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Fig. 5.4. Spatiotemporal receptive fields, direction maps, and combined OR/DR maps in animals. In addition to orientation and eye of origin, neurons in V1 are selective for direction of motion. These spatial and motion preferences can be described as spatiotemporal RFs, representing the sequence of patterns that would most excite the neuron. (a) A sample such RF for a V1 cell from the cat, measured through microelectrode recording (DeAngelis, Ghose, Ohzawa, and Freeman 1999; reprinted with permission, copyright 1999 by the Society for Neuroscience; gray scale added). Sample RFs in the two-dimensional visual space at times 20, 60, 100, and 120 ms are shown on top, and a continuous integration of the RFs along the vertical (which is the preferred orientation of the neuron) is drawn in the bottom plane. The neuron's spatial preferences change systematically over time, giving it a spatiotemporal preference for a black vertical line moving horizontally to the right. (b) Spatial arrangement of such preferences in a 3.2 mm × 1.6 mm area of ferret V1: Nearby neurons prefer similar directions in a manner similar to orientation maps (measured through optical imaging and displayed using the color arrow key on top; Weliky et al. 1996, reprinted with permission, copyright 1996 by Nature Publishing Group; annotations added and DR arrows removed by interpolation). Example map features are outlined in white as in Figure 2.4. (c) Interaction of direction preferences with the orientation map (Weliky et al. 1996; reprinted with permission, copyright 1996 by Nature Publishing Group; arrows changed from black to white). The 1.4 mm × 1.1 mm subarea of V1 around the right edge of the square in (b) is colored according to orientation preference (using the color bar key above the plot). Each arrow points in the preferred direction, and its length indicates how selective the neuron is for that preference. Direction and orientation preferences tend to be perpendicular, and orientation patches are often subdivided for opposite directions of motion.