Closed-loop round-trip latency

Round-trip tests were conducted using a head-fixed larval zebrafish with closed-loop OMR stimulation. We used the same protocol described in the one-dimensional closed-loop methods section with the following modification. We rendered a black rectangle on top of the gratings that covered an area slightly larger than the fish. In the upper left corner of this rectangle, we projected a square that flashed white when a bout was detected and black otherwise. The same digital signal from the bout detection algorithm was sent simultaneously to an Arduino-controlled LED that was visible to the camera to turn ON when a bout was detected. We used the same closed-loop feedback calculation as for the one-dimensional OMR experiment. We calculated the number of frames between when a bout was detected in the image and when the LED turned ON, as well as when a bout was detected and when the square from the projector flashed white. We then converted the number of frames to a time delay in ms.