APPARATUS AND METHOD FOR DISTINGUISHING SIMILAR-SOUNDING UTTERANCES IN SPEECH RECOGNITION

Abstract: An apparatus and method use speaker-specified hints to establish conditions for a speech recognition system to select a recognition result for a previously provided utterance from among various possible homophones. The hints may characterize the utterance by a linguistic property, such as an orthographic, morphological, or semantic property.

Description: Apparatus and Method for Distinguishing Similar-Sounding Utterances in Speech Recognition Technical Field The present invention relates to speech recognition systems, and more particularly, to dictation systems. Background One of the most difficult problems for speech recognition systems is how to choose the correct alternative from a list of words that are pronounced similarly or identically, but spelled differently. Such similar sounding words are known as homophones. For example, in English, "read, red" or "send, sent" are such homophones, as are the French words "parle, paries, parlent". Humans select the correct homophone by considering the context in which a given word appears, or by understanding the content of the text. This technique is, however, not yet feasible for computer systems. In current computer-based speech recognition systems, one alternative is selected. If that alternative is incorrect, the user may then go and correct the selection, for example, by choosing another alternative from a list of similar- sounding words. This method has the disadvantage that the user must spot the mistake in the recognized text, and then correct it. This takes extra time, breaks the flow of dictation, and carries the risk that some errors may be overlooked. Summary of the Invention In a preferred embodiment, the invention provides a method of utilizing a speech recognizer to distinguish a provided utterance from one or more similar- sounding utterances when a speaker-specified hint is provided. The method includes: a. identifying the hint and associating with it the provided utterance; b. using the hint to establish a condition for distinguishing the provided utterance; and c. selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the condition. In further embodiments, step (c) includes: (i) providing a list of alternative recognition possibilities and (ii) filtering the list based upon the condition. The speech recognizer may be used to provide entries in the list of alternative recognition possibilities. Alternatively, or in addition, a dictionary may be used to provide entries in the list. The hint may be a linguistic property characterizing the provided utterance or, in the same or an alternative embodiment, the hint may make reference to the context of previous dictation to characterize the provided utterance. Where the hint is a linguistic property, it may be an orthographic, morphological, or semantic property of the provided utterance. In a simple embodiment, for example, when the hint is an orthographic property, it may be a fractional spelling of the provided utterance. (As used in this description and in the following claims, the term "fractional spelling" means providing the spelling for a portion of the word, wherein the portion need not, but might possibly, include the beginning of the word, and does not include the whole word). Alternatively, the hint may provide some other desired criterion for selecting the provided utterance. The utterance may be a word, or alternatively, a phrase. For the purposes of this description and the following claims, a "hint" excludes a complete spelling of a word or phrase. Also, alternatively, a plurality of hints may be utilized. In such an embodiment, the method includes: (a) identifying the hints and associating with them the provided utterance; (b) using the hints to establish conditions for distinguishing the provided utterance; and (c) selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the conditions. A related embodiment provides an improved speech recognition system, of the type providing a text output in response to a spoken input. The improvement renders the system capable of distinguishing a provided utterance from one or more similar-sounding utterances when a speaker-identified hint is provided. The improvement includes: a. a hint recognizer which identifies the hint and associates with it the provided utterance; b. a condition specifier, coupled to the hint recognizer, which uses the hint to establish a condition for distinguishing the provided utterance; and c. a result selector, coupled to the condition specifier, which selects a recognition result that satisfies the condition. In a further embodiment, the result selector includes a filter operative on a list of alternative recognition possibilities. In a still further embodiment, the improvement also includes a dictionary, to which the result selector is coupled, to provide entries in the list of alternative recognition possibilities. As before, the hint may be a linguistic (e.g. orthographic, morphological, or semantic) property characterizing the provided utterance, or may make reference to the context of previous dictation to characterize the provided utterance, or may provide some other desired criterion for selecting the provided utterance. In yet a further embodiment, there is provided a system for utilizing a plurality of hints. The system of this embodiment includes: (a) a hint recognizer for identifying the hints and associating with them the provided utterance; (b) a condition specifier, coupled to the hint recognizer, for using the hints to establish conditions for distinguishing the provided utterance; and (c) a result selector, coupled to the condition specifier, for selecting a recognition result that satisfies the conditions. Another embodiment includes an improved speech recognition system wherein the improvement renders the system capable of distinguishing a provided utterance from one or more similar-sounding utterances when a speaker-identified hint is provided. The improvement includes: (a) means for identifying the hint and associating with it the provided utterance; (b) means for using the hint to establish a condition for distinguishing the provided utterance; and (c) means for selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the condition. Brief Description of the Drawings The foregoing aspects of the invention will be more readily understood by reference to the following detailed description taken with the accompanying drawings in which: Fig. 1 is a block diagram of a system to which the present invention is applicable. Fig. 2 is a logical flowchart of a method in accordance with a preferred embodiment of the invention. Detailed Description of Specific Embodiments A preferred embodiment of the present invention provides a solution to the homophone problem by allowing the user to give hints about the correct spelling of a word. Such user-provided hints may be given in an intuitive manner, while the dictation is going on, without requiring that the word be spelled in its entirety. In the example of "send, sent" the hint may be that the user dictates: "sent with-a-t" or "send with-a-d". A preferred embodiment may also be used for Asian languages to give hints about which character (KANJI, for example) to select for a word. Such a preferred embodiment may be used in virtually any language, particularly in languages having many homophonic words such as French and Chinese. Thus, as shown in Fig. 1, a preferred embodiment includes a speech recognition engine 1 such as is well-known in the art. For example, the speech recognition engine 1 may be a large vocabulary continuous speech recognition engine such as that used in VoiceXpress™ manufactured by Lernout & Hauspie Speech Products N.V., located in Burlington, MA. Further information on the design of a speech recognition system is provided, for example, in Rabiner and Juang, Fundamentals of Speech Recognition, Prentice Hall 1993, which is hereby incorporated herein by reference. In communication with the speech recognition engine 1 is a hint identifier and homophone selector 2 which identifies a speaker-specified hint received by the speech recognition engine 1, step 21 in Fig. 2. Such a hint is essentially a command to the speech recognition engine 1 rather than dictated text. Distinguishing spoken commands from dictated text is known in the art and described, for example, in U.S. Patent 5,794,196, issued to Yegnanarayanan et al., incorporated herein by reference, which describes recognizing isolated word commands embedded in a stream of continuously dictated text, and utilized in the VoiceXpress™ product which distinguishes continuously spoken natural language commands from continuously dictated text. Accordingly, the specific details of distinguishing a hint from dictated text are not relevant to the present invention. In step 22 of Fig. 2, the hint is associated with a previously provided input utterance. Based upon the hint, the hint identifier and homophone selector 2 establishes a condition for distinguishing the provided utterance, step 23 of Fig. 2. In step 24 a list may be provided of alternative recognition possibilities for the provided utterance. Typically, a dictionary 3 with linked entries will be available to the speech recognition engine 1 to provide such alternative recognition possibilities. In step 25, the list of alternative recognition possibilities is then filtered based on the condition established from the hint. Lastly, the hint identifier and homophone selector 2 will select, in step 26, the recognition result which satisfies the condition. In a preferred embodiment, system commands may be provided such as "spelled with X", "spelled with an X" , "with an X", "with X", "without X", or the equivalent. In such a dictation system, X may be one or more letters of the alphabet in the language of the system, e.g., "ά", "t", "double-1", "dt" (typical for Dutch). Alternatively, X may be a description or hint of a KANJI character, for example, related to the number of strokes of the character, or some other feature used to distinguish between KANJI characters. Other orthographic hints are also within the scope of a preferred embodiment. For example, a hint may include a designation of the alphabet in which the utterance is rendered, e.g., in Japanese, hiragara or katakana. As an alternative, or in addition, system commands may supply a hint about a morphological property, e.g., singular, plural, or past tense. Furthermore, a hint may be some other linguistic property characterizing the provided utterance — for example, a semantic property such as "the color" when uttered after "red". Such a hint also may refer to the context of previously dictated text to characterize a word, e.g., "as I used it before". These hints can be given by the user without disrupting the flow of the dictation. When a "Y spelled with X" command is recognized, the system looks up Y and considers various alternatives — homophones or alternative recognition results. These alternatives can be retrieved from a dictionary which contains links between all words that sound alike (sometimes referred to below and in the claims as a "linked dictionary"), or, from an alternatives list in the recognition result of the word Y. The alternatives are then filtered based on whether they fulfill the command criterion "X" (or not, in a case of "without X"). From the remaining alternatives, one is chosen, e.g., the alternative with the highest occurrence probability. The alternative filtering may be achieved in various manners. In one approach, all alternatives which lack the characters described in X are removed. Some pre-processing may be done, for example, "double L" would be replaced by "LL", then all alternatives not containing "LL" are removed. Another filtering approach exploits the fact that many hints are related to verb endings ("sent with a t"). Accordingly, the system may check whether the last letter(s) of the verb correspond to X. In this manner, X can be restrained to commonly confusable verb endings (e.g., d, t for English; e, s, es, t, ent for French). In another filtering approach, identifiers in a dictionary may be utilized to show to which letter a hint applies, if present (an index to a start position in the word string would suffice). For example, to differentiate KANJI characters, the hint may be stored in the dictionary entry for a word, such as in a field indicating the number of strokes in the character. As an alternative to generating a list of alternatives and then filtering for the condition established by the hint, it is within the scope of the present invention to use the condition in connection with a linked dictionary to produce directly a single recognition result satisfying the condition. A preferred embodiment also has language model and grammar implications. In speech recognition, a word or a command can only be recognized if it is part of a grammar of a language model. This also applies to the hints as used in a preferred embodiment. Different options are possible to add hints to a language model. For example, the hint phrase "spelled with" may be modeled in the same way as a "capitalize that" command. That is, the hint can occur at any point in the dictation, after any word. This can be modeled by giving the hint a unigram occurrence probability. The value of the probability should be in line with the probability assigned to other commands such as "capitalize that". Alternatively, "spelled with" may be constrained to occurring only after certain classes of confusable words; for example, only after verbs. In a hint such as "Y spelled with X", the X can also be modeled in different ways. For example, X may be part of the language model and treated in the same way as any other word, e.g., as a unigram, or bigram. Thus, a probability can be computed for the transitions "with X", "with a X", and "with an X" in the same way as with other recognition probabilities. Alternatively, X may be treated as a limited domain spelling grammar, which is entered when the system recognizes the phrase "spelled with". The grammar would incorporate all commonly given hints. Similarly, the recognition system may switch modes to a spelling grammar to recognize X. Or, the phrase "spelled with X" may be treated as a separate grammar. This grammar may be entered through normal dictation, or it may be activated when displaying an alternative list as a separate window. Although preferred embodiments have been described above with respect to the use of a single hint, it is within the scope of the present invention to provide a plurality of hints. In French, for example, one might usefully indicate that a verb is feminine and singular, thereby providing two hints. Although the present invention is particularly applicable to continuous dictation systems, it is also applicable to discrete dictation systems. Furthermore, while the invention may be employed for hint-giving during dictation, it may also be applied as a correction mechanism for text that has already been dictated. For example, hints may be used to select a recognition result from a displayed list of alternative recognition possibilities appearing in a window separate from the text. In this way a "Y spelled with X" command is not embedded in normal dictation mode, but provides a novel way to select alternatives in an alternatives list. Alternatively, when in the correction mode, a hint may cause the immediate selection of a recognition result, without the display of an alternatives list, in the manner described above for dictation. In such an embodiment, a hint need not necessarily be identified as such, since the system is already in a correction mode and may be configured to act on the hint directly without needing an identification step or a hint recognizer.

Claims: What is claimed is: 1. A method of utilizing a speech recognizer to distinguish a provided utterance from one or more similar-sounding utterances when a speaker-specified hint is provided, the method comprising: (a) identifying the hint and associating with it the provided utterance; (b) using the hint to establish a condition for distinguishing the provided utterance; and (c) selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the condition. 2. A method according to claim 1, wherein step (c) includes: (i) providing a list of alternative recognition possibilities and (ii) filtering the list based upon the condition. 3. A method according to claim 2, wherein the step of providing a list of alternative recognition possibilities includes using the speech recognizer to provide entries in the list. 4. A method according to claim 2, wherein the step of providing a list of alternative recognition possibilities includes utilizing a linked dictionary to provide entries in the list. 5. A method according to claim 2, wherein the step of providing a list of alternative recognition possibilities includes both using the speech recognizer and utilizing a linked dictionary to provide entries in the list. 6. A method according to claim 1, wherein the hint includes reference to the context of previous dictation to characterize the provided utterance. 7. A method according to claim 1, wherein the hint is a linguistic property characterizing the provided utterance. 8. A method according to claim 7, wherein the hint is an orthographic property characterizing the provided utterance. 9. A method according to claim 7, wherein the hint is a morphological property characterizing the provided utterance. 10. A method according to claim 7, wherein the hint is a semantic property characterizing the provided utterance. 11. A method according to claim 1, wherein the hint is a fractional spelling of the provided utterance. 12. A method according to claim 1, wherein the hint is a grammatical term characterizing the provided utterance. 13. A method according to claim 1, of utilizing a speech recognizer to distinguish a provided utterance from one or more similar-sounding utterances when a plurality of speaker-specified hints is provided, the method comprising: (a) identifying the hints and associating with them the provided utterance; (b) using the hints to establish conditions for distinguishing the provided utterance; and (c) selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the conditions. 14. An improved speech recognition system wherein the improvement renders the system capable of distinguishing a provided utterance from one or more similar-sounding utterances when a speaker-identified hint is provided and the improvement comprises: (a) a hint recognizer which identifies the hint and associates with it the provided utterance; (b) a condition specifier, coupled to the hint recognizer, which uses the hint to establish a condition for distinguishing the provided utterance; and JO- (c) a result selector, coupled to the condition specifier, which selects a recognition result that satisfies the condition. 15. A system according to claim 14, wherein the result selector includes a filter operative on a list of alternative recognition possibilities. 16. A system according to claim 15, wherein the improvement further comprises a dictionary, to which the result selector is coupled, to provide entries in the list of alternative recognition possibilities. 17. A system according to claim 14, wherein the hint includes reference to the context of previous dictation to characterize the provided utterance. 18. A system according to claim 14, wherein the hint is a linguistic property characterizing the provided utterance. 19. A system according to claim 18, wherein the hint is an orthographic property characterizing the provided utterance 20. A system according to claim 18, wherein the hint is a morphological property characterizing the provided utterance. 21. A system according to claim 18, wherein the hint is a semantic property characterizing the provided utterance. 22. A system according to claim 14, wherein the hint is a fractional spelling of the provided utterance. 23. A system according to claim 14, wherein the hint is a grammatical term characterizing the provided utterance. 24. A system according to claim 14, wherein a plurality of speaker-identified hints is provided and the improvement comprises: (a) a hint recognizer for identifying the hints and associating with them the provided utterance; (b) a condition specifier, coupled to the hint recognizer, for using the hints to establish conditions for distinguishing the provided utterance; and (c) a result selector, coupled to the condition specifier, for selecting a recognition result that satisfies the conditions. 25. An improved speech recognition system wherein the improvement renders the system capable of distinguishing a provided utterance from one or more similar-sounding utterances when a speaker-identified hint is provided and the improvement comprises: (a) means for identifying the hint and associating with it the provided utterance; (b) means for using the hint to establish a condition for distinguishing the provided utterance; and (c) means for selecting a recognition result, derived in conjunction with operation of the speech recognizer, that satisfies the condition. [72062]

Inventors: GALLOPYN GUIDO, SCHOOFS KOEN, GALLOPYN, GUIDO, SCHOOFS, KOEN
Applicants: LERNOUT & HAUSPIE SPEECHPROD, LERNOUT & HAUSPIE SPEECH PRODUCTS N.V
Application year: 1998
Main classification: G10L5
IPC codes: G10L15