Neural interactions between flicker-induced self-organized visual hallucinations and physical stimuli

Abstract

Spontaneous pattern formation in cortical activity may have consequences for perception, but little is known about interactions between sensory-driven and self-organized cortical activity. To address this deficit, we explored the relationship between ordinary stimulus-controlled pattern perception and the autonomous hallucinatory geometrical pattern formation that occurs for unstructured visual stimulation (e.g., empty-field flicker). We found that flicker-induced hallucinations are biased by the presentation of adjacent geometrical stimuli; geometrical forms that map to cortical area V1 as orthogonal gratings are perceptually opponent in biasing hallucinations. Rotating fan blades and pulsating circular patterns are the most salient biased hallucinations. Apparent motion and fractal (1/f ) noise are also effective in driving hallucinatory pattern formation (the latter is consistent with predictions of spatiotemporal pattern formation driven by stochastic resonance). The behavior of these percepts suggests that selforganized hallucinatory pattern formation in human vision is governed by the same cortical properties of localized processing, lateral inhibition, simultaneous contrast, and nonlinear retinotopic mapping that govern ordinary vision.1/f ͉ MacKay effect ͉ spatiotemporal pattern formation ͉ spontaneous cortical activity ͉ stochastic resonance T he visual cortex is active even in the absence of retinal stimulation; this spatiotemporally structured neural activity may have perceptual implications (1-9). For example, Kenet et al. (3) (in visual cortex of anesthetized cats) find a succession of spontaneous patterned neural states that correspond to those induced by simple oriented geometric patterns. These specific neural patterns, if present in awake humans, must be subliminal. This result raises two intriguing questions (6). (i) Do analogous perceptible patterns arise in humans? (ii) If so, can they interact with neural activity evoked by physical stimuli to affect perception? To tackle these questions we consider stereotyped geometric hallucinations, often triggered by migraine, drug intoxications, and empty-field flicker (10-20); these phenomena are thought to arise from autonomous activity in visual cortex. Although little is known about how spontaneous activity affects the perception of physical stimuli, it is possible to approach the second question from another direction: How do physical stimuli affect perception of spontaneous activity? Here we explore three circumstances in which physical stimuli dictate perceivable cortical pattern formation.The most common geometric hallucinatory forms are lattices, spirals, concentric circles, and fan shapes (Fig. 1). We regard these hallucinations as spontaneous states because they are apparently self-organized by visual cortex (14-20) and can arise without visual stimulation; these perceptible states may be analogous to Kenet et al.'s (3) subliminal states (9). Their geometric forms are predicted by neural network models that generate stripe patterns of neura...

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Predictive coding explains binocular rivalry: An epistemological review

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