Comparison of the influence of stimuli color on Steady-State Visual Evoked Potentials

Abstract

Introduction:The main idea of a traditional Steady State Visually Evoked Potentials (SSVEP)-BCI is the activation of commands through gaze control. For this purpose, the retina of the eye is excited by a stimulus at a certain frequency. Several studies have shown effects related to different kind of stimuli, frequencies, window lengths, techniques of feature extraction and even classification. So far, none of the previous studies has performed a comparison of performance of stimuli colors through LED technology. This study addresses precisely this important aspect and would be a great contribution to the topic of SSVEP-BCIs. Additionally, the performance of different colors at different frequencies and the visual comfort were evaluated in each case. Methods: LEDs of four different colors (red, green, blue and yellow) flickering at four distinct frequencies (8, 11, 13 and 15 Hz) were used. Twenty subjects were distributed in two groups performing different protocols. Multivariate Synchronization Index (MSI) was the technique adopted as feature extractor. Results: The accuracy was gradually enhanced with the increase of the time window. From our observations, the red color provides, in most frequencies, both highest rates of accuracy and Information Transfer Rate (ITR) for detection of SSVEP. Conclusion:Although the red color has presented higher ITR, this color was turned in the less comfortable one and can even elicit epileptic responses according to the literature. For this reason, the green color is suggested as the best choice according to the proposed rules. In addition, this color has shown to be safe and accurate for an SSVEP-BCI.

Influência Do Padrão De Cor Em Potenciais Evocados Visuais

“…Os autores de [15] afirmam que diferentes cores estão associadas a diferentes emoções e estados mentais; e a cor vermelha provocaria também maior ativação do estado mental. Entretanto, segundo o experimento realizado por [8], a cor vermelha é relatada como a menos confortável para os usuários.…”

“…Alguns estudos recentes [6,7,8,9, 10] avaliaram diferentes estímulos visuais com o objetivo de desenvolver ICMs confiáveis e confortáveis. No entanto, diversos aspectos ainda necessitam ser aprofundados para que tal técnica possa ser efetivamente utilizada no futuro.…”

“…Os estímulos podem ser: visuais, [1], auditivos [4] ou somato-sensoriais [5]. Todas estas modalidades têm sido objeto de investigação em literatura recente, no intuito de desenvolver mecanismos de comunicação baseados na atividade cortical (interfaces cérebro-máquina -ICMs) para sujeitos com deficiências motoras diversas.Alguns estudos recentes [6,7,8,9, 10] avaliaram diferentes estímulos visuais com o objetivo de desenvolver ICMs confiáveis e confortáveis. No entanto, diversos aspectos ainda necessitam ser aprofundados para que tal técnica possa ser efetivamente utilizada no futuro.…”

Pengaruh Latar Belakang Warna pada Objek Gambar terhadap Hasil Ekstraksi Sinyal EEG

“…Atau dapat dikatakan bahwa respon sinyal EEG terhadap beberapa kondisi yang ditentukan memiliki perbedaan yang tidak terlalu signifikan. Beberapa penelitian terkini telah dilakukan untuk mengamati pengaruh stimulus warna yang diberikan kepada seseorang terhadap sinyal EEG [8][9][10]. Perbedaan yang muncul dari beberapa stimulus warna memberikan hasil sinyal EEG yang cukup berbeda.…”

Do the stimuli of an SSVEP-based BCI really have to be the same as the stimuli used for training it?

“…Different stimuli have been used for SSVEP BCI-based applications, as reviewed by [14]. The same review also revealed that stimulation frequencies in the low (1-12 Hz) and medium (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) Hz) frequency band have been more often applied than those in the high frequency band (30-60 Hz). The first is graphic alternation, in which a simple form (circle, rectangles) is successively displayed and hidden at the preferred frequency.…”