In an unusual but fruitful collaboration between Tibetan Buddhist monks and neuroscientists, researchers have uncovered clues to how mental states--and their underlying neural mechanisms--can impact conscious visual experience. In their study, reported in the June 7 issue of Current Biology, the researchers found evidence that the skills developed by Tibetan Buddhist monks in their practice of a certain type of meditation can strongly influence their experience of a phenomenon, termed "perceptual rivalry," that deals with attention and consciousness.
The work is reported by Olivia Carter and Jack Pettigrew of the University of Queensland, Australia, and colleagues at the University of Queensland and the University of California, Berkeley.
Perceptual rivalry arises normally when two different images are presented to each eye, and it is manifested as a fluctuation--typically, over the course of seconds--in the "dominant" image that is consciously perceived. The neural events underlying perceptual rivalry are not well understood but are thought to involve brain mechanisms that regulate attention and conscious awareness.
Some previous work had suggested that skilled meditation can alter certain aspects of the brain's neural activity, though the significance of such changes in terms of actually understanding brain function remains unclear.
To gain insight into how visual perception is regulated within the brain, researchers in the new study chose to investigate the extent to which certain types of trained meditative practice can influence the conscious experience of visual perceptual rivalry.
With the support of His Holiness the Dalai Lama, 76 Tibetan Buddhist monks participated in the study, which was carried out at or near their mountain retreats in the Himalaya, Zanskar, and Ladakhi Ranges of India. The monks possessed meditative training ranging from 5 to 54 years; among the group were three "retreatist" meditators, each with at least 20 years of experience in isolated retreats.
The researchers tested the experience of visual rivalry by monks during the practice of two types of meditation: a "compassion"-oriented meditation, described as a contemplation of suffering within the world combined with an emanation of loving kindness, and "one-point" meditation, described as the maintained focus of attention on a single object or thought, a focus that leads to a stability and clarity of mind.
Whereas no observable change in the rate of "visual switching" during rivalry was seen in monks practicing compassion meditation, major increases in the durations of perceptual dominance were experienced by monks practicing one-point meditation. Within this group, three monks, including two of the retreatists, reported complete visual stability during the entire five-minute meditation period. Increases in duration of perceptual dominance were also seen in monks after a period of one-point meditation.
In a different test of perceptual rivalry, in this case prior to any meditation, the duration of stable perception experienced by monks averaged 4.1 seconds, compared to 2.6 seconds for meditation-naïve control subjects. Remarkably, when instructed to actively maintain the duration, one of the retreatist monks could maintain a constant visual perception during this test for 723 seconds.
The findings suggest that processes particularly associated with one-point meditation--perhaps involving intense attentional focus and the ability to stabilize the mind--contribute to the prolonged rivalry dominance experienced by the monks. The researchers conclude from their study that individuals trained in meditation can considerably alter the normal fluctuations in conscious state that are induced by perceptual rivalry and suggest that, in combination with previous work, the new findings support the idea that perceptual rivalry can be modulated by high-level, top-down neural influences.
The researchers include O.L. Carter, C. Callistemon, Y. Ungerer, G.B. Liu, and J.D. Pettigrew of University of Queensland; and D.E. Presti of University of California, Berkeley.
Carter, O.L., Presti, D.E., Callistemon, C., Ungerer, Y., Liu, G.B., and Pettigrew, J.D. (2005). Meditation alters perceptual rivalry in Tibetan Buddhist monks. Publishing in Current Biology, Vol. 15, June 7, 2005, pages R412-R413. www.current-biology.com