To further develop three-dimensional (3D) applications, it is important to elucidate the negative effects of 3D applications on the human body and mind. Thus, this study investigated differences in the effects of visual fatigue on cognition and brain activity using visual and auditory tasks induced by watching a 1-h movie in two dimensions (2D) and 3D. Eighteen young men participated in this study. Two conditions were randomly performed for each participant on different days, namely, watching the 1-h movie on television (...) in 2D (control condition) and 3D (3D condition). Before and after watching the 1-h movie on television, critical flicker fusion frequency (CFF: an index of visual fatigue), and response accuracy and reaction time for the cognitive tasks were determined. Brain activity during the cognitive tasks was evaluated using a multi-channel near-infrared spectroscopy system. In contrast to the control condition, the decreased CFF, and the lengthened reaction time and the decreased activity around the right primary somatosensory cortex during Go/NoGo blocks in the visual task at post-viewing in the 3D condition were significant, with significant repeated measures correlations among them. Meanwhile, in the auditory task, the changes in cognitive performance and brain activity during the Go/NoGo blocks were not significant in the 3D condition. These results suggest that the failure or delay in the transmission of visual information to the primary somatosensory cortex due to visual fatigue induced by watching a 3D movie reduced the brain activity around the primary somatosensory cortex, resulting in poor cognitive performance for the visual task. This suggests that performing tasks that require visual information, such as running in the dark or driving a car, immediately after using a 3D application, may create unexpected risks in our lives. Thus, the findings of this study will help outlining precautions for the use of 3D applications. (shrink)

ObjectiveTo explore the effect of independently developed transcranial pulsed current stimulation on alleviating athlete’s mental fatigue.MethodsA total of 60 college athletes were randomly divided into the active stimulation group and the sham stimulation group. Subjective questionnaires, behavior test, and functional near-infrared spectroscopy test were conducted before and after the experiment. Two-way ANOVA with repeated measures was used to compare the differences in mental fatigue indexes before and after the two experimental conditions.ResultsAfter 7 days of exercise training, there was a significant (...) difference in the main effect of the time factor in all indexes of the two groups. The scores of rated perceived exertion scale, positive and negative affect schedule, critical flicker frequency, and reaction time, in the tPCS treatment group, were better than those in the sham stimulation group. After 7 days of exercise training, all the subjects had different degrees of athlete’s mental fatigue; the subjects in the active stimulation group have a good evaluation of the tPCS developed by the research group without adverse actions.ConclusiontPCS intervention can improve emotional state, reduce the subjective evaluation of fatigue, improve behavioral levels such as attention and reaction time and increase cerebral prefrontal blood flow and oxygen supply. (shrink)

Two types of the attentional network, alerting and orienting, help organisms respond to environmental events for survival in the temporal and spatial dimensions, respectively. Here, we applied chromatic flicker beyond the critical fusion frequency to address whether awareness was necessary for activation of the two attentional networks. We found that high-frequency chromatic flicker, despite its failure to reach awareness, produced the alerting and orienting effects, supporting the dissociation between attention and awareness. Furthermore, as the (...) class='Hi'>flicker frequency increased, the orienting effect attenuated whereas the alerting effect remained unchanged. According to the systematic decline in temporal frequency sensitivity across the visual hierarchy, this finding suggests that unconscious alerting might be associated with activity in earlier visual areas than unconscious orienting. Since high-frequency flicker has been demonstrated to only activate early visual cortex, we suppose that neural activation in early visual areas might be sufficient to activate the two attentional networks. (shrink)

Our 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. What’s 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. (shrink)

Flickering light induces visual hallucinations in human observers. Despite a long history of the phenomenon, little is known about the dependence of flicker-induced subjective impressions on the flicker frequency. We investigate this question using Ganzfeld stimulation and an experimental paradigm combining a continuous frequency scan with a focus on re-occurring, whole percepts. On the single-subject level, we find a high degree of frequency stability of percepts. To generalize across subjects, we apply two rating systems, a (...) set of complex percept classes derived from subjects’ reports and an enumeration of elementary percept features, and determine distributions of occurrences over flicker frequency. We observe a stronger frequency specificity for complex percept classes than elementary percept features. Comparing the similarity relations among percept categories to those among frequency profiles, we observe that though percepts are preferentially induced by particular frequencies, the frequency does not unambiguously determine the experienced percept. (shrink)

Quantitative studies have assessed nurses’ attitudes toward and frequency of spiritual care [SC] and which factors are of influence on this attitude and frequency. However, we had doubts about the construct validity of the scales used in these studies. Our objective was to evaluate scales measuring nursing SC. Articles about the development and psychometric evaluation of SC scales have been identified, using, Web of Science, and CINAHL, and evaluated with respect to the psychometric properties and item content of (...) the scales. Item content was evaluated by each of the five authors with respect to the following questions: Does the item (1) reflect a general opinion about SC instead of a personal willingness to offer SC; (2) reflect general psychosocial care instead of specific SC; (3) focus solely on religious care; (4) contain the words ‘spiritual’ (care/needs/health/strengths, etc.); and (5) contain multiple propositions, or have an unclear meaning? We found eight scales. Psychometric analysis of these scales was often meager and the items of all but one scale suffered from two or more of the five problems described above. This leads us to conclude that many quantitative results in this area are based on findings with questionable scales. Suggestions for improvements are provided. (shrink)

Frequency selective surface -based intelligent spatial filters are capturing the eyes of the researchers by offering a dynamic behavior when exposed to the electromagnetic radiations. In this manuscript, a concept of creating complementary structures which stems from Babinet’s principle is illustrated. A hybrid complementary pair of FSS comprising double square loop FSS and double square slot FSS on either side of the dielectric substrate is proposed. DSLFSS offers band-pass behavior and can be placed as a superstrate, whereas DSSFSS behaves (...) as a band-stop intelligent spatial filter that blocks the radiations falling on it, thus making them applicable for use as a substrate. The technique utilized for analyzing DSLFSS and DSSFSS structures is based on the equivalent circuit modeling and transmission line methodology. The CPFSS structure offers the design simplicity, hence, suitable for placing them with the printed patch antenna radiators in wireless networking devices operating in sub-6 GHz 5G spectrum. DSLFSS offers band-pass behavior ranging from 2.99 to 5.56 GHz, whereas DSSFSS offers band-stop behavior ranging from 2.85 to 5.42 GHz covering all n77, n78, and n79 bands of FR1 spectrum of sub-6 GHz 5G range. The passband and the stopband offered by the two structures of CPFSS geometry are stable to oblique angles of incidence and the proposed design also offers polarization-independent behavior. The thickness of the dielectric region existing within the pair of designed structures is critical for the location of the passbands and the stopbands. The impact of the overall thickness of the dielectric substrate on the passbands and stopbands is also reported in this article. (shrink)

Von Mises defined a "physical" probability as a strict limit of the relative frequency of occurrence of an event in repeated trials. As a result of a number of criticisms of von Mises's approach, the more favored approach became the "propensity" interpretation. It is argued here that this interpretation is not compelling and that the only problem in von Mises's approach is the assumption that the relative frequency converges in a strict sense. This problem is then remedied by (...) deducing the axioms of probability theory from the assumption that the relative frequency converges only in the sense of the weak law of large numbers. (shrink)

'This excellent collection provides the reader with a comprehensive coverage of findings and theories about how people encode and summarize frequency information. While it is a smorgasbord of self-contained chapters with little cross-referencing, the high quality of the vast majority of these chapters yields a cognitive feast. They are written by eminent researchers who have opted to present both recent results and summaries of their most important work - certainly not the feared secondary idea or paper submitted because it (...) would be easier to publish in an edited volume than in critically peer reviewed journal.' Robyn M. Dawes, Charles J. Queenan, Jr. University Professor, Department of Social and Decision Sciences, Carnegie Mellon University, USAFrom childhood, each of us develops our own personal set of theories and beliefs about the world in which we live. Given the impossibility of knowing about every event that can ever take place, we use cognitive short cuts to try to predict and make sense of the world around us. One of the fundamental pieces of information we use to predict future events, and make sense of past events, is 'frequency' - how often has such an event happened to us, or how often have we observed a particular event? With such information we will make inferences about the likelihood of its future appearance. We will make judgements, assess risk, or even consumer decisions, on the basis of this information. We also form associations between events that frequently occur together, and even attribute causality between one event and the other as a result of their simultaneous appearance. How is it though that we process such information? How does our brain deal with information on frequencies? How does such information influence our behaviour, beliefs, and judgements? Important new findings on this topic have come from research within both social and cognitive psychology, though until now, never brought together in a single volume. This is the first book to bring together two disparate literatures on this topic - drawing on research from both cognitive psychology and social psychology. Including contributions from world leaders in the field, this is a timely, and long overdue volume on this topic. (shrink)

Gerd Gigerenzer's views on probabilistic reasoning in humans have come under close scrutiny. Very little attention, however, has been paid to his evolutionary component of his argument. According to Gigerenzer, reasoning about probabilities as frequencies is so common today because it was favored by natural selection in the past. This paper presents a critical examination of this argument. It will show first, that, _pace_ Gigerenzer, there are some reasons to believe that using the frequency format was not more (...) adaptive than using the standard (percentage) format and, second, that Gigerenzer's evolutionary argument and his other arguments such as his historical description of the notion of probability are in tension with each other. (shrink)

Precision targeting of specific white matter bundles that traverse the subcallosal cingulate has been linked to efficacy of deep brain stimulation for treatment resistant depression. Methods to confirm optimal target engagement in this heterogenous region are now critical to establish an objective treatment protocol. As yet unexamined are the time-frequency features of the SCC evoked potential, including spectral power and phase-clustering. We examined these spectral features—evoked power and phase clustering—in a sample of TRD patients with implanted SCC stimulators. (...) Electroencephalogram was recorded during wakeful rest. Location of electrical stimulation in the SCC target region was the experimental manipulation. EEG was analyzed at the surface level with an average reference for a cluster of frontal sensors and at a time window identified by prior study. Morlet wavelets generated indices of evoked power and inter-trial phase clustering. Enhanced phase clustering at theta frequency was observed in every subject and was significantly correlated with SCC-EP magnitude, but only during left SCC stimulation. Stimulation to dorsal SCC evinced stronger phase clustering than ventral SCC. There was a weak correlation between phase clustering and white matter density. An increase in evoked delta power was also coincident with SCC-EP, but was less consistent across participants. DBS evoked time-frequency features index mm-scale changes to the location of stimulation in the SCC target region and correlate with structural characteristics implicated in treatment optimization. Results also imply a shared generative mechanism between evoked potentials evinced by electrical stimulation and evoked potentials evinced by auditory/visual stimuli and behavioral tasks. Understanding how current injection impacts downstream cortical activity is essential to building new technologies that adapt treatment parameters to individual differences in neurophysiology. (shrink)

High-frequency oscillations emerged as a neural code for both positive affect and fluent attentional processing from evolutionary simulations with artificial neural networks. Visual 50 Hz flicker, which entrains neural oscillations in the gamma band, has been shown to foster attentional switching, but can it also elicit positive affect? A three-faces display was preceded by a 50, 25, or 0 Hz flicker on the position of the odd-one-out . Participants decided on the gender or on the subjective valence (...) of this neutral target in an approach-avoidance task, which served as an implicit affective measure. Only the detection of 25 Hz flicker, but not of 50 Hz flicker, was above chance . Faces primed by invisible 50 Hz flicker were explicitly evaluated more positively than with 25 Hz or 0 Hz. This gamma flicker also facilitated approach reactions, and inhibited avoidance reactions relative to 25 Hz and 0 Hz flicker in Blocks 1 and 2. Attentional switching was, moreover, enhanced by the 50 Hz flicker. According to the Affect–Gamma hypothesis, also in biological neural networks, high-frequency gamma oscillations may code for positive affect. (shrink)

:This essay advances a version of the flicker of freedom defense of the Principle of Alternative Possibilities and shows that it is invulnerable to the major objections facing other versions of this defense. Proponents of the flicker defense argue that Frankfurt-style cases fail to undermine PAP because agents in these cases continue to possess alternative possibilities. Critics of the flicker strategy contend that the alternatives that remain open to agents in these cases are unable to rebuff Frankfurt-style (...) attack on the grounds that they are insufficiently robust. Once we see that omissions are capable of constituting robust alternatives, even when they are not intentional, it becomes clear that agents in these cases do indeed possess robust alternative possibilities—alternatives that are ineliminable from cases of this sort. The upshot is that Frankfurt-style cases are theoretically incapable of providing us with good grounds for rejecting PAP. (shrink)

We investigated the impact of frequency of interruptions in a simulated medical visual search task. Participants performed the visual search task during which they were interrupted by a number-classification task in 25, 50, or 75% of all trials, respectively, reflecting the frequency conditions. Target presence and interruption were varied within-subjects, and interruption frequency was varied between-subjects. Globally, on a frequency condition level, participants in the low frequency condition had longer mean response times for the primary (...) visual search task than in the high condition, but there were no other performance differences between the three frequency conditions. Locally, on the level of specific interruption effects, accuracy decreased directly after interruptions for target present but not for target absent trials. Furthermore, interruptions caused significant interruption costs, reflected in slower overall RTs in interrupted than in uninterrupted trials. The combined findings show that especially for critical visual search tasks as in the medical field, interruptions—regardless of frequency—should be avoided. (shrink)

The aim of this paper is to evaluate the critical success factors and investigate the benefits that might be gained once implementing Electronic Customer Relationship Management at HEI from employee perspective. The study conducted at Al Quds Open University in Palestine and data collected from (300) employee through a questionnaire which consist of four variables. A number of statistical tools were intended for hypotheses testing and data analysis, including Spearman correlation coefficient for Validity, reliability correlation using Cronbach’s alpha, and (...) Frequency and Descriptive analysis. The overall findings of the current study show that all the features were important for staff and it was critical success factors, at the same time, websites were providing all the features discussed by the theory whereas staff showed their willingness to use those features if provided. It is also discovered that implementing Electronic Customer Relationship Management can cause staff retention, were provided efficiently and needed to be improved. Research limitations: The survey findings were based on QOU employee in Palestine, UAE and KSA branches not included in the study. (shrink)

The prevalence of dementia is increasing with the ever-growing population of older adults. Non-pharmacological, music-based interventions, including sensory stimulation, were reported by the Lancet Commission in 2020 to be the first-choice approach for managing the behavioural and psychological symptoms of dementia. Low frequency sinusoidal vibration interventions, related to music interventions through their core characteristics, may offer relief for these symptoms. Despite increasing attention on the effectiveness of auditory music interventions and music therapy for managing dementia, this has not included (...) low frequency vibration. This scoping review, following the JBI methodology guidelines, was conducted to investigate participants’ responses to both sound and mechanical vibration, the characteristics of the delivered interventions, methodological challenges, and the specifics of the research experiments reported. An extensive search was conducted in BMC, CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, ERIC, MEDLINE, Pedro, ProQuest Central, PsycINFO, Scopus, and Web of Science. Current Controlled Trials, Clinical Trials, and Google Scholar were also searched as well as a hand search in relevant journals. Studies on adults with all types of dementia, investigating tactile low frequency sound or mechanical vibration in any context were considered. Data from eight full-length studies were extracted using the data extraction table developed by the authors and were included in the analysis and critical appraisal. Issues in quality related to, for example, control groups and blinding. Few studies addressed participants’ subjective responses to the interventions. Reporting on the intervention characteristics was unclear. It appeared more frequent sessions led to better outcomes and home-based interventions potentially addressing the issue of access and feasibility. Future research should include neuroimaging to measure and confirm the hypothesised mechanism of cerebral coherence. Standardised reporting of intervention characteristics is also needed to ensure replicability of the experiments. Higher quality research is needed to investigate the impact and effect of low frequency vibration for the symptoms of dementia and compare outcomes in meta-syntheses. (shrink)

An innovative approach to improve the fidelity of low-frequency lateral motion cueing within full-flight simulators for non-maneuvering aircraft is presented. On the basis of the perception peculiarities by the human vestibular system of movement along the roll, the problem of low-frequency motion cueing of lateral movement by motion systems of flight simulators was formulated and solved. The critical challenge of simulating the set of angular motion cues that pilots perceive during flights is decided. This research highlights two (...) key outcomes. The fourth-order low-pass filter effectively extracts low-frequency motion cues from aircraft motion kinematic parameters, enhancing simulation accuracy. Secondly, proposed method significantly expands the range of simulated motion cues while ensuring their synchronization with high-frequency motion cues along relevant degrees of freedom. This formulation of the problem increases the range of simulated motion cues to ±0,3nz, which practically corresponds to the range of simulated motion cues of a transport aircraft, and thus increases the quality of motion cueing. The implementation of the developed method on the An-72TK-200 full flight simulator confirmed its effectiveness. In conclusion, this study introduces a promising methodology that enhances the quality of motion cueing, thus rendering flight simulations more realistic and beneficial for both pilots and aerospace engineering researchers in the real of non-maneuvering aircraft flight simulators. (shrink)

A previous study demonstrated that consonant recognition improved significantly in normal hearing listeners when useful frequency and time ranges were intensified by 6 dB. The goal of this study was to determine whether bilateral cochlear implant and bilateral hearing aid users experienced similar enhancement on consonant recognition with these intensified spectral and temporal cues in noise. In total, 10 BCI and 10 BHA users participated in a recognition test using 14 consonants. For each consonant, we used the frequency (...) and time ranges that are critical for its recognition, identified from normal hearing listeners. Then, a signal processing tool called the articulation-index gram was utilized to add a 6 dB gain to target frequency and time ranges. Consonant recognition was monaurally and binaurally measured under two signal processing conditions, unprocessed and intensified target frequency and time ranges at +5 and +10 dB signal-to-noise ratio and in quiet conditions. We focused on three comparisons between the BCI and BHA groups: AI-Gram benefits, enhancement in binaural benefits via the AI-Gram processing, and reduction in binaural interferences via the AI-Gram processing. The results showed that the mean AI-Gram benefit was significantly improved for the BCI and BHA groups. However, the mean binaural benefit was not improved after AI-Gram processing. Individual data showed wide ranges of the AI-Gram benefit and binaural benefit for both groups. Individual data also showed a decrease in binaural interference in both groups after AI-Gram processing. These results suggest that the frequency and time ranges, intensified by the AI-Gram processing, contribute to consonant enhancement for monaural and binaural listening and both BCI and BHA technologies. The intensified frequency and time ranges helped to reduce binaural interference but contributed less to the synergistic binaural benefit in consonant recognition for both groups. (shrink)

This innovative text is psychologically informed, both in its diagnosis of inferential errors, and in teaching students how to watch out for and work around their natural intellectual blind spots. It also incorporates insights from epistemology and philosophy of science that are indispensable for learning how to evaluate premises. The result is a hands-on primer for real world critical thinking. The authors bring a fresh approach to the traditional challenges of a critical thinking course: effectively explaining the nature (...) of validity, assessing deductive arguments, reconstructing, identifying and diagramming arguments, and causal and probabilistic inference. Additionally, they discuss in detail, important, frequently neglected topics, including testimony, including the evaluation of news and other information sources, the nature and credibility of science, rhetoric, and dialectical argumentation. The treatment of probability uses frequency trees and a frequency approach more generally, and argument reconstruction is taught using argument maps; these methods have been shown to improve students’ reasoning and argument evaluation. (shrink)

Narrow Band-pass filtering techniques have been a challenging task since the inception of audio and telecommunication applications. The challenge involves keeping quality factor, gain and mid-frequency of the filter independent of each other. The critical applications require a design that ensures mid-frequency immune to the circuit component tolerances. It becomes increasingly difficult for low-frequency applications where the shift in few Hz in mid-frequency would cause desired frequencies to fall outside the filter’s bandwidth and go undetected. (...) The selection of right topology of the filter for the best performance is the key to successful design. This book objectively compares the relative performance of none popular narrow band-pass filter topologies. The filter topologies are evaluated using a real-world practical example of designing an extremely narrow band-pass filter. The book provides guidelines for selecting the right topology for the low-frequency narrow band-pass filter. (shrink)

Speech comprehension across languages depends on encoding the pitch variations in frequency-modulated sweeps at different timescales and frequency ranges. While timescale and spectral contour of FM sweeps play important roles in differentiating acoustic speech units, relatively little work has been done to understand the interaction between the two acoustic dimensions at early cortical processing. An auditory oddball paradigm was employed to examine the interaction of timescale and pitch contour at pre-attentive processing of FM sweeps. Event-related potentials to (...) class='Hi'>frequency sweeps that vary in linguistically relevant pitch contour and timescale in Mandarin Chinese were recorded. Mismatch negativities were elicited by all types of sweep deviants. For local timescale, FM sweeps with F0 contours yielded larger MMN amplitudes than F1 contours. A reversed MMN amplitude pattern was obtained with respect to F0/F1 contours for global timescale stimuli. An interhemispheric asymmetry of MMN topography was observed corresponding to local and global-timescale contours. Falling but not rising frequency difference waveforms sweep contours elicited right hemispheric dominance. Results showed that timescale and pitch contour interacts with each other in pre-attentive auditory processing of FM sweeps. Findings suggest that FM sweeps, a type of non-speech signal, is processed at an early stage with reference to its linguistic function. That the dynamic interaction between timescale and spectral pattern is processed during early cortical processing of non-speech frequency sweep signal may be critical to facilitate speech encoding at a later stage. (shrink)

In the rationality debate, Gerd Gigerenzer and his colleagues have argued that human’s apparent inability to follow probabilistic principles does not mean our irrationality, because we can do probabilistic reasoning successfully if probability information is given in frequencies, not percentages (the natural frequency hypothesis). They also offered an evolutionary argument to this hypothesis, according to which using frequencies was evolutionarily more advantageous to our hominin ancestors than using percentages, and this is why we can reason correctly about probabilities in (...) the frequency format. This paper offers a critical review of this evolutionary argument. I show that there are reasons to believe using the frequency format was not more adaptive than using the standard (percentage) format. I also argue that there is a plausible alternative explanation (the nested-sets hypothesis) for the improved test performances of experimental subjects—one of Gigerenzer’s key explananda—which undermines the need to postulate mental mechanisms for probabilistic reasoning tuned to the frequency format. The explanatory thrust of the natural frequency hypothesis is much less significant than its advocates assume. (shrink)

The article discusses the use of algorithmic models in finance (algo or high frequency trading). Algo trading is widespread but also somewhat controversial in modern financial markets. It is a form of automated trading technology, which critics claim can, among other things, lead to market manipulation. Drawing on three cases, this article shows that manipulation also can happen in the reverse way, meaning that human traders attempt to make algorithms ‘make mistakes’ by ‘misleading’ them. These attempts to manipulate are (...) very simple and immediately transparent to humans. Nevertheless, financial regulators increasingly penalize such attempts to manipulate algos. The article explains this as an institutionalization of algo trading, a trading practice which is vulnerable enough to need regulatory protection. (shrink)

In a recent study, Becker and Elliott [Becker, C., & Elliott, M. A. . Flicker induced color and form: Interdependencies and relation to stimulation frequency and phase. Consciousness & Cognition, 15, 175–196] described the appearance of subjective experiences of color and form induced by stimulation with intermittent light. While there have been electroencephalographic studies of similar hallucinatory forms, brain activity accompanying the appearance of hallucinatory colors was never measured. Using a priming procedure where observers were required to indicate (...) the presence of one of eight target colors we compared electrophysiological correlates of hallucinatory color with brain states associated with other visual phenomena. Different target colors were accompanied by different patterns of EEG activation. However, in general, we found that the appearance of hallucinatory colors is preceded by a power decrease in the lower alpha band alongside an increase in gamma band frequencies. We argue that decreasing activity in the lower alpha band acts as a gating mechanism, inducing a switch in perception between different colors. The increasing gamma activation may correlate with the formation of a coherent conscious percept. (shrink)

In a recent study, Becker and Elliott [Becker, C., & Elliott, M. A.. Flicker induced color and form: Interdependencies and relation to stimulation frequency and phase. Consciousness & Cognition, 15, 175–196] described the appearance of subjective experiences of color and form induced by stimulation with intermittent light. While there have been electroencephalographic studies of similar hallucinatory forms, brain activity accompanying the appearance of hallucinatory colors was never measured. Using a priming procedure where observers were required to indicate the (...) presence of one of eight target colors we compared electrophysiological correlates of hallucinatory color with brain states associated with other visual phenomena. Different target colors were accompanied by different patterns of EEG activation. However, in general, we found that the appearance of hallucinatory colors is preceded by a power decrease in the lower alpha band alongside an increase in gamma band frequencies. We argue that decreasing activity in the lower alpha band acts as a gating mechanism, inducing a switch in perception between different colors. The increasing gamma activation may correlate with the formation of a coherent conscious percept. (shrink)