Page 40 - 2017Spring

Communication Across the Life Span
ing later in adulthood as one’s gender and social identity is established further.
Younger adolescents differ from young adults, not only in terms of the frequency ranges of the acoustic patterns of their speech but also because they are more internally variable in their speech production (e.g., Koenig et al., 2008). This greater variability in production can be measured directly from articulatory movements (Walsh and Smith, 2002). The acoustic consequences of this immature motor control can be seen in the form of larger variance in the acoustic char- acteristics of sounds in the speech of children and young adolescents when multiple repetitions of the same items are measured (e.g., Lee et al., 1999; Munson, 2004).
Another aspect that is still undergoing development is the rate at which children and adolescents articulate their speech, typically measured as the number of syllables pro- duced per second. The development of the conversational articulation rate, as measured from tasks such as story retell- ing or monologues on familiar topics, is of particular inter- est because it reflects the joint influence of two components: speech motor control and linguistic planning (Flipsen, 2002; Nip and Green, 2013). Developmental studies on the con- versational articulation rate typically show evidence of the age effects throughout the first and into the second decade of life (e.g., Flipsen, 2002; Sturm and Steery, 2007).
It is notable that even studies of later speech development seem to exclude adolescents older than 14-15 years; this is primarily because some early studies of speech perception and production in this age range suggested that performance stabilized from that age onward, but there may also be a more pragmatic reason because it can be difficult to entice older adolescents to participate in laboratory experiments. Evidence is accumulating though that further refinement in speech production abilities must occur in these years be- cause 14-15 year olds still differ significantly from young adults in studies of the coordination of motor articulation (e.g., Smith and Zelaznik, 2004) and acoustic characteristics (e.g., Hazan et al., 2016) of speech production.
In addition to physical changes in their vocal apparatus, ad- olescents are also undergoing significant cognitive changes as a result of changes to the brain structure, and this may impact their speech communication. For example, relative to young adults, adolescents have greater difficulty with per- spective taking, which is an essential requirement for effec- tive communication (Blakemore and Choudhury, 2006). It is also the case that school-age adolescents have yet to expe-
rience the great changes in language experience and expo- sure that undergraduate students, who constitute the typical “young adult” population in speech science studies, usually experience when leaving home to go to university. This great increase in language experience may well contribute to the differences seen between these two age groups despite their small age gap; this issue requires further investigation.
Further Changes in Speech
Production in Middle Age
As suggested above, adult norms in speech science studies usually equate to the performance of undergraduate stu- dents in their low- to mid-20s for practical reasons of par- ticipant recruitment rather than more principled selection criteria. Middle-aged adults are probably the least studied population in speech research. They are the hardest popula- tion to recruit due to limited availability in working hours, and there is also an expectation that they might not be a particularly interesting group to investigate because speech perception and production abilities are expected to be sta- ble. However, the few studies that have spanned a large age range in adulthood suggest that this may not be the case. For example, Jacewicz et al. (2010) showed that the articulation rate measured from spontaneous speech monologues in- creased from childhood into adulthood and did not “peak” until the adults were in their mid-40s.
There are many factors that could contribute to ongoing changes in speech production abilities throughout midadult- hood. First, our exposure to language in all its variants is incremental throughout the life span, and the learning of a new language in adulthood, for example, can affect the pro- duction of the native language (Chang, 2012). Sociophonetic factors linked to regional or social mobility are also influen- tial because individuals can change their accent significantly in adulthood as a result of moving to a new region or to a new work environment, although the extent of this change will most likely depend on the degree to which they wish to retain their identity (Evans and Iverson, 2007).
Speech production in midadulthood can also be affected by changes in physical or mental health. Major traumas such as stroke or cancers affecting the larynx or tongue can have a significant impact on speech. Less drastic physical changes such as those brought about by heavy smoking or excessive alcohol intake can also affect voice production and lead to perceptible changes in voice quality. Many occupations that involve individuals excessively using their voice can lead to voice changes; for example, teachers show a greater in-
38 | Acoustics Today | Spring 2017