 Various empirical results make it plausible that the brain takes account of expected precisions when it is processing perceptual signals. In the ventriloquist illusion, for example, it is plausible that expectations of precision have a role to play: It is because vision is expected to give a more precise indication of location than audition that sounds are heard to come from the location where their source is apparently seen. Other considerations make it equally plausible that attention plays a role in accommodating the variations in these expected precisions, as we move from one context to another. If we expect that the signal from vision is likely to be a noisy one—perhaps because a thick fog has started to descend—then we may place more weight than usual on the information that is present in the signal coming from audition. It seems likely that there is a role for attention in bringing about this change of weighting. It is more controversial to claim, as the advocates of this theory do, that “attention is nothing but precision optimization in hierarchical inference.” (Hohwy, 1014, p.244, citing Feldman &amp; Friston, 2010). Ransom et al. have suggested that, by taking attention always to be precision optimization, this theory struggles to account for certain forms of voluntary attention (Ransom et al. 2017). Clark has suggested that this challenge can be met if the sources of voluntary attention are identified with beliefs, rather than desires (Clark, 2017).