How literacy affects vision: further data on the processing of mirror images by illiterate adults

Resumo

In our former work (Kolinsky, Verhaeghe, Fernandes, Mengarda, Grimm-Cabral, & Morais, 2011), we showed that adults who remained illiterate for socio-economic reasons have difficulties at processing lateral mirror images. This probably reflects the fact that the Latin alphabet requires taking mirrorimage contrasts into account, in order to distinguish e.g., “b” from “d”, and hence that its acquisition pushes the beginning reader to “unlearn” the mirror symmetry invariance that characterizes our visual system. In addition, our results suggested that the illiterate's difficulties with orientation were not general: they had stronger difficulties with mirror images than with other orientation contrasts like rotations in the plane.

In the present study, we aimed at extending the latter result by using other materials and another task. In Experiment 1, we compared two groups of illiterates, both being required to sort circles on the basis of either their size or their orientation. Orientation contrasts involved mirror images in one group and a vertical vs. horizontal difference in the other group, angular separation being the same in both cases. Illiterates were indeed slower at sorting on orientation than on size. Yet, as labeling could have been easier with the vertical-horizontal contrast than with mirror images, in Experiment 2 we used a part-verification task in which we compared mirror images to images rotated in the plane. The illiterates' performance was worse with mirror images than with plane rotations. Thus, illiterates do not have general difficulties with orientation contrasts, but rather specific difficulties for discriminating lateral mirror images.