| Feature | Description |
|---|---|
| Hjorth Mobility | Measures the mean frequency or the rate of change of a signal, indicating how fast the signal changes. It is defined as the square root of variance of the first derivative of the signal y(t) divided by variance of the signal y(t). |
| Hjorth Complexity | Measures the change in frequency, for example, how the shape of the signal evolves. The parameter compares the signal's similarity to a pure sine wave, where the value converges to 1 if the signal is more similar. |
Both Hjorth parameters are commonly used in tactile signal processing for physical object properties detection, such as surface texture and material detection, and touch modality classification through artificial robotic skin.