A Semantic Priming Event-related Potential (ERP) Task to Study Lexico-semantic and Visuo-semantic Processing in Autism Spectrum Disorder

Summary

This paper describes a semantic priming ERP task using within-modality pairs of pictures and words to investigate semantic processing in individuals with autism spectrum disorder (ASD).

Abstract

Individuals with autism spectrum disorder (ASD) have characteristic deficits in understanding the meaning of language, or semantic processing. However, some evidence indicates that semantic processing of non-linguistic stimuli is intact, suggesting that semantic deficits may be language-specific. To appropriately characterize semantic processing deficits in individuals with ASD, comparison of within-modality linguistic (e.g., written words) and non-linguistic (e.g., pictures) stimuli is required. This paper describes such a methodology that makes use of a semantic priming paradigm during concurrent recording of electroencephalographic (EEG) data. EEG provides a dynamic measure of brain activity that is well-suited to characterize subtle differences in semantic processing that may not be observable at the behavioral level. The semantic priming paradigm presents a prime picture or word (e.g., dog) followed by a target picture or word that is either related (e.g., cat) or unrelated (e.g., pencil) to the prime. This paradigm can thus be used to evaluate semantic processing across different modalities, and to compare lexico-semantic and visuo-semantic processing abilities in individuals with ASD and how they might differ from TD individuals. The specific steps involved in creating the stimuli, performing the EEG testing, and analyzing the EEG data are discussed. Representative results illustrate how the N400 component of the event-related potential (ERP) is reduced following semantically-related prime-target pairs compared to unrelated pairs. Comparisons of the N400 between conditions, modalities, and groups can provide estimates of the success of semantic processing, and can thereby be used to characterize semantic deficits in individuals with ASD or other clinical populations.

Introduction

Researchers in cognitive psychology have long been interested in how people understand the meaning of language. Language processing involves a sequence of steps of increasing complexity, from letter and word recognition, to semantic processing, to syntactic parsing. Semantic processing refers to accessing the meaning of a stimulus, be it a word, picture, or sound. Following early steps of initial word recognition, access of a word's meaning, or semantics, is a crucial step in language processing. Semantic integration refers to the process of integrating the meaning of stimuli to understand their relationships, and is crucial for higher-level language processing su....

Protocol

All methods described here were approved by the Institutional Review Board of Johns Hopkins University, where the original study⁶ was performed.

1.Creating Stimuli

1. Create an initial list of concrete nouns from which prime-target pairs will be made.
   1. From a selected corpus such as Subtlex¹⁹, select approximately 500 concrete nouns and obtain variables of interest (e.g., frequency, length, concreteness, imageability, etc.) for each word.
      NOTE: Other corpuses, such as the Medical Research Council (MRC) Psycholinguistic Database

Results

If stimuli have been appropriately sorted into related and unrelated conditions, an N400 effect should be observed for both word and picture stimuli (Figure 2). This is identifiable as a greater negative amplitude in unrelated conditions compared to related conditions. For word stimuli, the effect should occur from 300–500 ms over central or centro-parietal scalp^6,10. For picture stimuli, the effect m.......

Discussion

The present paper has reported critical steps in developing a semantic priming ERP paradigm with picture and word stimuli for exploring semantic processing deficits in individuals with ASD. Major steps include creating the stimuli, programming the task, and performing EEG testing and analyses. The most time-consuming part of this procedure is likely to be the creation of stimuli, as this requires careful matching both between and within stimulus pairs, conditions, and modalities on variables such as length, frequency, an.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
EEG system	Electrical Geodesics, Inc. (EGI)		Geodesic EEG system (GES) 400 system: Net Amps 400 amplifier, NetStation 5.3, 128-channel HydroCel Geodesic Sensor nets
Potassium chloride	Electrical Geodesics, Inc. (EGI)
Plastic bucket	Electrical Geodesics, Inc. (EGI)		EGI provides a plastic bucket for mixing electrolyte but any clean container can be used
Baby shampoo	Johnson's
GNU Image Manipulation Program (GIMP)