Linear and logarithmic speed-accuracy trade-offs in speech production

We used picture description tasks to explore the scaling of speech time (ST) with task difficulty manipulated by changing the number of objects and number of their characteristics. In Experiment-1 linear scaling of ST with the index of difficulty (ID) was observed. The scaling coefficients were larger in subjects who spoke non-native English as compared to native both English and non-English. Experiment-2 explored a broader range of ID and resulted in logarithmic scaling of ST with ID. Chinese speakers were much faster than speakers of Indo- European languages. We interpret the findings as reflections of a basic scaling of action time with ID common across motor tasks (as in Fitts' law) and speech tasks. Scaling of ST with ID is sensitive to both native vs. second language and to cross-linguistic comparisons.