Spontaneous but not explicit processing of positive sentences impaired in Asperger's syndrome: Pupillometric evidence

Emotional prosody provides important cues for understanding the emotions of others in every day communication. Asperger's syndrome (AS) is a developmental disorder characterised by pronounced deficits in socio-emotional communication, including difficulties in the domain of prosody processing. We measured pupillary responses as an index of emotional prosodic processing when 15 participants with AS and 19 non-clinical control participants listened to positive, negative and neutral prosodic sentences. This occurred under a spontaneous and an explicit task instruction. In the explicit processing condition, the AS group and the non-clinical controls showed increased pupil dilations to positively and negatively intoned sentences when judging the valence of that prosodic sentence. This suggests higher processing demands for emotionally arousing information, as the effect was not found in comparison to neutrally intoned sentences. In the spontaneous processing condition, controls also responded with increased pupil dilations to positively intoned sentences, whilst individuals with AS showed increased pupil dilations to negative sentences. The latter result is further supported by diminished ratings of emotionally intense sentences in the AS group compared to healthy controls. Perception and recognition of positively valenced sentences in individuals with AS appears impaired and dependent on the general task set-up. Diminished pupil dilations in spontaneous positive processing conditions as well as reduced positive valence ratings give strong indications for a general negative processing bias of verbal information for adult individuals diagnosed with AS. (C) 2010 Elsevier Ltd. All rights reserved.