Word Processing
We have known since the 1970s that the brain can "fill in" inaudible sections of speech, but we don't know exactly how. To investigate, researchers played volunteers words that were partially obscured or inaudible to see how their brains responded. The experiment involved people who already had electrodes implanted into their brains to monitor epilepsy. These electrodes detect seizures but can also record other types of brain activity. The volunteers were played recordings of a word that could either be "faster" or "factor," with the middle sound replaced by noise. Data from the electrodes showed that their brains responded as if they had actually heard the missing "s" or "c" sound. This seems to be because the inferior frontal cortex region of the brain predicts what word someone is likely to hear, two-tenths of a second before the superior temporal gyrus starts processing the sounds a person has heard.