Cultural differences in perceptual reorganization in US and Pirahã adults

Abstract

Visual illusions and other perceptual phenomena can be used as tools to uncover the otherwise hidden constructive processes that give rise to perception. Although many perceptual processes are assumed to be universal, variable susceptibility to certain illusions and perceptual effects across populations suggests a role for factors that vary culturally. One striking phenomenon is seen with two-tone images-photos reduced to two tones: black and white. Deficient recognition is observed in young children under conditions that trigger automatic recognition in adults. Here we show a similar lack of cue-triggered perceptual reorganization in the Pirahã, a hunter-gatherer tribe with limited exposure to modern visual media, suggesting such recognition is experience- and culture-specific.

Figure 1. All stimuli used in the experiment.

Row 1 shows warm-up items with simpler transformations: houseboat and jaguar. Rows 2–6 show test items. Left column: squirrel monkey, alligator, woman in hut, sloths, older man. Right column: ocelot, howler monkey, toucan, tapir, fisherman. Cue items are shown to the left of test items. For full size stimuli, see Figures S1–S12 in File S1 in order to recreate viewing conditions under which recognition is trivial for western adults.

Figure 2. Upper left: an example two-tone stimulus from the Pirahã study.

Subjects were first presented the two-tone alone and asked to point to the location of an eye or person in the image. Red circles mark where Pirahã participants indicated an eye, and numbers indicate individual participants. Circles outside the image show responses of the form “there are no eyes here.” Only two participants (2,8) correctly pointed to an eye in this image during Stage 1. Upper right: Performance of Pirahã participants on the original photo, which was presented alone after the two-tone image was removed from view. All participants correctly pointed to one of the two eyes. Bottom row: performance of Pirahã participants on the two-tone image during Stage 3, when it was shown side-by-side with the photo. Two Pirahã participants succeeded uncued (2 & 8), two more succeeded with the photo present, indicating reorganization (3 & 4), and five did not show evidence of photo-triggered perceptual reorganization (1, 5, 6, 7, 9).

Figure 3. Summary of results from the Pirahã and the two U.S. control groups.

Bars show participants' accuracy on photographs, practice items, and candidate reorganization trials (those trials on which the two-tone image was not recognized uncued). Error bars show the standard error of the mean.

Figure 4. Example of misaligned photo and two-tone image pair.

This image shows the actual degree of misalignment, but participants were never informed about the degree or direction of misalignment or even if any misalignment or distortion occurred between the images. The intersection of the horizontal and vertical red lines shows the same geometric point relative to the frame of the images. Participants could identify these matching points even without reference to the underlying images (for example, if the cards were blank). Actual corresponding features are shown with the red dot, and were displaced 1.8 cm in a direction that varied from image pair to image pair.