The face inversion effect or the face upright effect?

The face inversion effect (FIE) refers to the observation that presenting stimuli upside-down impairs the processing of faces disproportionally more than other mono-oriented objects. This has been taken as evidence that processing of faces and objects differ qualitatively. However, nearly all FIE studies are based on comparing individuation of upright faces, which most people are rather good at, with individuation of objects most people are much less familiar with individuating (e.g., radios and airplanes). Consequently, the FIE may mainly reflect differences between categories in how they are processed prior to inversion, with within-category discrimination of upright faces being a much more familiar task than within-category discrimination among members belonging to other object classes. We tested this hypothesis by comparing inversion effects for faces and objects using object recognition tasks that do not require within-category discrimination (object decision and old/new recognition memory tasks). In all tasks (seven with objects and two with faces) we find credible inversion effects, but in no instance were these effects significantly larger for faces than for objects. This suggests that the FIE can be a product of familiarity with the type of identification process required in the upright conditions rather than some process that is selectively affected for faces when stimuli are inverted.

Lateralization of word and face processing in developmental dyslexia and developmental prosopagnosia.

In right-handed adults, face processing is lateralized to the right hemisphere and visual word processing to the left hemisphere. According to the many-to-many account (MTMA) of functional cerebral organization this lateralization pattern is partly dependent on the acquisition of literacy. Hence, the MTMA predicts that: (i) processing of both words and faces should show no or at least less lateralization in individuals with developmental dyslexia compared with controls, and (ii) lateralization in word processing should be normal in individuals with developmental prosopagnosia whereas lateralization in face processing should be absent. To test these hypotheses, 21 right-handed adults with developmental dyslexia and 21 right-handed adults with developmental prosopagnosia performed a divided visual field paradigm with delayed matching of faces, words and cars. Contrary to the predictions, we find that lateralization effects in face processing are within the normal range for both developmental dyslexics and prosopagnosics. Moreover, the group with developmental dyslexia showed right hemisphere lateralization for word processing. We argue that these findings are incompatible with the specific predictions of the MTMA.

Face recognition in developmental dyslexia: evidence for dissociation between faces and words.

Developmental dyslexia is primarily a reading disorder, but recent studies have indicated that face processing problems may also be present. Using a case-series approach, we tested face recognition and visual word recognition in 24 high school students diagnosed with developmental dyslexia. Contrary to previous findings, no face recognition problems were found on the group-level. Rather, a significant classical dissociation with impaired word reading and normal face recognition was demonstrated on a group-level and for six individuals with developmental dyslexia. However, four individuals with dyslexia did show face recognition problems. Thus, while problems in face recognition can be present in developmental dyslexia, the dissociation strongly suggests that face recognition can also be preserved. Combined with previously reported dissociations between face and word recognition in developmental prosopagnosia, this constitutes a double dissociation.