Altered states phenomena induced by visual flicker light stimulation.
Ontology highlight
ABSTRACT:
SUBMITTER: Bartossek MT
PROVIDER: S-EPMC8248711 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Uncomfortable images generally have a particular spatial structure, which deviates from a reciprocal relationship between amplitude and spatial frequency (f) in the Fourier domain (1/f). Although flickering patterns with similar temporal structure also appear uncomfortable, the discomfort is affected by not only the amplitude spectrum but also the phase spectrum. Here we examined how discomfort from flicker with differing temporal profiles also varies as a function of the mean light level and luminance contrast of the stimulus. Participants were asked to rate discomfort for a 17° flickering uniform field at different light levels from scotopic to photopic. The flicker waveform was varied with a square wave or random phase spectrum and filtered by modulating the slope of the amplitude spectrum relative to 1/f. At photopic levels, the 1/f square wave flicker appeared most comfortable, whereas the discomfort from the random flicker increased monotonically as the slope of the amplitude spectrum decreased. This special status for the 1/f square wave condition was limited to photopic light levels. At the lower mesopic or scotopic levels, the effect of phase spectrum on the discomfort was diminished, with both phase spectra showing a monotonic change with the slope of the amplitude spectrum. We show that these changes cannot be accounted for by changes in the effective luminance contrast of the stimuli or by the responses from a linear model based on the temporal impulse responses under different light levels. However, discomfort from flicker is robustly correlated with judgments of the perceived naturalness of flicker across different contrasts and mean luminance levels.
| S-EPMC7311306 | biostudies-literature
Project description:Flickering lights can be uncomfortable to look at and can induce seizures in observers with photosensitive epilepsy. However, the temporal characteristics contributing to these effects are not fully known. In the spatial domain, one identified source of visual discomfort is when images have Fourier amplitude spectra that deviate from the natural (?1/frequency, 1/f) statistical characteristics of natural scenes, especially if they contain excess energy at the medium frequencies at which the visual system is most sensitive. We tested for analogous effects in the temporal domain, manipulating both the amplitude and phase spectra of the flicker. Participants judged the relative discomfort of temporal luminance variations in a pair of uniform 17° fields with different temporal modulations. In general, discomfort increased with deviations from natural amplitude spectra, particularly those with excess energy at medium frequencies or biased toward sharper spectra. These ratings of discomfort were also consistent with ratings of how natural the modulations appeared. However, the temporal discomfort judgments were also strongly affected by the phase spectra of the flicker, with fixed vs. random spectra producing very different responses. This was not due to the perceived regularity or predictability of the flicker, but could arise from a number of other potential factors. Our findings suggest that, like spatial patterns, visual discomfort in time-varying patterns depends in part on how similar they are to the amplitude spectra of temporal variations in the natural visual environment, but also point to the critical role of the phase spectrum in the perceived discomfort of flicker.
| S-EPMC5703225 | biostudies-literature
Project description: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 self-organized 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.
| S-EPMC1895977 | biostudies-literature
Project description:The theory of "visual stress" holds that visual discomfort results from overactivation of the visual cortex. Despite general acceptance, there is a paucity of empirical data that confirm this relationship, particularly for discomfort from visual flicker. We examined the association between neural response and visual discomfort using flickering light of different temporal frequencies that separately targeted the LMS, L-M, and S postreceptoral channels. Given prior work that has shown larger cortical responses to flickering light in people with migraine, we examined 10 headache-free people and 10 migraineurs with visual aura. The stimulus was a uniform field, 50 degrees in diameter, that modulated with high-contrast flicker between 1.625 and 30 Hz. We asked subjects to rate their visual discomfort while we recorded steady-state visually evoked potentials (ssVEPs) from early visual cortex. The peak temporal sensitivity ssVEP amplitude varied by postreceptoral channel and was consistent with the known properties of these visual channels. There was a direct, linear relationship between the amplitude of neural response to a stimulus and the degree of visual discomfort it evoked. No substantive differences between the migraine and control groups were found. These data link increased visual cortical activation with the experience of visual discomfort.
| S-EPMC7424114 | biostudies-literature
Project description:BackgroundTwo competing theories have been advanced to explain the evolution of multiple cone classes in vertebrate eyes. These two theories have important, but different, implications for our understanding of the design and tuning of vertebrate visual systems. The 'contrast theory' proposes that multiple cone classes evolved in shallow-water fish to maximize the visual contrast of objects against diverse backgrounds. The competing 'flicker theory' states that multiple cone classes evolved to eliminate the light flicker inherent in shallow-water environments through antagonistic neural interactions, thereby enhancing object detection. However, the selective pressures that have driven the evolution of multiple cone classes remain largely obscure.ResultsWe show that two critical assumptions of the flicker theory are violated. We found that the amplitude and temporal frequency of flicker vary over the visible spectrum, precluding its cancellation by simple antagonistic interactions between the output signals of cones. Moreover, we found that the temporal frequency of flicker matches the frequency where sensitivity is maximal in a wide range of fish taxa, suggesting that the flicker may actually enhance the detection of objects. Finally, using modeling of the chromatic contrast between fish pattern and background under flickering illumination, we found that the spectral sensitivity of cones in a cichlid focal species is optimally tuned to maximize the visual contrast between fish pattern and background, instead of to produce a flicker-free visual signal.ConclusionsThe violation of its two critical assumptions substantially undermines support for the flicker theory as originally formulated. While this alone does not support the contrast theory, comparison of the contrast and flicker theories revealed that the visual system of our focal species was tuned as predicted by the contrast theory rather than by the flicker theory (or by some combination of the two). Thus, these findings challenge key assumptions of the flicker theory, leaving the contrast theory as the most parsimonious and tenable account of the evolution of multiple cone classes.
| S-EPMC3720213 | biostudies-literature
Project description:Glaucoma is a neurodegenerative disease, which results in characteristic visual field defects. Intraocular pressure (IOP) remains the main risk factor for this leading cause of blindness. Recent studies suggest that disturbances in neurovascular coupling (NVC) may be associated with glaucoma. The resultant imbalance between vascular perfusion and neuronal stimulation in the eye may precede retinal ganglion cell (RGC) loss and increase the susceptibility of the eye to raised IOP and glaucomatous degeneration. Caveolin-1 (Cav-1) is an integral scaffolding membrane protein found abundantly in retinal glial and vascular tissues, with possible involvement in regulating the neurovascular coupling response. Mutations in Cav-1 have been identified as a major genetic risk factor for glaucoma. Therefore, we aim to evaluate the effects of Cav-1 depletion on neurovascular coupling, retinal vessel characteristics, RGC density and the positive scotopic threshold response (pSTR) in Cav-1 knockout (KO) versus wild type C57/Bl6 mice (WT). Following light flicker stimulation of the retina, Cav-1 KO mice showed a smaller increase in perfusion at the optic nerve head and peripapillary arteries, suggesting defective neurovascular coupling. Evaluation of the superficial capillary plexus in Cav-1 KO mice also revealed significant differences in vascular morphology with higher vessel density, junction density and decreased average vessel length. Cav-1 KO mice exhibited higher IOP and lower pSTR amplitude. However, there was no significant difference in RGC density between Cav-1 KO and wild type mice. These findings highlight the role of Cav-1 in regulating neurovascular coupling and IOP and suggest that the loss of Cav-1 may predispose to vascular dysfunction and decreased RGC signaling in the absence of structural loss. Current treatment for glaucoma relies heavily on IOP-lowering drugs, however, there is an immense potential for new therapeutic strategies that increase Cav-1 expression or augment its downstream signaling in order to avert vascular dysfunction and glaucomatous change.
| S-EPMC8606647 | biostudies-literature
Project description:In the mammalian cerebral cortex, neural responses are highly variable during spontaneous activity and sensory stimulation. To explain this variability, the cortex of alert animals has been proposed to be in an asynchronous high-conductance state in which irregular spiking arises from the convergence of large numbers of uncorrelated excitatory and inhibitory inputs onto individual neurons. Signatures of this state are that a neuron's membrane potential (Vm) hovers just below spike threshold, and its aggregate synaptic input is nearly Gaussian, arising from many uncorrelated inputs. Alternatively, irregular spiking could arise from infrequent correlated input events that elicit large fluctuations in Vm (refs 5, 6). To distinguish between these hypotheses, we developed a technique to perform whole-cell Vm measurements from the cortex of behaving monkeys, focusing on primary visual cortex (V1) of monkeys performing a visual fixation task. Here we show that, contrary to the predictions of an asynchronous state, mean Vm during fixation was far from threshold (14?mV) and spiking was triggered by occasional large spontaneous fluctuations. Distributions of Vm values were skewed beyond that expected for a range of Gaussian input, but were consistent with synaptic input arising from infrequent correlated events. Furthermore, spontaneous fluctuations in Vm were correlated with the surrounding network activity, as reflected in simultaneously recorded nearby local field potential. Visual stimulation, however, led to responses more consistent with an asynchronous state: mean Vm approached threshold, fluctuations became more Gaussian, and correlations between single neurons and the surrounding network were disrupted. These observations show that sensory drive can shift a common cortical circuitry from a synchronous to an asynchronous state.
| S-EPMC4067243 | biostudies-literature
Project description:The aim of this study is to uncover the network dynamics of the human visual cortex by driving it with a broadband random visual flicker. We here applied a broadband flicker (1-720 Hz) while measuring the MEG and then estimated the temporal response function (TRF) between the visual input and the MEG response. This TRF revealed an early response in the 40-60 Hz gamma range as well as in the 8-12 Hz alpha band. While the gamma band response is novel, the latter has been termed the alpha band perceptual echo. The gamma echo preceded the alpha perceptual echo. The dominant frequency of the gamma echo was subject-specific thereby reflecting the individual dynamical properties of the early visual cortex. To understand the neuronal mechanisms generating the gamma echo, we implemented a pyramidal-interneuron gamma (PING) model that produces gamma oscillations in the presence of constant input currents. Applying a broadband input current mimicking the visual stimulation allowed us to estimate TRF between the input current and the population response (akin to the local field potentials). The TRF revealed a gamma echo that was similar to the one we observed in the MEG data. Our results suggest that the visual gamma echo can be explained by the dynamics of the PING model even in the absence of sustained gamma oscillations.
| S-EPMC8195374 | biostudies-literature
Project description:Mitochondrial morphology is central to normal physiology and disease development. However, in many live cells and tissues, complex mitochondrial structures exist and morphology has been difficult to quantify. We have measured the shape of electrically-discrete mitochondria, imaging them individually to restore detail hidden in clusters and demarcate functional boundaries. Stochastic "flickers" of mitochondrial membrane potential were visualized with a rapidly-partitioning fluorophore and the pixel-by-pixel covariance of spatio-temporal fluorescence changes analyzed. This Flicker-assisted Localization Microscopy (FaLM) requires only an epifluorescence microscope and sensitive camera. In vascular myocytes, the apparent variation in mitochondrial size was partly explained by densely-packed small mitochondria. In normotensive animals, mitochondria were small spheres or rods. In hypertension, mitochondria were larger, occupied more of the cell volume and were more densely clustered. FaLM provides a convenient tool for increased discrimination of mitochondrial architecture and has revealed mitochondrial alterations that may contribute to hypertension.
| S-EPMC4655370 | biostudies-literature
Project description:PurposeIntrinsically photosensitive retinal ganglion cells (ipRGCs) mediate nonimage-forming visual functions such as pupillary constriction and circadian photoentrainment. Optimizing daytime nonimage-forming photostimulation has health benefits. We aimed to enhance ipRGC excitation using flickering instead of steady light.MethodsHuman subjects were tested with a three-dimensional matrix of flickering 463-nm stimuli: three photon counts (13.7, 14.7 and 15.7 log photons cm(-2)), three duty cycles (12%, 47%, and 93%) and seven flicker frequencies (0.1, 0.25, 0.5, 1, 2, 4, and 7 Hz). Steady-state pupil constrictions were measured.ResultsAmong stimuli containing 13.7 log photons cm-2, the one flickering at 2 Hz with a 12% duty cycle evoked the greatest pupil constriction of 48% ± 4%, 71% greater than that evoked by an equal-intensity (12.3 log photons cm(-2) s(-1)) continuous light. This frequency and duty cycle were also best for 14.7 log photons cm-2 stimuli, inducing a 58% ± 4% constriction which was 38% more than that caused by an equal-intensity (13.3 log photons cm(-2) s(-1)) constant light. For 15.7 log photons cm-2 stimuli, the 1-Hz, 47% duty cycle flicker was optimal although it evoked the same constriction as the best 14.7 log photons cm(-2) flicker.ConclusionsPupillary constriction depends on flicker frequency and duty cycle besides intensity. Among the stimuli tested, the one with the lowest photon count inducing a maximal response is 13.3 log photons cm(-2) s(-1) flickering at 2 Hz with 12% duty cycle. Our data could guide the design of healthier architectural lighting and better phototherapy devices for treating seasonal affective disorder and jet lag.
| S-EPMC4516013 | biostudies-literature