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David Carmel, Nilli Lavie, Geraint Rees; Neural correlates of conscious flicker perception. Journal of Vision 2005;5(8):768. doi: 10.1167/5.8.768.
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© ARVO (1962-2015); The Authors (2016-present)
Beyond the Critical Flicker Fusion (CFF) threshold, flickering light is perceived as fused, so multiple physical events are perceived as a single, continuous event. Little is known about the brain mechanisms underlying such temporal parsing of perception; and many previous studies of flicker perception have compared frequencies above and below threshold, thus confounding physical stimulation with perceptual outcome. Here, we used event-related functional MRI to measure brain activity in response to a single LED flickering at or around the individually adjusted CFF threshold in thirteen participants. Conscious perception (flickering or fused light) therefore varied while physical stimulus parameters were kept constant. On each trial participants reported whether they perceived the light emitted by the LED to be flickering or fused, with catch trials controlling for response bias. Behaviorally, an equal number of trials were perceived to be flickering and fused. For physically identical stimuli, greater brain activation was observed on flicker (versus fused) trials in regions of left parietal and prefrontal cortex previously associated with psychological processes of time estimation. In contrast, greater activation was observed on fused (versus flicker) trials in occipital extrastriate areas. Our findings indicate that the integration of temporally discrete visual events may occur relatively early in the visual pathway, while the activity of higher-level cortical mechanisms may be important in separating such events into distinct percepts in time.
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