University of Twente Student Theses


Steady State Visual Evoked Potentials and the Visual Perception Curve

BERUMEN SALAZAR, J.G (2016) Steady State Visual Evoked Potentials and the Visual Perception Curve.

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Abstract:Repetitive visual stimulation (RVS), also known as flicker, induces oscillatory responses in the human visual cortex at the same, or harmonics of, the frequency of the stimulation. These responses are called Steady State Visual Evoked Potentials (SSVEP) are considered to be a strong and objective response of brain activity. SSVEP are used in research, clinical neuroscience and brain computer interfaces. The amplitude of the SSVEP is influenced by the frequency and modulation depth (MD), contrast in light change, of the RVS. However, besides two studies conducted at Philips Research (Van de Sant, et al., 2011; Lazo, et al., 2013) we have no knowledge of research addressing the effect of frequency and MD on SSVEP. In particular the lowest MDs necessary to elicit SSVEP are unknown. Such knowledge could help developing better tasks eliciting SSVEP at different amplitudes which could increase the accuracy of SSVEP detection, their use for the evaluation of the visual system, and also increase their applications. In order to study the effect of frequency and MD on SSVEP and to find the lowest MD necessary to elicit SSVEP we decided to use MDs around the Visual Perception Thresholds (VPT). The VPT are the lowest MD for a frequency at which people are able perceive flicker in RVS (Kelly, 1961; Perz, et al., 2011). We conducted an exploratory research where we evaluated a variety of frequencies (7-60 Hz) in combinations with MD at proportions (0.6 to 1.4) of the VPT in a RVS task. In addition, we combined the results of the two previously related Philips’s studies in order to increase the possibilities to create a SSVEP contrast sensitivity curve, a curve with the values of the lowest MD necessary to elicit SSVEP. We detected SSVEP for MDs around the VPT only for frequencies higher than 24 Hz and for MD lower the VPT. These SSVEP show an increase in amplitude with an increase in MD. We also created a SSVEP contrast sensitivity curve, which has a very similar shape to the VPC, especially for high frequencies. However, we did not find SSVEP at frequencies lower than 24 Hz, neither in our study nor in the two previous related studies. Our results indicate a close relationship between the VPC and the SSVEP contrast sensitivity curve, although the later may have higher MD for low frequencies.
Item Type:Essay (Master)
Faculty:BMS: Behavioural, Management and Social Sciences
Subject:77 psychology
Programme:Psychology MSc (66604)
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