“…Particularly relevant to our discussion is the fact that this evidence derives largely from speakers entering young or middle adulthood (e.g., Rickford & Price, 2013), not old age. Currently available longitudinal research on older adults is limited to case studies of public figures (e.g., MacKenzie, 2017; Reubold & Harrington, 2017;Shapp, Lafave, & Singler, 2014) and to small reference groups in larger speaker samples (e.g., Buchstaller, 2015;Gregersen, Maegaard, & Pharao, 2009;Naro & Scherre, 2015;Sankoff & Blondeau, 2007;Wagner & Sankoff, 2011). In either case, there is the difficulty of generalizing over small numbers of speakers as well as a lack of detailed relevant biological, psychological and social information of the kind described in Section 2.…”