Reduplication of verbs expresses iteration of activities or plurality of participants. Reduplication of nouns and adjectives in a noun phrase expressed plurality of referents. Reduplication of predicative adjectives expresses plurality or distributivity of the subject referent. All of these are iconic functions.
Source: Sandefur 1979: 117
Source: Bennett 1986: 3
Source: Bennett 1986: 6
Source: Sandefur & Sandefur 1982: 61
Source: Angelo et al. 1998a