In underapplication opacity, a phonological process fails to apply when it seems it should have. In a chain shift, a process fails to apply to derived forms, while in a saltation, a process fails to apply to non-derived forms. This paper argues that both chain shifts and saltations can be characterized as either one-dimensional (1D, involving a change along a single phonological dimension) or two-dimensional (2D, involving a change along two dimensions). While both 1D and 2D chain shifts and 2D saltations are attested, there seem to be of no attested cases of 1D saltations. This paper argues that gestural phonology represents 1D and 2D processes differently such that there is a bias against 1D saltations, providing an explanation for this typological asymmetry.