A recent publication (Rajesh P. N. Rao, Nisha Yadav, Mayank N. Vahia, Hrishikesh Joglekar, R. Adhikari, and Iravatham Mahadevan, "Entropic Evidence for Linguistic Structure in the Indus Script", Science, published online 23 April 2009; also supporting online material) claims a breakthrough in understanding the nature of the symbols found in inscriptions from the Indus Valley Civilization.
Two major types of nonlinguistic systems are those that do not exhibit much sequential structure (“Type 1” systems) and those that follow rigid sequential order (“Type 2” systems). […] Linguistic systems tend to fall somewhere between these two extremes […] This flexibility can be quantified statistically using conditional entropy, which measures the amount of randomness in the choice of a token given a preceding token. […]
We computed the conditional entropies of five types of known natural linguistic systems […], four types of nonlinguistic systems […], and an artificially-created linguistic system […]. We compared these conditional entropies with the conditional entropy of Indus inscriptions from a well-known concordance of Indus texts.
We found that the conditional entropy of Indus inscriptions closely matches those of linguistic systems and remains far from nonlinguistic systems throughout the entire range of token set sizes.
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