Abdomino-thoracic muscle activity after a challenge meal will be recorded by EMG: in the biofeedback group, patients will be instructed to control muscle activity, whereas in the placebo group patients will not. In each patient 3 sessions will be performed over a 10-day period. Physiological (muscular activity by EMG) and clinical outcomes (number of rumination events by questionnaries administered daily for 10 days) will be measured before and after treatment.