Critical frequencies in the perception of letters, faces, and novel shapes: evidence for limited scale invariance for faces.

Despite the common intuition that object recognition processes should be relatively scale invariant, a number of studies show that this is not the case. Using a critical-band masking paradigm, we examined the pattern of scale dependence of diagnostic spatial frequencies across a range of stimuli that varied in participants' prior experience and the 'ecological significance' of the stimuli, by which we mean the degree of universality and recency of the development of the stimulus in human culture, letters being an example of a culturally arbitrary stimulus and faces a universal one. We found scale dependence for letters, mirror-image letters, and novel shapes, consistent with prior results, as well as for inverted faces. However, upright faces showed a relatively scale-invariant pattern especially for face sizes that corresponded to those encountered in typical social interactions. This suggests an important difference between the processing of faces and other objects that may reflect their unique status as stimuli.