1. What is the difference between sensation and perception?
2. Which of these two phenomena is most likely to be culturally relative?
KEY TERM
Optical illusions.
Pictures or objects that create false visual impressions.
Optical illusions and carpentered worlds
Brunswik (1956) helped develop this alternative explanation. He suggested that people living in visually distinct environments (forests, cities, open plains) necessarily perceive the world (and therefore visual illusions) in different ways because the ecology and architecture (or lack of it) in their surroundings prime them differently for dealing with incoming sensory information. As in the hot–cold paradox, experience paves the way for diverse perceptions. For Brunswik the development of diverse perceptual habits in response to diverse physical surround- ings is a matter of environmental adaptation. Developing differing ways of seeing the world in response to experience has considerable sur- vival value. A drawback of such adaptations is that incoming informa- tion can sometimes be misinterpreted due to the inference habits we develop in response to our surroundings. Visual illusions are cunning devices for provoking such misinterpretations. Segall et al. (1990, p. 73) articulate this ecology-based view of the development of culturally relative perceptual habits:
If human groups differ in their visual inference systems, it is because their environments differ.
They tested this maxim using the carpentered world hypothesis (Figure 6.4) and the front-horizontal foreshortening hypothesis (Figure 6.5).
They also compared illusion-susceptibility in samples from different
The carpentered world hypothesis states that people who grow up in carpentered environments (with rectangular walls, floors, ceilings) perceive the world differently from those whose environments have alternative ecologies. Being surrounded by walls, floors and ceilings produces distinct perceptual habits. For example, it may lead to the habitual perception of the obtuse and acute angles in (2D) drawings of parallelograms as though they belonged to (3D, wall-like) rectangles extending into space. Carpentered-world dwellers are thus likely to be more susceptible to the Sander parallelogram illusion (below). Why?
Because they would misjudge A to be longer than B, since they perceive the (2D) parallelogram’s angles as though belonging to a (3D) rectangle extending into space.
Figure 6.4 Carpentered world hypothesis
cultural groups by using the Sander Parallelogram (see Figure 6.4), horizontal–vertical (see Figure 6.3) and Müller-Lyer illusions (see Figure 6.2). They wanted to know whether groups from different ecol- ogies would vary in their susceptibility. Over 1800 participants were tested, predominantly from Africa, though North Americans and the Filipinos also participated. There were three westernised or European groups, including South Africans of European descent and North American undergraduates. Among the non-westernised Africans were Bayankole open country dwellers and Bete forest dwellers. Findings generally supported the link between perceptual habits and cultural–
ecological differences.
• Cross-cultural differences in mean illusion-susceptibility showed up on all three illusions, so the likelihood of being misled seemed to be related to cultural background.
• On the Sander parallelogram and the Müller-Lyer illusion, westernised participants were most susceptible.
• On the horizontal–vertical illusion the Bayankole were more susceptible than westerners, while the Bete showed fewest illusion- supported responses.
Two aspects of the findings especially support the association between illusion-susceptibility and the shape of samples’ surroundings. First, westerners’ extra susceptibility to the Sander parallelogram supports the predictions of the carpentered world hypothesis (see Figure 6.4).
Vertical lines are often perceived as horizontal lines projected into the distance. Illustrators use vertical lines in this way, as in this representation of a football field.
Vertical line A represents the field’s halfway line – a horizontal line projected into the distance.
Front-horizontal foreshortening hypothesis predicts that the physical environment we habitually experience affects how we perceive these indicators of distance. People who live in open spaces or flat planes will have different perceptions from those who live in restricted environments, such as forests. Open-space dwellers will habitually perceive vertical lines as representing horizontal lines projected into the distance. For forest dwellers, this will not be the case. These ecologically based differences in perception are likely to yield different responses to the horizontal-vertical illusion (Figure 6.4). According to front-horizontal foreshortening, open-space dwellers will be most susceptible.
Figure 6.5 Front-horizontal foreshortening hypothesis
Second, on the horizontal–vertical illusion, open country dwelling Bay- ankole’s extra susceptibility, coupled with the (forest dwelling) Bete’s lesser susceptibility, supports the predictions of the front-horizontal foreshortening hypothesis (see Figure 6.5). Segall et al. (1990, p. 77) concluded:
These findings accorded well with a theory that attributes perceptual tendencies to ecologically valid inference habits.
Segall et al.’s data offer an explanation for Rivers’ finding that Europe- ans were most susceptible to Müller-Lyer, yet less susceptible to the horizontal–vertical illusion (Matsumoto & Juang, 2004). The carpen- tered world and front-horizontal foreshortening hypotheses can be used to shed retrospective light on Rivers’ apparently unexpected find- ings. Subsequent research also supports an environmental theory of differential illusion-susceptibility. Brislin and Keating (1976) built enlarged, wooden, three-dimensional versions of Müller-Lyer and found inhabitants of uncarpentered environments (in Pacific Microne- sian, Melanesian and Polynesian islands) to be less susceptible than North Americans, as Segall et al. would predict.
Limitations of Segall’s theory
1 Age before ecology
Support for Segall et al.’s ideas is not universal. Stewart (1973) and Weaver (1974) both found susceptibility to the Sander parallelogram and Müller-Lyer illusions to decline with age. This is puzzling, since the carpentered world hypothesis would predict that increased exposure to carpentry (with age) would increase susceptibility (Segall et al., 1999).
2 Analytic sophistication
It has been suggested that as children grow older, the perceptual habit-forming effects of the environment are overridden by the acquisition of more sophisticated perceptual abilities. These matur- ational changes enable older children and young adults to overcome any effect that ecologies may have on illusion susceptibility (Berry, 1969; Dasen, 1972). This would lead to the decline of illusion susceptibility with age.
3 Retinal pigmentation
Jahoda (1971) explored a biological explanation for cultural differ- ences in illusion-susceptibility, based on retinal pigmentation. Levels of retinal pigmentation affect the transmission of blue light, but not
red. Africans have higher pigmentation levels than do Northern Europeans. Jahoda found that when presented with blue and red versions of the Müller-Lyer illusion, Scots were equally susceptible to the two, yet Malawians’ susceptibility varied with colour. This sug- gests that physiology, not ecology, may be at the root of variations in susceptibility.
All of this suggests that factors besides environment and ecology are influential in the development of perceptual habits. Yet Segall et al.’s ecological theory is still taken seriously and has partial support. More- over, further evidence of cultural relativity in visual perception comes from research into our interpretation of pictures that are not optical illusions.
Pictorial perception and culture
Comic-book connoisseurs will know the cartoonist’s convention of rep- resenting people turning their heads in shock or disbelief by showing the head in various stages of rotation. You could call this the cartoon- ist’s take on a ‘double-take’. Yet on seeing such an illustration one group of South African Bantu schoolchildren thought the boy pictured was a three-headed freak (Duncan et al., 1973). Perhaps then, this artistic convention is not culturally universal. Cultural relativism in the portrayal of the (three-dimensional) world in (two-dimensional) pictures presumably reflects regional artistic conventions. Furthermore, artistic styles differ historically as well as culturally. For instance, the conven- tion of drawing two lines in convergence (like tramlines) to convey dis- tance only emerged in European art during the fifteenth- to seventeenth-century Renaissance period (Berry et al., 2002). Argu- ably, then, habits of picture perception involve skills that are taught and learned differently in different places and at different times. Support for picture perception as a function of culturally learned codes comes from Winter (1963), who observed South African miners misinterpreting ‘red for danger’ warnings on safety posters. Conventions in colour coding and the use of depth cues (see key concept overleaf) in pictures are not, it seems, universally applied across cultures (Gombrich, 1977).
Arguably, cultural differences in picture perception relate to more general differences in cognition. When shown photographs and asked to describe them, Japanese participants were more likely to convey an overall (holistic) impression of the contents, including background and contextual elements, as compared with North Americans, who focused on central, de-contextual elements (Nisbett, 2003).
Another factor that has been linked to cultural differences in picture perception in general (and the use of depth cues in particular) is school- ing. Correlations between levels of western-style schooling and the application of depth cues in picture perception have often been observed (Duncan et al., 1973). Deregowski (1972) wanted to know more about cultural variations in picture perception. He reviewed sev- eral cross-cultural studies in which the same pictures were shown to people from different cultural groups and their interpretations recorded (see key study).