Most investigators place reflective beads on the basilar membrane to m
easure its vibration with optical methods. It is therefore important t
o find out if the beads faithfully follow the motion of the structures
on which they are placed. Vibration of the beads on the basilar membr
ane and basilar membrane adjacent to the beads are measured in the thi
rd turn of the guinea pig cochlea in a temporal bone preparation. It i
s shown that the Leads do not follow the motion of the organ. The mech
anism by which this departure may occur is investigated by modeling th
e motion of the beads on tile Claudius' cells. (C) 1998 Published by E
lsevier Science B.V.