Age-related deficits in speech production: From phonological planning to motor implementation

Speaking is one of the most complex motor actions that humans can perform, requiring the coordination between linguistic, cognitive, affective and sensorimotor systems. Perhaps counter-intuitively, it is also one of the easiest acts that humans perform, on a daily basis, from a very early age till the end of life, without even thinking about it. With age, however, spoken language production undergoes significant changes, with potential impacts on interpersonal communication and social participation. Unfortunately, the neurobiological mechanisms involved are unclear, which impedes efforts towards the development of clinical interventions, differential diagnosis strategies and even prevention strategies for this population. In the present study, we examined age differences in speech production using a simple diadochokinetic rates task in which phonological and sequential complexity were manipulated. 85 cognitively healthy adults (20-93 years) were recruited from the general population. Cognitive level, hearing and depression symptoms were measured. Participants produced short and long sequences of simple and complex syllables aloud as quickly, steadily and accurately as possible. Performance was assessed in terms of articulation rate, articulation rate stability and accuracy. Results show that, controlling for cognition, hearing and depression, articulation rate stability and accuracy declined significantly with age. The phonological manipulation had more impact on performance than the sequential manipulation. These findings were interpreted as reflecting age-related central disruptions at the level of phonological and motor planning, which provides important new cues into underlying neurobiological mechanisms.