Subvocalization, or silent speech, is the internal speech typically made when reading; it provides the sound of the word as it is read.Carver, R. P. (1990) Reading Rate: A Comprehensive Review of Research and Theory (1990)Cleland, D. L., Davies, W. C and T. C. 1963. Research in Reading. The Reading Teacher, 16(4), 224-228 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.Rayner, Keith and Pollatsek, Alexander (1994) The Psychology of Reading
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. It is one of the components of Alan Baddeley and Graham Hitch's phonological loop proposal which accounts for the storage of these types of information into short-term memory.Smith, J. D., Wilson, M., & Reisberg, D. (1995). The role of subvocalization in auditory imagery. Neuropsychologia, 33(11), 1433-1454.
History of subvocalization research Subvocalization has been considered as far back as 1868. Only in 1899 did an experiment take place to record movement of the larynx through silent reading by a researcher named H.S. Curtis, who concluded that silent reading was the only mental activity that created considerable movement of the larynx.
In 1950, Åke Werner Edfelt reached a breakthrough when he created an electrically powered instrument that can record movement. He concluded that newer techniques are needed to accurately record information and that efforts should be made to understand this phenomenon instead of eliminating it. After failed attempts trying to reduce silent speech in study participants, in 1952, it came to the conclusion that silent speech is a developmental activity which reinforces learning and should not be disrupted during development. In 1960, Edfelt seconded this opinion.
Techniques for studying subvocalization Subvocalization is commonly studied using electromyography (EMG) recordings,Locke, J., & Fehr, F. (1972). Subvocalization of Heard or Seen Words Prior to Spoken or Written Recall. The American Journal of Psychology, 8(1), 63-68. concurrent speaking tasks,Levy, B. A. (1971). Role of Articulation in Auditory and Visual Short-Term Memory. Journal of Verbal Learning and Verbal Behavior, 10, 123-132.Daneman, M., & Newson, M. (1992). Assessing the Importance of Subvocalization in Normal Silent Reading. Reading and Writing: An Interdisciplinary Journal, 4, 55-77.Slowiaczek, M., & Clifton, C. (1980). Subvocalization and reading for meaning. Journal of Verbal Learning and Verbal Behavior, 19.5, 573-582. shadowing, and other techniques.
EMG can be used to show the degree to which one is subvocalizing or to train subvocalization suppression.Cole, R. A., & Young, M. (1975). Effect of subvocalization on memory for speech sounds. Journal of Experimental Psychology: Human Learning and Memory, 1(6), 772-779. 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. In the case of suppression training, the trainee is shown their own EMG recordings while attempting to decrease the movement of the articulatory muscles. The EMG recordings allows one to monitor and ideally reduce subvocalization.
In concurrent speaking tasks, participants of a study are asked to complete an activity specific to the experiment while simultaneously repeating an irrelevant word. For example, one may be asked to read a paragraph while reciting the word "cola" over and over again. Speaking the repeated irrelevant word is thought to preoccupy the articulators used in subvocalization. Subvocalization, therefore, cannot be used in the mental processing of the activity being studied. Participants who had undergone the concurrent speaking task are often compared to other participants of the study who had completed the same activity without subvocalization interference. If performance on the activity is significantly less for those in the concurrent speaking task group than for those in the non-interference group, subvocalization is believed to play a role in the mental processing of that activity. The participants in the non-interference comparison group usually also complete a different, yet equally distracting task that does not involve the articulator muscles (e.g. tapping). This ensures that the difference in performance between the two groups is in fact due to subvocalization disturbances and not due to considerations such as task difficulty or a divide in attention.
Shadowing is conceptually similar to concurrent speaking tasks. Instead of repeating an irrelevant word, shadowing requires participants to listen to a list of words and to repeat those words as fast as possible while completing a separate task being studied by experimenters.
Techniques for subvocalization interference may also include counting, chewing or locking one's jaw while placing the tongue on the roof of one's mouth.
Subvocal recognition involves monitoring actual movements of the tongue and vocal cords that can be interpreted by electromagnetic sensors. Through the use of electrodes and nanocircuitry, synthetic telepathy could be achieved allowing people to communicate silently.
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.Buller, D. J. (2005). Adapting Minds: Evolutionary Psychology and the Persistent Quest for Human Nature. Massachusetts: The MIT Press There has been a great amount of exploration on the evolutionary basis of universal grammar. The idea is that although the specific language one initially learns is dependent on one's culture, all languages are learned through the activation of universal "language modules" that are present in each of us. This concept of a modular mind is a prevalent idea that will help explore memory and its relation to language more clearly, and possibly illuminate the evolutionary basis of subvocalization. Evidence for the mind having modules for superior function is the example that hours may be spent toiling over a car engine in an attempt to flexibly formulate a solution, but, in contrast, extremely long and complex sentences can be comprehended, understood, related and responded to in seconds. The specific inquiry into subvocalization may be minimal right now but there remains much to investigate in regard to the modular mind.
Associated brain structures and processes The brain mechanics of subvocalization are still not well understood. It is safe to say that more than one part of the brain is used, and that no single test can reveal all the relevant processes. Studies often use event-related potentials; brief changes in an EEG (electroencephalography) to show brain activation, or fMRIs.
Subvocalization is related to inner speech; when inner speech is used, there is bilateral activation in predominantly the left frontal lobe.Girbau, D. (2007). A Neurocognitive Approach to the Study of Private Speech. The Spanish Journal of Psychology, 10(1), 41-51 This activation could suggest that the frontal lobes may be involved in motor planning for speech output.
Subvocal rehearsal is controlled by top-down processing; conceptually driven, it relies on information already in memory.Klob, B. & Whishaw, I.Q. (2009). ‘’Fundamentals of Human Neuropsychology’’ (6th ed.). New York, NY: Worth Publishers There is evidence for significant left hemisphere activation in the inferior and middle frontal gyri and inferior parietal gyrus during subvocal rehearsal. Broca's area has also been found to have activation in other studies exploring subvocal rehearsal.Burgess, N. & Hitch, G. J. (1999). Memory for Serial Order: A Network Model of the Phonological Loop and its Timing. Psychological Review, 106(3), 551-581
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. Silent-reading activates similar areas of the auditory cortex that are involved in listening.
Finally, the phonological loop; proposed by Baddeley and Hitch as "being responsible for temporary storage of speech-like information"Baddeley, A., Eysenck, M. W. & Anderson, M. C. (2009). Memory. New York, NY: Psychology Press 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.Gruber, O. (2001). Effects of Domain-specific Interference on Brain Activation Associated with Verbal Working Memory Task Performance. Cerebral Cortex, 11, 1047-1055
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. This loop, proposed by Baddeley and Hitch, represents a system that is composed of a short-term store in which memory is represented phonologically, and a rehearsal process. This rehearsal preserves and refreshes the material by re-enacting it and re-presenting it to short-term storage, and subvocalization is a major component of this rehearsal. The phonological loop system features an interaction between subvocal rehearsal and specific storage for phonological material. The phonological loop contributes to the study of the role of subvocalization and the inner voice in auditory imagery.Hubbard, T.L. (2010). Auditory imagery: empirical findings. Psychological Bulletin, 136(2), 302-329. Subvocalization and the phonological loop interact in a non-dependent manner demonstrated by their differential requirements on different tasks. The role of subvocalization within the workings of memory processes is heavily reliant on its involvement with Baddeley's proposed phonological loop.
Working memory
There have been findings that support a role of subvocalization in the mechanisms underlying working memory and the holding of information in an accessible and malleable state. Some forms of internal speech-like processing may function as a holding mechanism in immediate memory tasks.Standing, L., Bond, B., Smith, P., Isley, C. (1980). Is the immediate memory span determined by subvocalization rate? British Journal of Psychology, 71(4), 535-539 The working memory span is a behavioural measure of "exceptional consistency" Standing, L., & Curtis, L. (1989). Subvocalization rate versus other predictors of the memory span. Psychological Reports,65(2), 487-495. 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. fMRI data suggests that a sequence of five letters approaches the individual capacity for immediate recall that relies on subvocal rehearsal alone.Logie, R.H., Venneri, A., Sala, S.D., Redpath, T.W., Marshall, I. (2003). Brain activation and the phonological loop: the impact of rehearsal. Brain and Cognition, 53(2), 293-296.
Short-term memory