12. A speech recognition method comprising: generating, at a primary speech recognition unit, word lattice information by performing speech recognition on input speech; generating one or more word strings based on the word lattice information; calculating bidirectional language model scores of the generated word strings selectively using forward and backward language models for each of words in each of the generated word strings; and outputting one or more of the generated word strings with high scores as results of the speech recognition of the input speech based on the calculated bidirectional language model scores, wherein each of the generating, the calculating, and the outputting is performed by a processor.
19. The speech recognition method of claim 12 , wherein the outputting the word strings with high scores comprises: calculating acoustic model scores of the generated word strings in consideration of a liaison between the words in each of the generated word strings; adding up the acoustic model scores and the bidirectional language model scores of the generated word strings to calculate integrated scores of the generated word strings; and selecting one or more word strings with high integrated scores from the generated word strings and outputting the selected word strings as the results of the recognition of the input speech.