Validating the Influences of Methodological Decisions on Assessing the Spatiotemporal Stability of Speech Movement Sequences Using Children's Speech Data

Abstract

Purpose: Prior research introduced quantifiable effects of three methodological parameters (number of repetitions, stimulus length, and parsing error) on the spatiotemporal index (STI) using simulated data. Critically, these parameters often vary across studies. In this study, we validate these effects, which were previously only demonstrated via simulation, using children's speech data.

Method: Kinematic data were collected from 30 typically developing children and 15 children with developmental language disorder, all spanning the ages of 6-8 years. All children repeated the sentence "buy Bobby a puppy" multiple times. Using these data, experiments were designed to mirror the previous simulated experiments as closely as possible to assess the effects of analytic decisions on the STI. Experiment 1 manipulated number of repetitions, Experiment 2 manipulated stimulus length (or the number of movement units in the target phrase), and Experiment 3 manipulated precision of parsing of the articulatory trajectories.

Results: The findings of all three experiments closely mirror those of the prior simulation. Experiment 1 showed consistent underestimation of STI values from smaller repetition counts consistent with the theoretical model for all three participant groups. Experiment 2 found speech segments containing fewer movements yield lower STI values than longer ones. Finally, Experiment 3 showed even small parsing errors are found to significantly increase measured STI values.

Conclusions: The results of this study are consistent with the findings of prior simulations in showing that the number of repetitions, length of stimuli, and amount of parsing error can all strongly influence the STI independent of behavioral factors. These results further confirm the importance of closely considering the design of experiments, which employ the STI.

Figure 1.

Illustration of parsing for the three subcomponents of the phrase “buy Bobby a puppy” for a sample typically developing 6-year-old participant.

Figure 2.

Plots of the bias of the spatiotemporal index (STI) versus number of repetitions for (a) typically developing 6-year-olds, (b) typically developing 8-year-olds, and (c) children with developmental language disorder (DLD). The bias is calculated at the participant level via random subsampling and then averaged across participants for each group to generate the displayed curves. The blue line depicts the bias of the standard STI, and the green line depicts the bias following bias correction.

Figure 3.

Plot of the spatiotemporal index (STI) values versus average duration for the phrase “buy Bobby a puppy” (BBAP) and each of the three subcomponents displayed for the (a) 6-year-olds, (b) 8-year-olds, and (c) children with developmental language disorder (DLD).

Figure 4.

Plots displaying (a) the average spatiotemporal index (STI) for each participant group and (b) Cohen's d value for between-groups differences with reference to the maximum amount of injected parsing error (∈). 6YO = 6-year-olds; 8YO = 8-year-olds; DLD = children with developmental language disorder.

Figure 5.

Plot displaying the amount of increase in the spatiotemporal index (STI) value resulting from the insertion of ∈ = 100 ms of parsing error against the average duration for each participants productions of the phrase “buy Bobby a puppy.” 6YO = 6-year-olds; 8YO = 8-year-olds; DLD = children with developmental language disorder.