Decomposing response times in Williams syndrome in separate cognitive processes

ABSTRACT

Williams Syndrome (WS) is a rare neurodevelopmental disorder of genetic origin. The syndrome is characterised by a selective set of deficits in a number of cognitive domains. In spite of a wealth of studies, response times (RTs) of WS have attracted little attention. In the present study, we fill this gap by analysing data from a receptive vocabulary task using the Diffusion Decision Model (DDM). Our results show that the speed of accumulation, decision threshold and non-decision time parameters of WS individuals are similar to these of typically developing 5-year-old preschoolers. In addition, WS verbal intelligence scores were associated with the speed of accumulation of lexical information. Finally, the performance of WS and preschooler individuals was correlated across the vocabulary task and an additional orientation discrimination task only at the group but not at the individual level; therefore, pointing to domain-specific lexical and perceptual processing in WS.

KEYWORDS:

• Williams syndrome
• diffusion decision model
• receptive vocabulary
• orientation discrimination
• atypical development

Acknowledgements

We would like to thank all children and their families for participating in the study, as well as the “Aghia Sofia” General Children's Hospital and Dr. Eleni Frissira for granting us access to the WS participants. We would like to thank Ioanna Kolokytha for helping us with data collection. Also, thanks to Kevin Trutmann for his helpful comments on an earlier draft of the paper. Parts of the paper were presented in the 9th Athens Postgraduate and PhD Candidate conference in October 2017 in Greece. We also acknowledge the Onassis Foundation for funding the first author through its Scholarship programme for Hellenes. All errors are our own.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 Though several theoretical frameworks have been proposed to explaining the complex array of behavioural, cognitive and neurological characteristics of individuals with WS (e.g., nativist approaches (Bellugi et al., 1988; Pinker, 1999), neuroconstructivist ones (Karmiloff-Smith, 1998, 2009; Karmiloff-Smith et al., 2003), hypotheses of dorsal-stream disorder (Atkinson et al., 2006; Landau & Hoffman, 2005), among others), a universally accepted framework still remains elusive. An extensive discussion is beyond the scope of the current paper.

2 Some versions of the DDM model across-trial variability in the non-decision time parameter resulting in a distribution (and not point estimates) of the non-decision time. However, in our analysis we assumed that across-trial variability is zero for simplicity.

3 In addition, the DDM employs several parameters that encode the extent of parameter variability from trial to trial (Ratcliff, 1978; Ratcliff & Rouder, 1998). Parameter variability has been primarily used to make the model fit human RT data better.

4 HDIs of coefficients of response accuracy are given on the logit scale.

5 HDIs of coefficients of RTs are given in log(RT) scale.

Additional information

Funding

This work was supported by Alexander S. Onassis Public Benefit Foundation.