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S. H. Larsen led the 1974 study connecting changes in bacterial flagellar motor rotation direction to chemotaxis. Tethered-cell observations made motor rotation visible, allowing responses to chemical stimuli to be related to switching behavior rather than only to the net movement of a swimming bacterium.^[ref]

The distinction is useful because directional migration need not mean that a cell points toward a stimulus and moves straight to it. Modulating movement and reorientation can bias a trajectory statistically. The publisher's original byline identifies S. H. Larsen as Steven H. Larsen.