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This study addressed human performance characteristics of chord sequences using a framework where each alphabetic letter is represented by a unit of three three-finger chords recalled according to a mnemonic. Fourteen participants conducted the chording task during four one-hour sessions. First, sequences of related chords formed temporal units were the inter-unit time (847 ms) was longer than the intra-unit time (117 ms). The hold times for the chords in a unit formed a distinct long-short-long rhythm (151 ms, 133 ms and 144 ms). The rate of errors was smallest for the first chord (27.1%) followed by the last chord (34.8%) and largest for the middle chord in a unit (38.1%). Practice manifested itself in significantly shorter inter-chord time and chord hold times. Chords were built and released in steps, where the time to add a finger, or release a finger, was related to the number of fingers already used. Moreover, it took longer to release a chord (25 ms) than to construct a chord (16 ms). The chord hold times were related to the Hamming distance between successive chords. Both the inter-chord times and the chord hold times were reduced through practice. Chord transitions with a Hamming distance of one resulted in most errors and chord transitions with two identical or complementary chords had the lowest error rate. Implications of these results are that chording speed may increase if frequent chord transitions are designed to have a small Hamming distances. Errors are reduced by designing chord alphabets such that frequent chord transition involving just one finger changes are avoided.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).