The Speech Recognition Threshold (SRT) is a foundational measurement in audiology, representing a person’s ability to hear and understand spoken language at the softest possible level. This test is a standard component of a comprehensive hearing evaluation. Recorded in decibels, the SRT indicates the quietest intensity at which an individual can successfully recognize and repeat specific speech materials. This measurement gives clinicians initial insight into how hearing loss might affect a patient’s daily communication.
Defining Speech Recognition Threshold
The Speech Recognition Threshold is formally defined as the minimum intensity level, measured in decibels hearing level (dB HL), at which a patient can correctly identify and repeat a specific set of speech sounds 50% of the time. It is a true threshold measurement, focusing on the lowest volume required for understanding speech, rather than just hearing the sound itself.
The SRT is distinct from the Speech Recognition Score (SRS), which is also known as the Word Recognition Score (WRS). The SRT measures the threshold of audibility and intelligibility for speech, whereas the SRS measures the clarity of speech understanding when words are presented at a comfortable, louder volume. SRS is expressed as a percentage of words correctly repeated, while SRT is an intensity level in dB HL. The primary purpose of the SRT is to verify the reliability of a patient’s pure tone audiogram results.
The SRT reflects a patient’s overall hearing sensitivity for the frequencies most important for speech understanding. If a patient has a hearing loss, the SRT will be elevated, meaning they require a louder volume to meet the 50% recognition criterion. This threshold serves as a baseline for determining appropriate starting levels for other speech tests and for guiding the development of personalized treatment plans.
Administering the SRT Measurement
The administration of the SRT measurement relies on the use of specific auditory stimuli known as spondee words. Spondees are two-syllable compound words, such as “baseball,” “hotdog,” or “airplane,” that are spoken with equal stress on both syllables. These words are used because their recognition rapidly increases from 0% to 100% correctness with only a small increase in intensity, allowing for an accurate and efficient determination of the 50% threshold.
Before testing begins, the patient is familiarized with the list of spondee words to ensure that any incorrect responses are due to hearing difficulty rather than unfamiliar vocabulary. The test is typically performed in a soundproof booth with the patient wearing headphones or insert earphones. The audiologist begins by presenting the spondee words at an intensity level that the patient can clearly hear, often \(30\) to \(40\) dB above their estimated hearing threshold.
To find the threshold, the audiologist employs a descending technique, similar to the process used for pure tone testing. The intensity is systematically decreased, often in \(10\) dB steps, after a correct response, and increased in \(5\) dB steps after an incorrect response.
The patient’s task is to repeat the word they hear, even if they must guess. The test continues until the lowest level where they can correctly repeat approximately \(50\%\) of the presented words is found. The words may be presented via a recorded list, which ensures standardization, or through the audiologist’s monitored live voice, which requires careful control to ensure the voice level remains consistent.
Clinical Importance and Comparison to PTA
The clinical significance of the SRT lies in its function as a powerful cross-check for the results of the pure tone audiogram. The pure tone audiogram measures hearing thresholds at specific frequencies using beeps, and the Pure Tone Average (PTA) is calculated by averaging the thresholds obtained at \(500\), \(1000\), and \(2000\) Hertz (Hz). These three frequencies are acoustically important because they represent the primary frequency range of human speech.
According to the cross-check principle, the SRT value should closely agree with the PTA, ideally falling within \(6\) to \(10\) dB of each other. This close alignment confirms the reliability of the patient’s responses during both the pure tone and the speech tests. If the SRT and PTA agree, the audiologist can have greater confidence in the diagnosis and the subsequent treatment recommendations.
A significant discrepancy between the SRT and the PTA can indicate several clinical issues that require further investigation. For instance, if the SRT is much better (lower) than the PTA, it may suggest the patient was exaggerating their hearing loss during the pure tone test, a condition referred to as non-organic hearing loss. Conversely, if the SRT is significantly worse (higher) than the PTA, it may point to a unique type of hearing impairment, such as a central auditory processing disorder.
The SRT also serves a role in setting the presentation level for other speech tests, such as the Word Recognition Score. By knowing the softest level at which a patient can understand speech, the audiologist can select an appropriate, comfortable volume for the subsequent measurements. This ensures that the subsequent measurements accurately reflect the patient’s ability to understand speech in real-world listening situations.