What do the horizontal lines on an audiogram represent?

The horizontal lines on an audiogram actually represent frequency levels, which are measured in hertz (Hz). An audiogram is a graphical representation of a person's hearing ability across different frequencies.

In this context, the horizontal axis of the audiogram depicts the frequency of sounds, ranging from low to high frequencies. This allows clinicians to assess hearing sensitivity across the frequency spectrum, which is crucial for diagnosing hearing loss and determining appropriate interventions.

It's important to note that while the other options mention concepts related to hearing, they do not represent what the horizontal lines signify in the context of an audiogram. Noise intensity, for instance, is generally represented on the vertical axis alongside sound pressure level (measured in decibels), while speech recognition ability is assessed through different methods that do not utilize the horizontal lines on an audiogram. Sound duration is also not a variable represented in this specific format, as audiograms focus primarily on frequency and intensity rather than the time dimension of sounds.