Audio-Visual Brainwave Entrainment (AVBE)

Transcription

1 Technical note Issued: 2/2010 Audio-Visual Brainwave Entrainment (AVBE) Ronald M. Aarts Nicolle H. van Schijndel Pedro Fonseca Philips Research Eindhoven c Koninklijke Philips Electronics N.V. 2010

2 Concerns: Period of Work: Notebooks: End Report 2009 None Authors address R. M. Aarts N. H. van Schijndel P. Fonseca c KONINKLIJKE PHILIPS ELECTRONICS N.V All rights reserved. Reproduction or dissemination in whole or in part is prohibited without the prior written consent of the copyright holder. ii c Koninklijke Philips Electronics N.V. 2010

3 Title: Author(s): Reviewer(s): Technical Note: Additional Numbers: Subcategory: Audio-Visual Brainwave Entrainment (AVBE) Ronald M. Aarts ; Nicolle H. van Schijndel ; Pedro Fonseca A. Kohlrausch, S.C. Pauws Project: Emotions 2009 ( ) Customer: Philips Research Keywords: Abstract: brainwave entrainment (BWE), audio-visual entrainment, brain entrainment, audio-visual stimulation, auditory entrainment, binaural beats, and photic stimulation This report gives an overview of the field of audio-visual brainwave entrainment (AVBE), focusing on scientific literature that investigates the effect on health and wellbeing. The term brainwave entrainment refers to the use of periodic sensory stimuli to stimulate targeted frequencies in the brain. Such sensory stimuli can be auditory, visual or a combination of the two. First auditory entrainment will be discussed, with special attention for a specific form of auditory entrainment stimuli: binaural beats. This chapter is followed by a chapter on visual entrainment, and a chapter that compares the two types of entrainment. Subsequently, the effect of entrainment on performance is discussed. The following chapters are about the lasting (positive) effects of entrainment and potential negative effects. Finally, some tentative conclusions are formulated. Conclusions: Rhythmic sensory (auditory or visual) stimuli can have a profound effect on the brain. Consequences of entrainment for human behavior and underlying neurological mechanisms for that are less established. Preliminary evidence suggests positive effects on aspects like shortterm stress relief, pain, and cognitive abilities (attention, memory), but this is not yet without controversy. Comparing auditory with visual entrainment, auditory entrainment is favored, because visual entrainment has a (small) risk of evoking (epileptic) seizures. In conclusion, preliminary findings are promising, but further research is required. c Koninklijke Philips Electronics N.V iii

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5 Contents 1 Introduction 1 2 Auditory entrainment Binaural beats Visual entrainment 5 4 Auditory versus visual entrainment 7 5 Enhancing performance Auditory entrainment Visual Combined audio-visual Lasting effects of entrainment 12 7 Negative effects 13 8 Summary 14 9 Conclusions 15 c Koninklijke Philips Electronics N.V v

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7 Section 1 Introduction This report gives an overview of the field of audio-visual brainwave entrainment (AVBE). An early publication on this sensory stimulation method is [1] and a large stream of publications have followed since. The present report does not give an exhaustive literature review on general brainwave entrainment, but its scope is mainly limited to literature investigating the effect on health and wellbeing, for example by alleviating stress. The main purpose of the report is to bring non experts to a certain level of understanding about brainwave entrainment, without going too much in depth. Other forms of audiovisual stimulation like music-assisted relaxation [2] will not be discussed. The text is heavily based on the chapter Audio-visual entrainment in David Vernon s book [3] about techniques to enhance human performance and Huang s comprehensive review paper on the psychological effects of brainwave entrainment [4]. The term entrainment is used for the effect that two oscillating systems interacting with each other tend to approach each other in terms of frequency. A simple example of this is the self-synchronizing clocks at the wall an effect which was noticed by the Dutch mathematician and physicist Christiaan Huygens (see e.g. Wikipedia s entries Entrainment and Odd sympathy ). The term brainwave entrainment (also called audio-visual entrainment (AVE), brain entrainment, audio-visual stimulation, auditory entrainment and photic stimulation ) refers to the use of rhythmic sensory stimuli to stimulate targeted frequencies in the brain. Such sensory stimuli can be auditory, visual or a combination of the two. Research has repeatedly confirmed that stimuli with frequencies between about 8 and 12 Hz, which corresponds with the alpha range of the electroencephalogram (EEG), induce a frequency-following response in the brain as visible in EEG recordings ([5, 6, 7, 8, 9, 10, 11]). There is also entrainment possible beyond this frequency range, but for wellbeing applications the range is usually restricted to the EEG-alpha range. As stated earlier, we limited the scope of this report. As a consequence we will not discuss some related topics like the artist Brion Gysin (see wiki/brion_gysin) who created the Dream Machine (light bulb, turn table, rotating cylinder with cut outs) who thought he would change the world by photic stimulation in the sixties (see The remainder of this report is organized as follows. First auditory entrainment will be discussed, with special attention for a specific form of auditory entrainment stimuli: binaural beats. This chapter is followed by a chapter on visual entrainment, and a chapter that compares the two types of entrainment. Then, Chapter 5 will go into the c Koninklijke Philips Electronics N.V

8 effect of entrainment on performance. The subsequent chapters are about the lasting (positive) effects of entrainment and potential negative effects. The report ends with a summary and conclusions. 2 c Koninklijke Philips Electronics N.V. 2010

9 Section 2 Auditory entrainment For auditory entrainment, rhythmic (repetitive) sounds are used to promote rhythmic brain activity of a particular frequency. The most commonly used methods for generation of such stimuli are 1) isochronic beats: single tone that periodically increases and decreases in amplitude, or, in the extreme case, turns on and off. 2) monaural beats: two tones presented to the same ear, close in frequency, which are perceived as one beating tone with the beat frequency equal to the frequency difference between the two tones, 3) binaural beats: two tones, one presented to the right ear, the other one to the left ear, which are also perceived as a beating tone similar as in method 2. Since the auditory system has very low sensitivity for tones below 20 Hz (an important frequency range for entrainment), simple generation of a sinusoid with such a low frequency can not be used for auditory entrainment. Instead one could generate a pulse train with the inter-pulse interval corresponding to the entrainment frequency. Since almost all research investigating the effect of auditory entrainment on health and wellbeing used binaural beats, these stimuli are discussed below in more detail. 2.1 Binaural beats In 1839 the German experimenter H. W. Dove found that when he presented a participant with two separate frequencies composed of different wavelengths, one to each ear, this produced the sensation of a third phantom frequency called a binaural beat in addition to the two carrier frequencies [12]. The difference between the two carrier signals waxes and wanes as the two distinct frequencies mesh in and out of phase with one another. These differences produce an amplitude modulated standing wave, the binaural beat, which can be perceived. In this sense, the binaural beat is a fluctuating rhythm perceived as the frequency of the difference between the two auditory carrier signals. For example, if a 100-Hz tone is presented to the left ear and a 110-Hz tone is simultaneously presented to the right ear, one perceives the frequency difference as a distinct frequency component of 10 Hz. However, this binaural beat of 10 Hz is not heard in the literal sense of the word, but rather the brain encodes it as an auditory beat, and as such it can be used to entrain the neural activity of the brain via the frequency following response. [3] Clear evidence that a binaural beat can entrain the electrocortical activity of the brain comes from researchers who have found that binaural beats produce an auditory evoked response as measured with an electroencephalograph [13, 14, 15]). [3]. Recently c Koninklijke Philips Electronics N.V

10 Pratt et al. [16] found that neural activity with slightly different volley frequencies from left and right ear converges and interacts in the central auditory brainstem pathways to generate beats of neural activity to modulate activities in the left temporal lobe. Cortical potentials recorded to binaural beats are distinct from onset responses. The brain activity corresponding to the auditory illusion of low frequency beats can be recorded from the scalp. See [17] for a more elaborated literature review on binaural beats. See 5.1 for information about the behavioral and cognitive effects of listening to binaural beats. 4 c Koninklijke Philips Electronics N.V. 2010

11 Section 3 Visual entrainment For visual entrainment, visual (photic) stimulation can be achieved by flashing lights into the eyes of the individual using any source of flickering light with a fixed wavelength. It is typically implemented with general purpose LEDs which can be mounted on a support at a short distance to the eyes of the subject, either on the center or on the periphery of his field of vision (see Figure 3.1). The LEDs then flash out a pre-set frequency pattern entraining the brain via the optic nerve, where it has been shown to induce the EEG of the brain to match the frequency of the flickering lights. This is based on early research showing that rhythmic electrical potential changes can be recorded from the occipital region of the scalp when an individual is required to look at a flickering light field and that the elicited waves are of the same order of magnitude and rhythm as the flickering field [19]. Over time this finding stimulated researchers to examine what happens to the electrocortical activity of the brain when an individual is exposed to flickering lights (see e.g. [20, 21, 6]). For instance, when [6] recorded the EEG of people exposed to a flickering light he found they exhibited flicker-following potentials in both the occipital and central regions of the scalp. These potentials represent a frequency following response to visual stimuli. [3]. Because EEG recordings of the occipital cortex have a good signal to noise ratio, especially when compared with recordings of other areas of the cortex, this effect, called steady-state visually evoked potential (SSVEP for short) has received significant attention since very early (see [22] for a review of early work and [23] for a recent review on this area). Since then a number of researchers have confirmed this effect [24, 25, 11]. Because SSVEPs are so easily visible in the EEG it led researchers to implement brain-computer interfaces (BCI) based on this principle. This has been done for decades with quite some success for disabled subjects (see [26] Figure 3.1: LED boxes with diffusion panel used for SSVEP BCI [18]. c Koninklijke Philips Electronics N.V

12 for a comprehensive review) and, more recently, for healthy subjects [27], [28]. There has been relevant recent work done in this area in Philips Research [18, 29]. Intermezzo about the alpha range of the EEG In the previous text the alpha range of the EEG was mentioned and specified to be between 8 and 12 Hz. Let us have a closer look at this. This intermezzo is also applicable to auditory and combined audio-visual entrainment. Although the EEG has traditionally been divided into a number of components with generally agreed upon frequency ranges, there is increasing evidence that the frequency range of a specific component can vary between individuals (e.g., [30]). [30] has suggested that instead of using a generic frequency range for everyone, each person s EEG should be identified individually using the peak of their EEG activity as an anchor point. In this way, rather than alpha simply representing a fixed frequency range of 8 12 Hz it would represent a 2-Hz window either side of an individual s peak frequency. This has been referred to as the individual alpha frequency (IAF) range. [3]. This idea that EEG frequency ranges can vary between individuals has led some to suggest that the audio-visual entrainment mechanisms might differ from subject to subject. It might be that when the stimulus frequency matches the individual s peak alpha frequency as opposed to using the midpoint of a traditional bandwidth [31], the entrainment effect is stronger. Apart from personal differences in EEG frequency ranges, it is now clear that several cognitive factors such as attention [32] significantly alter the entrainment and the corresponding SSVEP. Although visual entrainment engages predominantly with the primary visual cortex, research has shown that it is capable of eliciting changes in cortical activity that are widely distributed across the cortex [33]. [3]. The effects of such entrainment may thus spread beyond the localized regions of the visual cortex, although its effectiveness at entraining a particular frequency component of the EEG may depend on the individual s resting baseline activity, mental state and current cognitive activity. To further confirm this point, pioneering work by Silberstein [34] has shown that cognitive processes have an important effect on the amplitude of SSVEPs recorded on different locations of the cortex, even outside the occipital region. Further work has confirmed that mental and emotional states have an impact on SSVEPs ([35, 36, 37]), giving birth to a technique called steady-state visual evoked potential topography, which is used e.g. to assess which cortical areas are active following determined cognitive processes. 6 c Koninklijke Philips Electronics N.V. 2010

13 Section 4 Auditory versus visual entrainment After discussing entrainment with auditory or visual stimuli, the issue remains which stimulus type is most effective and whether it is beneficial to combine the two sensory modalities. The study of [24] addresses this, comparing the effectiveness of auditory stimulation, visual stimulation and combined audio-visual stimulation. The study did not include any condition where the subjects had their eyes open when focusing on the light source and therefore the effects of visual entrainment are expectedly lower. The entrainment procedure involved a single seven minute period during which the participant was stimulated at a frequency of 18.5 Hz. Post training examination of the EEG revealed a significant increase in the amplitude of each person s EEG at 18.5 Hz for all types of stimulation. This is consistent with previous research and confirms that audio and/or visual entrainment can produce a frequency following effect in the brain. Importantly, additional analysis comparing the different modalities of entrainment showed that the auditory eyes-closed condition produced the most effective change in EEG. [3]. It may seem counter-intuitive that the combined audio-visual entrainment did not produce more of an effect on the EEG than either audio or visual conditions alone. However, Frederick et al. [24] account for this by suggesting that simultaneous stimulation in both the auditory and visual domains interferes with, rather than reinforces, the entrainment effect. Overall, data resulting from a direct comparison of the effectiveness of audio to visual entrainment is limited and as such any conclusions reached at this stage are necessarily tentative. [3]. While the results of this study suggest higher effectiveness when using audio, the study design did not include any condition where the subjects had to look and keep visual attention on the flickering light. Extensive work on SSVEP-based BCI has shown that visual entrainment is extremely strong and predictable as well as being very easily measured with EEG. Furthermore, the relative size of the occipital cortex makes this modality particularly attractive for entrainment purposes since it comprises a larger number of neural assemblies that synchronously fire when a particular stimulus is given. It is very difficult to conclude that one modality is more effective than the other. They target different processes and therefore different cortical areas. Furthermore, the reason why there is entrainment in the first place is not yet understood and any conclusions, even when based on these kinds of studies, will inevitably suffer from under-completion and will not be exhaustive in nature. c Koninklijke Philips Electronics N.V

14 Section 5 Enhancing performance From the previous chapter it can be concluded that audio-visual entrainment causes a frequency-following brain response, but the question still remains what this means for human wellbeing and health, as manifesting itself in cognition, mood, stress, and pain. Although research agrees that in general emotional and cognitive changes are reflected in changes in the EEG, the amount of research addressing the psychological and cognitive effects of brainwave entrainment is limited. Below a summary is given. 5.1 Auditory entrainment With respect to cognitive skills, more specifically attention, a study by Lane et al. [38] found a significant positive effect of binaural beats testing 29 healthy adults. They used a three-stage procedure which involved participants initially completing a range of questionnaires, with included measuring mood, followed by a task measuring attention and then a second set of questionnaires which again measured mood. The participants completed this procedure three times, listening to different audiotapes during performance of the attention task each time. During the first session they listened to a tape containing only pink noise. This was used to obtain baseline levels of mood and cognition. During the second session they were presented with an audiotape containing binaural beats of 1.5 Hz and 4 Hz, aimed at entraining delta and low theta activity. In the third session the audiotape contained binaural beats of 16 and 24 Hz and was aimed at entraining beta activity. The presentation order of the tapes was counterbalanced across the group and interestingly the participants didn t know that they were listening to auditory binaural beats, they were simply told that the tones presented through their headphones were to block out any external sounds. [38] found that the participants detected more targets during the attention task when they were simultaneously listening to a tape containing binaural beats entraining beta and produced more false alarms when they were listening to a tape entraining delta and theta. [3]. In addition, Joyce et al. [39] found a positive effect on attention within a group of 34 students diagnosed with ADHD. A study of Wahbeh et al. [40] however did not find an effect on attention, which may be due to the small number of subjects (4 healthy subjects) and the low binaural beat frequency of 7 Hz (theta stimulation). On mood, the study of Lane et al. [38] also found a significant positive effect (less negative mood in the case of beta-frequencies). An uncontrolled pilot study (8 subjects) of Wahbeh et al. [41] suggests the same. However, the later randomized double-blind 8 c Koninklijke Philips Electronics N.V. 2010

15 crossover study with 4 subjects of Wahbeh et al. [40] did not show an effect on mood using theta stimulation. With respect to short-term stress relief, Le Scouarnec et al. [42] found a significant reduction in anxiety using binaural beats within a group of 14 adults seeking help for mild anxiety problems (pre-post design). Moreover, Padmanabhan et al. [43] showed that pre-operative anxiety significantly reduced for a group of 36 adults listening to binaural beats embedded in a music track as compared to a control group of 36 listening to the same music track but without the beats and a control group of 36 without acoustic stimuli. Differences in this randomized double-blind study were substantial with mean [95% confidence intervals] decreases in anxiety scores of 26.3% [19 33%] in the binaural group (p = vs. music group, p < vs. control group), 11.1% [6 16%] in the music group (p = 0.15 vs. control group) and 3.8% [0 7%] in the control group. The small study with theta stimulation of Wahbeh et al. [40] again did not find any effects on short-term stress. The studies of Le Scouarnec and Wahbeh [42, 41] also looked into more long-term stress and burnout. [42] did not find a significant effect; the small uncontrolled pilot study of [41] (8 healthy subjects) found a significant positive effect on trait anxiety, quality of life and insulin-like growth factor-1 and dopamine. Pain was significantly reduced in a study by Manns et al. [44]. They applied a combination of electromyographic biofeedback and auditory entrainment within a group of 33 adults with a pain dysfunction syndrome in a pre-post study design. This time no binaural beats are used, but isochronic tones of constant frequency and duration that were adjusted and selected by the patient. 5.2 Visual The use of visual stimulation to entrain the EEG has been shown to impact on the psychological status of a person and affect imagery ability as well as arousal levels [45, 46, 47]. For instance, [45] proposed that visual entrainment may be one of the easiest methods to bring about a hypnagogic state and facilitate the emergence into conscious awareness of visual imagination images. A hypnagogic state refers to the dreamlike experience that often represents the state between being fully awake and falling asleep which may be accompanied by physical immobility and lucid visual and auditory hallucinations. To test this idea they examined the visual entrainment effect of three different frequencies (6 Hz, 10 Hz and 18 Hz) on the imagery ability of a group of female students. They found that entrainment of the lower frequency ranges of 6 and 10 Hz led participants to produce more complex images compared to when a higher frequency of 18 Hz was used. [46] attempted to extend these results by examining the effects of visual entrainment on imagery across five different frequencies (5, 10, 15, 20 and 25 Hz). They found that such visual stimulation induced a range of complex imagery phenomena similar to the images perceived during sleep onset and dreaming. The work of [45] is encouraging, although more needs to be done to explore possible differential effects resulting from entrainment of a 6 Hz frequency compared to one of 10 Hz. Unfortunately, the work of von Gizycki and colleagues is less robust and as such its results are more ambiguous. For instance, their procedure involves the visual entrainment of five distinct frequencies. Yet it remains unclear what the rationale was for using such a wide range of frequencies and in addition to this they fail to identify which c Koninklijke Philips Electronics N.V

16 of the five frequencies, or combination, was responsible for eliciting the effect on imagery. They also failed to include any controls and as such it is difficult to attribute the alleged effects on enhanced imagery to visual entrainment. An alternative approach adopted by [10] involves the use of a flicker training paradigm to induce visual entrainment and influence cognition. Rather than repeatedly flash a light into the eyes of a participant she is presented with a flickering stimulus on a computer screen, such as a rectangle that changes color from gray to white, which is set to change color, or flicker, at a specific frequency. Williams (2001) used this paradigm to induce a visual entrainment effect using a flickering stimulus at one of three distinct frequencies (8.7 Hz, 10 Hz and 11.7 Hz). Each time the flickering stimulus was shown it was immediately followed by the brief presentation of a three letter trigram forming either a nonsense word (e.g., TEF) or a real word (e.g. BID) and participants were asked to classify the trigram as either nonsense or real as quickly as they could. The fact that a target immediately followed a flickering stimulus may make this paradigm more sensitive to the subtle changes in cortical activity brought about by visual entrainment, particularly if they fade over time. The different frequencies of the flickering stimulus were found to have no effect on the speed of participant s responses with regard to whether a trigram was classified as nonsense or real. However, in a follow up memory task participants were required to recognize which were the old trigrams they had seen during the classification task when presented with a randomly mixed group of old and new trigrams. Williams (2001) found that participants recognized significantly more of the trigrams that followed the 10-Hz flicker compared to those that followed either the 8.7 Hz or the 11.7 Hz flicker. In addition Williams (2001) was also able to show that the flickering stimulus was capable of entraining EEG activity, with each of the entrainment frequencies showing an increase in amplitude following presentation of the flickering stimulus. These findings suggest that a 10-Hz flicker is sufficient to elicit changes in cortical activity 1 and that such changes are capable of improving recognition memory. This is consistent with research showing that better memory performance is associated with greater amplitude in the alpha (8 12 Hz) frequency range of the EEG [48]. [3]. Although this is suggestive of a confirmation of the results of the study, it should be taken with care since the relation between alpha and cognitive performance is not fully understood. More recently [49] used a similar visual flicker entrainment paradigm to show that frequencies close to 10 Hz can improve the recognition of elderly participants aged between years. This led them to propose that visual entrainment can selectively facilitate the neural mechanisms of the brain, as evidenced by changes in EEG, and that such changes in cortical activity can directly influence psychological states. Overall, use of the flicker paradigm provides compelling evidence that visual stimulation at 10 Hz can produce clear changes in the EEG and lead to enhanced memory performance. Furthermore, the fact that such a finding has been shown to be stable across different age groups suggests that it may produce a general effect on cognition. [3]. 5.3 Combined audio-visual A few studies [50, 51, 52] used combined audio-visual stimulation in their entrainment procedure. With respect to cognitive skills, the study of Olmstead [50] found that AVE improved 1 Not only a rate of 10 Hz, but a wide range of stimulation frequencies change cortical activity. 10 c Koninklijke Philips Electronics N.V. 2010

17 arithmetic skills of children with learning difficulties in a pre-post study design. A combination of flickering lights and binaural beats was used with a frequency changing between 14 Hz and 40 Hz. This study did not look into the effects of the different stimulation modalities (light vs. sound) separately. With respect to anxiety, the patients in the study of Morse and Chow [51] experienced significantly less fear during a dental procedure in case the routine method of calming words of the dentist was combined with AVE (10 Hz) compared to only the routine method. In addition to this control group (10 persons) and the AVE group (10 persons), there was a group of 10 persons that only had visual entrainment of 10 Hz (in addition to the calming words). This group also experienced significantly less anxiety as compared to the control group. Compared with the AVE group, no significant differences were observed. Morse and Chow report that an advantage of adding the auditory stimuli is that these mask disturbing sounds from dental procedures such as drilling. With respect to stress and burnout, Ossebaard [52] found small (significant) effects on short-term stress, but no long-term effects. This study used combined audio-visual stimulation of the alpha range with frequencies of 10 Hz and stimulation of the beta range with frequencies of 30, 25 and 16 Hz. On the beneficial effects of AVE, these studies provide some limited preliminary evidence. Even less is known, unfortunately, about whether visual stimulation is more effective than auditory stimulation or vice versa, or about whether there is an advantage of combining the two. c Koninklijke Philips Electronics N.V

18 Section 6 Lasting effects of entrainment Given that AVE can affect the amplitude and/or frequency of the electrocortical activity of the brain, which in turn may enhance an individual s ability to perform certain tasks, an important point to consider is the duration of such effects. Are such changes enduring or does such training elicit only short-term benefits? [25] examined what effect an eight minute period of visual entrainment within both the alpha (10 Hz) and beta frequency (22 Hz) ranges would have on participants EEG. They found that stimulation within the alpha frequency produced only a transient enhancement and was moderated by individual s baseline activity. However, entrainment of the beta frequency component produced more prolonged changes in the EEG that were maintained for up to 24 minutes. Thus, a single session of entrainment can generate changes in the EEG that can last beyond the end of the stimulation period itself, albeit for a limited amount of time. This would suggest that the entrainment of a specific frequency component may affect the brain s natural ability to produce that frequency and in so doing, facilitate its production beyond that of the entrainment period. Moreover, [25] points out that more robust entrainment effects may be elicited if individual differences in baseline EEG activity are taken into account. Nevertheless, [31] found that changes in electrocortical activity as a result of entrainment failed to last for very long. They examined the effects of AVE on the human EEG and found that a single twenty minute session, where those taking part were either stimulated at their dominant alpha frequency or at twice their dominant alpha frequency, exhibited a significant change in their EEG in the desired direction. However, EEG recordings taken 30 minutes after the entrainment ended showed little evidence of these effects persisting. Taken together these results would suggest that a single period of entrainment is capable of producing changes in the EEG in the desired frequency range, but that such changes may last for up to 24 minutes, but not beyond. Such results, while limited, are encouraging. If a single entrainment session is capable of producing changes in the EEG that last beyond the stimulation itself, it seems probable that a more persistent effect may be obtained with a greater number of sessions. More research is needed which not only takes into account individual differences in baseline EEG activity but also compares the effectiveness of the various entrainment methods to ascertain which is the most effective at producing long-term effects and why. [3]. 12 c Koninklijke Philips Electronics N.V. 2010

19 Section 7 Negative effects One should be cautious with audio-visual entrainment, in particular with visual entrainment. Repetitive visual stimulation, e.g. of flashing lights or visual patterns, may provoke photic- or pattern-induced seizures. Especially people with a (family) history of seizures or epilepsy have to be cautious; for extreme cases, even an electric toothbrush can induce seizures [53]. However, also people without such history may suffer from seizures after repetitive visual stimulation as was seen in the Pokemon cartoon incident in Japan [54, 55]. Fisher et al. write: Photosensitivity, an abnormal EEG response to light or pattern stimulation, occurs in approximately 0.3 3% of the population. The estimated prevalence of seizures from light stimuli is approximately 1 per 10,000, or 1 per 4,000 individuals 5 24 years old. People with epilepsy have a 2 14% chance of having seizures precipitated by light or pattern. In the Pokemon cartoon incident in Japan, 685 children visited a hospital in reaction to red-blue flashes on broadcast television. Only 24% who had a seizure during the cartoon had previously experienced a seizure. Photic or pattern stimulation can provoke seizures in predisposed individuals, but such stimulation is not known to increase the chance of subsequent epilepsy. Intensities of million candlepower are in range to trigger seizures. Frequencies of Hz are most provocative, but the range is 1 65 Hz. Light-dark borders can induce pattern-sensitive seizures, and red color also is a factor. Seizures can be provoked by certain TV shows, movie screen images, videogames, natural stimuli (e.g, sun on water), public displays, and many other sources. [54]. c Koninklijke Philips Electronics N.V

20 Section 8 Summary This report gives an overview of the field of audio-visual brainwave entrainment (AVBE), focusing on scientific literature that investigates its effect on health and wellbeing. The term brainwave entrainment refers to the use of rhythmic sensory stimuli to stimulate targeted frequencies in the brain. Such sensory stimuli can be auditory, visual or a combination of the two. First auditory entrainment will be discussed, with special attention for a specific form of auditory entrainment stimuli: binaural beats. This chapter is followed by a chapter on visual entrainment, and a chapter that compares the two types of entrainment. Subsequently, the effect of entrainment on performance is discussed. The following chapters are about the lasting (positive) effects of entrainment and potential negative effects. Finally, some tentative conclusions are formulated. 14 c Koninklijke Philips Electronics N.V. 2010

21 Section 9 Conclusions Rhythmic sensory (auditory or visual) stimuli have a profound effect on the brain. First scientific evidence of this entrainment effect has already been reported as early as 1934 [19]. Since then, many papers have been published, mostly in less known journals. This year, however, proof appeared in the high-impact journal Clinical Neurophysiology [16]. Consequences of entrainment for human behavior and underlying neurological mechanisms for that are less established. Preliminary evidence suggests positive effects on aspects like short-term stress relief, pain, and cognitive abilities (attention, memory), but this is not yet without controversy. Comparing auditory with visual entrainment it is still unclear which sensory type is more effective. Synergy in combining the two has not been reported so far. Since visual entrainment has a (small) risk of evoking (epileptic) seizures, auditory entrainment is favored. In addition, auditory stimulation better fits eyes-closed situations such as during relaxation. In summary, preliminary findings are promising, but further research is required. c Koninklijke Philips Electronics N.V

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