The 24-year-old Marine suffered a fractured skull when he was struck by an object, likely a tear gas canister fired by police.
Doctors at highland hospital expect him to make a full recovery, but say it could be a slow process.
"He's got some pressure on the brain that is causing him not to be able to speak, but he does understand everything that is said to him; he immediately responds when you ask him a question, he gestures," Alameda County Medical Center spokesperson Curt Olsen said.
Doctors are optimistic Olsen will make a complete recovery.
Thursday night, a vigil took place in his honor in Oakland and at several other occupy sites across the country.
