• Adults aged 18 to 35 years
• Had lower extremity musculoskeletal surgery within the previous 6 months.
• An age-matched control group of adults without a history of lower extremity musculoskeletal surgery will also be included.

• are between the ages of 18-35 years,
• either have had an anterior cruciate ligament reconstruction (ACLR) surgery or have not had an injury to either of your knees,
• have not been medically diagnosed with a concussion in the previous 6 months,
• have not been medically diagnosed with colorblindness,
• have no known neurological (nervous system) disorder (i.e. Multiple Sclerosis),
• have not taken opioid medication (pain medication) in the last 2 weeks,
• are not pregnant of planning to become present during study participation, and
• have no contraindications to brain MRI (you will complete a screening form).

ACL Group:

• Age of 18-35 years
• History of only one ACL reconstruction within the previous 2 years
• Medical clearance for return to unrestricted activity

Uninjured Group:

• Age of 18-35 years
• No history of lower limb surgery
• No history of significant lower limb injury within previous 6 months (defined as seeking medical attention, or missing >3 consecutive practices or games)

• Adult, aged 18-30 years old
• Native speaker of American English
• Either non-smoker / non-vaper for at least 5 years -OR- a daily vaper for a minimum of 6 months.

• 3;6 – 4;11 years of age
• Speech that is very difficult to understand and would benefit from augmentative and alternative communication (AAC)
• Diagnosis of cerebral palsy with typical language comprehension or
• Diagnosis of childhood apraxia with typical language comprehension or
• Diagnosis of Down syndrome
• Ability to directly select symbols on a tablet or speech generating device
• Available to attend 1-hour intervention sessions at UCF twice weekly for 2 years.

•   5 to 90+ years
•   Ability to understand and carry out test instructions in English

• Age 12-45 years
• History of knee injury (e.g., ACL tear, meniscus tear, patellofemoral pain, osteoarthritis) or surgery (e.g., ACL reconstruction, meniscectomy or repair, total knee arthroplasty) within the last 2 years