EEG_data.mat

We recorded EEG signals and response times of 20 healthy subjects during the visual stimuli classification task. During this task, the ambiguous visual stimuli, Necker cubes, with a different ambiguity degree (<b>a</b>) were presented in random order. We instructed the subjects to press the left or the right key to report their interpretation of each Necker cube orientation.<br>Ambiguity <b>a</b> depends on the contrast of the middle edges and affects the Necker cube orientation (See attached Fig1). In our experiment, we used the Necker cube images with eight different ambiguity degrees, <b>a</b>={0.0, 0.15, 0.4, 0.45, 0.55, 0.6, 0.85, 1}. Half of them, <b>a</b> = {0.0, 0.15, 0.4, 0.45}, are left-oriented (Fig1, A), and another half, <b>a</b>={0.55, 0.6, 0.85, 1}, are right-oriented (Fig1, B). While for <b>a</b>≈0 85 and <b>a</b>≈1 the Necker cubes have a clear orientation (left and right), for <b>a</b>≈0.5 the identification of the cube orientation is a more difficult task since the image becomes ambiguous.<br>The attached MATLAB structure contains 20 cells representing data of 20 subjects. Each cell includes field <i>Trial</i>, which contains 80 EEG trials recorded for 31 channels. The field <i>Label</i> contains the names of the channels. The first 40 trials are chosen from the beginning of the experiment and belong to the condition <b>T1</b>. The rest 40 trials are chosen from the end of the experiment and belong to the condition <b>T6</b>. Each trial has 4 s. length, and the stimulus is presented in the middle of the trial. The field <i>PresentationMoment </i>contains the moments of the stimuli presentations and the field <i>Ambiguity</i> contains the stimulus ambiguity degree <b>a</b>. The field <i>ReactionTime</i> contains the reaction time for each trial, and the field <i>Button</i> contains the identification of the button pressed (1-for the left and 2-for the right). The field <i>Background</i> contains the rest-state EEG signals recorded before the stimuli presentation. EEG signals are sampled at 250 Hz, filtered by a band-pass FIR filter with cut-off points at 1 Hz (HP) and 100 Hz (LP) and by a 50-Hz notch filter. Eyes blinking and heartbeat artifacts are removed with Independent Component Analysis (ICA)