1. Audio medium for educational use, having plural channels from which prerecorded sounds may be reproduced, comprising a multiplicity of sets or prerecorded sounds on said medium, each said set having a dichotic presentation and a diotic presentation, each said dichotic presentation having a stimulus on one of said channels and a first response, corresponding to said stimulus, on a second of said channels, and each said diotic presentation having a second response on both said one and said second channels, said second response of each said set corresponding to the said stimulus of that set.