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Figure 1 | BMC Neuroscience

Figure 1

From: High-performance classification of contour percepts from EEG recordings

Figure 1

The left panel shows the difference of the evoked visual potentials (EVPs) for contour stimuli versus non-contour stimuli, averaged over the observers. First signatures of contour integration processes appear at around 180 ms after stimulus onset in the occipital-parietal electrodes (below the white line), followed by the frontal electrodes at about 220 ms (P200), lasting about 70 ms. EVP differences with the opposite sign appear from about 320 ms and extend for about 140 ms. Mean reaction time was around 550 ms, with large variations across observers. Differences in EVPs occurring after 300 ms (i.e., ~200 ms before the observer's responses) are likely to reflect mixtures of late contour integration and early motor preparatory processes. These periods were thus excluded from classification, using only wavelet coefficients from 50 to 300 ms after stimulus onset (black dashed line). The right panel shows classification performances. With a chance level at 50% and an error probability of 2%, performances >53.8% are considered significantly different from chance level. Performance varies considerably over observers, and is highest in the parietal-occipital electrodes (right panel), for wavelet frequencies between 3-4 Hz (not shown).

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