Meditation Alters Perceptual Rivalry in Tibetan Buddhist Monks
O. L .Carter1*, C. Callistemon1, D. E. Presti2, G. B. Liu1, Y. Ungerer1 & J. D. Pettigrew1
1 Vision, Touch and Hearing Research Centre, University of Queensland, Australia.
2 Dept. Molecular and cell Biology, University of California, Berkeley.
Correspondence to be made to:
Olivia Carter, Vision Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, St Lucia, Australia 4072
Ph: + 61 7 3365 3929
fax: + 61 7 3365 4522
The insights and skills attained by Tibetan Buddhist monks over hundreds of years of meditative training are likely to benefit neuroscientific studies of the mind: a point made recently at a forum between Buddhist leaders and distinguished scientists. Perceptual rivalries such as binocular rivalry and motion induced blindness (MIB) are phenomena currently used by scientists to study the neural mechanisms underlying the selection and maintenance of the contents of consciousness and attention [2, 4], as they involve fluctuations in conscious awareness despite constant external stimulation. Tapping into the ability of Tibetan Buddhist monks to control the flow of items being attended and accessing consciousness, meditation was found to dramatically alter the inherent fluctuations in conscious state associated with perceptual rivalry.
Previous research with highly accomplished meditators has been impeded by their preference for remote locations and an understandable wariness towards invasive forms of research. With the support of His Holiness the Dalai Lama, 76 Tibetan Buddhist monks varying in experience (including 3 ³retreatist² meditators with many years experience in isolated mountain retreats) were tested using non-intrusive perceptual measures at, or near, their mountain retreats in the Himalaya, Zanskar and Ladakhi Ranges of India. Binocular rivalry was induced with head-mounted display goggles (Fig. 1A) that presented horizontal and vertical green stationary gratings to the right and left eye respectively (see supplementary information for details). Volunteers selected from 3 types of meditation (approximately translated as ³compassion,² ³emptiness² and ³one-point²). In cases where coordinated button-press responses were not possible, verbal reports were recorded.
The 3 different kinds of meditation each produced reliable, characteristic changes in the perceptual alternation rate and proportion of mixed/grid percept during binocular rivalry, contrasting sharply with the qualitative re-test reliability of perceptual alternations observed in over 1000 meditation-naive individuals tested previously. However, the most striking effects were produced by ³one-point² meditation, a procedure entailing sustained focused attention on a single thought or object. Extreme increases in perceptual dominance durations (reports collected via button-press, as shown in Fig. 1C‑D, or verbally) were reported by 50% of monks after a period of one-point meditation. Additional prolongation/stabilization was reported (verbally) by the same monks when they viewed the rivalry display during one-point meditation. Within this group, 3 (including 2 ³retreatists²) reported complete perceptual stability throughout the entire 5min meditation period. The finding that the proportion of prolongation/ stabilization varied considerably across the different meditation conditions (Fig. 1B), despite each of the monks serving as their own controls by participating in at least two of the three meditation conditions, suggests that the prolongation results from the intense attentional focus required during one-point meditation, rather than the process of meditation per se. Interestingly the stable percepts reported all involved qualitative distortions: i.e. one monk reported bright, thick vertical gratings set in front of dark, thin horizontal gratings.
Volunteers were also tested on MIB (see supplementary information for details), where the mean disappearance duration reported was 4.1sec (s.d.±3.9sec), compared to 2.6sec (s.d.±1.6sec) recorded from a group of 61 meditation-naive volunteers tested previously (t=2.8, p<0.001) (Fig 2). The most extreme finding came from one ³retreatist² who commented that he could maintain the disappearance indefinitely. After recommencing, he reported the first reappearance of any of the three yellow target dots after 723 seconds of sustained MIB disappearance!
The primary result of this study is that meditation can measurably affect the normal fluctuations in conscious state induced during binocular rivalry and motion-induced blindnes. The known association between meditation and changes in neural activity in prefrontal regions of the cortex[6, 7] that have been similarly implicated in sustained attentional and binocular rivalry adds further support to the debated role of high-level attentional mechanism in perceptual rivalry[2, 4]. Furthermore, the finding that meditation type and training duration had varying effects on binocular rivalry is consistent with studies suggesting that different types of meditation and training duration lead to distinguishable changes in neural activation patterns[7, 10]. Therefore, this study offers an initial contribution towards increased understanding of the biological processes underlying meditation and rivalry, while additionally highlighting the synergistic potential for further exchange between practitioners of meditation and neuroscience in the common goal of understanding consciousness.
This investigation was financially supported by the Heffter Research Institute, Santa Fe, New Mexico, USA, and a Stanley Foundation grant to J. D. Pettigrew. We would like to thank His Holiness the Dalai Lama for his support and help facilitating the study, Tenzin Geyche and Tenzin Sherab for essential logistical assistance and Tsering Topgyal for recruitment of monks. We would also like to thank Tashi Choephel, Kelsang Wangmo, Ngodup Burkhar, Tenzin Sherab and Dorjee Dhondup who assisted with Tibetan and Ladakhi translations and the monks from the Institute of Buddhist Dialectics and the Namgyal and Thiksey monasteries for their participation.
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Figure 1. A) Retreatist meditator wearing display goggles. B) The proportion of monks reporting changes in rivalry switch rate during ³compassion² (C), ³emptiness² (E), after ³one-point² (P-1st) and during ³one-point² (P) meditation (slower = red, faster = yellow, stabilization = blue, the remainder reported no change). C) A representative frequency histogram showing phase duration (time between perceptual switch) for horizontal, vertical and mixed (grey) percepts after no meditation and D) the same monk showing longer durations after one-point meditation.
Figure 2. Histogram showing the frequency of respective disappearance intervals during MIB for monks tested in the current study (red) compared to a group of 61 meditation-naive volunteers (blue) tested previously [for details see ref 5]. The two extreme values were not included in the statistical analysis reported in the text.
Supplementary information (available online)
Materials and Methods:
The binocular rivalry stimulus consisted of green stationary square wave gratings with a spatial frequency of 1.5 cycles/degree of visual angle and were presented as a disc that subtended 4º of visual angle (horizontal to the left eye and vertical to the right eye). The display and data collection was controlled by custom software (Bireme.com) on a Toshiba laptop computer. Subjects reported the predominance of the vertical gratings by pushing a button with a ridge aligned perpendicular to the observer (fixed onto the V-key) and the predominance of the horizontal gratings by pushing a button on which there was a ridge aligned from left to right (fixed onto the B-key). If the subject experienced a combination of the two orientations, either as a grid or a patchwork, they were instructed to press the space bar, but only in cases when the mixed percept was stable and not considered to be ³transitional.² Each testing period consisted of 4x60sec trials, with a 30sec break between each trial.
Volunteers were asked to perform as many of the 3 types of meditations that they felt comfortable with (translated as Compassion: focusing on the suffering of others, while radiating good will; Emptiness: calming of the mind allowing thoughts to flow unattended through awareness; One-point: focusing all of one's attention on a single object or thought). Rivalry responses were acquired before (baseline) and during the respective meditation types. Responses were also collected after 5-10 minutes of one-point meditation. In the cases where the monks were unable or uncomfortable with the combined task of meditating, viewing and reporting binocular rivalry switches (this was necessarily the case during one-point meditation) they were asked to simply describe their visual experience after the completion of the rivalry period.
MIB was also tested, with volunteers verbally reporting the duration of disappearance and reappearance of the yellow target dots, prior to any meditation. The display used was similar to that shown at http://www.weizmann.ac.il/~masagi/MIB/mib.html, the only modification was the addition of a small fixation cross at the center of the stimulus.
Four translators aided communication with the monks in Tibetan or Ladakhi as required. Volunteers were made aware that they were free to withdraw from participation in the study at any time.