Objectives: The current study investigated subtle details of the use of facial information for identity recognition, using non-verbal mental age to assess changes in biases over developmental time in ASD and typically-developing (TD) controls. The objective of this comparison was to determine whether the two groups relied on similar facial information for identity recognition at any point in development, and if these biases followed similar trajectories with increasing mental age.
Methods: Thirty-two males between the ages of 7 and 15 completed the study. Fifteen were diagnosed with ASD, the remaining seventeen being TD controls. Participants completed a face identity recognition task in which they first learned new faces and then these faces were presented with noise masks covering low, middle and high spatial frequency bands. Lower accuracy when a particular spatial frequency band was masked would imply that this band was used during face recognition.
Results: The use of each spatial frequency was plotted over developmental time for each group. In the TD group, an early bias toward high spatial frequencies decreased significantly with increasing mental age (Adj. R2 = .48, p =.001). Participants with the highest mental ages showed an adult-like bias toward middle spatial frequencies for upright but not inverted faces. By contrast, individuals with ASD did not show a bias to one spatial frequency band for upright faces at any stage of development. Middle and high spatial frequencies were equally important for those with lower mental ages, while none of the three spatial frequency bands were used preferentially by participants with higher mental ages.
Conclusions: Our novel findings for upright face recognition in ASD challenge earlier claims regarding a local bias, as would have been suggested by a reliance on high spatial frequencies. In addition, individuals in this group followed different developmental pathways from TD controls, who specialized over developmental time toward a band of middle spatial frequencies for identity recognition in upright trials. The failure to specialize toward the optimal band of spatial frequencies for face recognition could be the result of a lack of early interest in faces, and therefore reduced face-specific experience, in ASD compared to TD controls.
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