Why would growing up in different surroundings change what you see?
One long-standing idea is that illusions exploit habits of everyday vision. If you grow up surrounded by straight-edged buildings, rectangular rooms, and roads that recede into the distance, your visual system learns to read certain flat patterns as depth cues. The Müller-Lyer figure may then trigger that depth-reading habit, making one line look longer. Groups whose environments contain few rectangles would, on this account, be less susceptible [5].
Cross-cultural comparisons are consistent with this: rural populations have shown a striking lack of susceptibility to at least some illusions compared with urban groups [3]. The same line of work treats culture and environment as shaping perception itself, not just how people talk about what they see [3].
What the cross-cultural differences actually look like
The differences are not all-or-nothing. Studies of Australian Aboriginal groups tested with the Müller-Lyer and horizontal-vertical illusions found that specific environmental, cultural, and ecological factors may influence how susceptible people are, and that susceptibility develops over childhood [4]. In other words, the effect is not fixed at birth; it can change as a person grows up in a particular setting.
The pattern is also illusion-specific. A group can be relatively unaffected by one geometric illusion while still showing others, which fits the idea that different illusions draw on different visual habits rather than a single general 'culture effect' [3][4].
Not everyone agrees that culture is the cause
A recent critical review challenges the cultural byproduct hypothesis directly, using the Müller-Lyer illusion as its case study. It argues against the notion that cultural factors shape susceptibility and points instead to other factors, including comparisons with nonhuman animals and the statistics of natural scenes [1]. That is a claim about explanation, not a denial that group differences exist.
So the honest answer has two layers: cross-cultural differences in illusion susceptibility are real and have been observed [3][4][5], but whether culture or environment is the cause, rather than a correlate of some broader perceptual factor, is still contested [1]. The evidence supports 'context matters' more firmly than it supports any single mechanism.
Sources used in this answer
Is visual perception WEIRD? The Müller-Lyer illusion and the cultural byproduct hypothesis.
A critical review argues against the cultural byproduct hypothesis for the Müller-Lyer illusion, pointing to nonhuman animal comparisons and natural scene statistics instead of culture as the source of susceptibility.
Visual perception theory in psychology
Discusses visual perception theory and notes that genuine cross-cultural variation in susceptibility to geometric illusions exists, with differently structured visual environments linked to different susceptibility.
Visual illusions reveal wide range of cross-cultural differences in visual perception
Comparing rural and urban populations, the study found a striking lack of susceptibility to an illusion among rural participants, indicating that culturally shaped environments can alter visual perception.
Cognitive development in Aborigines of Central Australia: concrete operations and perceptual activities
Testing Australian Aboriginal groups on the Müller-Lyer and horizontal-vertical illusions, the study found that specific environmental, cultural, and ecological factors may influence susceptibility and that it develops over childhood.
The relationship between visual illusions and cues to distance
Proposes that cultures containing few rectangles will be less susceptible to geometric illusions, linking illusion strength to distance cues and everyday visual environment.