A Letter to the Editor on "Effect of Visual Biofeedback Obtained Using the Iowa Oral Performance Instrument on the Suprahyoid Muscle Activation Level During Effortful Swallowing Maneuver".

The author has provided an alternative biofeedback method to help maintain the effortful swallowing (ES) maneuver target effort to utilize a constantly high swallowing pressure. The author has identified ES with visual feedback (i.e. the Iowa Oral Performance Instrument (IOPI)) produced higher EMG activation levels than without. However, the author accepted higher activation levels as higher muscle force production, attributed the lower EMG activation levels in 4th set to fatigue, and did not consider other possibilities. As the author stated in the discussion "his/her method caused participants to focus more efforts to achieve the goal" in feedback condition and enhanced the participant's focus on the exercise plan. This situation, caused by the focus of attention, can be explained with the "constrained action hypothesis". Also, EMG levels are highly correlated to muscle force, but EMG does not directly measure the force produced. This causes some unpredictable factors that can influence the force but not the EMG data. To conclude, the increased EMG activity or the participants' negative feedback could be caused by the focus of attention, and future studies should consider this perspective.