problem, also known as the subjective unity of perception, as "How do the brain mechanisms actually construct the phenomenal object?". Revonsuo equates this to "consciousness-related binding", emphasizing the entailment of a phenomenal aspect. As Revonsuo explores in 2006, there are nuances of difference beyond the basic BP1:BP2 division. Smythies speaks of constructing a phenomenal object ("local unity" for Revonsuo) but philosophers such as Descartes, Leibniz, Kant and James (see Brook and Raymont) have typically been concerned with the broader unity of a phenomenal experience ("global unity" for Revonsuo) – which, as Bayne illustrates may involve features as diverse as seeing a book, hearing a tune and feeling an emotion. Further discussion will focus on this more general problem of how sensory data that may have been segregated into, for instance, "blue square" and "yellow circle" are to be re-combined into a single phenomenal experience of a blue square next to a yellow circle, plus all other features of their context. There is a wide range of views on just how real this "unity" is, but the existence of medical conditions in which it appears to be subjectively impaired, or at least restricted, suggests that it is not entirely illusory. There are many neurobiological theories about the subjective unity of perception. Different visual features such as color, size, shape, and motion are computed by largely distinct neural circuits but we experience an integrated whole. The different visual features interact with each other in various ways. For example, shape discrimination of objects is strongly affected by orientation but only slightly affected by object size. Some theories suggest that global perception of the integrated whole involves higher order visual areas. There is also evidence that the posterior parietal cortex is responsible for perceptual scene segmentation and organization. Bodies facing each other are processed as a single unit and there is increased coupling of the extrastriate body area (EBA) and the posterior superior temporal sulcus (pSTS) when bodies are facing each other. This suggests that the brain is biased towards grouping humans in twos or dyads. History Early philosophers Descartes and Leibniz noted that the apparent unity of our experience is an all-or-none qualitative characteristic that does not appear to have an equivalent in the known quantitative features, like proximity or cohesion, of composite matter. William James in the nineteenth century, considered the ways the unity of consciousness might be explained by known physics