Which adjustment might help a patient describe speech as sounding clearer rather than like they have a "mouth of marbles"?

Increasing the gain ratio is a likely adjustment that can help a patient perceive speech as clearer, eliminating the feeling of having a "mouth of marbles." The gain in hearing aids amplifies sounds, including speech, making them louder and potentially more intelligible. When the gain ratio is increased, the device boosts the amplitude of the sounds that the user needs to hear, allowing the user to understand speech better by making distinct phonetic sounds more audibly pronounced.

The other adjustments, while they may serve specific purposes, do not directly address the clarity of speech in a significant way. Decreasing the kneepoint would modify the dynamic range for sound amplification but may not enhance speech clarity. Increasing the attack time affects how quickly the hearing aid responds to incoming sounds but does not necessarily improve the clarity of those sounds. Setting the maximum power output (MPO) to low limits the loudness without enhancing clarity, which could lead to missing critical speech sounds altogether.

Thus, increasing the gain ratio is the most effective option for enhancing speech clarity for the patient.