At least since Aquinas - and it is an Aristotelian idea - the object of perception is taken to be dual, usually because the intellect perceives as much as the senses - or maybe perceives something out of what the senses perceive. Id quo and id quod: what is seen in what I see (or rather, what I see in what is seen...). Locke's idea was to bring stereoscopy to the very nature of perception - the object of perception alone is stereoscopical. Whitehead's diagnosis was that no one lived up to this message and the object started with Locke himself to be disassembled into deliverances of the senses and the workings of the intellect. This was, in a sense, a reactionary move where Locke's message was put aside. The message was that perceptual representation is by nature two-fold - affordances and creation, sensual and real objects in Harman. Maybe it helps to think of the photograph model diagnosed in the direct reference theorists by Evans (in Varieties of Reference): no matter what the subjective form (or sensual object, or image in the Cartesian theater)looks like, it is an image of the objective datum (or the object out there, or the real object). To perceive is maybe like to refer (in a direct theory account): it matters what is perceived. However, Whitehead would add that it also matters the image (the description) we make of what is perceived. These image constitute what is perceived. It is as if the reference was no more than what the descriptions point at and yet the descriptions were somehow irrelevant in the very act of referring.