In psychology, Fechner's Law says that the change in the intensity of a sensation is a function of the change in the intensity of the stimulus divided by the magnitude of the current intensity of the stimulus.
What this means is that if you are listening to music at 23 decibels and your turn it up 17 decibels, you will feel a certain increase in the sound. If you then turn it up another 17 decibels the difference you hear is less than the difference the original time you turned it up.
This applies to all types of stimuli, including heat, noise, and sight.