In this condition it rests as on a knife edge, from which it may be made to swing in one or other of two opposite 1 If very weak, a continuous sound stimulus is only heard intermittently.

(Into the responsibility of inhibitory processes or refractory periods for such fluctuations I cannot here enter.

) If strong overtones are present, one or other of them may successively attract the attention (cf.

C.

Stumpf, Tonpsychologie, i.