The effect of contrast on surround influences.

<p>(A) Surround contrast tunings with fixed center contrast in macaque V1 and varying surround stimuli (reprinted by permission from the Society for Neuroscience: The Journal of Neuroscience, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003191#pcbi-1003191-g006" target="_blank">Figure 6B</a> from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003191#pcbi.1003191-Webb1" target="_blank">[35]</a>). The gray markers correspond to responses to a uniform surround at different contrast. (B) Surround contrast tunings with fixed center contrast in the sparse coding model. As with the neuron responses in (A), the model cell is most suppressed for iso-oriented surround stimuli at high contrast. (C) Center contrast tunings with fixed surround contrast in macaque V1 simple cells with varying surround orientations (data replotted from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003191#pcbi.1003191-Cavanaugh1" target="_blank">[43]</a>, <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003191#pcbi-1003191-g005" target="_blank">Figure 5A</a>). (D) Center contrast tunings with fixed surround contrast in the sparse coding model. As with the neuron responses in (C), the model cell shows that (especially at high contrast) an iso-oriented surround (asterisk markers) is more effective than an orthogonal surround (cross markers) at suppressing the response to the center alone (white circle markers). As mentioned in the text (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003191#s3" target="_blank">Discussions</a>), the lack of contrast saturation in the present sparse coding model is evident in this figure by the model response at high contrast.