Dragonflies have remarkable aerial prey interception ability. One possible explanation for why dragonflies are able to catch prey so well is that they use binocular cues, i.e. stereopsis, to follow the approach of a flying prey. We compared the neuronal responses to a virtually approaching object (expanding on a projection screen) and a physically approaching object to determine if triangulation is used as a binocular tool to find the time of interception. The time course of expansion was identical for the two stimuli, so the only difference was the possibility that distance could be detected based on binocular cues. Surprisingly, the projected virtual approaching object elicited greater responses than the real approaching object. One explanation for this result is that the virtually approaching object did not expand continuously. Due to the fact that the object expanded on a screen, it was actually expanding in small jumps, which increased in size as the object expanded. Even though the frame rate of the projector was very high (360 Hz), the dragonfly’s fast visual system may have detected these jumps
During the experiments, we also found neurons that responded to sound, especially to stimuli within the range of 100-900Hz. This is exciting because this is the first report of dragonflies being able to hear.