27 May 2022

Buddhist Meditation and Sensory Deprivation

Buddhist meditation techniques are coming under increasing scientific scrutiny as researchers realise that the altered states engendered by meditation may provide clues to how the brain creates the mind. These pioneering studies are laudable and producing some very interesting observations. However, there is a lacuna in scientific accounts of meditation, for example, reports of light experiences… “are well documented in traditional Buddhist texts but are virtually undocumented in scientific literature on meditation.” (Lindahl et al 2014). When someone sits down, closes their eyes, tunes out the world, and begins to focus on the sensations of breathing, they enter a state of substantially reduced sensory input, i.e. sensory deprivation. I suggest that sensory deprivation appears to have been overlooked as a factor in meditation. This is a theme I hope to develop, but here I just want to establish that in thinking about meditation, sensory deprivation cannot be ignored. 

Sensory Deprivation

Research on sensory deprivation began in the 1950s. In the early experiments, students were placed in very low stimulation environments with every effort made to reduce sensory stimulation. As Oliver Sacks describes the results,

At first the test subjects tend to fall asleep, but then, on awakening, they became bored and craved stimulation… and at this point, self-stimulation of various sorts began: mental games, counting, fantasies, and, sooner or later, visual hallucinations. (2012: 35)

Similar effects observed amongst people kept in solitary confinement gave Sacks his chapter title: The Prisoner’s Cinema. We also know that it is quite common for people who lose their sight to start having vivid hallucinations, which is known as Charles Bonnet Syndrome.

In the 1960s isolation tanks were invented. In these contraptions the subject lies floating in a warm buoyant salt solution, in a light-proof and sound-proof, box. “Such immersion chambers could produce ‘altered states’ much more profound that those described in the original experiments” (Sacks 2012: 37). However, interest in sensory deprivation declined in the 1970s and has only recently revived.

Although visual hallucinations are the most common side effect of sensory deprivation, hallucinations in other modalities also occur, notably with respect to proprioception. Sacks notes that long periods of physical immobility—for example, in children afflicted by polio and confined to an iron lung—may also produce hallucinations:

“Most commonly these are corporeal hallucinations, in which limbs may seem to be absent, distorted, misaligned, or multiplied.”(Sacks 2012: 42)

Physical immobility is a commonly practiced austerity amongst Indian religieux down to the present and talk of multiplied limbs ought to ring bells for devotees of Indian myth. 

Imaging studies have shown that visual hallucinations have different patterns of brain activity to visual stimulus, with the conclusion that “hallucination is the result of a direct, bottom-up activations of regions in the ventral visual pathway, regions rendered hyperexcitable by a lack of normal sensory input” (Sacks 2012: 41. Emphasis added). That is to say, deprived of stimulation, the brain may lower the threshold of excitability to the point it begins to self-stimulate. Merabet et al (2004) showed that there are limits to this effect. Simply blindfolding test subjects but allowing them access to stimulation of the other senses at will, did not reproduce the effects of sensory deprivation. This suggests that physical immobility alone is insufficient and must be accompanied by more general sensory monotony (which certainly afflicted those confined to iron lungs). 

We now know (e.g. Feldman-Barrett 2018) that the brain operates on an allostatic principle: that is to say it is constantly predicting patterns of activation, which at a coarse-grained level become our sensory experience and (motor) responses to it. We can think of hallucinations due to sensory deprivation as the brain expecting input and trying to fill in the gaps when the expected input is missing, largely by lowering the threshold at which the brain responds to the stimulus. Something like this mechanism is also now thought to be at work in tinnitus and phantom limb syndrome.

The kinds of hallucinations reported in sensory deprivation studies are strikingly similar to those reported by Buddhist meditators.


Consider this description from a modern Buddhist meditation manual:

What does it mean, for example, if we find ourselves experiencing beautiful colours, marvellous patterns, voices, or other sounds in our meditation? … What seems to happen is that we achieve a good level of concentration, so that we are no longer aware of our body and sense-impressions. But it is as though our senses still insist on trying to operate, in spite of the fact that they are now disconnected from the physical world (Kamalashila 1994: 58).

Here, Kamalashila has precisely described the short-term, hallucinatory, effects of sensory deprivation. However, note that his explanation, while not inaccurate, is not grounded in any explanatory framework. Buddhism doesn't really have a good explanation for these phenomena. 

Kamalashila refers to this type of hallucination using the Pāli term, samāpatti, although traditionally this term refers to attaining either jhāna or āyatana states (Nyanatiloka 2004: 186). Modern Theravādin meditators call the same hallucinations nimitta or “signs” but, again, traditionally nimitta refers to the aspects of the object that allow us to recognise the object from what appears in our sensorium. Modern Buddhists want to put a traditional name to the hallucinations engendered by meditation, but lack one. I think we can frame this as a legitimation strategy: yes, you are hallucinating, but we have a technical term  (in a "sacred" language) which valorises those experiences as "signs" of states of withdrawal from sensory experience. 

Compare the following description of the types of hallucination that are common in meditation with Sacks’ account (above) of corporeal hallucinations due to being immobile:

You may feel as though your body has become enormous… Or you may feel tiny, microscopic. You may feel as though you have been turned upside down, or that you are now sitting facing the opposite way. Or you may experience your body in terms of some totally indescribable physical sensation.  (Kamalashila 1994: 58).

Sacks and Kamalashila appear to be describing the same phenomenon or at least the same kinds of phenomena. Which makes the link between meditation and sensory deprivation seem plausible. 

Kamalashila (1994: 58) tells us that, “Eventually these signs will pass, as you enter a smoother phase of concentration”. He emphasises that the hallucinations themselves have no significance. They are just weird experiences and not connected to insight or liberation. Although Kamalashila says that these experiences tend to fade away as we become more concentrated, he in fact contradicts himself the next time he mentions samāpatti, saying:

“Sometimes we may go beyond the hindrances [to meditation] altogether and transcend the world of the senses and he ordinary mind… When we enter the state of absorption at this deeper level, some of the contents of our subconscious minds will come ‘up’ into our consciousness” (1994: 65).

He adds that these upwellings of experience are unconnected to the physical senses “may well be vision-like” and explicitly invokes Carl Jung’s theory of archetypes of the collective unconscious (reflecting the bias towards Romanticism in Triratna). It seems, from this, that we don’t necessarily stop hallucinating in states of absorption (jhāna), but rather that the hallucinations we do have become more subtle and more vivid at the same time. This second type of hallucination has a much greater sense of verisimilitude, or even hyper-reality. We are more likely to assign some special meaning to these experiences. As Thomas Metzinger noted with respect to out-of-body experiences (also common in meditation):

For anyone who actually had [an out-of-body experience] it is almost impossible not to become an ontological dualist afterwards. In all their realism, cognitive clarity and general coherence, these phenomenal experiences almost inevitably lead the experiencing subject to conclude that conscious experience can, as a matter of fact, take place independently of the brain and body. (2009: 78)

Metzinger is equally clear, however, that the dualist account of out-of-body experiences fails to explain the phenomenology of out-of-body experiences. Metzinger, who had many such experiences as a young man, eventually concluded that out-of-body experiences were the result of disruption of the integration of different streams of information about the body: especially the visual sense and the felt sense of the body. In other words the sensation of being "out of your body" is a hallucination.

Making the Connection

I can find few studies that link meditation and sensory deprivation in the scholarly or scientific literature. It does pop up in some popular level accounts, for example: A blog post by Bridget W Webber (I Didn’t Think of Meditation as Sensory Deprivation Before Then I saw thelight, literally.) and one by Rose Eveleth (The Ancient, Peaceful Art of Self-GeneratedHallucination). One scientific study that does make the link explicit is Lindahl et al (2014):

“Taken together, these studies also provide evidence in support of the hypothesis that certain meditative practices – especially those that deliberately decrease social, kinesthetic, and sensory stimulation and emphasize focused attention – have perceptual and cognitive outcomes similar to sensory deprivation.”

Why is this important? 

Refining our understanding of meditation helps us to communicate about it and to explain the effects of withdrawal from sensory experience. And it helps those who are researching meditation and the mind to ask better research questions. Since Buddhism lacks an explanatory framework for meditation, it's up to us to come up with one. 

What is needed now is a systematic investigation of sensory deprivation and the contribution it makes to meditation experiences. Could hallucinations engendered by sensory deprivation be the whole story of Buddhist visions? I think this is entirely possible. 



Kamalashila. (1994). Meditation: The Buddhist Way of Tranquillity and Insight. Windhorse Publications.

Lindahl, J. R., Kaplan, C. T., Winget, E. M., and Britton, W. B. (2014) “A phenomenology of meditation-induced light experiences: traditional Buddhist and neurobiological perspectives.” Frontiers in Psychology 03 January 2014 | https://doi.org/10.3389/fpsyg.2013.00973 (Online version of the article is unpaginated).

Merabet, L, Maguire, D, Warde, A, Alterescu, Stickgold, R, and Pascual-Leone, A. (2004). “Visual Hallucinations During Prolonged Blindfolding in sighted subjects.” Journal of Neuro-Opthalmology 24(2): 109-13.

Sacks, Oliver. (2012). Hallucinations. Picador.

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