How does Carson McCullers use imagery in Wunderkind?

Physical descriptions of Bilderbach, presented from Frances's viewpoint, are marked by images of masculine strength and virility, suggesting that she feels a sexual attraction for him. Yet on the surface, he doesn't appear to be an especially virile specimen: he has "thin hair," "smoke-yellowed teeth," and a "narrow face"; he wears horn-rimmed glasses, and while his voice is "deep," it is also "blunt" and "guttural." Moreover, he is married and obviously middle-aged, and so would seem to be an inappropriate and unattainable object for her desires.