Abstract
Habak, Wilkinson and Wilson (2008, Vision Res, 48(1), 9-15) reported that face identification accuracy was lower in older subjects than younger subjects, especially for faces presented at different viewpoints. In addition, they found that identification accuracy for faces presented in different viewpoints improved in younger subjects, but not older subjects, as stimulus duration increased from 500 to 1000 ms. This result led Habak et al. to propose that the accumulation of information used to refine neural representations saturates earlier in the older visual system than in the younger visual system. However, Habak et al. used artificially constructed stimuli that differed in outer contour and hair in addition to the geometry of internal features, and may not have been discriminated on the basis of facial features per se. We therefore investigated the effect of stimulus duration in older (n=8) and younger (n=8) observers using pictures of faces that differed in viewpoint but had identical outer contours and no hair, forcing subjects to base identification on internal facial features. Observers viewed a high-contrast target face for 250ms, 500ms, 1000ms, or 2000ms followed by a 10-face choice response. Faces in the response window were presented in fronto-parallel view; target faces were presented at one of several oblique viewpoints. A repeated measures ANOVA revealed significant main effects of age (p<0.001) and duration (p<0.0001), but the age x duration interaction was not significant (p=0.28). Moreover, contrary to Habak et al, we found significant linear trends in both younger (p<0.05) and older (p<0.001) observers, and performance did not reach an asymptote in either group, even with durations up to 2000 ms. Thus, although older observers performed worse than younger observers, both groups accumulated stimulus information across time at similar rates, calling into question the neural saturation hypothesis as a general explanation of age-related face perception deficits.