Regarding the number of human Indriya(s) and their functions all philosophical scriptures are of the same opinion. In Mahābhārata, it is at least hundred times mentioned that there are ten indriya(s), and the eleventh is mind. So it has become a common consensus that scholars know that five indriya(s) are the cause of cognition regading form, smell, etc. The eyes, the ear, the nose, the tongue and the skin– are the means of cognition of such faculties as rūpa(form), etc. In Nārada-Asita saṃvāda of Mahābhārata, it is said that darśana(seeing), śravaṇa(hearing), ghrāṇa (smelling), sparśana(touching) and rasana(tasting) are the five attributes of these indriya(s). But the indriya(s) are themselves inanimate, so they can’t have the cognition of rūpa, gandha, rasa, sparśa and śavda– but the conscious being, with a knowledge of the field concerned, can have these cognitions by means of the indriya(s). The process of this cognition is also described in Mahābhārata. It is said that the creatutres at first receive the impressions of sound etc. with the help of the auditory organ etc. Then it judges the subject with mind, and determines it with intelligence. Thus the jīvātmā realises the subjects of cognition received by the indriya(s). In Mahābhārata, with a brief description of this, it is further said that citta, mana and vuddhi can be added to these five organs, and these eight are jñānendriya(s)–
aṣṭau jñānendriyāṇyāhuretānyadhyātmacintakāḥ.

One thing should be clarified here, that in ancient Sāṃkhya tradition, or in the later Kārikā-Kaumudī tradition, the importance of karmendriya is lesser than that of jñānendriya(s), although there is no problem in recognising their status as indriya(s). In Nārada-Asita saṃvāda of Mahābhārata, the function and attributes of the jñānendriya(s) and karmendriya(s) have been discussed. It is said that karmendriya(s) are five in number– hasta, pada, pāyu, śiśna and mukha (elsewhere in Mahābhārata, ‘vāk’ is mentioned instead of mukha). Mukha is called indriya because it is associated with eating and talking, the feet are gamanendriya, and the hands are also considered as indriya because they act–
pāṇipādañca pāyuśca mehanaṃ pañcamaṃ mukham
iti saṃśavdyamānāni śṛṇu karmendriyāṇyapi.
jalpanābhyavahārthaṃ mukhamindriyamucyate
gamanendriyaṃ tathā padau karmaṇaḥ karaṇe karau.
In Mahābhārata, vala is counted as the sixth karmendriya. This vala is basically five kinds of prāṇavāyu– prāṇa, apāna, etc. The Mahābhārata-Sāṃkhya considers that these act as the ‘sender’ of stimulant to the karmendriya(s), but in traditional Sāṃkhya philosophy, vacana, grahaṇa, gamana, upasarga and ānanda– are the attributes of the five karmendriya(s).

In Mahābhārata, Bhagavadgītā and Purāṇa, e erywhere the indriya(s) are described as prakṛtisthita. If the reflection of Puruṣa takes place in vuddhi, as a result of guṇakṣobha, the suddha-satvastha Puruṣ gets identified with the measures of Prakṛti. As per the saṃskāra of the previous birth, he shifts as jīvātmā from one body to another. At this time of self-forgetting, he becomes the seer and enjoyer of the deeds and and their fruits, both śubha (good) and aśubha. All ancient and modern scriptures have more or less accepted this ultimate result of the process of abhibyakti(evolution through expression).

Before being manifested, the indriya(s) remain abyakta (un-expressed), as the body of a tortoise (kūmaśarīavat), inherent in Prakṛti-śarīa. Again, at the time of pralaya, these get dissolved in unmanifested prakṛti. So these are called liṅga or jñāpaka. How these indriya(s) become subject to the Atman’s realisation of viṣaya, and come to be consedered as linṅga– is described in Vṛhadāraṇyak Upaniṣad–
rūpaṃ rūpaṃ pratirūpo vabhūva/
tadasya rūpaṃ praticakṣaṇāya
indro māyābhiḥ pururūpa īyate
yukta-hyasya harayaḥ śatā daśeti.

The significance of this famous śloka uttered in Vṛhadāraṇyak Śruti lies in the notion that — Paramātman or the Supreme Self, uding His Māyā, became manifested in the form of each and every namable objects, individually. Due to the multiplicity of indriyas, the objects acceptable by them are also many in number. It is to manifest these external objects that the indriya(s) get associated with ‘Indra’ or Ātman. In Sāṃkhyadarśana it is said that, when the proportion or balance of the attributes of Prakṛti gets distracted, the indifferent, inactive Puruṣa with a pure-self, considers Himself as completely identified with the joy-and-sorrow-oriented results enjoyed by Prakṛti. So, Vācaspati Miśra, in Sāṃkhyatattvakaumudī, has described the true self of the indriya(s)–
ubhayamapi etad indrasya ātmanaḥ
cihnatvāt indriyaṃ uchyate.
So, both jñānendriya and Karmendriya(s) are counted as indriya(s), because they are the signns of Indra or Ātman. Here Vācaspati has analysed the term, by adding to the śavda ‘indra’, the ‘taddhita’ ‘gha’ pratyaya. The taddhita pratyaya functions as liṅga (indicator) or jñapaka(denoter).

So, according to the opinion of Vācaspati, the status of eye, year or vāk, pāṇi as indriya gets confirmed by virtue of being the liṅga of Indra or Ātman.

We have already found the tradition of this discourse regarding the relation of the indriya(s) with indra or Ātman. In Mahābhārata, Sulabhā says to Janaka–
pṛthagātmān ātmānaṃ saṃśliṭā jatukāṭhavat
na caiṣāṃ codanā kacidastītyeva viniścayaḥ.

Sulabhā here says that , śrotra, tvak, cakṣu, rasanā, and nāsika– these are five jñānendriya(s), and the subjects which are brought into cognition by them– śavda, sparśa, rūpa, rasa, gandha- are separate, but they are associated with the Ātman, like jatukāṣṭha. There is, however, no stimulant with which they can move and control themselves. When they accept the external subjects of cognition, being driven by mana, vuddhi, ahaṃkāra; Ātman remains the inactive seer and enjoyer of their functions.

In another chapter of Mahābhārata, it is further said, in support of the previous utterance–
śrotrādīni na paśyanti svaṃ svamātmānamātmanā
sarvajñaḥ sarvadarśī ca sarvajñstāni paśyati.

In this śloka of Manu-Vṛhaspati-saṃvāda, it is said that, the indriya(s) like karṇa cannot see their own appearance by themselves. But the all-knowing and all-seeing jīvātman can see the indriya(s). So it is reinforced that Ātman himself can be the inactive seer of the actions of the indriya(s), but the indriya(s) themselves are more ‘inactive’ in this regard.

From the above discourse on ething becomes clear thatthe indriya(s) get related to the human body as a result of saṃskāra, initiated by dharma or adharma, or by providence-controlled good or ill-deeds. But they cannot know the subjects of their own cognition by themselves, nor can they know themselves. When vuddhi (intelligence) and ahaṃkāra(ego) get in touch with the karma-related saṃkāra, then the indriya(s) can engage themselves in their respective functuions, as directed by the Ātman, in the form of Jīvātman.
In one śloka of Bhagavadgīta, regrding the true nature of indriya(s) it is said–
mamaivāṃśo jīvaloke jīvabhūtaḥ sanātanaḥ
manaḥ ṣaṣṭhānīndriyāni prakṛtisthāni karṣati.

In the above śloka, it is said that – when Paramātman gets reflected as Jīvātman, he attracts the prakṛtistha, unconscious indriya(s) for bearing joys and sorrows. Then the indriya(s) get ready for acceptiong subjects of cognition. In his commentary on the above-mentoned śloka, Ācārya Madhusūdana Sarasvatī has said in this context, though Paramātman is ‘niraṃś’ by nature (without parts), still by virture of the illusion cast by Māya, parts of Paramātman can be imagined, just as part of the sun is imagined to be reflected in water. But this imagination is not actually a ‘part’ , but ‘partlike’. From śrotra to mana– the indriya(s) are the ‘karaṇa'(s) of the subject-cognition of Ātman.

Just as a tortoise take out its hidden limbs, Jīvātman draws out these indriya(s) suspended in Ajñāna as Kāraṇa, so that they can be able to receive cognition. In Gītā, too, Madhusūdana Sarasvatī has accepted the role of Providence and said, as long as Providence, the progenitor of conscious enjoyment is powerful, the living being remains awake and relates his alert indriya(s) in the enjoyment of objects. While dreaming, the indriya(s) may be asleep, but the mind remains active and helps in the desire for enjoyment. When his karma due to enjoyment or Providence is exhauted, then comes sleep. Since there is no enjoyment then, the indriya(s) that make enjoyment possible in the awakening state, and the indriya(s) that make enjoyment possible during sleep, remains ‘nirvyāpāra’ and suspended in their own kāraṇa. So the indriya(s) are the cause of enjoyment, and when they can present the subjects of cognition in front of the living state, Jīvātmā can enjoy them.

In Mahābhārata also, likewise in Gītā, the relation between Ātman and the indriya(s) is explained with the help of a beautiful allegory. In Manu-Vṛhaspati-Saṃvāda Manu has said–
yathendriyarthān yugapat samantāt
nopekṣate kṛtsnamatulyakālam
tathā calaṃ sañcarate sa vidvāṃ
-stasmāt sa ekaḥ paramaḥ śarīrī.