Fig. 1

Layout of orientation preferences in the visual cortex of a tree shrew (modified from Bosking et al. [10]). Here orientation preference is color-coded (for instance neurons in blue regions are more sensitive to vertical stimuli). Maps of sensitivity to different stimulus angles were obtained by optical imaging; summing these with appropriate complex phases yields Fig. 1: see Swindale [11]. In particular, at singular points (pinwheels), all orientations meet (see the upper right corner); for a fine-scale experimental study of the neighbourhood of such points, see [8]