Flicker-induced color and form: Interdependencies and relation to stimulation frequency and phase

Abstract

Publication InformationBecker, C., & Elliott, M. A. (2006 AbstractOur understanding of human visual perception generally rests on the assumption that conscious visual states represent the interaction of spatial structures in the environment and our nervous system. This assumption is questioned by circumstances where conscious visual states can be triggered by external stimulation which is not primarily spatially defined. Here, subjective colors and forms are evoked by flickering light while the precise nature of those experiences varies over flicker frequency and phase. WhatÕs more, the occurrence of one subjective experience appears to be associated with the occurrence of others. While these data indicate that conscious visual experience may be evoked directly by particular variations in the flow of spatially unstructured light over time, it must be assumed that the systems responsible are essentially temporal in character and capable of representing a variety of visual forms and colors, coded in different frequencies or at different phases of the same processing rhythm.

Electrophysiological correlates of flicker-induced color hallucinations

“…Target colors were those colors reported most reliably in the free-report study described in Becker and Elliott (2006, Experiment 1). These colors have also been tested successfully in a primed response-time paradigm similar to the one employed in the present study (Becker & Elliott, 2006, Experiment 2) and distributions over flicker frequency were found to be very similar. Participants were reminded before each session that a response should only be given to the unequivocal experience of the target color.…”

“…This paradigm was employed with the aim to directly link EEG-frequency changes to the occurrence and report of a specific hallucinatory color. Previous experiments (Becker & Elliott, 2006) have shown that the distribution of color experiences over stimulation frequency are comparable for a free-report and a primed response-time paradigm with a slight overall increase in reports for the primed response-time design.…”

“…In addition, peak frequencies, i.e. those most effective in inducing hallucinatory phenomena were found to vary according to the type and set (form or color) within which a given hallucinatory phenomenon could be naturally classified (Becker & Elliott, 2006). Taken as a whole, forms were reported across the 8-40 Hz range (median frequency: 25 Hz) while colors were reported across the range 5-56 Hz (median frequency: 30 Hz).…”

“…It is often assumed that the visual experience is directly related to spatial or spectral characteristics of the external stimulus, so that, for example, spatial properties of the external stimulus are directly mapped onto spatial properties of the internal experience. However and as recently shown by Becker and Elliott (2006), hallucinatory visual experiences are a class of phenomenal experience which cannot necessarily be mapped directly onto the spatial and spectral properties of a stimulus. Becker and Elliott showed that experience of hallucinatory colors and forms can be reliably induced by the uniform stimulation of the visual field with flickering light.…”

Bandpass characteristics of high-frequency sensitivity and visual experience in blindsight

“…We considered it possible that the type of non-specific visual experience reported in blindsight may be reported more often at the temporal frequencies found in previous studies, that is to say at around 20 Hz. Our expectation was based upon other findings in which hallucinatory visual experiences both structured and unstructured are readily induced by stimulus flicker at around 20 Hz (Becker & Elliott, 2006;Becker, Gramman, Müller, & Elliott, 2009). If a non-specific Type II blindsight were found to accompany flicker at 20 Hz, the visual experiences accompanying blindsight might be best characterized in terms of transient hallucinations rather than in terms of the visual experience of stimulus events.…”