Computational diversity in complex cells of cat primary visual cortex.

A previous study has suggested that complex cells perform a MAX-like operation on their inputs: when two bar stimuli are presented within the receptive field, regardless of their relative separation, the cell's response is similar in amplitude to the larger of the responses elicited by the individual stimuli. This description of complex cells seems at odds with the classical energy model in which complex cells receive input from multiple simple cells with overlapping receptive fields. The energy model predicts, and experiments have confirmed, that bar stimuli should facilitate or suppress one another depending on their relative separation. We have recorded intracellularly from a population of complex cells and studied their responses to paired bar stimuli in detail. A wide range of behavior was observed, from the more classical separation-dependent interactions to purely MAX-like responses. We also found that the more MAX-like a cell was, the broader its spatial-frequency tuning as measured with drifting gratings. These observations are consistent with energy models in which classical complex cells receive input from simple cells with similar preferred spatial frequencies, and MAX-like complex cells receive input from simple cells with disparate preferred spatial frequencies. Generalized energy models, then, can account for diverse modes of computation in cortical complex cells.