When children learn how to tie their shoelaces, they do so in discrete steps — making a loop or tugging at the lace. Through repetition, these individual motions merge into elemental actions called “chunks” that remain so organized even after extensive practice.

Movement chunking, as the phenomenon is known, is a strategy that reduces long strings of information into shorter, more manageable pieces that are easier to remember. Scientists know that for people with Parkinson’s disease, Huntington’s disease and stroke, this movement chunking is severely disrupted. Understanding chunking and how it works is crucial for early diagnosis, treatment and rehabilitation therapy. Yet, science has no concrete explanation for it.

But now, a group of researchers, including UC Santa Barbara neurologist Scott Grafton, has developed a comprehensive theory for why chunking occurs. The research frames chunking as an economic tradeoff in the motor system, where merging small chunks becomes optimally “cost-effective” at certain learning stages.