Let's solve each part step by step using the graph and the information provided: ### 1. **Threshold Level (for 3000 Hz, blue line)** - **Definition:** The threshold level is the sound level at which the spike rate starts to increase **above the spontaneous rate** (10 spikes/sec). - **How to Find:** Look at the blue line (3000 Hz) and find the dB SPL at which the spike rate first rises above 10 spikes/sec. **From the graph:** - At 20 dB SPL: Spike rate ≈ 10 spikes/sec (matches spontaneous rate) - At 25 dB SPL: Spike rate ≈ 13 spikes/sec (first clear increase above spontaneous rate) **Threshold Level =** **25 dB SPL** --- ### 2. **Saturation Level (for 3000 Hz, blue line)** - **Definition:** The saturation level is the sound level at which the spike rate starts to **plateau** or saturate (no longer increases significantly with increasing sound level). - **Given:** Saturation rate = 55 spikes/sec. - **How to Find:** Find the dB SPL at which the blue line approaches or reaches 55 spikes/sec. **From the graph:** - At 50 dB SPL: Spike rate ≈ 52 spikes/sec - At 55 dB SPL: Spike rate ≈ 54 spikes/sec - At 60 dB SPL: Spike rate ≈ 55 spikes/sec **Saturation Level =** **60 dB SPL** --- ### 3. **Dynamic Range** - **Definition:** The dynamic range is the difference between the threshold and saturation levels. - **Calculation:** \[ \text{Dynamic Range} = \text{Saturation Level} - \text{Threshold Level} \] \[ = 60\, \text{dB SPL} - 25\, \text{dB SPL} = 35\, \text{dB} \] --- ## **Summary Table** | Quantity | Value | |------------------|---------------| | Threshold Level | **25 dB SPL** | | Saturation Level | **60 dB SPL** | | Dynamic Range | **35 dB** | --- **Final Answers:** - **Threshold level:** 25 dB SPL - **Saturation level:** 60 dB SPL - **Dynamic range:** 35 dB

Let's analyze the graph step-by-step to determine the threshold level, saturation level, and dynamic range for the 3000 Hz (blue) spike rate curve. --- ### **Given Data:** - Spontaneous rate: **10 spikes/sec** - Saturation rate: **55 spikes/sec** --- ## 1. **Finding the Threshold Level** **Definition:** The threshold is the lowest sound level at which the spike rate exceeds the spontaneous rate (10 spikes/sec). **Step-by-step:** - Look at the blue curve (3000 Hz) and identify the sound level where the spike rate just begins to rise above 10 spikes/sec. - From the graph: - At **20 dB SPL**, spike rate ≈ **10 spikes/sec** (equals spontaneous rate) - At **25 dB SPL**, spike rate ≈ **13 spikes/sec** (above spontaneous rate) **Interpretation:** - The spike rate remains at 10 spikes/sec at 20 dB SPL, but this is just at the spontaneous rate. - The threshold is typically defined as the point where the rate **first exceeds** spontaneous activity. **Therefore:** - The threshold level is at **25 dB SPL** because at 20 dB SPL the rate is still at spontaneous level, and at 25 dB SPL, it increases above spontaneous. **Final calculation:** \[ \boxed{\text{Threshold} \approx 25\, \text{dB SPL}} \] --- ## 2. **Finding the Saturation Level** **Definition:** The saturation level is at the sound level where the spike rate approaches the maximum (55 spikes/sec). Usually, saturation is considered when the rate is within a small margin of the maximum. **Step-by-step:** - From the graph, observe the spike rate as the sound level increases: - At **50 dB SPL**, rate ≈ **52 spikes/sec** - At **55 dB SPL**, rate ≈ **54 spikes/sec** - At **60 dB SPL**, rate ≈ **55 spikes/sec** **Interpretation:** - The rate approaches 55 spikes/sec at around **60 dB SPL**. - Since the rate is very close to maximum at 60 dB SPL, this is taken as the saturation level. **Final calculation:** \[ \boxed{\text{Saturation level} \approx 60\, \text{dB SPL}} \] --- ## 3. **Calculating the Dynamic Range** **Definition:** The dynamic range is the difference between the saturation level and the threshold level: \[ \text{Dynamic Range} = \text{Saturation Level} - \text{Threshold Level} \] **Calculation:** \[ 60\, \text{dB} - 25\, \text{dB} = 35\, \text{dB} \] --- ## **Summary of Calculations:** | Quantity | Approximate Value | |-------------------------|------------------------------| | **Threshold Level** | **25 dB SPL** | | **Saturation Level** | **60 dB SPL** | | **Dynamic Range** | **35 dB** | --- ## **Final Answer:** **The threshold level is approximately 25 dB SPL.** **The saturation level is approximately 60 dB SPL.** **The dynamic range is approximately 35 dB.**

The threshold level is the minimum sound level at which the neuron’s firing rate begins to rise above spontaneous activity. The saturation level is the sound level at which the neuron’s firing rate plateaus near its maximum, indicating maximum responsiveness. The dynamic range is the span of sound levels over which the neuron’s firing rate increases from threshold to saturation, reflecting its sensitivity and capacity to encode different sound intensities.