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

AUT autism group, CON control group

^aIllusion used by Hoy, Hatton and Hare [8] but individual results for each illusion not reported

^bIllusion used by Bölte et al. [9] but individual results for each illusion not reported

^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