“…This variability appears to result from factors such as muscle tone, head and eye position, subject state, and recording filter pass band. PAMR is reduced when subjects are more relaxed (Gibson, 1974;Humphries et al, 1976) or asleep (Davis, 1976;Streletz et al, 1977). PAMR amplitude is increased by neck traction (Cody & Bickford, 1969), head lowering (Yoshie & Okudaira, 1969;Dus & Wilson, 1975), teeth gritting (Dus & Wilson, 1975;Gibson, 1978), propping the head forward (Yoshie & Okudaira, 1969;Thornton, 1975), pushing the head against a force (Clifford-Jones et al, 1979), or lateral eye movement (Patuzzi & O'Beirne, 1999b;Patuzzi & Thomson, 2000).…”