Subvocalization, or silent speech, is the internal speech typically made when reading; it provides the sound of the word as it is read. This is a natural process when reading, and it helps the mind to access meanings to comprehend and remember what is read, potentially reducing cognitive load.
This inner speech is characterized by minuscule movements in the larynx and other muscles involved in the articulation of speech. Most of these movements are undetectable (without the aid of machines) by the person who is reading.
thumb|alt=the larynx and associated musculature|The larynx and associated musculature
History of subvocalization research
Subvocalization has been considered as far back as 1868. who concluded that silent reading was the only mental activity that created considerable movement of the larynx. concurrent speaking tasks, shadowing, EMG is used to record the electrical activity produced by the articulatory muscles involved in subvocalization. Greater electrical activity suggests a stronger use of subvocalization.
Evolutionary background
The exploration into the evolutionary background of subvocalization is currently very limited. The little known is predominantly about language acquisition and memory. Evolutionary psychologists suggest that the development of subvocalization is related to modular aspects of the brain. There has been a great amount of exploration on the evolutionary basis of universal grammar. This activation could suggest that the frontal lobes may be involved in motor planning for speech output. There is evidence for significant left hemisphere activation in the inferior and middle frontal gyri and inferior parietal gyrus during subvocal rehearsal.
Silent speech-reading and silent counting are also examined when experimenters look at subvocalization. These tasks show activation in the frontal cortices, hippocampus and the thalamus for silent counting. is an active subvocal rehearsal mechanism, activation originating mostly in the left hemispheric speech areas: Broca's, lateral and medial premotor cortices and the cerebellum.
Role of subvocalization in memory processes
The phonological loop and rehearsal
The ability to store verbal material in working memory, and the storage of verbal material in short-term memory relies on a phonological loop. Subvocalization and the phonological loop interact in a non-dependent manner demonstrated by their differential requirements on different tasks. The working memory span is a behavioural measure of "exceptional consistency" and is a positive function of the rate of subvocalization. Experimental data has shown that this span size increases as the rate of subvocalization increases, and the time needed to subvocalize the number of items comprising a span is generally constant.
Short-term memory
The role of subvocal rehearsal is also seen in short-term memory. Research has confirmed that this form of rehearsal benefits some cognitive functioning.
The production of acoustic errors in short-term memory is also thought to be, in part, due to subvocalization. Individuals who stutter and therefore have a slower rate of subvocal articulation also demonstrate a short-term reproduction of serial material that is slower as compared to people who do not stutter.
Encoding
Subvocalization plays a large role in memory encoding. Subvocalization appears to facilitate the translating of visual linguistic information into acoustic information as words being heard are already in acoustic form and therefore enter short-term memory directly without use of subvocal articulation. For example, subvocalization is not used in the making of homophone judgements is thought to allow for the integration of past concepts with those currently being processed. Speedreading courses often prescribe lengthy practices to eliminate subvocalizing when reading. Normal reading instructors often simply apply remedial teaching to a reader who subvocalizes to the degree that they make visible movements on the lips, jaw, or throat.
At the slower rates (memorizing, learning, and reading for comprehension), subvocalizing by the reader is very detectable. At the faster rates of reading (skimming and scanning), subvocalization is less detectable. For competent readers, subvocalizing to some extent even at scanning rates is normal.
Typically, subvocalizing is an inherent part of reading and understanding a word. Micro-muscle tests suggest that full and permanent elimination of subvocalizing is impossible. This may originate in the way people learn to read by associating the sight of words with their spoken sounds. Sound associations for words are indelibly imprinted on the nervous system—even of deaf people, since they will have associated the word with the mechanism for causing the sound or a sign in a particular sign language.
At the slower reading rates (100–300 words per minute), subvocalizing may improve comprehension. These findings suggest that subvocalization is common to both auditory imagery and rehearsal.
In objection to a subvocalization mechanism basis for auditory imagery is in the fact that a significant amount of auditory imagery does not involve speech or stimuli similar to speech, such as music and environmental sounds. However, to combat this point, it has been suggested that rehearsal of non-speech sounds can indeed be carried out by the phonological mechanisms previously mentioned, even if the creation of nonspeech sounds within this mechanism is not possible.
Role in speech
There are two general types of individuals when it comes to subvocalization. There are Low-Vocalizers and High-Vocalizers. Using electromyography to record the muscle action potential of the larynx (i.e. muscle movement of the larynx), an individual is categorized under a high or low vocalizer depending on how much muscle movement the muscles in the larynx undergo during silent reading.
Regulation of speech intensity
Often in both high and low vocalizers, the rate of speech is constantly regulated depending on intensity/volume of words (said to be affected by long delays between readings) and increasing the delay of speech and hearing ones' voice is an effect called “delayed auditory feedback”. As articulation of similar words is affecting subvocalization, there is an increase in acoustic errors for short-term memory and recall. An example of articulation suppression is repeating the same word over many times such as the<nowiki/>' and attempting to memorise other words into short-term memory. Even though primary cues may be given for these words in attempt to retrieve them, words will either be recalled for the incorrect cue or will not be recalled at all. Using an electromyography to record muscle movement, individuals experiencing hallucinations showed greater muscle activation before these hallucinations occurred. This small fact could be a clue to finding if there is a true link between subvocalization and hallucinations, but it is very difficult to see this connection because not many patients experience hallucinations.