The authors propose a training program for a listener to quantify the horizontal extension of an auditory image-auditory source width (ASW). The proposed program controls the ASW of a five-channel sound source by spreading it across five front loudspeakers, displays the corresponding change in visual width, and trains listeners to remember the spread angle through an isomorphic mapping to the corresponding visual cue. To evaluate the efficacy of the training, the authors conducted pre- and post-training tests. The results show that the width judgment error of the post- training test was significantly smaller than the pre-training test. (C) 2017 Acoustical Society of America