Patient competency and capacity

Discuss patient competency and capacity as it relates to informed consent in health care. How would a physician determine if a patient who can not speak have the capacity to understand and consent to treatment or to make their own medical decisions. If the patient is unable to verbally answer (yet can answer "yes" and "no" questions by nodding) or too weak to sign the consent, would this require a guardian to consent to treatment?   Resources that you can use or feel free to use your own: https://www.ncbi.nlm.nih.gov/books/NBK430827/ https://www.hhs.gov/ohrp/regulations-and-policy/index.html https://www.hhs.gov/ohrp/regulations-and-policy/guidance/checklists/index.html