Bottom-Up Driven Speechreading in a Speechreading Expert: The Case of AA (JK023)

In Brief Objective: This case study tested the threshold hypothesis (Rönnberg et al., 1998), which states that superior speechreading skill is possible only if high-order cognitive functions, such as capacious verbal working memory, enable efficient strategies. Design: In a case study, a speechreading expert (AA) was tested on a number of speechreading and cognitive tasks and compared with control groups (z scores). Sentence-based speechreading tests, a word-decoding test, and a phoneme identification task were used to assess speechreading skill at different analytical levels. The cognitive test battery used included tasks of working memory (e.g., reading span), inference-making, phonological processing (e.g., rhyme-judgment), and central-executive functions (verbal fluency, Stroop task). Results: Contrary to previous cases of extreme speechreading skill, AA excels on both low-order (phoneme identification: z = +2.83) and high-order (sentence-based: z = +8.12 and word-decoding: z = +4.21) speechreading tasks. AA does not display superior verbal inference-making ability (sentence-completion task: z = −0.36). Neither does he possess a superior working memory (reading span: z = +0.80). However, AA outperforms the controls on two measures of executive retrieval functions, the semantic (z = +3.77) and phonological verbal fluency tasks (z = +3.55). Conclusions: The performance profile is inconsistent with the threshold hypothesis. Extreme speechreading accuracy can be obtained in ways other than via well-developed high-order cognitive functions. It is suggested that AA’s extreme speechreading skill, which capitalizes on low-order functions in combination with efficient central executive functions, is due to early onset of hearing impairment. This case study tested the threshold hypothesis (Rönnberg et al., 1998), which states that superior speechreading skill requires use of efficient strategies that tax high-order cognitive functions, such as capacious verbal working memory. A speechreading expert (AA) was tested on a number of speechreading and cognitive tasks, and compared with control groups. Contrary to previous cases of extreme speechreading skill, AA excels on both low-order and high-order speechreading tasks. AA does not display superior verbal working memory or verbal inference-making ability, but he displays excellent executive retrieval functions. The performance profile is thus inconsistent with the threshold hypothesis. Superior speechreading ability can be obtained in ways other than through well-developed high-order cognitive functions. It is suggested that AA’s extreme speechreading skill, which capitalizes on low-order functions in combination with efficient central executive functions, is due to early onset of hearing impairment.