Adjacent simple cells recorded and "isolated" simultaneously from the same microelectrode placement were usually tuned to the same orientation and spatial frequency. The responses of the members of these "spatial frequency pairs" to drifting sine-wave gratings were cross-correlates. Within the middle range of the spatial frequency selectivity curves, the responses of the paired cells differed in phase by approximately 90 percent. This phase relationship suggests that adjacent simple cells tuned to the same spatial frequency and orientation represent paired sine and cosine filters in terms of their processing of afferent spatial inputs and truncated sine and cosine filters in terms of the output of simple cells.