An electronic device with a display, a touch-sensitive surface, one or more processors, and memory detects a first portion of a gesture, and determines that the first portion has a first gesture characteristic. The device selects a dynamic disambiguation threshold in accordance with the first gesture characteristic. The dynamic disambiguation threshold is used to determine whether to perform a first type of operation or a second type of operation when a first kind of gesture is detected. The device determines that the gesture is of the first kind of gesture. After selecting the dynamic disambiguation threshold, the device determines whether the gesture meets the dynamic disambiguation threshold. When the gesture meets the dynamic disambiguation threshold, the device performs the first type of operation, and when the gesture does not meet the dynamic disambiguation threshold, the device performs the second type of operation.