Fire event for ObservableCollection Item change

I have a ListView bound to a ObservableCollection which is made up of objects which inherits from INotifyPropertyChanged.

In my ListView cells I have a label and slider, you slide the slider and it updates to the bound label. All the bindings are working fine but I can't see any way to get the ObservableCollection to raise an event when the slider moves and the cell bound item is changed.

any ideas?