Single neurons in macaque area V4 were recorded during an attentionally demanding free-viewing visual search task. Eye movements and neuronal activity were recorded while the subject inspected a sample target (a 3-6 deg B&W natural scene photograph) for 2-3s. The subject had to report the appearance of the sample within an array of distractor photographs. Under these conditions some V4 neurons show non-spatial, pattern-specific modulations of firing rate dependent on search target (see Mazer et al; SFN Abs. 2001). To further characterize these changes, we used reverse correlation to compute spatiotemporal receptive fields (STRFs) contingent on the search target. Each STRF is a model of a cell's selectivity for stimulus orientation, spatial frequency and spatial phase. The complex statistics of visual stimuluation during free-viewing make it difficult to determine whether STRF changes reflect attentional modulation or are merely due to the spectral properties of the stimuli falling in the receptive field du...