ABSTRACT
How Bright is the light where you are reading this book? How loud are the sounds around you? (Is there music playing? Are people talking?) Over the course of hundreds of years, scientists and technicians have developed very accurate instruments for quantifying the physical properties of such stimuli. For example, you could walk into a camera shop today and buy a photometer to measure the brightness of a light or go to an electronics store and buy a sound-level meter to measure the loudness of a sound.
