The role of complex cells in object recognition.

Primate's primary visual cortex (V1) is dominated by complex cells. This choice of nature seems puzzling, as complex cells are insensitive to spatial phase--information which is generally believed to be essential for perceptual characterization and recognition of images. Modeling complex cells as Gabor wavelet magnitudes, we have mathematically and empirically examined the information content of their responses. Our results show that in spite of phase insensitivity of individual complex cell responses, population responses contain sufficient information to capture the perceptual essence of images. A complex cell type representation seems to be not only sufficiently discriminating for object identification, but also--due to its inherent ambiguities--robust to changes in background, lighting, and small deformations.