The “speech banana” is a concept in audiology that visually represents the sounds most important for human communication. This distinct, banana-shaped area is plotted onto an audiogram, a graph used to measure a person’s hearing sensitivity. It provides a simple way for audiologists and patients to see which parts of spoken language, or phonemes, may be difficult to hear due to hearing loss. Since nearly all common speech sounds fall within this range of pitch and loudness, the speech banana acts as a gauge for functional hearing ability.
Defining the Visual Map
The audiogram provides the structured plot for the speech banana. The horizontal axis represents frequency, or pitch, measured in Hertz (Hz). Lower pitches are plotted on the left side, and higher pitches move toward the right. The vertical axis measures intensity, or loudness, in Decibels (dB). Softer sounds are located near the top of the graph, while louder sounds are plotted toward the bottom. The speech banana is an overlay that clusters the phonemes of human speech onto this grid, typically spanning frequencies from about 250 Hz to 4000 Hz at normal conversational levels.
The Sounds of Speech
The phonemes within the speech banana vary in pitch and loudness, which gives the area its distinctive curved shape. Low-frequency sounds, such as the vowels /o/ and /a/, are generally louder and carry the acoustic power of speech. These sounds are often the easiest to hear, even for individuals with some degree of hearing loss.
Conversely, high-frequency sounds are quieter and include consonants like /s/, /f/, /th/, and /sh/. These quieter, high-pitched sounds are responsible for the clarity and intelligibility of spoken language. Vowels allow a person to know that someone is speaking, while consonants provide the specific information needed to distinguish between words like “sat,” “fat,” and “that.” Nearly all common sound combinations fall within this speech range.
Measuring Hearing Loss Impact
Audiologists use the speech banana to explain the impact of hearing loss on conversation understanding. A patient’s hearing threshold—the softest level they can hear at different frequencies—is plotted on the audiogram. Any speech sounds that fall above this threshold line are likely not heard by the patient. This comparison helps visualize why a person may report being able to hear but not understand what is being said. If the hearing loss affects the high-frequency range, the softer consonant sounds are missed, resulting in muffled speech and difficulty with comprehension.
Strategies for Accessing Speech Sounds
The goal of hearing intervention is to restore a person’s access to the sounds within the speech banana. Hearing aids are programmed to selectively amplify the specific frequencies and intensities of speech that fall above the patient’s hearing threshold. This process brings conversational sounds back into a range the patient can comfortably hear.
For profound hearing loss, a cochlear implant may be recommended; it bypasses damaged parts of the inner ear to directly stimulate the auditory nerve. Both technologies are fine-tuned to ensure the listener can perceive the full spectrum of the speech banana, particularly the high-frequency consonants, to maximize speech understanding.