The Nagoya High Court on Tuesday reduced the prison sentence for a 21-year-old man by six months, saying his ability to make proper decisions was greatly diminished when he fatally assaulted his grandfather in March 2004.

The Nagoya District Court had sentenced Tomohiko Asano to 3 1/2 years for the incident, but the high court pared it to three years.

Presiding Judge Makoto Kawahara said Asano had been frustrated over university entrance examinations and was pondering what to do with his life. The sounds made by his grandfather, Toshiyuki, 76, who lived with him, were a constant irritant, Kawahara said.

The judge said Asano's repeated beating of his grandfather to get him to speak, when he had lost his ability to do so, was "irrational" and he was in such an extremely agitated state that he was not able to think rationally.