known as the precedence effect.
After hearing a signal, the ears will suppress any subsequent signals (such as an echo or reverberation) for about 40 milliseconds; assuming that these later signals are quieter than the original signal.
It is believed that we use time delay to locate the source of a signal (the source is closer to the first ear to hear it). The Haas effect also refers to this phenomena. In electronic systems time delay localization is best experienced through headphones.