Patent Publication Number: US-8990082-B2

Title: Non-scorable response filters for speech scoring systems

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/467,503, filed Mar. 25, 2011, entitled “Non-English Response Detection Method for Automated Proficiency Scoring System,” and to U.S. Provisional Patent Application No. 61/467,509, filed Mar. 25, 2011, entitled “Non-scorable Response Detection for Automated Speaking Proficiency Assessment,” both of which are herein incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The technology described herein relates generally to automated speech assessment systems and more particularly to a method of filtering out non-scorable responses in automated speech assessment systems. 
     BACKGROUND 
     Automated speech assessment systems are commonly used in conjunction with standardized tests designed to test a non-native speaker&#39;s proficiency in speaking a certain language (e.g., Pearson Test of English Academic, Test of English as a Foreign Language, International English Language Testing System). In these tests, a verbal response may be elicited from a test-taker by providing a test prompt, which asks the test-taker to construct a particular type of verbal response. For example, the test prompt may ask the test-taker to read aloud a word or passage, describe an event, or state an opinion about a given topic. The test-taker&#39;s response may be received at a computer-based system and analyzed by an automated speech recognition (ASR) module to generate a transcript of the response. Using the transcript and other information extracted from the response, the automated speech assessment system may analyze the response and provide an assessment of the test-taker&#39;s proficiency in using a particular language. These systems may be configured to evaluate, for example, the test-taker&#39;s vocabulary range, pronunciation skill, fluency, and rate of speech. The present inventors have observed, however, that in some assessment scenarios, such automated speech assessment systems may be unable to provide a valid assessment of a test taker&#39;s speaking proficiency. 
     SUMMARY 
     The present disclosure is directed to systems and methods for scoring non-native speech. A speech sample spoken by a non-native speaker is received, and automatic speech recognition and metric extraction is performed on the speech sample to generate a transcript of the speech sample and a speech metric associated with the speech sample. A determination is made as to whether the speech sample is scorable or non-scorable based upon the transcript and the speech metric, where the determination is based on an audio quality of the speech sample, an amount of speech of the speech sample, a degree to which the speech sample is off-topic, whether the speech sample includes speech from an incorrect language, or whether the speech sample includes plagiarized material. When the sample is determined to be non-scorable, an indication of non-scorability is associated with the speech sample. When the sample is determined to be scorable, the sample is provided to a scoring model for scoring. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a computer-implemented system where users can interact with a non-scorable speech detector for detecting non-scorable speech hosted on one or more servers through a network. 
         FIG. 2  is a block diagram depicting elements of a non-scorable speech detector. 
         FIG. 3  is a block diagram depicting an example in which non-scorable speech filters have independently-operating filters. 
         FIG. 4  is a block diagram depicting an example in which non-scorable speech filters have filters that collectively make a scorability determination for a speech sample. 
         FIG. 5A  is a block diagram illustrating example speech metrics considered by an audio quality filter. 
         FIG. 5B  is a block diagram illustrating example speech metrics considered by an insufficient-speech filter. 
         FIG. 6A  is a block diagram illustrating example speech metrics considered by an off-topic filter. 
         FIG. 6B  is a block diagram illustrating example speech metrics considered by an incorrect-language filter. 
         FIG. 7  is a block diagram illustrating example speech metrics considered by a plagiarism-detection filter. 
         FIG. 8  is a block diagram depicting non-scorable speech filters comprising a combined filter. 
         FIG. 9  is a flowchart depicting a method for scoring a response speech sample. 
         FIGS. 10A ,  10 B, and  10 C depict example systems for use in implementing a method of scoring non-native speech. 
     
    
    
     DETAILED DESCRIPTION 
     Automated speech assessment systems may be used to automatically assess a test-taker&#39;s proficiency in speaking a certain language, without a need for any human intervention or requiring only limited human intervention. These systems may be configured to automatically evaluate, for example, the test-taker&#39;s vocabulary range, pronunciation skill, fluency, and rate of speech. The present inventors have observed, however, that conventional automated scoring systems which lack a human scorer to screen test-taker responses may be complicated by a diverse array of problems. These problems may include, for example, poor audio quality of the sample to be scored, off-topic responses that do not address the test prompt, responses lacking an adequate amount of speech, responses using a language different than an expected language, and plagiarized responses, among others. These problems may make it difficult for conventional automated speech assessment systems to provide a valid assessment of the test-taker&#39;s speaking proficiency and may result in erroneous, unrepresentative scores being assessed. 
     In some situations, the problems may be the result of technical difficulties (e.g., test-taker&#39;s microphone being unplugged inadvertently, problems with the computer designated to receive the response, high background noise). In other situations, the problems may be created intentionally by a test-taker attempting to “game the system.” For example, a test-taker lacking knowledge on a subject presented by a test prompt may simply respond with silence, or alternatively, the test-taker may respond by speaking about a subject that is irrelevant to the test prompt. In either situation, if the response is allowed to pass to the automated speech assessment system, an erroneous, unrepresentative score may be assessed. 
       FIG. 1  depicts a computer-implemented system  100  where users  104  can interact with a non-scorable speech detector  102  for detecting non-scorable speech hosted on one or more servers  106  through a network  108 . The non-scorable speech detector  102  may be used to screen a speech sample  112  prior to its receipt at a scoring system so that the scoring system will not attempt to score faulty speech samples that are not properly scorable. To provide this screening, the non-scorable speech detector  102  may be configured to receive the speech sample  112  provided by a user  104  (e.g., and stored in a data store  110 ) and to make a binary determination as to whether the sample  112  contains scorable speech or non-scorable speech. If speech sample  112  is determined to contain non-scorable speech, then the non-scorable speech detector  102  may filter out the sample  112  and prevent it from being passed to the scoring system. Alternatively, if speech sample  112  is determined to contain scorable speech, then the sample  112  may be passed to the scoring system for scoring. Speech determined to be non-scorable by the non-scorable speech detector  102  may comprise a variety of forms. For example, non-scorable speech may include speech of an unexpected language, whispered speech, speech that is obscured by background noise, off-topic speech, plagiarized or “canned” responses, and silent non-responses. 
     The non-scorable speech detector  102  may be implemented using a processing system (e.g., one or more computer processors) executing software operations or routines for detecting non-scorable speech. User computers  104  can interact with the non-scorable speech detector  102  through a number of ways, such as over one or more networks  108 . One or more servers  106  accessible through the networks  108  can host the non-scorable speech detector  102 . It should be understood that the non-scorable speech detector  102  could also be provided on a stand-alone computer for access by a user  104 . The one or more servers  106  may be responsive to one or more data stores  110  for providing input data to the non-scorable speech detector  102 . The one or more data stores  110  may be used to store speech samples  112  and non-scorable speech filters  114 . The non-scorable speech filters  114  may be used by the non-scorable speech detector  102  to determine whether the speech sample  112  comprises scorable or non-scorable speech. The speech sample  112  may comprise non-native speech spoken by a non-native speaker. 
       FIG. 2  is a block diagram depicting elements of a non-scorable speech detector  202 . The non-scorable speech detector  202  comprises an automatic speech recognition (ASR)/metric extractor module  204  and non-scorable speech filters  206 . As described above, the objective of the non-scorable speech detector  202  is to determine whether a speech sample  208  contains scorable speech  212  or non-scorable speech  214 . The ASR/metric extractor module  204  is configured to receive the speech sample  208  and to perform a number of functions. First, the ASR/metric extractor module  204  may perform an automated speech recognition (ASR) function, yielding a transcript of the speech sample  208 . The transcript of the speech sample  208  may be accompanied by one or more confidence scores, each indicating a reliability of a recognition decision made by the ASR function. For example, a confidence score may be computed for recognized words of the speech sample  208  to indicate how likely it is that the word was correctly recognized. Confidence scores may also be computed at a phrase-level or a sentence-level. 
     In addition to providing the ASR function, the ASR/metric extractor module  204  may also perform a metric extracting function, enabling the module  204  to extract a plurality of speech metrics  210  associated with the speech sample  208 . As an example, the ASR/metric extractor module  204  may be used to extract a word metric from the speech sample  208  that identifies the approximate number of words included in the sample  208 . The speech metrics  210  extracted by the metric extracting function may be dependent on the ASR output, or the metrics may be independent of and unrelated to the ASR output. For example, metrics used in determining whether a response is off-topic may be highly dependent on the ASR output, while metrics used in assessing an audio quality of a sample may function without reference to the ASR output. 
     The transcript of the speech sample and the speech metrics  210  may be received by the non-scorable speech filters  206  and used in making the binary determination as to whether the speech sample  208  contains scorable speech  212  or non-scorable speech  214 . If the speech sample is determined to contain non-scorable speech  214 , the speech sample  208  may be identified as non-scorable, and the sample  208  may not be provided to a scoring system for scoring so that it is withheld and not scored. Alternatively, if the speech sample  208  is determined to contain scorable speech  212 , the speech sample  208  may be provided to the scoring system for scoring. 
     The non-scorable speech filters  206  may include a plurality of individual filters, which may be configured to work independently of one another or in a collective manner, as determined by filter criteria  216 . Filter criteria  216  may also be used to enable or disable particular filters of the non-scorable speech filters  206 . For example, in certain testing situations utilizing open-ended test prompts, filter criteria  216  may be used to disable an off-topic filter, which would otherwise be used to filter out irrelevant or off-topic responses. As another example, if audio quality is determined to be of utmost importance for a given testing situation (e.g., speech samples taken under conditions causing high background noise in the sample), an audio quality filter may be enabled and all other filters may be disabled using the filter criteria  216 . Combinations of multiple filters may also be combined with filter criteria  216  using various machine-learning algorithms and training and test data. For example, a Waikato Environment for Knowledge Analysis (WEKA) machine learning toolkit can be used to train a decision tree model to predict binary values for samples (0 for scorable 1 for non-scorable) by combining different filters. Training and test data can be selected from standardized test data samples (e.g., Test of English as a Foreign Language data). 
     Filter criteria  216  may also be used to enable a step-by-step, serial filtering process. In the step-by-step process, the plurality of filters comprising the non-scorable speech filters  206  may be arranged in a particular order. Rather than being received and evaluated by the plurality of filters in a parallel, simultaneous manner, the sample  208  may be required to proceed through the ordered filters serially. Any one particular filter in the series may filter out the sample  208  as non-scorable, such that filters later in the series need not evaluate the sample  208 . 
       FIG. 3  is a block diagram depicting an example in which non-scorable speech filters  302  have independently-operating filters. Speech metrics  303  for a speech sample may be received by an audio quality filter  304 , an insufficient speech filter  306 , an off-topic filter  308 , an incorrect language filter  310 , and a plagiarism detection filter  311 . In the example of  FIG. 3 , a single veto from any one of the five filters identifying the speech sample as non-scorable will cause the non-scorable speech filters  302  to output a value identifying the sample as non-scorable speech  312 . The non-scorable speech filters  302  will output a value identifying the sample as scorable speech  314  only when all filters have each determined that the sample is scorable in this example. 
     By contrast,  FIG. 4  is a block diagram depicting an example in which non-scorable speech filters  402  have filters that collectively make a scorability determination  412  for a speech sample. As in  FIG. 3 , non-scorable speech filters  402  receive speech metrics  403  for the sample, which are used by an audio quality filter  404 , an insufficient speech filter  406 , an off-topic filter  408 , an incorrect language filter  410 , and a plagiarism detection filter  411 . However, rather a single filter independently determining that the sample is non-scorable, the example of  FIG. 4  makes the scorability determination  412  based on probabilities or sample scores from each of the five individual filters. Thus, in  FIG. 4 , each filter assigns a probability or sample score to the sample, and after scores from all five filters have been considered, the sample is identified as scorable speech  416  or non-scorable speech  414 . For example, a decision to score the speech sample can be made if all filters yield probabilities or scores over a certain threshold, or over individual thresholds set up for each filter. Suitable threshold scores or probabilities may be set through straightforward trial-and-error testing or reference speech samples. 
       FIG. 5A  is a block diagram illustrating example speech metrics considered by an audio quality filter  502 . A speech sample to be scored may suffer from various types of audio quality issues, including volume problems where the sample is too loud or too soft, noise problems where speech is obscured by loud background noise such as static or buzzing, microphone saturation problems caused by a test-taker&#39;s mouth being too close to a microphone, and problems caused by a low sampling rate. These audio quality issues may make it difficult for an automated scoring system to provide a valid assessment of speech contained in the sample. To address these issues, the audio quality filter  502  may be utilized to distinguish noise and other audio aberrations from clean speech and to filter out samples that should not be scored due to their audio quality problems. 
     The metrics considered by the audio quality filter  502  may primarily comprise acoustic metrics (e.g., pitch, energy, and spectrum metrics), some of which are not dependent on an ASR output. In the example of  FIG. 5A , numerous low-level descriptor acoustic metrics are utilized by the audio quality filter  502 . These low-level descriptor metrics include both prosodic metrics and spectrum-related metrics  510 . Prosodic metrics may include frequency contour metrics  504 , jitter and shimmer metrics  506 , peak speech level metrics  508 , and pitch and power metrics  513 . Spectrum-related metrics  510  may include Mel-Frequency cepstral coefficient metrics, logarithmic power of Mel-Frequency band metrics, and eight line spectral pair frequencies computed from eight linear predictive coding (LPC) coefficient metrics. Jitter metrics may include both local, frame-to-frame pitch period length deviations and differential, frame-to-frame pitch period length deviations (i.e., jitter of the jitter). Shimmer metrics may include local, frame-to-frame amplitude deviations between pitch periods. The pitch and power metrics  513  may be used to evaluate pitch and power values throughout the duration of the sample, respectively. Spectrum-related metrics  510  may be particularly useful in detecting speech with loud background noise because noise may have different spectral characteristics than speech (e.g., noise tends to have no or few peaks in the frequency domain). Numerous other metrics may be used as part of the audio quality filter  502 . For example, a signal-to-noise ratio (SNR) metric  512  may be used to approximate a ratio between a total energy of noise and a total energy of speech in the sample. 
     The audio quality filter  502  uses metrics, either independently or in various combinations, to make a binary determination as to whether a given response contains scorable speech  514  or non-scorable speech  516 . The audio quality filter metrics may be evaluated using various machine-learning algorithms and training and test data to determine the best individual metrics and the best combinations of metrics. For example, a support vector machine (SVM) training algorithm can be used for training the audio quality filter  502 . The filter  502  can be trained using representative samples, such as samples randomly selected from standardized test data (e.g., Test of English as a Foreign Language data). Certain metrics can be selected for consideration by the audio quality filter  502 , such as the spectrum-related metrics  510 . In one example, the audio quality filter  502  can be configured to consider the Mel-Frequency cepstral coefficient metric in detecting poor audio quality in responses. 
       FIG. 5B  is a block diagram illustrating example speech metrics considered by an insufficient-speech filter  552 . The insufficient-speech filter  552  may be used to detect situations where a test-taker, in response to a test prompt, says nothing at all. The insufficient-speech filter  552  may also be used to detect instances where the test-taker provides a spoken response that is of an insufficient duration. Further, the insufficient-speech filter  552  may also be used to detect instances where a microphone has become unplugged and no sample signal is received. In traditional automated scoring systems, the response containing insufficient speech may be accepted by a scoring system and may be scored erroneously. To address this issue, the insufficient-speech filter  552  may be used to detect non-scorable responses that do not contain a sufficient amount of spoken speech and to prevent such non-scorable responses from being scored by the scoring system. 
     The metrics considered by the insufficient-speech filter  552  may comprise both ASR-based metrics  558  and non-ASR-based metrics. In the example of  FIG. 5B , ASR-based metrics  558  may comprise fluency metrics, silence metrics  560 , ASR-confidence metrics, and word metrics. Fluency metrics may be configured to evaluate the fluency of a test-taker&#39;s response. Silence metrics  560  may be configured to approximate measures of silence contained in the response, such as the mean duration of silent periods and the number of silent periods. ASR-confidence metrics may be considered by the insufficient-speech filter  552  because low speech recognition reliability may be indicative of samples lacking a sufficient amount of speech. Word metrics may be used to approximate a number of words in the response, which can also be used to indicate whether the response lacks a sufficient amount of speech. 
     Non-ASR-based metrics may comprise voice activity detection (VAD)-related metrics  562 , amplitude metrics, spectrum metrics  564 , pitch metrics  556 , and power metrics  554 . VAD-related metrics  562  are used to detect voice activity in a sample and may be used, for example, to detect a proportion of voiced frames in a response and a number and total duration of voiced regions in a response. Amplitude metrics may be used to detect abnormalities in energy throughout a sample. Such energy abnormalities may be relevant to the insufficient speech filter because silent non-responses may have an abnormal distribution in energy (e.g., non-responses may contain very low energy). Power metrics  554  and pitch metrics  556  may be designed to capture an overall distribution of pitch and power values in a speaker&#39;s response using mean and variance calculations. Spectrum metrics  564  may be used to investigate frequency characteristics of a sample that may indicate that the sample consists of an insufficient amount of speech. 
     The insufficient speech filter  552  uses metrics, either independently or in various combinations, to make a binary determination as to whether a given response contains scorable speech  566  or non-scorable speech  568 . The insufficient speech filter metrics may be evaluated using various machine-learning algorithms and training and test data. In one example, the insufficient speech filter  552  includes decision tree models trained using a WEKA machine learning toolkit. Training and test data for the example can be drawn from an English language test of non-native speakers responding to spontaneous and recited speech prompts over a phone. In one example, the insufficient speech filter  552  is configured to consider both fluency metrics and VAD-related metrics  562  in detecting responses lacking a sufficient amount of speech. 
       FIG. 6A  is a block diagram illustrating example speech metrics considered by an off-topic filter  602 . In speech assessment situations where scoring is automated, a test-taker may inadvertently or purposely supply a response that is not sufficiently related to a provided test prompt. For example, a test-taker may attempt to respond to a test-prompt about politics by talking about sports, a topic with which he or she may be more comfortable. In traditional automated scoring systems, the irrelevant response may be accepted by a scoring system and may be nevertheless scored, even though this would be improper considering the purpose of the test. To enable more reliable scores and to prevent test-takers from gaming the system (cheating), the off-topic filter  602  may be used to validate the relevancy of responses before passing them on to the scoring system. Once detected, off-topic responses can be denoted as non-scorable speech and treated accordingly (i.e., withheld and not scored). Off-topic responses are considered to be those with irrelevant material and/or an excessive amount of mispronounced or unintelligible words as judged by a human listener. 
     The metrics considered by the off-topic filter  602  may be based on similarity metrics. Such similarity metrics may function by comparing a spoken response to an item-specific vocabulary list or reference texts including but not limited to the item&#39;s prompt, the item&#39;s stimuli, transcription of pre-collected responses, and texts related to the same topic. Transcriptions of pre-collected responses may be generated by human or a speech recognizer. For example, when a response is off-topic, most of the response&#39;s words may not be covered by an item-specific vocabulary list. Thus, item-specific vocabulary metrics  610  may be used to approximate an amount of out-of-vocabulary words provided in response to a given test prompt. Similarly, word error rate (WER) metrics may be used to estimate a similarity between a spoken response and the test prompt used to elicit the response. 
     There are many ways of determining similarity between response and the reference texts. One method is a Vector Space Model (VSM) method, which is also used in automated essay scoring systems. Under this method, both response and the reference texts are converted to vectors, whose elements are weighted using TF*IDF (term frequency, inverse document frequency). Then, a cosine similarity score between vectors can be used to estimate similarity between the responses the vectors originally represented. 
     Another method of determining similarity between responses and reference texts is the pointwise mutual information (PMI) method. PMI was introduced to calculate semantic similarity between words. It is based on word co-occurrence in a large corpus. Given two words, w 1  and w 2 , their PMI is computed using: 
               PMI   ⁡     (       w   1     ,     w   2       )       =     log   ⁢           ⁢   2   ⁢         p   ⁡     (         w   1     &amp;     ⁢           ⁢     w   2       )           p   ⁡     (     w   1     )       ×     p   ⁡     (     w   2     )           .             
This indicates a statistical dependency between words w 1  and w 2  and can be used as a measure of the semantic similarity of the two words. Given the word-to-word similarity, the similarity between two documents may be calculated using the following function:
 
               sim   ⁡     (       D   1     ,     D   2       )       =       1   2     ⁢     (           ∑     w   ∈     {     D   1     }         ⁢     (     max   ⁢           ⁢     Sim   ⁡     (     w   ,     D   2       )       ×     idf   ⁡     (   w   )         )           ∑     w   ∈     {     D   1     }         ⁢     idf   ⁡     (   w   )           +         ∑     w   ∈     {     D   2     }         ⁢     (     max   ⁢           ⁢     Sim   ⁡     (     w   ,     D   1       )       ×     idf   ⁡     (   w   )         )           ∑     w   ∈     {     D   2     }         ⁢     idf   ⁡     (   w   )             )             
For each word w in document D 1 , a word in document D 2  having a highest similarity to word w is found. Similarly, for each word in D 2 , the most similar words in D 1  are identified. A similarity score between the two documents may be calculated by combining the similarity of the words they contain, weighted by their word specificity (i.e., inverse document frequency values).
 
     Other metrics unrelated to similarity measures may be considered by the off-topic filter  602 . For example, an ASR confidence metric  604  may be considered by the off-topic filter  602 . For example, an ASR system may generate a significant number of recognition errors when processing off-topic responses. Other metrics produced during the ASR process may also be considered by the off-topic filter  602 , such as response-length metrics  606 , words-per-minute metrics, number-of-unique-grammatical-verb-form metrics, and disfluency metrics  608 , among others. For example, the disfluency metrics  608  may be used to investigate breaks, irregularities, or non-lexical utterances that may occur during speech and that may be indicative of an off-topic response. 
     The off-topic filter  602  uses metrics, either independently or in various combinations, to make a binary determination as to whether a given response contains scorable speech  612  or non-scorable speech  614 . For example, the off-topic filter metrics can be evaluated using receiver operating characteristic (ROC) curves. ROC curves can be generated based on individual off-topic filter metrics and also based on combined off-topic filter metrics. Training and testing data can be selected from speech samples (e.g., responses to the Pearson Test of English Academic (PTE Academic)), with human raters identifying whether selected responses were relevant to a test prompt. In one example, the off-topic filter  602  may be configured to consider the ASR confidence metrics  604  in identifying off-topic responses. 
       FIG. 6B  is a block diagram illustrating example speech metrics considered by an incorrect-language filter  652 . In responding to a test prompt requesting a response in a particular language, test-takers may attempt to game the system (cheat) by instead answering in their native language. To address this issue, the incorrect language filter  652  may be used to identify a likelihood that a speech sample includes speech from a language different from an expected language. In an example, the expected language is English, and the incorrect-language filter is configured to make a binary determination as to whether the response is in English or not. 
     The incorrect-language filter  652  can be operable for use with both native speakers and non-native speakers of a particular language. Non-native speakers&#39; speech tends to display non-standard pronunciation characteristics, which can make language filtering more challenging. For instance, when native Korean speakers speak in English, they may replace some English phonemes not in their language with their native phones, and epenthesize vowels within consonant clusters. Such behavior tends to reduce the phonetic and phonotactic distinctions between English and other languages, which may make language filtering more difficult. Further, the frequency of pronunciation errors is influenced by speakers&#39; native language and proficiency level, with lower proficiency speakers being more likely to exhibit greater degrees of divergence from standard pronunciation. 
     The metrics considered by the incorrect-language filter  652  may comprise a number of metrics based on a combination of a phone recognizer and a language-dependent phone language model. Metric extraction may involve use of a plurality of language identification models to determine a likelihood that a particular language is used in a speech file. Each of the plurality of the language identification models may be associated with a different language. The language identification models may focus on phonetic and phonotactic differences among languages, wherein the frequencies of phones and phone sequences differ according to languages and wherein some phone sequences occur only in certain languages. 
     In the example of  FIG. 6B , language identification models may be used to extract certain metrics from a speech sample, such as language-identification-based metrics  654 , a fluency metric  656 , and various ASR metrics  662 . The language-identification-based metrics  654  may include, for example, a most likely language metric, a second most likely language metric, a confidence score for most likely language metric, and a difference from expected language confidence metric. The most likely language metric and the second most likely language metric utilize the language identification models to approximate the most likely and second most likely languages used in the sample. The difference from expected language confidence metric may be used to compute a difference between a confidence score associated with the language most likely associated with the speech sample and a second confidence score associated with the second most likely used language. Further, a speaking rate metric configured to approximate a speaking rate used in the sample may be considered by the incorrect language-filter  652 . 
     The incorrect-language filter  652  uses metrics, either independently or in various combinations, to make a binary determination as to whether a given response contains scorable speech  664  or non-scorable speech  666 . The incorrect-language filter metrics may be evaluated using various machine-learning algorithms and training and test data. For example, a Waikato Environment for Knowledge Analysis (WEKA) machine learning toolkit can be used to train a decision tree model to predict binary values for samples (0 for English and 1 for non-English). Training and test data can be selected, such as from the Oregon Graduate Institute (OGI) Multilanguage Corpus or other standard language identification development data set. For example, where the objective is to distinguish non-English responses from English responses, and the speakers are non-native speakers, English from non-native speakers can be used to train and evaluate the filter  652 . Because the English proficiency levels of speakers may have an influence on the accuracy of non-English response detection, the responses used to train the filter  652  can be selected to include similar numbers of responses for a variety of different proficiency levels. Certain metrics may be considered by the incorrect language filter  652 , such as the ASR metrics  662  and the speaking rate metric. In one example, the incorrect language filter  652  may be configured to consider the ASR metrics  662  and the speaking rate metric together in identifying responses containing an unexpected language. 
       FIG. 7  is a block diagram illustrating example speech metrics considered by a plagiarism-detection filter  702 . Prior to testing, a test-taker may memorize “canned” responses from websites, books, and other sources, and during testing, the test-taker may seek to repeat from memory such responses. To address this issue, the plagiarism-detection filter  702  may be used to identify a likelihood that a response has been repeated from memory during testing. 
     The metrics considered by the plagiarism-detection filter  702  may be similar to the similarity metrics considered by the off-topic filter of  FIG. 6A . The metrics considered by the plagiarism-detection filter  702  may compare a test-taker&#39;s response with a pool of reference texts. If a similarity value approximated by a metric is higher than a predetermined threshold, the response may be tagged as plagiarized and prevented from being scored by an automated scoring system. Because the similarity metrics of the plagiarism-detection filter  702  require that a response speech be compared to one or more reference texts (e.g., exemplary test responses published on the interne or in books), certain metrics of the plagiarism-detection filter  702  may be ASR-based metrics. Similar to the off-topic filter of  FIG. 6A , the plagiarism-detection filter  702  may consider ASR confidence metrics  706 , response length metrics  708 , and item-specific vocabulary metrics  710 . The plagiarism-detection filter  702  uses the metrics, either independently or in various combinations, to make a binary determination as to whether a given response contains scorable speech  712  or non-scorable speech  714 . 
       FIG. 8  is a block diagram depicting non-scorable speech filters  802  comprising a combined filter  804 . In the example of  FIG. 8 , speech metrics  806  are received by the combined filter  804 , which makes a determination as to whether a given speech sample contains scorable speech  808  or non-scorable speech  810 . The combined filter  804  may combine aspects of the audio quality filter, insufficient speech filter, off-topic filter, incorrect language filter, and plagiarism detection filter in making a scorability determination. The combination of the various filters may allow for a plurality of diverse metrics to be considered together in making the scorability determination. Thus, metrics that were previously associated with only a single filter may be used together in the combined filter  804 . Combinations of filters and metrics may be evaluated with training and test data sets and/or trial and error testing to determine particular sets of filters and metrics that provide accurate determinations of a sample&#39;s scorability. 
       FIG. 9  is a flowchart depicting a method for scoring a response speech sample. The response speech sample is received  904  at a non-scorable response detector, which may be configured to perform an ASR function and a metric extraction function  906 . The non-scorable response detector may be further configured to make a binary determination  908  as to whether the speech sample contains scorable speech or non-scorable speech. If the speech sample is determined to be non-scorable  912 , an indication of non-scorability may be associated with the speech sample  913 , such that the sample will not receive a score. Alternatively, if the speech sample is determined to be scorable  910 , the speech sample may be provided to a scoring system for scoring  911 . Filtering out non-scorable speech from the scoring model in this manner may help to ensure that all scores assessed are valid and representative of the speech sample. As noted above, the non-scorable response detector may be used in situations where the scoring model comprises an automated scoring system and no human scorer is used to screen responses prior to their receipt at the scoring model. 
       FIGS. 10A ,  10 B, and  10 C depict example systems for use in implementing a method of scoring non-native speech. For example,  FIG. 10A  depicts an exemplary system  1300  that includes a standalone computer architecture where a processing system  1302  (e.g., one or more computer processors located in a given computer or in multiple computers that may be separate and distinct from one another) includes a non-scorable speech detector  1304  being executed on it. The processing system  1302  has access to a computer-readable memory  1306  in addition to one or more data stores  1308 . The one or more data stores  1308  may include speech samples  1310  as well as non-scorable speech filters  1312 . 
       FIG. 10B  depicts a system  1320  that includes a client server architecture. One or more user PCs  1322  access one or more servers  1324  running a non-scorable speech detector  1326  on a processing system  1327  via one or more networks  1328 . The one or more servers  1324  may access a computer readable memory  1330  as well as one or more data stores  1332 . The one or more data stores  1332  may contain a speech sample  1334  as well as non-scorable speech filters  1336 . 
       FIG. 10C  shows a block diagram of exemplary hardware for a standalone computer architecture  1350 , such as the architecture depicted in  FIG. 10A  that may be used to contain and/or implement the program instructions of system embodiments of the present invention. A bus  1352  may serve as the information highway interconnecting the other illustrated components of the hardware. A processing system  1354  labeled CPU (central processing unit) (e.g., one or more computer processors at a given computer or at multiple computers), may perform calculations and logic operations required to execute a program. A non-transitory processor-readable storage medium, such as read only memory (ROM)  1356  and random access memory (RAM)  1358 , may be in communication with the processing system  1354  and may contain one or more programming instructions for performing the method of scoring non-native speech. Optionally, program instructions may be stored on a non-transitory computer readable storage medium such as a magnetic disk, optical disk, recordable memory device, flash memory, or other physical storage medium. 
     A disk controller  1360  interfaces one or more optional disk drives to the system bus  1352 . These disk drives may be external or internal floppy disk drives such as  1362 , external or internal CD-ROM, CD-R, CD-RW or DVD drives such as  1364 , or external or internal hard drives  1366 . As indicated previously, these various disk drives and disk controllers are optional devices. 
     Each of the element managers, real-time data buffer, conveyors, file input processor, database index shared access memory loader, reference data buffer and data managers may include a software application stored in one or more of the disk drives connected to the disk controller  1360 , the ROM  1356  and/or the RAM  1358 . Preferably, the processor  1354  may access each component as required. 
     A display interface  1368  may permit information from the bus  1352  to be displayed on a display  1370  in audio, graphic, or alphanumeric format. Communication with external devices may optionally occur using various communication ports  1372 . 
     In addition to the standard computer-type components, the hardware may also include data input devices, such as a keyboard  1373 , or other input device  1374 , such as a microphone, remote control, pointer, mouse and/or joystick. 
     Additionally, the methods and systems described herein may be implemented on many different types of processing devices by program code comprising program instructions that are executable by the device processing subsystem. The software program instructions may include source code, object code, machine code, or any other stored data that is operable to cause a processing system to perform the methods and operations described herein and may be provided in any suitable language such as C, C++, JAVA, for example, or any other suitable programming language. Other implementations may also be used, however, such as firmware or even appropriately designed hardware configured to carry out the methods and systems described herein. 
     The systems&#39; and methods&#39; data (e.g., associations, mappings, data input, data output, intermediate data results, final data results, etc.) may be stored and implemented in one or more different types of computer-implemented data stores, such as different types of storage devices and programming constructs (e.g., RAM, ROM, Flash memory, flat files, databases, programming data structures, programming variables, IF-THEN (or similar type) statement constructs, etc.). It is noted that data structures describe formats for use in organizing and storing data in databases, programs, memory, or other computer-readable media for use by a computer program. 
     The computer components, software modules, functions, data stores and data structures described herein may be connected directly or indirectly to each other in order to allow the flow of data needed for their operations. It is also noted that a module or processor includes but is not limited to a unit of code that performs a software operation, and can be implemented for example as a subroutine unit of code, or as a software function unit of code, or as an object (as in an object-oriented paradigm), or as an applet, or in a computer script language, or as another type of computer code. The software components and/or functionality may be located on a single computer or distributed across multiple computers depending upon the situation at hand. 
     While the disclosure has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the embodiments. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents. 
     It should be understood that as used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. Further, as used in the description herein and throughout the claims that follow, the meaning of “each” does not require “each and every” unless the context clearly dictates otherwise. Finally, as used in the description herein and throughout the claims that follow, the meanings of “and” and “or” include both the conjunctive and disjunctive and may be used interchangeably unless the context expressly dictates otherwise; the phrase “exclusive of” may be used to indicate situations where only the disjunctive meaning may apply.