Electrophysiological model of human temporal contrast sensitivity based on SSVEP

Abstract

The present study aims to connect the psychophysical research on the human visual perception of flicker with the neurophysiological research on steady-state visual evoked potentials (SSVEPs) in the context of their application needs and current technological developments. In four experiments, we investigated whether a temporal contrast sensitivity model could be established based on the electrophysiological responses to repetitive visual stimulation and, if so, how this model compares to the psychophysical models of flicker visibility. We used data from 62 observers viewing periodic flicker at a range of frequencies and modulation depths sampled around the perceptual visibility thresholds. The resulting temporal contrast sensitivity curve (TCSC) was similar in shape to its psychophysical counterpart, confirming that the human visual system is most sensitive to repetitive visual stimulation at frequencies between 10 and 20 Hz. The electrophysiological TCSC, however, was below the psychophysical TCSC measured in our experiments for lower frequencies (1–50 Hz), crossed it when the frequency was 50 Hz, and stayed above while decreasing at a slower rate for frequencies in the gamma range (40–60 Hz). This finding provides evidence that SSVEPs could be measured even without the conscious perception of flicker, particularly at frequencies above 50 Hz. The cortical and perceptual mechanisms that apply at higher temporal frequencies, however, do not seem to directly translate to lower frequencies. The presence of harmonics, which show better response for many frequencies, suggests non-linear processing in the visual system. These findings are important for the potential applications of SSVEPs in studying, assisting, or augmenting human cognitive and sensorimotor functions.

Frequency-tagging of spatial attention using periliminal flickers

“…It is also important to consider that the success of eliciting SSVEP responses using light stimulation of extremely low contrast and intensity may be, at least partly, related to the surface covered by the flickers. Indeed, it can be argued that the flickers implemented in the present study, but also in previous studies reporting SSVEP responses elicited by imperceptible flickers (Lingelbach et al, 2021; Tsoneva et al, 2023), were rather large. Indeed previous research has shown that flicker size is positively correlated with SSVEP response amplitude (Duszyk et al, 2014; Ng et al, 2012).…”

“…This study aimed to assess the validity of minimally intrusive (periliminal) and imperceptible (subliminal) kering light stimulation as an approach to enhance frequency-tagging implementations. The present study builds upon previous research that had demonstrated the feasibility of recording SSVEP responses with imperceptible flickers (Tsoneva et al, 2023; Lingelbach et al, 2021). In the present study, the contrast and intensity of flickering visual stimulation were reduced down to the perceptual visibility threshold, reducing their intrusiveness.…”

“…Another pending question concerns whether other cognitive processes can be effectively frequency-tagged using periliminal (or even subliminal) flickers. The systematic investigation of subliminal SSVEP response over a wide range of frequencies carried by (Tsoneva et al, 2023) suggests that both lower and higher frequencies may be used in imperceptible frequency-tagging to tag specific neural networks. Future frequency-tagging studies are however needed to provide empirical evidence supporting the validity of this approach at frequencies that are not within the range of frequencies at which SSVEP responses are maximal (12 to 20 Hz, see Ladouce et al (2022); Tsoneva et al (2023); Murillo López et al (2021)).…”

“…The systematic investigation of subliminal SSVEP response over a wide range of frequencies carried by (Tsoneva et al, 2023) suggests that both lower and higher frequencies may be used in imperceptible frequency-tagging to tag specific neural networks. Future frequency-tagging studies are however needed to provide empirical evidence supporting the validity of this approach at frequencies that are not within the range of frequencies at which SSVEP responses are maximal (12 to 20 Hz, see Ladouce et al (2022); Tsoneva et al (2023); Murillo López et al (2021)). Another issue pertains to the ecological validity of the target detection task performed by the participants which may be considered rather artificial and transient with regard to its pacing.…”

“…By decreasing the luminosity of the brightest state of the flicker, which in turn diminishes the amplitude modulation depth, also leads to a reduction in the overall mean luminance intensity of the flickering stimulation. Some studies have demonstrated the feasibility of this method by inducing SSVEP responses using imperceptible flickers with LEDs, where the amplitude modulation depth was reduced below the perceptual visibility threshold (Lingelbach et al, 2021; Tsoneva et al, 2023). While these latter offer interesting insights about the use of such low amplitude depth VEPs, they lack temporal information regarding the signal-to-noise measures over the occipital in response to such stimuli.…”