MIT Department of Electrical Engineering & Computer Science

SPECIAL EECS SEMINAR

Wednesday, April 12, 1995
Grier Room B, 34-401B

Refreshments at 1:45 PM
Talk at 2:00 PM

Visualizing and Quantifying Sound-Induced Motions of Receptor Cells in the Inner Ear

Dennis M. Freeman
Massachusetts Institute of Technology

Microscopic mechanics of sensory receptor cells play an important signal processing role in the inner ear. However, there are few direct measurements -- in large part because the mearsurements are technically challenging. The important structures are small (micrometers) and the motions are even smaller (nanometers).

We use (1) a light microscope to project magnified images of cells onto a CCD camera, (2) optical sectioning to obtain a stack of images that characterize the entire 3D structure, and (3) stroboscopic illumination to create slow motion video sequences in response to audio-frequency stimuli. We have investigated algorithms based on optical flow to estimate the sub-pixel displacements caused by sound. We found that bias is the predominant component of error in the estimate under almost all imaging conditions. We have developed a new alogrithm that reduces bias substantially.

We have used our system, which can resolve displacements as small as 14 nm, without averaging, to measure sub-micrometer motions of clusters of cells (50 micrometer dimensions), and of individual sensory receptor cells (5 micrometer dimenions), and of individual sensory hairs that project from each sensory receptor cell (sub-micrometer dimensions). Although this system was designed to study mechanics of the inner ear, it has much broader application (e.g., characterizing comb motors and other man-made micro-machines.)