Stream Segregation In Autism: An Auditory Embedded Figures Task?

Background: One of the first enhanced cognitive abilities reported in the autism literature was the superior performance of autistics in the Embedded Figures Task in vision (Shah & Frith, 1983). In audition, stream segregation paradigms can represent a well-suited counterpart to this task. Current cognitive models (Happé & Frith, 2006; Mottron et al., 2006) propose that superior disembodying ability in autistics is related to an enhanced processing of local elements. A local superiority has been observed in the auditory modality, for instance, many studies reported enhanced pitch processing in autism (Bonnel et al., 2003; Jones et al., 2009). However, the relation between superior local processing and more complex auditory cognitive tasks has not yet been investigated.

Objectives: First, we examined the ability of autistic individuals to segregate auditory sequences and to discriminate sound frequencies. Second, we explored the relation between the levels of performance in those two tasks.

Methods: Our preliminary sample included eleven non autistic and eight autistic adults, matched on age. (1) Stream segregation task (Bey & McAdams, 2002): a target melody of 6 notes was presented alone, then embedded with a distractor melody. We used four embedded conditions in which the distractor melodies are transposed by 0, 6, 12 or 24 semi-tones. Participants had to decide whether the embedded target melody was similar to the target melody presented alone. (2) Frequency discrimination task (Bonnel et al., 2003): pitches were presented in pairs and participants had to decide whether they were the same or different. In different pairs, the two sounds differed by 1, 2, 3, or 4% in pitch frequency.

Results: In the segregation task, results indicate that the autistic group performed better than the typical group when there was no transposition of the distractor (0 semitone condition), F(1,17) = 8.29, p < .01. Moreover, our results indicate that, in this condition, the typical group performed the task at chance level, which was not the case for the autistic group. In the frequency discrimination task, a main effect of increasing difficulty has been observed, F(3,53) = 25.24, p < .001. There were no significant group effect and no interaction. Then, to explore the link between these tasks, a correlation has been carried out across all participants. This analysis revealed a trend (r = 0.383 p = 0.1) which suggests that a superior ability to segregate streams might be related to the ability to discriminate frequency.

Conclusions: In this preliminary work, the autistic group presented with a superior ability to detect a simple melody embedded in a more complex auditory sequence. Thus, this task might represent a promising counterpart for the Embedded Figures Task in the auditory modality. We also suggest that this ability may be related to pitch discrimination. More subjects will be tested to validate this finding.