6. The method of claim 4 , wherein: for each of the plurality of different spoken utterances, the respective phoneme-independent representation is decomposed to further obtain a respective content reference sequence; the at least one spectral signature of the input speech signal is further decomposed into at least one content input sequence; and determining that the input speech signal is associated with the user further comprises determining that the input speech signal is associated with the user if the at least one content input sequence is similar to at least one of the respective content reference sequences.
6. The method of claim 4 , wherein: for each of the plurality of different spoken utterances, the respective phoneme-independent representation is decomposed to further obtain a respective content reference sequence; the at least one spectral signature of the input speech signal is further decomposed into at least one content input sequence; and determining that the input speech signal is associated with the user further comprises determining that the input speech signal is associated with the user if the at least one content input sequence is similar to at least one of the respective content reference sequences. 7. The method of claim 6 , further comprising: determining similarity based on a distance calculated between the at least one content input sequence and the at least one of the respective content reference sequences.