High spontaneous-rate fibers have low thresholds while low SR fibers have high thresholds.

Evidence

The threshold of a neuron is defined as the lowest sound level that leads to a measureable increase in the driven spike rate. High spontaneous rate fibers have low thresholds, whereas low spontaneous fibers have high thresholds. Figure 2–8 shows that the high spontaneous rate fiber begins firing above its spontaneous rate at a very low input stimulus level (<5 dB SPL). On the other hand, the low spontaneous rate fiber does not fire above its spontaneous rate until an input level of roughly 25 dB SPL is achieved. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 235

Categorization

• XREF: Plausibly connects to rate-level functions and firing dynamics the reader compiled in earlier chapters.