Final answer:
Justin's improved control over intrusive thoughts is attributed to neurological maturation, which is part of the brain's development and its ability to efficiently process and integrate new information.
Step-by-step explanation:
Justin's growing ability to control the intrusion of other thoughts while focusing on material can be attributed to neurological maturation. This development reflects the brain's increasing efficiency in processing information and its ability to integrate new information and learn through changes known as plasticity. It's the result of neurodevelopment rather than the use of mnemonics, organization or reiteration. Mnemonic devices are indeed helpful for memory retention and recall, but the control of intrusive thoughts is more directly related to the maturation of cognitive processes as the brain refines its ability to focus and filter out unrelated stimuli.