An electronic device displays a user interface in a first display state. The device detects a first portion of a gesture on a touch-sensitive surface, including detecting intensity of a respective contact of the gesture. In response to detecting the first portion of the gesture, the device displays an intermediate display state between the first display state and a second display state. In response to detecting the end of the gesture: if intensity of the respective contact had reached a predefined intensity threshold prior to the end of the gesture, the device displays the second display state; otherwise, the device redisplays the first display state. After displaying an animated transition between a first display state and a second state, the device, optionally, detects an increase of the contact intensity. In response, the device displays a continuation of the animation in accordance with the increasing intensity of the respective contact.