Dr. Epley has been instrumental in defining the mechanisms and treatment of BPPV variants, including those of the horizontal canals. Cupulolithiasis is a horizontal canal BPPV variant usually defined as direction-changing apogeotropic nystagmus. In recent years, the favored cupulolithiasis mechanism of otoconia adhering persistently to the cupula has been called into question. Epley was the first to propose mechanistic theories which better match the most recent evidence. From the beginning, he has demonstrated mastery over the semicircular canal pathology and otoconial mechanics.