An empirical comparison of pie vs. linear menus. - John R. Callahan; Don Hopkins; Mark D. Weiser; Ben Shneiderman (CHI, 1988)

Designing to Facilitate Browsing: A Look Back at the Hyperties Workstation Browser. - Ben Shneiderman; Catherine Plaisant; Rodrigo A. Botafogo; Don Hopkins; William J. Weiland (Hypermedia, 1991)