Dahlgren & Marton (1978)
Dahlgren (1989)
Inglis (1992)
Laurillard (1993)
Martin & Milton (1992)
Ballantyne & Packer (in press)
Clacherty & Ballantyne (1990)
Ballantyne & Gerber (1994)
Hounsell (1984)
Hounsell (1987)
Prosser & Webb (1992)
Alexandersson (1981)
Spinelli (1989)
Ihde (1986)
Ekeblad & Bond (1995)