Simmons's graduate research involved studies of echolocation in bats, under the mentorship of E. Glen Wever, one of the giants in physiological acoustics.
At that time, acceptance of the processes underlying spatial perception by echolocation was not universal, and one of the exciting moments of his graduate training came when a skeptical Nobel Laureate, Georg von Békésy, on one of his periodic visits to Wever's lab, came to see the behaving bats in "Building B.
It was not until some years later that Simmons found out that this was a set-up engineered by Wever and Donald Griffin, who was then at the Rockefeller University, to convince Békésy about the bat's extraordinary use of echolocation to determine target range.
Simmons continued his research on bat echolocation after he moved to Washington University in St. Louis, Missouri in 1971, as an assistant professor in the Neural Science Program that was housed in the Psychology Department.
In 1984, Simmons moved to Brown University in Providence, Rhode Island, where his wife Andrea had been hired as an assistant professor in the Psychology Department.
In this experiment, Simmons found that the echolocating bat can discriminate a jitter in echo delay in the submicrosecond range, corresponding to a change in target distance of less than 0.1 mm.
Many researchers in the field challenged the report, because they asserted it was not biologically possible for the bat's sonar system to discriminate such small time differences at ultrasonic frequencies.
One of his manuscripts published with co-authors Albert Feng and Shelley Kick in Science[2] had a profound impact on the study of the neurophysiology of echolocating bats.