How Brain Waves Help Us Make Sense of Speech (Extract)

Understanding a sentence that someone else utters may seem effortless to you, but it's actually a complex process because you have to parse that sentence into many parts to understand what it means. Speech consists of a hierarchy of components that each takes place on a different timescale. Speech cues such as intonation occur on a relatively long timescale, unfolding over hundreds of milliseconds. At the other end of the spectrum is the phoneme — the smallest unit of speech — which lasts only tens of milliseconds.

Similarly, distinct sets of neurons in the brain fire rhythmically at different rates, and these oscillations can also be arranged in a hierarchy. For instance, slow delta-wave oscillations can influence the magnitude of faster theta oscillations, which in turn can alter the amplitude of even faster gamma oscillations. Rhythmic brain activity plays an important role in a variety of cognitive processes, including attention, memory, and decision-making.