The stroke suffered by artificial-heart recipient William J. Schroeder Thursday appears to have caused more extensive brain damage than earlier thought, a brain specialist said yesterday.

Schroeder shows "some problems with memory, particularly short-term memory," including confusion about the day of the week and slowness in recognizing family members, Dr. Gary Fox said.

Fox, a neurologist, examined Schroeder yesterday morning and reviewed test results at the Humana Heart Institute International in Louisville where Schroeder is being treated.

Fox said brain scans show three small sites of damage in the lower brain, rather than the single site found earlier. These results suggest a "shower of emboli" -- several small blood clots -- temporarily cut off the blood supply to Schroeder's brain.

But Fox emphasized that it was too early to tell how long-lasting the mental effects of the stroke might be. The damage was small compared with that suffered by many stroke victims, and Fox said Schroeder's initial quick recovery of functions was encouraging.

Doctors sought to give Schroeder a "psychological boost" yesterday by wheeling him to the hospital lobby to hear third-graders sing Christmas carols. He joined them briefly in singing "Silent Night." He was also moved out of the intensive-care unit into a private room.

Dr. Allan M. Lansing, head of Humana's heart program said there was "no doubt that he is dramatically better than he was at any time during the weekend. I have seen people look infinitely worse than Mr. Schroeder and recover completely . . . . He wasn't even conscious three days ago. Today he is paying attention."

Physically, Lansing said, Schroeder yesterday was "looking the best I've seen him looking" since the Nov. 25 implant surgery. "But he still lacks the spirit and enthusiasm he had last week," he added.

Other than a bleeding episode on the night of his surgery, Schroeder's first 18 days with the artificial heart showed remarkable progress. But Thursday night he had a a stroke that temporarily left him unconscious, paralyzed on the right side and unable to talk.

Yesterday, Fox said Schroeder's depression "may or may not be related" to the brain damage caused by the stroke. Lansing reported that Schroeder yesterday saw a psychiatrist who found a "significant element of depression."

The doctors suggested that in addition to the physical and psychological impact of the stroke, Schroeder's persistent sleepiness and drowsiness might be related to a high blood pressure drug, Aldomet, being discontinued.

Fox concluded that Schroeder had a form of "organic brain syndrome," which is characterized "primarily by mental problems, particularly memory for recent events. In addition there is some impairment in intellectual function but the big thing is recent memory."

He said that yesterday morning he asked Schroeder about a basketball game played by the high school team in his hometown, Jasper, Ind., and found "he has essentially no recall for what happened over the weekend. He thinks it's still Friday."

Later, he added that Schroeder appeared "very slow in his response to everything. He has difficulties at times in recognizing members of his family . . . . He has to be prodded, yes, but he can come up with the right answer."

Asked why the changes in Schroeder's mental state were not reported until yesterday, Fox replied that when he examined him Monday morning he was "wide awake" but that attending doctors were at an "extreme disadvantage" over the weekend because the patient had been sleepy and unresponsive.

Fox also said an initial CAT (computerized axial tomography) brain scan done Thursday night after the stroke pinpointed only a small area of damage in the left lower portion of the brain. A test done Saturday that Fox read yesterday found three affected areas.

He said the additional evidence of damage did not suggest "anything new happened." Such lesions may take several days to show up on the tests, he said, adding that more may appear. The areas affected showed small abnormalities on the left and right sides of the thalamus and in the basal ganglia, areas of the lower brain that are "way stations" that "receive and pass messages on to other centers in brain."