Fig. 1
Examples of blur in natural images and stimuli used to explore selectivity for shape and blur. a, b Examples of different types of blur in natural scenes. a Focal blur (white arrows) conveys information about depth while shading blur (red arrows) conveys information about 3D structure. b Penumbral blur is associated with cast shadows (blue arrows); during grouping, cast shadows do not interfere with perception of physical object boundaries and shading. c–e Stimulus set used to assess tuning for shape and blur in V4 neurons. c A standard set of 51 shapes were used to assess shape selectivity of V4 neurons. Stimulus size is defined relative to the diameter of the large circle (black arrow). d Each shape was presented at up to 8 unique orientations at 45° increments; all rotations for one example shape are shown. For shapes with radial symmetry, duplicates were excluded. e To assess tuning for blur, a subset of preferred and non-preferred shapes were presented at up to 9 levels of Gaussian blur (see Methods: ‘Visual stimulation’). Example stimuli β ≥ 0.32 were cropped here for display purposes
