One limitation of the MSM is that it states that ST is a unitary store, meaning that there is only one type of short-term memory. However, people that suffer from amnesia show that this is not true. Eg, Shallice and Warrington (1970) studied a patient, KF, who had amnesia. They found that KF's STM for digits were poor when they read them aloud to him. But his recall was better when he read them to himself. It's a limitation because STM says that there's one store but KF says there's one store for sound and one for visual.