Movies of natural scenes were presented through an aperature that was either 1X, 2X, or 3X the size of the classical receptive field (CRF).  This manipulation has previously been shown to cause V1 neurons to increase their sparseness

Figure 2.  Two examples of movies presented through 1X, 2X, and 3X of the classical receptive field (CRF) aperatures.  By clicking on the movies below, you can watch the movies and hear the V1 neuron discharge under the different conditions.  Note that the increase in sitmulation size from 1X to 3X results in a marked sparsening of the discharge: spikes are confined to a smaller number of movie frames in the 3X condition versus the 1X presentation.