The solution in a flawed system is to manage the two frequencies not to effectively turn off the frequency that is providing traffic on IFR aircraft. Had the PF focused on the Center frequency and the PM focused on the CTAF then they might have been alerted to the AC taxiing for 36. That is a workaround however. The center frequency was providing useful information its just that a crew experiencing a high workload didn't hear it. What is the first human sense to shutdown in a stressful situation?Hearing.