Elsevier

Neuropsychologia

Volume 47, Issue 5, April 2009, Pages 1323-1331
Neuropsychologia

Startle modulation in autism: Positive affective stimuli enhance startle response

https://doi.org/10.1016/j.neuropsychologia.2009.01.025Get rights and content

Abstract

Behavioral evidence suggests that emotion processing deficits in individuals with autism spectrum disorders (ASD) may occur at the level of basic (early, rapid, automatic) affective processes. Consistently, neurological evidence indicates that key brain areas associated with basic affective processing are atypical in ASD. The current study sought to better specify these deficits by comparing different components of basic affective processing in 14 adolescents and adults with ASD and 14 typical controls matched for age and verbal ability. Participants viewed affective pictures, and their responses were assessed with (i) affective eyeblink startle modulation, an indicator of the brain's aversive motivational system; (ii) facial electromyography, an online indicator of implicit valence appraisal; and (iii) self-report, an indicator of overt valence appraisal. The results show that in contrast to the typical pattern, in which exposure to negative stimuli increases startle whereas exposure to positive stimuli decreases startle, individuals with ASD showed startle potentiation to both positive and negative stimuli. Atypical potentiation during positive stimuli occurred despite individuals with ASD demonstrating appropriate implicit valence appraisals, reflected in their facial EMG responses, and appropriate overt appraisals, reflected in their self-reported ratings of the stimuli. Potentiation of startle to both positive and negative stimuli suggests a disruption in basic affective processes in ASD at the level of the early motivational response. This atypical pattern of responses has implications for understanding social and emotion deficits in ASD and calls for further investigation of basic affective processes.

Section snippets

Motivational response system: affective startle modulation

The modulation of a startle response during exposure to affective stimuli has been used extensively to study aversive and appetitive response systems in the brain (Davis, 1997; LeDoux, 2000). This method has several benefits. Responses are not contingent upon motor planning, language, or participants’ voluntary actions (Ornitz, Lane, Sugiyama, & de Traversky, 1993). Startle modulation is evident across the lifespan, from infancy through adulthood (Balaban, 1995; McManis, Bradley, Berg,

Spontaneous online evaluation: facial electromyography

To assess online, implicit evaluation of stimuli, the current study assessed automatic activation of the facial muscles associated with the expression of emotion (Cacioppo, Martzke, Petty, & Tassinary, 1988; Dimberg, 1982; Winkielman & Cacioppo, 2001). In particular, activity over the corrugator supercilii, which knits the brow as in a frown, typically shows greater activity during exposure to negative stimuli. The zygomaticus major, which pulls the lips back as in a smile, shows increased

Overt evaluations: self-report of experienced affect

We also collected self-reports of experienced affect. This is important because what people consciously feel and explicitly report after viewing a stimulus may differ from the basic motivational response to the stimulus (assessed via startle) and from the implicit valence appraisals (assessed via facial EMG) or both. Based on evidence that people with ASD comprehend emotional situations and express a full range of emotion (Sigman & Ruskin, 1999), we did not expect significant group differences

Participants

Fourteen high functioning adolescents and adults with ASD were matched to a group of 14 typically developing individuals on chronological age and verbal ability as measured by the Peabody Picture Vocabulary Test (Dunn & Dunn, 1997) (see Table 1). Participants were recruited from Denver, Colorado, area clinics, support groups, community advertisements, and the university research pool. Participants were paid or received course credit. Consent and/or assent were obtained from all participants or

Startle modulation

As described above, affective startle modulation taps the functioning of the basic appetitive-defensive motivational system. Based on reports of psychological and neurological atypicalities with core affect functioning, we predicted that participants with ASD would show atypical affective startle modulation. We first examined whether there were any effects related to the social content of the pictures. There were no significant main effects or interactions with the other factors for social

Discussion

The current study assessed startle modulation, facial EMG, and self-reported affective responses during emotional stimuli to examine different components of affective processes in individuals with ASD and typical controls. There were three important findings.

First, and most critically, the results supported our prediction of atypical startle modulation, with ASD individuals showing startle potentiation to both positively and negatively valenced stimuli. This pattern contrasts with typical

Conclusion

In typically developing individuals, a combination of affective processes that mark certain stimuli as important or salient and direct action towards relevant stimuli typically support appropriate social and emotional behavior. Consequently, deviations in those processes may result in functional deficits. The present study reveals that focused examination of separate components of affective processes can enhance understanding of differences related to ASD, revealing both strengths and deficits.

Acknowledgements

This research was conducted at the University of Denver, CO, USA and supported by a grant from the National Alliance for Autism Research to McIntosh and Winkielman. We appreciate the assistance and input of Bruce Pennington, Yuko Munakata, Adi Curiel, John Curtin, Mark Starr, Sally Rogers and the time and commitment of the individuals who participated in this research.

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