Abstract
Introduction:
When a 6-year-old girl claims that she cannot sleep without her teddy bear, hardly anybody will look surprised. However, when an adult man says the same thing, this is bound to raise some eyebrows. Besides linguistic content, the voice also carries information about a person's identity relevant for communication, such as idiosyncratic features related to the gender and age of the speaker (Campanella 2007). A previous ERP study investigated inter-individual differences in the cognitive processes that mediate the integration of social information in a linguistic context (Van den Brink submitted). Individuals with an empathizing-driven cognitive style showed larger ERP effects to mismatching information about the speaker than individuals who empathize to a lesser degree. The present ERP study tested individuals with Autism Spectrum Disorder (ASD) to investigate verbal social information processing in a clinical population that is impaired in social interaction.
Methods:
Participants. The ERP experiment was conducted with 20 Dutch adult males clinically diagnosed with ASD (verbal IQ > 100), 22 healthy men and 12 healthy women.
Materials. Experimental materials consisted of 160 Dutch sentences with a lexical content that either did or did not fit probabilistic inferences about the speaker's sex, age, and social-economic status, as could be inferred from the speaker's voice. Translated examples of speaker identity (SI) incongruent utterances are "Before I leave I always check whether my make up is still in place", in a male voice, "Every evening I drink some wine before I go to sleep" in a young child's voice, and "I have a large tattoo on my back" spoken in an 'upper-class' accent. In addition, participants heard 48 sentences containing classic lexical semantic (LS) anomalies which are pure linguistic violations, known to elicit an N400, matched with semantically congruent sentences (e.g., "You wash your hands with horse and water" vs. "You wash your hands with soap and water").
Procedure. Participants listened to 352 sentences, spoken by 21 different people. They were asked to indicate after each sentence how odd they thought the sentence was, using a 5-point-scale ranging from "perfectly normal" to "extremely odd". Participants filled out Dutch translations of the Autism and Empathizing Questionnaires (AQ: Baron-Cohen 2001; EQ: Baron-Cohen 2004).
EEG recording. EEG was recorded from 28 electrodes referenced to the left mastoid. Electrode impedances were below 5 kOhm. Signals were recorded using a 200 Hz low-pass filter, a time constant of 10 sec., and a 500 Hz sampling frequency. After off-line re-referencing of the EEG signals to the mean of the left and right mastoid, they were filtered with a 30 Hz low-pass filter. Segments ranging from 200 ms before to 1500 ms after the acoustic onset of the critical word were baseline-corrected. Segments containing artifacts were rejected (12.7%).
Results:
Behavioral results. EQ scores differed significantly between groups (p < .001), with average scores of 22.1 for ASD, 40.6 for men, and 52.1 for women. Statistical analysis of the rating data (see Figure 1) consisted of ANOVAs with the within-subject factors Manipulation (LS, SI) and Congruity (congruent, incongruent), and the between-subject factor Group (ASD, men, women). A significant interaction between Manipulation and Group (p < .01) indicated that the participant groups rated the items differently. For the LS items, a main effect of Congruity (p < .001), but no interaction of Congruity by Group (F < 1) was obtained. For the SI items a main effect of Congruity (p < .001), as well as an interaction of Congruity by Group (p < .01) was found. The ASD group rated the SI violations as less odd than the male and female participant group (2.9 versus 3.4 and 3.7, respectively). In addition, significant positive correlations with EQ score were found for SI effect size (see Figure 2) as well as SI violations (both p < .01).
ERP results. Figure 3 displays the ERP waveforms for the three participant groups. Mean amplitude values in the N400 and Late Positive Component latency ranges (300-600 and 700-1000 ms) from 7 centro-parietal electrodes did not reveal a Congruity by Group interaction. However, a significant correlation was found between the size of the SI effect in the N400 latency window and EQ score (p < .01), with individuals who scored high on EQ showing a larger positive effect. Participants were subdivided into three groups based on EQ score; low empathizers (M = 20; 16 ASD, 2 men), medium empathizers (M = 37; 4 ASD, 12 men, 2 women), and high empathizers (M = 53; 8 men, 10 women). See Figure 4 for the SI difference waveforms for the three EQ groups. Individuals who empathize to a larger degree show an earlier and significantly larger positive effect (p < .05), related to decision making than low empathizers (i.e. mostly individuals with ASD).
Conclusions:
Our results evidently show that empathy matters for verbal social information processing, but not for lexical semantic processing. Behavioral results reveal that individuals who scored low on the EQ had more difficulties detecting violations of speaker and message. At the neuronal level, individuals who empathize to a lesser degree showed a delayed onset of, as well as a smaller positive ERP effect, which has been related to decision-making processing (Nieuwenhuis 2005). We conclude that high-functioning individuals with ASD, who demonstrate low empathizing abilities, do not experience problems in pure linguistic processing, as indexed by the behavioral and electrophysiological results for the lexical semantic manipulation. However, differences in onset latency, as well as size of the late positive effect in the speaker identity manipulation, suggest that they do have difficulties with assigning value to social information in language processing.
References:
Baron-Cohen, S. (2001), 'The Autism spectrum Quotient (AQ): Evidence from Asperger Syndrome/High Functioning Autism, males and females, scientists and mathematicians', Journal of Autism and Developmental Disorders, vol. 31, pp. 5-17.
Baron-Cohen, S. (2004), 'The Empathy Quotient: An investigation of adults with Asperger Syndrome or High Functioning Autism, and normal sex differences', Journal of Autism and Developmental Disorders, vol. 34, pp. 163-175.
Campanella, S. (2007), 'Integrating face and voice in person perception', Trends in Cognitive Sciences, vol. 11, no. 12, pp. 535-543.
Nieuwenhuis, S. (2005), 'Decision making, the P3, and the locus coeruleus-norepinephrine system', Psychological Bulletin, vol. 131, no. 4, pp. 510-532.
Van den Brink, D. (submitted), 'Empathy matters: ERP evidence for inter-individual differences in social language processing'.
