Q.An anthropologist compares the responses of two groups to the same set of geometrical illusion figures: one group has grown up in a dense forest region with round huts, and the other has grown up in a Western city dominated by rectangular buildings. Predict, with reasons, which illusion each group is likely to be more susceptible to.

The forest-dwelling group is expected to be more susceptible to the vertical-horizontal illusion, while the city-dwelling group is expected to be more susceptible to the Muller-Lyer illusion, because of the different physical environments each group is habitually exposed to. …

This prediction can be based directly on the cross-cultural findings of Segall, Campbell, and Herskovits, who compared the responses of samples from remote African villages (with environments broadly similar to the forest-dwelling group described here) and Western urban settings (broadly similar to the city-dwelling group described here) to the same set of geometrical illusion figures, including the Muller-Lyer and vertical-horizontal illusions.

The forest-dwelling group, whose physical environment repeatedly exposes them to tall vertical objects such as trees, would be expected -- following this research -- to show greater susceptibility to the vertical-horizontal illusion, in which a vertical line is misperceived as longer than a horizontal line of the same length. The proposed explanation is that repeated, habitual exposure to genuinely tall vertical objects leads this group to develop a general perceptual tendency to overestimate vertical extent, which then carries over into how they judge the two lines in this illusion figure.

The city-dwelling group, whose physical environment is dominated by rectangular buildings and sharp right-angled corners (a so-called 'carpentered' environment), would be expected to show greater susceptibility instead to the Muller-Lyer illusion, in which a line bounded by outward-pointing (arrowhead-like, diverging) wing marks is misperceived as shorter than an identical line bounded by inward-pointing (bracket-like, converging) wing marks. The proposed explanation is that repeated, habitual exposure to enclosed, angular corners in their built environment leads this group to develop a tendency to underestimate the length of lines that end in such enclosed angles, which then carries over into how they perceive the Muller-Lyer figure. …