John Michael Montgomery has cited the medical condition known as acoustic neuroma for his poor performance of the national anthem at a televised NASCAR race earlier this month. Acoustic neuroma is a non-cancerous growth that interferes with a nerve running between the brain and the inner ear. The condition affects the balance and hearing of the patient. On his official Web site, Montgomery posted an apology for his performance at NASCAR's Nextel Cup race in Atlanta. In acknowledging his illness, Montgomery says his doctors feel that the condition can be corrected without affecting his tour dates.