As far as the first question is concerned "how is tanmAtra perceived?", the answer lies in what is known as gYAnendriya-s, the capacity to perceive or experience tanmAtra through mahAbhUta. That is, if we take the example of a flower, we can smell it, if: a. the flower has the property or tanmAtra gandha or smell b. the perceiver has the capabilties to process the tanmAtra called smell Thus the five tanmAtras have their corresponding abstract sense-power or gYAnendriya: a. shrota or the power to Hear b. tvak or the power to Feel c. chakShus or the power to See d. rasana or the power to Taste e. ghrANa or the power to Smell
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