Complex sentence: Gwen Bell Dooley demonstrated Lana's cognitive capability to distinguish between two numerical sets of objects which she then labelled with either "more" or "less", whichever was requested.
Split into simpler sentences: Gwen Bell Dooley demonstrated Lana's cognitive capability to distinguish between two numerical sets of objects. Lana could correctly label the set of objects with either "more" or "less", whichever was requested.