Source: A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)
). In Buddhist psychology, the twelve āyatanas are the six senses or modes of perception and the six kinds of object they correspond to, namely: (1) sight and colour/form (rūpa-āyatana); (2) hearing and sound (śabda-āyatana); (3) smell and scent (gandha-āyatana); (4) taste and flavours (rasa-āyatana); (5) touch and tangible objects (sparśa-āyatana); and (6) the mind and ideas (mano-āyatana
). Each āyatana is thus the sphere or domain of a particular sense, and encompasses everything that can be experienced through that particular ‘sense-door’. See also ṣad-āyatana.
Source: Pali-English Dictionary, TW Rhys Davids, William Stede,
Āyatana (nt.) [Sk. āyatana, not found in the Vedas; but freq. in BSk. From ā + yam, cp. āyata. The pl. is āyatanā at S iv.70. -- For full definition of term as seen by the Pāli Commentators see Bdhgh's expln at DA i. 124, 125, with which cp. the popular etym. at KhA 82: "āyassa vā tananato āyatassa vā saŋsāradukkhassa nayanato āyatanāni" and at Vism 527 "āye tanoti āyatañ ca nayatī ti ā."] -- 1. stretch, extent, reach, compass, region; sphere, locus, place, spot; position, occasion (corresponding to Bdhgh's definition at DA i.124 as "samosaraṇa") D iii.241, 279 (vimutti˚); S ii.41, 269; iv.217; v.119 sq., 318. sq.; A iii.141 (ariya˚); v.61 (abhibh˚, q. v.) Sn 406 (rajass˚ "haunt of passion" = rāgādi -- rajassa uppatti -- deso SnA 381); J i.80 (raj˚). Freq. in phrase araññ˚ a lonely spot, a spot in the forest J i.173; VvA 301; PvA 42, 54. -- 2. exertion, doing, working, practice, performance (comprising Bdhgh's definition at DA i.124 as paññatti), usually -- ˚, viz. kamm˚ Nd1 505; Vbh 324, 353; kasiṇ˚ A v.46 sq., 60; Ps i.28; titth˚ A i.173, 175; Vbh 145, 367; sipp˚ (art, craft) D i.51; Nd2 505; Vbh 324, 353; cp. an˚ non -- exertion, indolence, sluggishness J v.121. -- 3. sphere of perception or sense in general, object of thought, sense -- organ & object; relation, order. -- Cpd. p. 183 says rightly: "āyatana cannot be rendered by a single English word to cover both sense -- organs (the mind being regarded as 6th sense) and sense objects". -- These āyatanāni (relations, functions, reciprocalities) are thus divided into two groups, inner (ajjhattikāni) and outer (bāhirāni), and comprise the foll.: (a) ajjhatt˚: 1. cakkhu eye, 2. sota ear, 3. ghāna nose, 4. jivhā tongue, 5. kāya body, 6. mano mind; (b) bāh˚: 1. rūpa visible object, 2. sadda sound, 3. gandha odour, 4. rasa taste, 5. phoṭṭhabba tangible object, 6. dhamma cognizable object.
-- For details as regards connotation & application see Dhs trsl. introduction li sq. Cpd. 90 n. 2; 254 sq. -- Approximately covering this meaning (3) is Bdhgh's definition of āyatana at DA i.124 as sañjāti and as kāraṇa (origin & cause, i. e. mutually occasioning & conditioning relations or adaptations). See also Nd2 under rūpa for further classifications. -- For the above mentioned 12 āyatanāni see the foll. passages: D ii.302 sq.; iii.102, 243; A iii.400; v.52; Sn 373 (cp. SnA 366); Ps i.7, 22, 101, 137; ii. 181, 225, 230; Dhs 1335; Vbh 401 sq.; Nett 57, 82; Vism 481; ThA 49, 285. Of these 6 are mentioned at S i.113, ii.3; iv.100, 174 sq.; It 114; Vbh 135 sq., 294; Nett 13, 28, 30; Vism 565 sq. Other sets of 10 at Nett 69; of 4 at D ii.112, 156; of 2 at D ii.69. -- Here also belongs ākāsɔ ānañcɔ āyatana, ākiñcaññ˚ etc. (see under ākāsa etc. and s. v.), e. g. at D i.34 sq., 183; A iv.451 sq.; Vbh 172, 189, 262 sq.; Vism 324 sq. -- Unclassified passages: M i.61; ii.233; iii.32, 216, 273; S i.196; ii.6, 8, 24, 72 sq.; iii.228; iv.98; v.426; A i.113, 163, 225; iii.17, 27, 82, 426; iv.146, 426; v.30, 321, 351, 359; Nd1 109, 133, 171, 340; J i.381 (paripuṇṇa˚); Vbh 412 sq. (id.).
-- uppāda birth of the āyatanas (see above 3) Vin i.185. -- kusala skilled in the ā. M iii.63. -- kusalatā skill in the spheres (of sense) D iii.212; Dhs 1335. -- ṭṭha founded in the sense -- organs Ps i.132; ii.121.
As can be seen above, there are both "inner" and "outer" aspects of senses, which seems right in line with the two Objectivist positions in which the OP has interest.