• AQ.
• Autism-spectrum quotient Questionnaire
• Autistic-like traits
• inter-individual differences
• local-global
• psychophysics
• pupillometry

In my thesis project, I explored the inter-individual variability of perception. For this aim, I exploited two main methodologies: psychophysics (with both visual and haptics stimuli) and pupillometry (the measurement of subtle variations of the diameter of our eye-pupils). My experiments included participants of different ages (from 6-year-olds to adults) and with different neurocognitive profiles (neurotypical, with diagnosis of Autistic Spectrum Disorder or with unrelated disabilities). The following conclusions may be drawn from the results of my research and the literature review that preceded it:

Chapter 1 (literature review) highlights the lack of consensus on the best methodological approach for measuring perceptual variability, which is known to occur both within individuals (with age) and across individuals (particularly linked with autistic-like traits).
Chapter 2 presents an experiment comparing pupillometric and psychophysical findings for a visual illusion of size (Ponzo illusion). It shows that pupil responses are sensitive to illusory changes in perceived size of the light source and that these subtle pupil modulations are a sensitive index of illusion susceptibility, which correlates with autistic-like traits in a sample of neurotypical adults.
Chapter 3 reports an extension of the study by Turi et al. (Turi, Burr, & Binda, 2018), in which we confirmed a tight relationship between inter-individual differences in pupillary responses to an illusory bistable stimulus and autistic-like traits in a sample of neurotypical adults. We show that this correlation is still reliably found in passive viewing non-illusory conditions.
Chapter 4 presents an experiment using a simplified child-friendly pupil-based test in a population of children with and without diagnosis of Autistic Spectrum Diseases (ASD). We replicate previous evidence (Binda, Pereverzeva, & Murray, 2013) that pupil responses are sensitive to the high-level content of visual images: despite equal luminance, pictures of the sun evoke stronger constriction than pictures of the moon and control images. Contrary to the predictions from theories that assign lower weight to contextual and prior information in autistic individuals (Pellicano & Burr, 2012), we find that this effect is equally strong irrespective of autistic traits or autism diagnosis. While this shows the limits of the pupillometric approach, it also testifies to its selectivity – future work will need to define the range of stimuli and tasks for which pupil-based testing provides meaningful indices of perceptual variability.
Chapter 5 reports the last experimental study, in which we compared the developmental path of local-global preferences across sensory modalities: vision and haptics. We found that the two modalities share a gradual shift from local to global preference from childhood to adulthood, but the haptic modality shows a more marked local preference. This opens interesting questions relating local preference with serial exploration (typical of haptics but not of vision) and on the way potential cross-modal conflicts in local-global preference are handled by our perceptual system – to be addressed in future work.
Overall, the data presented in this thesis provides new evidence on the importance to quantify inter-individual variability in local-global perception, both with objective biomarkers (such as pupillary responses) and with psychophysics tools. At the same time, my research project opened several outstanding questions, which might lay the foundations for future advances in this topic.