Published in Annual Meeting, Neuroscience, (602.03), Nov 2013.
We recently reported that neurons in V2 respond selectively to synthetic stimuli whose higher-order statistical dependencies are matched to those in photographs of naturally- occurring visual texture. V2 cells, but not V1 cells, respond more strongly to these “naturalistic” stimuli than to “noise” stimuli with matching power spectra, an effect we term “modulation” (Freeman, Ziemba et al., Nature Neurosci., 2013). We found that this modulation was often stronger when stimuli extended beyond the classical receptive field. Here, we examine in more detail the size dependency of these effects by measuring responses to both naturalistic and noise stimuli of a range of sizes. We observed a variety of behaviors in V2 neurons. Some exhibited significant modulation at small sizes, revealing sensitivity to naturalistic stimuli within the classical receptive field. For most neurons, however, modulation was modest when the noise and naturalistic stimuli were presented in small patches, and gradually strengthened with increasing size, suggesting a special role for regions outside the classical receptive field center. To better characterize this effect, we fit a ratio-of-Gaussians model to size tuning data for each stimulus class. This analysis reveals that the suppressive (“surround”) Gaussian was, on average, weaker for naturalistic than for noise stimuli. This attenuation of surround suppression accounts for the changes in size tuning better than a change in gain or extent of the receptive field center. The mechanisms responsible for the modulation to naturalistic stimuli in V2 neurons may therefore pool across areas of the visual field that are larger than the conventional classical receptive field.