SSVEP database elicited by four visual stimuli types

The database consists of 108 electroencephalographic files from 27 participants performing a 5-target selection task. 

Each participant performed one experimental session.

All datasets were collected on channels PO7, PO3, POz, PO4, PO8, O1, Oz, and O2, according to the 10–20 EEG electrode placement standard.

For the visual stimuli, we consider the On-Off and Checkerboard patterns with luminance modulated by rectangular and sinusoidal functions, resulting in a total of four types of visual stimuli: Checkerboard pattern with the rectangular modulated signal (Sxx-C.txt); Checkerboard pattern with sinusoidal modulated signal (Sxx-mC.txt); On-Off pattern with sinusoidal modulated signal (Sxx-mOO.txt) and On-Off pattern with rectangular modulated signal  (Sxx-OO.txt), where "Sxx" represents the subject number and 01 <= xx <= 27.

In each file columns 1 to 8 correspond to EEG data and column 9 corresponds to the marks channel.

Each phase of the experiment block is identified with a marker.

The phases of one experiment trial are Fixation(201), Target Presentation(202), Preparation(203), Stimulation(101-105), and Rest(200).

Marker numbers 101, 102, 103, 104, and 105, encodes de target frequency applied during the "Stimulation" stage in a trial. They are associated with the stimulation frequencies as follows: 101 - 24 Hz; 102 - 20 Hz; 103 - 15 Hz; 104 - 10.909 Hz and, 105 - 8.57 Hz

Files can be easily accessible with EEG-dedicated MATLAB toolboxes, such as Fieldtrip and EEGLAB.

本数据库包含27名被试完成5目标选择任务时采集的108份脑电图（electroencephalographic, EEG）文件。每名被试仅完成一次实验环节。

所有数据集均依据10-20脑电图电极放置标准，在PO7、PO3、POz、PO4、PO8、O1、Oz及O2通道上采集得到。

针对视觉刺激，我们采用亮度分别通过矩形函数与正弦函数调制的开-关（On-Off）与棋盘格（Checkerboard）两种模式，最终得到四类视觉刺激：搭载矩形调制信号的棋盘格模式（Sxx-C.txt）、搭载正弦调制信号的棋盘格模式（Sxx-mC.txt）、搭载正弦调制信号的开-关模式（Sxx-mOO.txt）以及搭载矩形调制信号的开-关模式（Sxx-OO.txt）。其中Sxx代表被试编号，取值范围为01 ≤ xx ≤27。

每份文件的第1至8列为脑电图数据，第9列为标记通道。

实验区块的每个阶段均通过标记进行标识。单次实验试次的阶段包括：注视（Fixation，201）、目标呈现（Target Presentation，202）、准备阶段（Preparation，203）、刺激阶段（Stimulation，101-105）与休息阶段（Rest，200）。

标记编号101、102、103、104及105分别编码单次试次“刺激”阶段所应用的目标频率，对应关系如下：101对应24 Hz；102对应20 Hz；103对应15 Hz；104对应10.909 Hz；105对应8.57 Hz。

该数据集可通过Fieldtrip、EEGLAB等脑电图专用MATLAB工具箱便捷读取。