The infrared receivers on the BOE Shield-Bot read the infrared signals sent by the remote. The remote flashes its IR LED on/off very rapidly—at 38.5 kHz—for certain periods of time, with periods of off-time in between.
The IR receivers on the Shield-Bot are tuned to look for 38.5 kHz signals. While these IR signals are detected, the receivers send a LOW signal to the Arduino I/O pin. In between these IR bursts when the signal is not detected, the receivers send a HIGH signal to the Arduino I/O pin/. The Arduino sketch measures the lenghts of the HIGH and LOW signals, and decodes them to know which button on the remote was pressed. Each button corresponds to different navigation instructions for the Shield-Bot servo motors. Pretty slick!