They then used a functional MRI and
magnetoencephalography to see how the brain behaves when the acoustic stimulus is very clear, or,
on the contrary, when it is ambiguous and requires an active mental representation of the phoneme and its interpretation by the brain.
There are other noninvasive brain scanners —
magnetoencephalography, positron - emission tomography and near - infrared spectroscopy, and so
on — but each also has its trade - offs.