L-Cuts are when the camera cuts from the subject who is talking to a different subject(s) whilst the audio remains.
J-Cuts are when the audience hears the second clip before hearing the audio attached.
The scene where the Arthur is in therapy utilises a L-Cut shot where the therapist is speaking and the camera cuts to Arthur listening, whilst the studio of the therapist continues.
The scene with Arthur and his Mother uses a J-Cut shot, this is because they hear the introductory music to the Murray show and it cuts their conversation and draws attention to the next shot, being Murray in his show.