The handle of literacy: evidence from preliterate children and illiterate adults on orientation discrimination of graspable and non-graspable objects

Prior research reported an apparently developmental trajectory on mirror-image discrimination (Gregory, Landau, & McCloskey, 2011): reflections across the object principal axis (OPA) and across the external vertical axis (EVA) are hard to discriminate by children, but only OPA reflections are problematic for adults. In this study, we investigated how literacy acquisition and object visuomotor properties affect this trajectory. Six-year-old children (preliterate preschoolers vs. first graders: Experiment 1) and illiterate, ex-illiterate, and schooled literate adults (Experiment 2), searched for graspable (e.g. hammer) or non-graspable (e.g. sock) target-objects amongst orientation-contrast distractors. OPA and EVA errors were predominant in non-readers, but EVA errors dropped sharply in readers. Graspability enhanced OPA and EVA mirror-image discrimination, especially in non-readers. Thus, the reduction of EVA mirror-image errors is not driven by maturation, cognitive development, or schooling; the underlying mechanisms are mostly learning to read and to a smaller extent the operation of the dorsal stream.