Participants and Phenotypic Assessments

This project was completed with the oversight and approval of the Institutional Review Boards at the University of Washington and Arizona State University as previously mentioned (^{51, 52}). Adults gave written consent and parents gave written permission for their minor children to participate. Altogether, 89 participants were included in the study, 44 males and 45 females, with an average age of 32.45 and a standard deviation of 19.74. Thirty-six participants were in, 2- or 3-generational families with dyslexia, with the average family size being 5.14 ranging from 4 to 7 (⁵³).

To be included in the dyslexia group, participants were required to score below −1 SD in at least one of five measures of reading and/or spelling, described below. To be included in the typical control group, participants were required to score above −1 SD in all five measures. All participants were required to be free from any developmental or sensory condition that could introduce confounding.

Sight word recognition and nonword decoding were assessed under untimed conditions with the Word Identification (WID) and Word Attack (WATT) subtests of the Woodcock Johnson Reading Mastery Test, Third Edition (⁵⁴) and under timed conditions using the Sight Word Efficiency (SWE) and Phonemic Decoding Efficiency (PDE) subtests of the Test of Word Reading Efficiency (TOWRE) (⁵⁵). Spelling ability was assessed with the Spelling subtest of the Wechsler Individual Achievement Test – Second Edition (WIAT-2) (⁵⁶).

In addition to assessments of reading and spelling, participants were asked to produce rapid sequences of syllables (“papapa …,” “tatata …,” “kakaka …”) to measure motor speeds in a motor speech task. Average syllable durations were computed and transformed into z scores based on published norms (⁵⁷) To measure rapid naming speeds, the RAN/RAS: Rapid Automatized Naming and Rapid Alternating Stimulus Test was administered (⁵⁸). Participants named the items in an array of 50 as rapidly as possible. This test includes the following subtests: Letters, Numbers, Colors, Objects, Letters alternating with Numbers, and Letters alternating with Numbers and Colors. For each subtest, completion time is converted to a standard score based on participant age.