Individual-level contextual alignment and aperiodic slope reveal improved comprehension of unexpected language

In everyday language use, individuals are required to comprehend complex, continuous and often unexpected linguistic inputs to effectively communicate with others. Evidence from other domains of processing such as memory and learning suggest that individuals these unexpected inputs can often be remembered or learnt just as well as predictable inputs in follow up testing. However, language comprehension research often focuses on how individuals process these stimuli rather than how the information which is gathered can be used at a later time. It is proposed that, in line with memory and learning, individuals can utilise unexpected language inputs to support a deeper understanding of the information which is being communicated. Further, this will be related to the interaction between an individuals alignment to local context and inter-individual differences in information processing, such as aperiodic slope. The present study uses an alignment metric which measures the relationship between individual level N400 amplitudes (a neurophysiological metric of predictability) and surprisal (a text-collection-based metric of predictability), where higher alignment suggests the individual has a stronger preexisting schema. A steeper aperiodic slope has been suggested to reflect greater adaptation of predictive models in response to prediction errors; therefore, it is hypothesised that depth of language comprehension will be modulated by both alignment and aperiodic slope. To explore this, 30 participants (23F, 1 not reported; mean age: 22.2 years [SD:4.4]) listened to 12 short stories (3 genres, audio-visual presentation) while their electroencephalogram (EEG) was recorded. Comprehension was tested via 6 multiple choice questions per story. An additional combined analysis, including a reanalysis of 40 audio- modality participants, provided evidence across both modalities that comprehension was improved for more surprising stories. Further, when considering inter-individual differences, the relationship between predictability and comprehension was shown to be modulated by both alignment and aperiodic activity. Comprehension of unexpected stories (as measured by N400 amplitudes) was improved only lower aligned, steeper aperiodic slope individuals. This finding is considered a reflection of complementary processing strategies which are weighted towards incoming stimuli, increasing the likelihood of model updating and therefore resulting in improved comprehension of unexpected stories.