Oral speech and writing obviously involve different neurophysiological mechanisms both for production and perception (however, both use ascending and descending connections with the brain to bring signals for comprehension (perception/monitoring) and to carry instructions for articulation and typing (production/monitoring), the main difference, perhaps, is found on the peripheral level: perception time of signals, their survival time in the buffer memory, the different stages of auditory and visual signal decoding).
The table below summarizes activities involved in the production and perception of oral speech and written (typed) utterances:
| processing |
oral speech |
written utterances |
| production |
motor pathways from the brain to the vocal tract — ascending and descending connections (control of articulatory organs) |
motor pathways from the brain to the hand-arm system — ascending and descending connections (finger-pressings) |
| perception |
auditory pathways from sensory organs to the brain — ascending and descending connections — the five stages of sound perception (searching the acoustic signal for significant properties) |
visual pathways from sensory organs to the brain — ascending and descending connections — the six stages of written character processing, based on “expectations of how things should be” (control of eye movements over two-dimensional arrays consisting of contrasts of dark and light) |
Major differences between the nature of hand-arm and vocal tract functions7:
- the hand-arm system is not specialized for the function of typing (i.e. human hands and arms are capable of carrying out many other operations that have nothing to do with writing, while human articulatory organs are not);
- the hand-arm system uses a keyboard, while the articulatory apparatus operates directly, without mediators;
- the hand-arm system does not manipulate light, which is the medium of visual perception of written characters, while both the articulatory and the auditory systems manipulate sounds (i.e. use the same medium for production and perception);
- the continuity of the auditory-vocal tract system and discontinuity of the hand-arm-visual system (e.g. speech production normally involves both articulatory and motor processes (the latter for feedback), while typing does not necessarily involve simultaneous reading);
- while typing, a person uses ready (encoded) characters (i.e. finger-pressing of different keys on a keyboard involves similar movements for different characters), while oral speech requires articulation of distinctly varying sounds.
Footnotes:
7 Based on Garman, M., (1990). Psycholinguistics, Cambridge University Press.