Auditory receptive field mapping
The ultimate book on the topic is probably http://www.amazon.com/Spatial-Hearing-Revised-Psychophysics-Localization/dp/0262024136 . It's a bit dated but contains and excellent review of the main psycho-acoustic research on spatial hearing. 

It is a very complicated topic. For example azimuth and elevation perception work completely different and hence azimuth resolution is quite a bit better than elevation resolution. The actually resolution (or jnd for just noticeable difference) depends heavily on the actual and the properties of the signal.