A comprehensive hearing evaluation includes specialized tests that measure an individual’s ability to hear and understand sound. The Speech Recognition Threshold (SRT) is a foundational measurement assessing hearing sensitivity for spoken language. Represented in decibels (dB), the SRT provides information that complements the detection of pure tones. This measurement is integral to understanding how hearing loss impacts daily communication and helps establish a baseline for further speech testing.
Defining the Speech Recognition Threshold
The Speech Recognition Threshold (SRT) defines the lowest intensity level at which a person can correctly identify and repeat standardized speech material at least 50% of the time. Expressed in decibels Hearing Level (dB HL), this threshold reflects the softest level at which speech sounds become intelligible. Unlike the Pure Tone Threshold (PTT), which measures simple detection, the SRT requires cognitive processing to understand and recognize the word. The SRT is a direct measure of a person’s ability to perceive speech. The 50% accuracy criterion is used to reliably define the threshold of understanding.
The Procedure of SRT Testing
The SRT test relies on “spondee words,” which are two-syllable compound words like “hotdog” or “ice cream” pronounced with equal stress. These words are easily recognizable and have a steep psychometric function, meaning a small change in volume results in a large change in recognition percentage. The audiologist first familiarizes the patient with the list to ensure results reflect hearing ability, not vocabulary knowledge. The patient’s task is to repeat the word back immediately upon hearing and recognizing it.
The audiologist uses a descending technique to find the threshold, typically starting at a comfortably loud level and presenting a word. If the word is repeated correctly, the intensity is lowered in steps, often by 10 dB, until the patient misses a word. The intensity is then increased in smaller steps, usually 5 dB, until the patient correctly repeats the word again, a process known as a bracketing technique. This procedure continues until the audiologist finds the lowest intensity level where the patient can correctly repeat half of the words presented at that volume. Using recorded speech materials is preferred over live voice to ensure the stimulus intensity is precisely controlled and consistent.
Clinical Significance and Interpretation of SRT Results
The primary clinical application of the SRT score is to validate the results of the Pure Tone Average (PTA). The PTA is calculated by averaging the pure tone hearing thresholds at the speech frequencies of 500 Hz, 1000 Hz, and 2000 Hz. Because the SRT and the PTA both measure hearing sensitivity within the range of sounds most important for understanding speech, they are expected to correlate closely. Ideally, the SRT score should be within about 6 to 10 dB of the patient’s PTA.
A close agreement between these two measures provides a crucial “cross-check” that confirms the reliability of the entire hearing evaluation. If a significant discrepancy exists, it signals a potential issue that the clinician must investigate further. For instance, an SRT that is substantially better (lower dB HL) than the PTA may indicate the patient is exaggerating their hearing loss, a condition known as non-organic hearing loss. Conversely, if the PTA is much better than the SRT, it could suggest a technical error during the pure tone test or, in some cases, an auditory processing difficulty where the patient can hear the tones but struggles to recognize complex speech sounds. The SRT also serves a practical purpose by establishing the reference level for other subsequent speech tests, such as Word Recognition Score testing.