Consonant Age of Acquisition Reveals Nonlinear Effects in Nonword Repetition Performance

Recent work has shown significant sublexical effects of long-term memory in nonword repetition (NWR) using a dichotomous consonant age of acquisition (CAoA) variable (Moore, 2018; Moore, Fiez, and Tompkins, 2017). Performance consistently decreased when stimuli comprised consonants acquired later versus earlier in speech development. To address potential confounds related to stimulus design and linearity, the purpose of this study was to test whether performance decreases as the CAoA value of stimuli increases in various linguistic tasks using a continuous CAoA variable. Thirty-one college students completed NWR and other linguistic tasks in which the stimuli varied in average CAoA values. Data were analyzed using multilevel modeling. After accounting for phonotactic probability, CAoA was a statistically significant predictor of performance across the models reported. The relationship was more complex in some of the models in which CAoA showed a statistically significant nonlinear relationship with the outcome measure. Results from this study support previous work showing that CAoA affects performance on NWR and other linguistic tasks that vary in their memory, auditory perceptual, and articulatory demands. Importantly, this line of work was extended here by demonstrating that the CAoA effect is robust across novel stimulus sets and study designs, and may be more complex than previously understood when using a dichotomous CAoA variable. Quadratic results suggest that the CAoA variable has a differential effect on performance for low to moderate CAoA values, but for higher CAoA values the effect is similarly negative. The nonlinear relationship between CAoA and measures of speed and accuracy on some of the tasks warrants further study into the complex relationship between various predictive factors that contribute to language performance.