Merleau-Ponty argued that in perceiving an object, we sense that it can be more clearly perceived and so our bodies are drawn in such a way as to get a firmer grip:
My body is geared onto the world when my perception presents me with a spectacle as varied and as clearly articulated as possible, and when my motor intentions, as they unfold, receive the responses they expect from the world. This maximum sharpness of perception and action points clearly to a perceptual ground, a basis of my life, a general setting in which my body can co-exist with the world. ( 1962, p. 250)Merleau-Ponty outlines two aspects of perception: (1) maximal grip and the (2) intentional arc.
1) In our dealings with objects, we move to reach an appropriate perspective//stance/position in relation to objects of perception. This position depends on the concrete circumstances of the situation. We do this when we look at a painting, moving close enough to see a desired level of detail, but not so close as to lose sight of the whole thing: too far away and you can't make out the image, too close and you're drowned in too much detail. Small paintings require a closer stance than large ones. This isn't limited to vision, either. When you get in your car and the seat is off place, you immediately feel the discomfort of not being at the proper distance from the steering wheel. One slides the seat closer or farther away to reach a maximal grip on the task at hand.
2) Additionally, as we acquire skills the way the world shows up for us alters. Merleau-Ponty's example is difference between the way a city looks when we are lost and when we know our way around it. As we learn our way around a city, our embodied skill of navigating the area improves and we know not only what to look for, but what to anticipate. The light hitting your eye is the same, but the world literally looks different. George Sturt provides a great example of this (hat tip to ATS):
Sturt could go into a forest and immediately see these qualitative distinctions in the trees (bear in mind that the meaningful distinctions aren't in his head, they are out there in the world). This feedback loop is the intentional arc.