No Maturational Effects In A Visuo-Tactile Cross-Modal Size Discrimination Task In ASD

Background: Autism Spectrum Disorders (ASD) are currently characterized by a triad of impairments including social dysfunction, communication deficits and perseverative behaviours. Expected changes in the DSM-V will include unusual sensory reactions and interests as part of one of two diagnostic criterions. Many theories suggest that anomalies in basic sensory processing might underlie atypical sensory behaviours in ASD and explain some of their current core symptoms. However, there is a lack of empirical evidence to support this hypothesis. Previous findings have shown anomalies in audio-visual speech integration (e.g., Bebko et al., 2006) and auditory-somatosensory integration (Russo et al., 2010) in autistic children. To our knowledge, no study has looked at the developmental trajectory of multisensory processing in ASD.

Objectives: The general objective of the study was to investigate multisensory processing differences in ASD children and adolescents in a visuo-tactile cross-modal size discrimination task. A more specific aim was to study the development of visuo-tactile cross-modal abilities in ASD children and adolescents.

Methods: 26 ASD children and adolescents (aged 5 to 18 years) with typical intelligence and 20 age-, gender- and PIQ-matched typically developing (TD) children and adolescents discriminated ecological coin-like stimuli on the basis of tactile (T), visual (V) or cross-modal (CM) visuo-tactile information. In a simultaneous two-alternative forced-choice task, performances were measured based on difference thresholds, which evaluate the smallest difference at which observers are capable of discriminating size. The correct answer was considered as the identification of the bigger of two stimuli. An adaptive staircase protocol (two down/one up) was used in order to adjust the difference among stimuli between trials relative to the subject’s answer.

Results: Preliminary results showed that for both groups difference thresholds were lower (better performance) for the visual versus the tactile and cross-modal conditions. However, ASD children and adolescents, as a group, were less capable to discriminate stimuli in all three conditions, compared to TD children and adolescents. The biggest difference in performance was found in the CM condition, with ASD participants being significantly less capable to make a judgment across senses. Whereas typicals showed an improvement in performance as a function of age in all three conditions, no maturational effects were observed in the ASD group.

Conclusions: The present study corroborates and extends previous findings of anomalies in multisensory processing in ASD. A critical finding of our study seems to be the lack of maturation observed in the ASD group in their sensory processing abilities. The ASD group, unlike the TD group, did not improve as a function of age in any of the three sensory modalities. These findings therefore show the great importance of understanding how these sensory processing abilities develop over time in ASD as this may impact our understanding of their core symptoms, including their atypical sensory behaviours.