Complex cells as cortically amplified simple cells

The majority of synapses in primary visual cortex mediate excitation betwee n nearby neurons, yet the role of local recurrent connections in visual pro cessing remains unclear. We propose that these connections are responsible for the spatial-phase invariance of complex-cell responses. In a network mo del with selective cortical amplification, neurons exhibit simple-cell resp onses when recurrent connections are weak and complex-cell responses when t hey are strong, suggesting that simple and complex cells are the low- and h igh-gain limits of the same basic cortical circuit. Given the ubiquity of i nvariant responses in cognitive processing, the recurrent mechanism we prop ose for complex cells may be widely applicable.