Echo questions are primarily used to seek a confirmation or repetition of some portion of the stimulus, either because the listener finds what they thought they heard surprising or was unable to hear the speaker clearly.
A special case of polar echo questions is the bare predication[1] construction (also called the incredulity response[2]).
First or second person pronouns will be inverted to reflect the change of speaker: Echo questions may also reduce the original stimulus by omitting portions, or replacing them with pro-forms.
[1] For example, all of the following are possible echo question responses to the stimulus "He's taking their dalmatian puppy to the vet once his mom gets back with the car."
(the focused constituent is marked in italics): Rodney Huddleston accounts for such modifications by theorizing that the relevant repetition is of the illocutionary act associated with the stimulus, rather than its surface form.
Japanese does not have a dedicated intonational pattern for echo questions, but they may optionally be marked lexically with the sentence-final particle -tte.