Abstract
Speech motor actions are performed quickly, while simultaneously maintaining a high degree of accuracy. Are speed and accuracy in conflict during speech production? Speed-accuracy tradeoffs have been shown in many domains of human motor action, but have not been directly examined in the domain of speech production. The present work seeks evidence for Fitts’ law, a rigorous formulation of this fundamental tradeoff, in speech articulation kinematics by analyzing USC-TIMIT, a real-time magnetic resonance imaging data set of speech production. A theoretical framework for considering Fitts’ law with respect to models of speech motor control is elucidated. Methodological challenges in seeking relationships consistent with Fitts’ law are addressed, including the operational definitions and measurement of key variables in real-time MRI data. Results suggest the presence of speed-accuracy tradeoffs for certain types of speech production actions, with wide variability across syllable position, and substantial variability also across subjects. Coda consonant targets immediately following the syllabic nucleus show the strongest evidence of this tradeoff, with correlations as high as 0.72 between speed and accuracy. A discussion is provided concerning the potentially limited applicability of Fitts’ law in the context of speech production, as well as the theoretical context for interpreting the results.
Highlights
The present work applies certain influential ideas of Paul Fitts [1] in the domain of speech production, his formulation of so-called speed-accuracy tradeoffs in human motor action
The primary goal is to analyze speech articulation using a large database of real-time magnetic resonance data, in order to assess whether articulatory kinematics conform to Fitts’ law
USC-TIMIT contains data gathered from both midsagittal rtMRI and electromagnetic articulography (EMA), but only the rtMRI data was utilized in the present analysis
Summary
The present work applies certain influential ideas of Paul Fitts [1] in the domain of speech production, his formulation of so-called speed-accuracy tradeoffs in human motor action. One important outcome of that work was a rigorous formulation of perhaps the most robust and widely replicated laws of human motor action: for discrete, targeted actions, the time taken to complete a movement displays a linear relationship with task difficulty, where difficulty is a function of movement distance and the tolerable error in reaching the target. This law is typically described as a speed-accuracy relationship, given the intuitive notion that movement time and speed are quantities that are closely, if inversely, related, and that tolerable error is the reciprocal of accuracy. The initial position can be thought of as the context in which the task takes place
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