Brief Answer:

I believe that the context in which pictures or radio are being viewed/listened to affects the answer of this. For example if you are trying to understand what a particular place looked like, take London in the 1950’s, a picture would be a suitable medium. Pictures give us a sense of place and time however they can only tell us so much. Radio on the other hand can pull together a range of mediums such as voice clips, sound effects, ambience etc to create a fuller and more accurate illusion of 1950’s London. From the Arnheim source he makes it clear that a visual medium doesn’t allow the viewer to use their own imagination and fill in the gaps like radio does. With this in mind, Radio is superior (to an extent).