## Heatmaps and Line Graphs: Spatial Hearing Analysis in Different Environments
### Overview
The image presents a spatial hearing analysis comparing three environments: Nocturnal nature, Forrest walk, and City center. It consists of three heatmaps (A) showing Interaural Level Difference (ILD) probability density as a function of frequency, and two line graphs (B & C) depicting Scale-σ and Location-μ respectively, also as a function of frequency. The line graphs compare the three environments.
### Components/Axes
* **Heatmaps (A):**
* **X-axis:** ILD [dB] (ranging approximately from -10 dB to 10 dB)
* **Y-axis:** Frequency [kHz] (ranging approximately from 0 kHz to 11 kHz)
* **Color Scale:** Prob density (ranging approximately from 0 to 0.16)
* **Environments:** Nocturnal nature, Forrest walk, City center. Each heatmap represents one environment.
* **Dashed White Lines:** Vertical lines are present in each heatmap, positioned at approximately 0 dB ILD.
* **Line Graph B:**
* **X-axis:** Frequency [kHz] (ranging approximately from 0.1 kHz to 10 kHz)
* **Y-axis:** Scale - σ (ranging approximately from 1.5 to 3)
* **Lines:** Nocturnal nature (dashed black), Forrest walk (solid gray), City center (solid black).
* **Shaded Areas:** Light gray shaded areas around each line represent uncertainty.
* **Line Graph C:**
* **X-axis:** Frequency [kHz] (ranging approximately from 0.1 kHz to 10 kHz)
* **Y-axis:** Location - μ (ranging approximately from -4 to 2)
* **Lines:** Nocturnal nature (dashed black), Forrest walk (solid gray), City center (solid black).
* **Shaded Areas:** Light gray shaded areas around each line represent uncertainty.
### Detailed Analysis or Content Details
**Heatmaps (A):**
* **Nocturnal Nature:** The heatmap shows a concentration of probability density around 0 dB ILD and frequencies between 2 kHz and 8 kHz. There is a diagonal band of higher probability density extending from the bottom-left to the top-right.
* **Forrest Walk:** Similar to Nocturnal Nature, the heatmap shows a concentration around 0 dB ILD and frequencies between 2 kHz and 8 kHz. The diagonal band is less pronounced than in Nocturnal Nature.
* **City Center:** The heatmap shows a more diffuse distribution of probability density, with a slight concentration around 0 dB ILD and frequencies between 2 kHz and 6 kHz. The diagonal band is barely visible.
**Line Graph B (Scale - σ):**
* **Nocturnal Nature (dashed black):** Starts at approximately 1.7 at 0.2 kHz, increases to approximately 2.6 at 2 kHz, then decreases slightly to approximately 2.5 at 10 kHz.
* **Forrest Walk (solid gray):** Starts at approximately 1.8 at 0.2 kHz, increases to approximately 2.7 at 2 kHz, then decreases to approximately 2.4 at 10 kHz.
* **City Center (solid black):** Starts at approximately 1.7 at 0.2 kHz, increases to approximately 2.6 at 2 kHz, then remains relatively constant at approximately 2.5 to 2.6 at 10 kHz.
**Line Graph C (Location - μ):**
* **Nocturnal Nature (dashed black):** Starts at approximately 1.2 at 0.2 kHz, decreases to approximately -1.5 at 2 kHz, then increases to approximately -0.5 at 10 kHz.
* **Forrest Walk (solid gray):** Starts at approximately 0.8 at 0.2 kHz, decreases to approximately -2.0 at 2 kHz, then increases to approximately 0.2 at 10 kHz.
* **City Center (solid black):** Starts at approximately 0.4 at 0.2 kHz, decreases to approximately -2.5 at 2 kHz, then increases to approximately 1.0 at 10 kHz.
### Key Observations
* The heatmaps suggest that in Nocturnal Nature and Forrest Walk, sounds are more likely to have an ILD close to 0 dB, indicating a more centered sound source. The City Center shows a more diffuse ILD distribution.
* The Scale-σ values are similar across all three environments, with a peak around 2 kHz.
* The Location-μ values show a clear trend of decreasing towards negative values at 2 kHz in all environments, then increasing again at higher frequencies. The City Center exhibits the most negative Location-μ value at 2 kHz.
### Interpretation
The data suggests that the spatial hearing characteristics differ significantly between the three environments. Nocturnal nature and forest walks provide a more natural and centered soundscape, as indicated by the concentration of ILD around 0 dB in the heatmaps. The city center, with its more diffuse ILD distribution, likely presents a more complex and less predictable soundscape.
The line graphs reveal that the scale and location parameters of the spatial hearing model are influenced by the environment. The similar Scale-σ values suggest that the overall precision of spatial localization is comparable across the environments. However, the differences in Location-μ values indicate that the perceived location of sound sources is shifted differently in each environment, particularly at 2 kHz. The more negative Location-μ in the city center might reflect the impact of urban noise and reverberation on spatial perception.
The dashed lines in the heatmaps, consistently positioned at 0 dB ILD, likely represent a reference point or a common auditory processing mechanism. The uncertainty represented by the shaded areas in the line graphs highlights the variability in spatial hearing perception. The overall pattern suggests that the auditory system adapts to the acoustic characteristics of the environment to optimize spatial localization.
