Auditory nerve fibers divide into three types by spontaneous firing rate.

Evidence

Auditory nerve fibers are characterized based on their spontaneous firing rate (SR), with low (15% of fibers), medium (25% of fibers), and high (60% of fibers) spontaneous firing rates. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 699

Neurons demonstrate saturation, which occurs when increases in stimulus level no longer lead to increases in firing rate. … The characteristics of the three different fiber types are as follows:

• high SR/low threshold fibers. These fibers respond at low levels, have high spontaneous rates, and small dynamic ranges. They saturate at about 25 to 30 dB SPL. Roughly 60% of fibers fall into this category. • medium SR/medium threshold fibers. These fibers code for moderate stimulus levels and have moderate spontaneous rates. Their dynamic range is still small but is larger than that of the low-threshold fibers. Roughly 25% of fibers fall into this category. • low SR/high threshold fibers. These fibers code for high stimulus levels and have low spontaneous rates. Their dynamic range is the largest of all fibers but rarely exceeds 60 dB (Palmer & Evans, 1979). Roughly 15% of fibers fall into this category.

— Jennifer Lentz, Psychoacoustics- Perception of Normal…, 239

Categorization

• DEFINE: Defines neural saturation and lays out the three-fiber classification scheme.
• XREF: Connects to the three-fiber population model relevant to cochlear implant coding and hearing-loss characterization.
• corroborated: 2 independent passages support this claim — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 699; Jennifer Lentz, Psychoacoustics- Perception of Normal…, 239