# Table 1 Summary of previous studies assessing susceptibility to visual illusions in autistic individuals

Illusion and example Study Method Summary of group differences in susceptibility
Ebbinghaus (or Titchener circles)
Happé [7] Same/different AUT < CONa,b
Ropar and Mitchell [10] Method-of-adjustment AUT = CON
Ropar and Mitchell [10] Same/different AUT = CON
Ropar and Mitchell [12] Method-of-adjustment AUT ≈ CONc
Schwarzkopf et al. [16] Forced choice AUT = CON
Müller-Lyer
Happé [7] Same/different AUT = CONa,b
Ropar and Mitchell [10] Method-of-adjustment AUT > CON
Ropar and Mitchell [10] Same/different AUT = CON
Ropar and Mitchell [12] Method-of-adjustment AUT = CON
Ishida et al. [13] Method-of-adjustment AUT = CON
Ponzo
Happé [7] Same/different AUT < CONa,b
Ropar and Mitchell [10] Method-of-adjustment AUT = CON
Ropar and Mitchell [10] Same/different AUT = CON
Ropar and Mitchell [12] Method-of-adjustment AUT = CON
Ishida et al. [13] Method-of-adjustment AUT < CON
Illusory (Kanisza) figures
Happé [7] “How many triangles?” AUT < CONa
Milne and Scope [15] Forced choice AUT = CON
Poggendorff
Happé [7] “Which line joins up with which?” AUT < CONa,b
Hering
Happé [7] “Are lines straight or curvy?” AUT < CONa,b
Horizontal-vertical (or Hat)
Ropar and Mitchell [10] Method-of-adjustment AUT < CON
Ropar and Mitchell [10] Same/different AUT = CON
Ropar and Mitchell [12] Method-of-adjustment AUT < CON
Shepard’s tables
Mitchell et al. [14] Method-of-adjustment AUT < CON
1. AUT autism group, CON control group
2. aIllusion used by Hoy, Hatton and Hare [8] but individual results for each illusion not reported
3. bIllusion used by Bölte et al. [9] but individual results for each illusion not reported
4. cIndividuals with Asperger’s syndrome and typically developing children aged 11 were less susceptible to the illusion than those with autism, typically developing children aged 8 and children with moderate learning difficulties