Inversion effects for faces and objects in developmental prosopagnosia: A case series analysis

The disproportionate face inversion effect (dFIE) concerns the finding that face recognition is more affected by inversion than recognition of non-face objects; an effect assumed to reflect that face recognition relies on special operations. Support for this notion comes from studies showing that face processing in developmental prosopagnosia (DP) is less affected by inversion than it is in normal subjects, and that DPs may even display face inversion superiority effects, i.e. better processing of inverted compared to upright faces. To date, however, there are no reports of direct comparisons between inversion effects for faces and objects, investigating whether the altered inversion effect in DP is specific to faces. We examined this question by comparing inversion effects for faces and cars in two otherwise identical recognition tasks in a group of DPs (N = 16) and a matched control group, using a case series design. Although both groups showed inversion effects for both faces and cars, only the control group exhibited a significant dFIE, i.e. a larger inversion effect for faces than cars. In comparison, the DPs were not significantly more affected by inversion than the control group when assessed with a face processing task that did not require recognition. Importantly, in both settings the DPs are better with upright than with inverted faces, and on the individual level no DP was found to perform significantly better with inverted than with upright faces. In fact, the DPs are impaired relative to the control group with both upright and inverted faces and to a less extent also with upright and inverted cars. These results yield no evidence of inversion superiority in DP but rather suggest that their face recognition problem is not limited to operations specialized for upright faces.