Elizabeth Louie, David Bressler, and David Whitney (2007)
Holistic crowding: selective interference between configural representations of faces in crowded scenes.
Journal of Vision 7(2):1-11.
It is difficult to recognize an object that falls in the peripheral visual field; it is even more difficult when there are other objects surrounding it. This effect, known as crowding, could be due to interactions between the low-level parts or features of the surrounding objects. Here, we investigated whether crowding can also occur selectively between higher-level object representations. Many studies have demonstrated that upright faces, unlike most other objects, are coded holistically. Therefore, in addition to featural crowding within a face (Martelli, Majaj, & Pelli, 2005), we might expect an additional crowding effect between upright faces due to interference between the higher-level holistic representations of these faces. In a series of experiments, we tested this by presenting an upright target face in a crowd of additional upright or inverted faces. We found that recognition was more strongly impaired when the target face was surrounded by upright compared to inverted flanker (distractor) faces; this pattern of results was absent when inverted faces and non-face objects were used as targets. This selective crowding of upright faces by other upright faces only occurred when the target-flanker separation was less than half the eccentricity of the target face, consistent with traditional crowding effects (Bouma, 1970; Pelli, Palomares, & Majaj, 2004). Likewise, the selective interference between upright faces did not occur at the fovea and was not a function of the target-flanker similarity, suggesting that crowding-specific processes were responsible. The results demonstrate that crowding can occur selectively between high-level representations of faces and may therefore occur at multiple stages in the visual system.