a1 Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. firstname.lastname@example.org http://www.psych.auckland.ac.nz/people/Corballis/Corballis.htm
Recognising that signed languages are true languages adds to the variety of forms that languages can take. Such recognition also allows one to differentiate those aspects of language that depend on the medium (voiced or signed) from those that depend on more cognitive aspects. At least some aspects of language, such as symbolic representation, time markers, and generativity, may derive from the communication of the products of mental time travel, and from the sharing of remembered past and planned future episodes.