An essential step in understanding visual processing is to characterize the neuronal receptive fields (RFs) at each stage of the visual pathway,but RF characterization beyond V 1 simple cells remains a major challenge.Recent application of spike-triggered ovariance (STC) analysis has greatly facilitated characterization of complex cell RFs in anesthetized animals.Here we apply STC to RF characterization in awake monkey V1.We found up to 9 subunits for each cell,including one or two dominant excitatory subunits as described by the standard model,along with additional excitatory and suppressive subunits with weaker contributions.Compared to the dominant subunits,the non-dominant excitatory subunits prefer similar orientations and spatial frequencies but have larger spatial envelopes.