Interesting question. May I ask you to clarify your question a bit? I was not sure what you meant, exactly, by lexical tone processing. Are you asking about prelexical tone processing abilities, such as tone discrimination and identification or about lexical processing (i.e., the role of tone in lexical access)? Regarding the former, Nancy Kula and myself have discrimination data on Bemba tone spreading and tone scaling (abstract on the 12th OCP conference).
In general I am interested in any kind of lexical tone processing in African languages. I am aware that a lot has been done theoretically on some languages. I am though at this point in time mainly interested in those who have done studies like yours that have used experimental techniques in gathering and analyzing their data.
You might want to look at Michael R. Marlo's work. He is at the University of Missouri-Columbia in the English Department and also on the Research Gate site.