotations are labeled as '(' for start and ')' for stop, along with auxiliary strings indicating the focal frequency of the flashing windows.

The FREQUENCIES3.txt file indicates the approximate marked frequencies of the flickering windows, equal for each session, adaptation, and subject. These values are equal to those contained in the .win annotations.

General Information Files

The SUBJECTS file contains the gender and sex of each subject. The CORR file contains certain channel numbers (indices starting from 1) and the international 10-20 EEG channels they correspond to for the 256 channel EEG setup used in experiments 1 and 2. Note that the header files for each record also contain this information.

Authors and Contact

Authors: Kostantinos Georgiadis, Georgios Liaros, Vangelis P. Oikonomou, Elisavet Chatzilari, Katerina Adam, Spiros Nikolopoulos, Ioannis Kompatsiaris

Please contact:
Kostantinos Georgiadis, Research Associate, Information Technologies Institute, Center of Research and Technology Hellas, 6th Charilaou - Thermi, kostas.georgiadis at iti.gr

Dr. Spiros Nikolopoulos, Post-Doctoral Research Associate, Information Technologies Institute, Center of Research and Technology Hellas, 6th Charilaou - Thermi, nikolopo at iti.gr