Do you see a human face in the above schematic drawing? Sartre says that "the representative elements in the consciousness of a schematic drawing are not the lines properly so called, but the movements projected onto these lines" (The Imaginary, p. 34). To imagine a face in these lines it is absolutely required that the body "adopts a certain attitude, plays a certain mime to animate this ensemble of lines" (p. 31; Sartre's ensemble of lines differs slightly from the one I've presented, but the point remains the same.) To see a face the white space on the left of the top lines must be different from the white space on the right; an absent line, in this case the line of a jaw, is enacted to separate figure from ground, to make the face appear as a face. This argument applies not just to schematic drawings but to all imagination. The image, according to Sartre, is "an act that aims in its corporeality at an absent or nonexistent object, through a physical or psychic content that is given not as itself but in the capacity of 'analogical representative' of the object aimed at" (p. 20, Sartre's emphasis).
Do you have to have a feeling about the face in order to imagine it? Can it be imagined without feeling? Sartre is concerned with something called "intuituion," and he says, speaking specifically of an affective sense that unites the signs of an imitation, though he means to make a broader point about imagination, that affectivity substitutes itself "for the intuitive elements peculiar to perception in order to realize the object as imaged" (p. 29). Sartre identifies two correlative elements of the mental image: matter and knowledge. The matter in the case of the face seen in the schematic drawing above would be something like a quasi-face. What of the knowledge? Sartre says:
Knowledge is not substituted in its ideational form for the failing matter. As such, it cannot fill the gaps in intuition. It must undergo degradation, to which we will return. It passes to the intuitive in the form of mime; it flows in movements. An new phenomenon appears: symbolic movement, which, by its very nature as movement, is on the side of intuition and, by its signification, on the side of pure thought.
(p. 51, Sartre's emphasis)
Perhaps it's telling that Sartre regards symbolic movement as a degraded form of knowledge (as I read him), and he didn't identify feeling as a primary element of the mental image. Would he be saying also that feeling is a degraded form of knowledge?
I very much like the idea that the body imagines. However, I've been playing around with the idea for a few days and I'm not sure it holds up. I imagine music all the time. It's easy for me to hear irreal sounds. I don't think my ears move to imagine music the way my eye moves to enact a face in a schematic drawing. When I try to hold perfectly still and imagine music, perhaps there is movement in my lungs, but it is not obvious. I will have to reflect on it some more.