Neural correlates of metacontrast masking across different contrast polarities

Abstract

Metacontrast masking is a powerful illusion to investigate the dynamics of perceptual processing and to control conscious visual perception. However, the neural mechanisms underlying this fundamental investigative tool are still debated. In the present study, we examined metacontrast masking across different contrast polarities by employing a contour discrimination task combined with EEG (Electroencephalography). When the target and mask had the same contrast polarity, a typical U-shaped metacontrast function was observed. A change in mask polarity (i.e., opposite mask polarity) shifted this masking function to a monotonic increasing function such that the target visibility was strongly suppressed at stimulus onset asynchronies less than 50 ms. This transition in metacontrast function has been typically interpreted as an increase in intrachannel inhibition of the sustained activities functionally linked to object visibility and identity. Our EEG analyses revealed an early (160-300 ms) and a late (300-550 ms) spatiotemporal cluster associated with this effect of polarity. The early cluster was mainly over occipital and parieto-occipital scalp sites. On the other hand, the later modulations of the evoked activities were centered over parietal and centro-parietal sites. Since both of these clusters were beyond 160 ms, the EEG results point to late recurrent inhibitory mechanisms. Although the findings here do not directly preclude other proposed mechanisms for metacontrast, they highlight the involvement of recurrent intrachannel inhibition in metacontrast masking.

Motion processing impaired by transient spatial attention: Potential implications for the magnocellular pathway

“…The procedure of the fixation training is summarized in the Supplementary Material (Figure S.1B). The participants also performed an initial experimental training on motion direction discrimination and performed as many blocks as needed to get an accuracy ≥ 0.75 (Aydin, Ogmen, & Kafaligonul, 2021;Hung & Carrasco, 2021). On average, they completed 1.15 ± 0.37 training blocks, with the same length and procedure as the main experimental blocks.…”

“…Twenty-two observers with normal or corrected-to-normal vision, who were naïve to the purpose of the study, took part in the experiment. Two participants were excluded from data analysis, since their average accuracy scores were below the pre-determined 75% accuracy threshold (Aydin, Ogmen, & Kafaligonul, 2021;Hung & Carrasco, 2021). Accordingly, the data of the remaining 20 participants (12 females and 8 males, with a mean age of 25.8 ± 3.9 years) were included in the further analysis.…”

Understanding structure–function relationships in the mammalian visual system: part one

“…The final paper in this volume addresses the link between neural activity and visual perception. Using electroencephalography in human participants, Aydin et al (2021) report how neural activity is associated with a perceptual phenomenon known as metacontrast masking, in which the perception of target stimuli is interrupted by mask stimuli that are presented near the target stimuli. Based on the fact that metacontrast masking significantly depends on the contrast polarity of mask stimuli and stimulus onset asynchrony, they demonstrated a human neural response showing properties similar to the perceptual effect of metacontrast masking.…”