Āyatana

In Buddhism, āyatana is a "center of experience" or "mental home," which create one's experience. The related term refers to six cognitive functions, namely sight, hearing, smelling, tasting, body-cognition, and mind-cognition.
Āyatana may refer to both ordinary experience and the chain of processes leading to bondage, as to awakened experience centered in detachment and meditative accomplishment. The Buddhist path aims to relocate one from the ordinary, sensual centers of experience to the "mental home" of the purified, liberated awareness of the jhanas.
Traditionally, the term āyatana is translated as "sense base", "sense-media" or "sense sphere," due to the influence of later commentators like Buddhaghosa. The are traditionally understood as referring to the five senses and the mind.

Etymology

Āyatana is a Buddhist term that does not have a single definition or meaning. The standard PTS Pāli-English Dictionary by Davids & Stede gives the following meanings of āyatana:

. stretch, extent, reach, compass, region; sphere, locus, place, spot; position, occasion
. exertion, doing, working, practice, performance
. sphere of perception or sense in general, object of thought, sense-organ & object; relation, order

While āyatana is usually translated as "base" or "sphere," or more specifically as "sense field," "sense base", "sense-media" or "sense sphere," according to Ellis, "these are inadequate translations because they are based on later Buddhist traditions and commentarial literature and not on an historical understanding of the term."
In Vedic literature āyatana is "used for a regular place, position, etc. occupied by a person." In some Upanishads it refers to a "dwelling place" or "resort," or a "resting place for the mind," indicating that āyatana means "the place in which experience happens" or a "center of experience." According to Ellis, "center of experience" or "mental home" is a more adequate interpretation than "base" or "sphere."
Ellis notes that āyatana in the suttas most commonly appears in compound form, namely saḷāyatana or cha phassāyatanā, the "six āyatanas of sensual experience." According to Ellis, "This context is so dominant that translators like Bodhi and Walshe translate ‘sense bases’ even if the Pāli texts only mentions āyatana, and not saḷāyatana."
Ellis further notes that saḷāyatana is traditionally interpreted anatomically, and understood as referring to the five senses and the mind. Yet, according to Olivelle, saḷāyatana refers instead to cognitive functions, and is therefore understood by Ellis as referring to sight, hearing, smelling, tasting, body-cognition, and mind-cognition.

In the Pali Canon

Throughout the Pali Canon, the saḷāyatana are referenced in hundreds of discourses. In these diverse discourses, the sense bases are integrated in various mnemonic lists.

Internal and external ''āyatana''

The āyatana are further refined as six internal āyatana and six corresponding external āyatana. Together they form:
The saḷāyatana are related to the indriya, the five senses and the mind; the indriya become saḷāyatana when they are distorted by a defiled mind. Indriya also refers to the five spiritual facultues, which contribute to an awakened state of mind.

Five skandhas

Based on these six pairs of āyatana, a number of mental factors arise, as described in the five skandhas. Thus, for instance, when the auditive cognitive function is triggered by sound, the associated consciousness arises. With the presence of these three elements – hearing function, sound and hearing function-related consciousness – "contact" arises, which in turn is apprehended as a pleasant or unpleasant or neutral "feeling" or "sensation". With feeling, "craving" arises.
Such an enumeration can be found, for instance, in the "Six Sextets" discourse, where the "six sextets" are examined and found to be empty of self.
The saḷāyatana are included in the Twelve Nidanas, a list compiled of several sublists including the five skandhas, which describes the process of becoming.

"The All"

In a discourse entitled, "The All", the Buddha states that there is no "all" outside of the six pairs of the saḷāyatana. In the next codified discourse, the Buddha elaborates that the All includes the first five aforementioned sextets. References to the All can be found in a number of subsequent discourses. In addition, the Abhidhamma and post-canonical Pali literature further conceptualize the saḷāyatana as a means for classifying all factors of existence.

"Aflame with lust, hate and delusion"

In "The Vipers" discourse, the Buddha likens the internal saḷāyatana to an "empty village" and the external saḷāyatana to "village-plundering bandits." Using this metaphor, the Buddha characterizes the "empty" sense organs as being "attacked by agreeable & disagreeable" sense objects.
Elsewhere in the same collection of discourses, the Buddha's Great Disciple Sariputta clarifies that the actual suffering associated with sense organs and sense objects is not inherent to these saḷāyatana but is due to the "fetters" that arise when there is contact between a sense organ and sense object.
In the "Fire Sermon", delivered several months after the Buddha's awakening, the Buddha describes all saḷāyatana and related mental processes in the following manner:

Liberation

The Buddha taught that, in order to escape the dangers of the saḷāyatana, one must be able to apprehend the saḷāyatana without defilement. In "Abandoning the Fetters", the Buddha states that one abandons the fetters "when one knows and sees... as impermanent" the , objects, sense-consciousness, contact and sensations. Similarly, in "Uprooting the Fetters", the Buddha states that one uproots the fetters "when one knows and sees... as nonself" the aforementioned five sextets.
To foster this type of penetrative knowing and seeing and the resultant release from suffering, in the Satipatthana Sutta the Buddha instructs monks to meditate on the saḷāyatana and the dependently arising fetters as follows:
In the Four Noble Truths, one of many summaries of the Buddhist path to liberation, dukkha is observed to arise with craving. In the chain of Dependent Origination, craving arises with sensations when the saḷāyatana is activated by contact. To detach from tanha and dukkha, one should develop awareness and sampajañña ) of the chain of events triggered by the saḷāyatana, and practice restraint and detachment and dhyana ).
Ellis notes that āyatana may also refer to the various stages of meditation, and "even the state of liberated Buddhist
masters is termed āyatana."' As such, they are also a "center of experience" or "mental home," in which our normal states of mind are abandoned and one relocates in the purified, liberated awareness of the jhanas.

In post-canonical Pali texts

The Vimuttimagga, the Visuddhimagga, and associated Pali commentaries and subcommentaries all contribute to traditional knowledge about the saḷāyatana.

Understanding sense organs

When the Buddha speaks of "understanding" the eye, ear, nose, tongue and body, what is meant?
According to the first-century CE Sinhalese meditation manual, Vimuttimagga, the sense organs can be understood in terms of the object sensed, the consciousness aroused, the underlying "sensory matter," and an associated primary or derived element that is present "in excess." These characteristics are summarized in the table below.
The compendious fifth-century CE Visuddhimagga provides similar descriptors, such as "the size of a mere louse's head" for the location of the eye's "sensitivity", and "in the place shaped like a goat's hoof" regarding the nose sensitivity. In addition, the Visuddhimagga describes the sense organs in terms of the following four factors:
Thus, for instance, it describes the eye as follows:
In regards to the sixth internal āyatana of mind, Pali subcommentaries distinguish between consciousness arising from the five physical saḷāyatana and that arising from the primarily post-canonical notion of a "life-continuum" or "unconscious mind" :

The roots of wisdom

In the fifth-century CE exegetical Visuddhimagga, Buddhaghosa identifies knowing about the saḷāyatana as part of the "soil" of liberating wisdom. Other components of this "soil" include the aggregates, the faculties, the Four Noble Truths and Dependent Origination.

Related Buddhist concepts

Aggregates :

In a variety of suttas, the aggregates, elements and saḷāyatana are identified as the "soil" in which craving and clinging grow. In general, in the Pali Canon, the aggregate of material form includes the five material sense organs and associated sense objects ; the aggregate of consciousness is associated with the sense organ of mind; and, the mental aggregates are mental sense objects.
Both the aggregates and the saḷāyatana are identified as objects of mindfulness meditation in the Satipatthana Sutta. In terms of pursuing liberation, meditating on the aggregates eradicates self-doctrine and wrong-view clinging while meditating on the saḷāyatana eradicates sense-pleasure clinging.

Dependent Origination :

As indicated in Figure 2 above, the six saḷāyatana are the fifth link in the Twelve Causes of the chain of Dependent Origination and thus likewise are the fifth position on the Wheel of Becoming. The arising of the six saḷāyatana is dependent on the arising of material and mental objects ; and, the arising of the six saḷāyatana leads to the arising of "contact" between the saḷāyatana and consciousness which results in pleasant, unpleasant and neutral feelings.

Elements :

The eighteen elements include the twelve saḷāyatana. The eighteen elements are six triads of elements where each triad is composed of a sense object, a sense organ and the associated sense-organ-consciousness. In other words, the eighteen elements are made up of the twelve saḷāyatana and the six related sense-consciousnesses.

Karma :

In a Samyutta Nikaya discourse, the Buddha declares that the six internal senses bases are "old kamma, to be seen as generated and fashioned by volition, as something to be felt." In this discourse, "new kamma" is described as "whatever action one does now by body, speech, or mind." In this way, the internal saḷāyatana provide a link between our volitional actions and subsequent perceptions.