Adaptive Plasticity Under Adverse Listening Conditions is Disrupted in Developmental Dyslexia

Abstract

Objective: Acoustic distortions to the speech signal impair spoken language recognition, but healthy listeners exhibit adaptive plasticity consistent with rapid adjustments in how the distorted speech input maps to speech representations, perhaps through engagement of supervised error-driven learning. This puts adaptive plasticity in speech perception in an interesting position with regard to developmental dyslexia inasmuch as dyslexia impacts speech processing and may involve dysfunction in neurobiological systems hypothesized to be involved in adaptive plasticity. Method: Here, we examined typical young adult listeners (N = 17), and those with dyslexia (N = 16), as they reported the identity of native-language monosyllabic spoken words to which signal processing had been applied to create a systematic acoustic distortion. During training, all participants experienced incremental signal distortion increases to mildly distorted speech along with orthographic and auditory feedback indicating word identity following response across a brief, 250-trial training block. During pretest and posttest phases, no feedback was provided to participants. Results: Word recognition across severely distorted speech was poor at pretest and equivalent across groups. Training led to improved word recognition for the most severely distorted speech at posttest, with evidence that adaptive plasticity generalized to support recognition of new tokens not previously experienced under distortion. However, training-related recognition gains for listeners with dyslexia were significantly less robust than for control listeners. Conclusions: Less efficient adaptive plasticity to speech distortions may impact the ability of individuals with dyslexia to deal with variability arising from sources like acoustic noise and foreign-accented speech.

Increased reliance on top-down information to compensate for reduced bottom-up use of acoustic cues in dyslexia

“…We argue that people with DD are less able to use sensory low-level information efficiently, which leads to greater reliance on top-down information as a compensatory mechanism. This notion is consistent with previous findings in which the ability of dyslexics to generalize speech perceptual learning was intact when trained and untrained information shared high-level top-down information (Gabay et al, 2017) but not when shared information was based only on low-level sub-lexical cues (Gabay et al, 2017;Gabay & Holt, 2021).…”

“…In typical listeners, the learning of distorted speech generalizes across stimuli that share high-level representations (new talker, same tokens) but also to new items that do not share high-level representations with the trained one (same talker, new tokens) (Banai & Lavner, 2012Gabay et al, 2017). By contrast, for individuals with DD, such generalization is confined to situations in which trained and untrained information shares the same high-level top-down information (new talker, same tokens) (Gabay et al, 2017) but is not observed in situations in which only low-level sub-lexical cues are shared between the trained and untrained information (same talker, new tokens) (Gabay et al, 2017;Gabay & Holt, 2021). Therefore, it seems that people with DD are capable of adapting to acoustic challenges when utilization of top-down information is possible.…”

“…The most frequent symptoms of DD are phonological in nature but studies suggest a broader range of deficits in the disorder (Démonet et al, 2004 ). These go beyond the linguistic domain and include impairments in motor skills (Howard Jr et al, 2006 ; Nicolson & Fawcett, 1994 ; Stoodley et al, 2006 ) and temporal processing deficiencies (Farmer & Klein, 1995 ; Gabay et al, 2019 ). Domain-specific accounts postulate that DD arises from difficulties in processing (Snowling, 2001 ) or accessing phonological information (Ramus & Szenkovits, 2008 ), leading to less distinct phonological representations.…”

Speech-specific perceptual adaptation deficits in children and adults with dyslexia

“…It is possible that individuals with dyslexia have a reduced capacity for rapidly adapting to speech cues in order to identify and discriminate between phonemes, resulting in underspecified phonological representations. Indeed, there is evidence for both general auditory and speech-specific adaptation deficits in individuals with dyslexia (Ahissar Amitay et al, 2002;Gabay et al, , 2019, 2021Perrachione et al, 2016).…”

Electrophysiological correlates of perceptual prediction error are attenuated in dyslexia

“…The challenges to developing fluent reading skills in dyslexia must therefore come from latent dysfunction in either the circuits that develop into the reading network or the plasticity processes that support repurposing those circuits for reading. In this study, we investigated the neural bases of differences in rapid perceptual adaptation in dyslexia—a recently documented, domain-general deficit that may reflect weakness in the plasticity processes that support learning to read (Ahissar et al, 2006; Gabay & Holt, 2020; Jaffe-Dax et al, 2016; Oganian & Ahissar, 2012). Specifically, we aimed to expand on the evidence for diminished neural adaptation in dyslexia (Perrachione et al, 2016) by determining whether this phenomenon is due to differences in bottom-up feedforward processing, top-down expectations, or their interaction.…”