Chunking as a method of learning can be applied in a number of contexts, and is not limited to learning verbal material.[14] Karl Lashley, in his classic paper on serial order, argued that the sequential responses that appear to be organized in a linear and flat fashion concealed an underlying hierarchical structure.[15] This was then demonstrated in motor control by Rosenbaum et al. (1983).[16] Thus sequences can consist of sub-sequences and these can in turn consist of sub-sub-sequences.