The discovery of visual field maps in human can be traced to neurological cases, arising from war injuries, described and analyzed independently by Tatsui Inouye (a Japanese Ophthalmologist) and Gordon Holmes (a British Neurologist). They observed correlations between the position of the entry wound and visual field loss (see Fishman, 1997 for an historical review).
Areas of visual cortex are sometimes defined by their retinotopic boundaries, using a criterion that states that each area should contain a complete map of the visual field. However, in practice the application of this criterion is in many cases difficult (Rosa, 2002). Those visual areas of the brainstem and cortex that perform the first steps of processing the retinal image tend to be organized according to very precise retinotopic maps. The role of retinotopy in other areas, where neurons have large receptive fields, is still being investigated (Wandell et al., 2005).
Visual field maps (retinotopic maps) are found in many mammalian brains, though the specific size, number, and spatial arrangement of these maps can differ considerably between species.
Retinotopic maps in cortical areas other than V1 are typically more complex, in the sense that adjacent points of the visual field are not always represented in adjacent regions of the same area. For example, in the second visual area (V2), the map is divided along an imaginary horizontal line across the visual field, in such a way that the parts of the retina that respond to the upper half of the visual field are represented in cortical tissue that is separated from those parts that respond the lower half of the visual field. Even more complex maps exist in the third and fourth visual areas V3 and V4, and in the dorsomedial area (V6). In general, these complex maps are referred to as second-order representations of the visual field, as opposed to first-order (continuous) representations such as V1 (Rosa, 2002).