Confusion about filter bias

Hi! Thanks for sharing your amazing work!
I am confused about the role of filter bias in models/model_stereoPrediction.py (line 112), Could you explain how the filter bias help this task?
```
## add a bias
output = ConcatLayer([input, filters_biases])
output = FeaturePoolLayer(output, pool_size=2, pool_function=theano.tensor.sum)
```
Thank you very much!