Sentence Correction

The use of GMAT books is based on the assumption that studying produces hormones in an individual that create unconscious physical responses.

....that studying produces .... is a noun clause.

Let's drill down further

studying produces hormones in an individual that create unconscious physical responses.

How do I know whether "individual" modifies "unconscious physical responses" or hormones modify "unconscious physical responses" ?

Thanks
Voodoo Child