We have previously used the real-time change of muscle thickness detected using ultrasound, namely sonomyography (SMG), for prosthesis motor control purposes. In the present study, we further compared subjects’ performance using SMG and surface electromyography (EMG) in a series of discrete tracking tasks, both with and without a concurrent auditory attention task. Sixteen healthy subjects used different signals in a random order to control the cursor on a personal computer screen to cancel the letter ‘‘E’’ in a sequence of vertically arranged letters. Subjects’ performance was evaluated under isometric contraction and wrist extension using the extensor carpi radiali muscle. The percentage of successfully cancelled Es using SMG decreased by 21 ± 16% and 17 ± 11% in isometric contraction and wrist extension tests, respectively, compared with the corresponding performances using force and angle signals. The corresponding reduction recorded by using EMG was 40 ± 29% and 41 ± 25%. In addition, there was a significant decrease by using EMG compared with that by SMG (p , 0.001). The results also demonstrated that there was no significant difference of performances of canceling E between the single and dual tasks by using any of the control signals (p . 0.99). Furthermore, the SMG control provided more consistent performances under the single and dual tasks compared with EMG control.