The Blueprint of a Listener | Part 1 of 3 | Stimulus Processing And Decoding

This one is a bit dense… So although it isn’t terribly lengthy I decided to break it up into three parts so you don’t fry your brain on it Although this is extremely foundational information, I believe it is important to know what exactly is going on in a person’s brain while you are talking to them. Hopefully this will give you a different view of the neurology that is transpiring as you speak… So let’s get right into it.

The most renowned and referenced model of the listener is known as the Geschwind-Wernicke’s model which proposes that there are distinct areas of the brain that handle specific functions. So perception, comprehension and speech production is by a specific model and each of these models is serially linked. This means that they have to happen in sequence. The “serial” component is the spark of much debate and many neurologists are leaning more toward a “parallel” and interactive functioning model. However, the locus of specific processing seems to be very accurate and this model is the basis of most research in language processing and production.

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Initial sound stimulus processing:

When you hear a word spoken, you obviously initially pick the vibrations up with your ear drum. The auditory signal is the routed immediately to what is known as the primary auditory cortex. This is the hub of “sound” processing in the brain. Especially when dealing with language…. The neurons in the auditory cortex are tonotopically organized (meaning that particular neurons respond only to certain frequencies). Based on these frequency ranges, when voices/speech is detected, it is sent to the Wernicke’s area of the brain.

Between the primary auditory cortex and the Wernicke’s area, the sound that is being processed must be “made” into a representative “word” in the mind. So, how does this happen you ask? Allow me to explain…

One of the major difficulties is that speech doesn’t command an exclusive acoustic channel. Thus listeners first task is to separate speech from other auditory input which happens in both the auditory cortex and Wernicke’s area. There a few things happening to filter language out from the rest of the noise.

One of the most important aspects is that speech is periodic (occurs in regular intervals) in its delivery and noise is aperiodic. This means that the “regular structure” of speech will stand out against other background noise.

Because of the periodic function our auditory system exploits grouping mechanisms which effectively assign acoustic signals to putative (commonly accepted) sources according to their frequency characteristics. This is a result of the tonotopically organized auditory cortex. What this means is that we have speech groupings that we “expect” based on frequency and pattern and we separate the speech coming at us from other noise based on those expecting groupings. (Periodic intonation, frequency, etc…)

Decoding of sound to create “words”:

Once the noise you are hearing is distinguished as speech, decoding can then begin… This occurs mainly in Wernicke’s area. Now the field of linguistics describes speech as a series of phonetic segments and each segment is a single phoneme. A phoneme is the smallest units in terms of which spoken language can be sequentially described). Ex. Key is |ki| or “kuh” – “ee” (two parts/sounds). The decoding begins by breaking out each phoneme and understanding what it is…

Decoding can be affected by tone, volume, placement of accent, pitch contour and frequency/timing of each “segment”. Our brain uses all of these aspects of the spoken language to determine word and syntactic “boundaries”. What all of this means is that there are “prosodic” structures (the rhythm, stress, and intonation of speech) that we have learned that are used to “fit” the sound waves into an expected order to “make sense” of them. Prosodic structures can constitute timing, stress based rhythm of syllables, vowel harmony, cues in pitch contour which signal a word break or an accent in a word.

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In the next post we will talk about the mental lexicon and the development of meaning to the listener.

To learn more about the neurological workings of the listener and other information that contributes to effective communication, please visit my site The Communication Expert.