 For instance, there are metameric sounds (as there are metamers among colors), that is, sounds that feel identical to the ear although the corresponding medial properties are different. There is no one-to-one psychophysical correlation between auditory content and sounds as waves (Churchland 2007: 222). Moreover, ultrasounds, above 20.000 Hz and infrasounds, below 20 Hz, have the same physical nature as sounds—they are mechanical vibrations transmitted by an elastic medium—but they are not audible (as infrared and ultraviolet are not visible in the domain of colors): do they count as sounds? It further appears that the relationship between sound and sounding object remains underspecified. Do sound waves depend upon sounding objects in the sense in which we usually think sounds (as auditory events) do?