The problem of being bad at faces

Abstract

Developmental prosopagnosia has received increased attention in recent years, but as yet has no confirmed genetic or structural markers. It is not certain whether this condition reflects simply the low-end of the spectrum of normal face recognition, an 'under-development', or a pathologic failure to develop such mechanisms, a 'mal-development'. This difference in views creates challenges for the diagnosis of developmental prosopagnosia by behavioural criteria alone, which also vary substantially between studies, with secondary effects on issues such as determining its prevalence. After review of the literature and the problems inherent to diagnoses based solely on behavioural data, we propose as a starting discussion point a set of two primary and four secondary criteria for the diagnosis of developmental prosopagnosia.

Keywords: Development; Diagnosis; Face recognition; Perception; Prosopagnosia.

Figure 1

Two views of developmental prosopagnosia. The graphs plot hypothetical proportions of subjects in the population as a function of their face recognition skill, which increases along the x-axis. A. The normative view. Face recognition is a continuous, normally distributed ability in the population, and those with developmental prosopagnosia (DP) are those on the low-end of this spectrum. B. The pathologic view. In addition to this normally distributed ability, there is a discrete population of developmental prosopagnosia subjects (bold curve, labeled DP) with different face processing mechanisms. These overlap with the low end of the distribution of the normal population.

Figure 2

A hypothetical qualitative difference in perceptual performance that might distinguish developmental prosopagnosia from those bad at faces. Suppose that there is some perceptual measure A that is a linear function of face recognition skill in the normal population, so that those on the low end of the normal distribution still follow this linear function. If the developmental prosopagnosic subjects performed worse on measure A than predicted by the linear relationship in healthy subjects, then they would occupy a part of this performance space that was distinct from that containing those simply bad at faces (the dashed oval).