Editing Stimulus modality (section)

===Description===
The stimulus modality for [[hearing]] is sound. Sound is created through changes in the pressure of the air. As an object vibrates, it compresses the surrounding molecules of air as it moves towards a given point and expands the molecules as it moves away from the point. Periodicity in sound waves is measured in [[hertz]]. Humans, on average, are able to detect sounds as pitched when they contain periodic or quasi-periodic variations that fall between the range of 30 to 20000 hertz.<ref name=Carlson />