Verbal apraxia it is a motor disorder of speech characterized by slowed speech, distortions of vowels and consonants and frequent pauses between words or between syllables. There are children with developmental apraxia, but this type of problem can also arise in the adult following brain injury (stroke, head injury) or neurodegenerative diseases. It often occurs in association with acquired speech disorder (aphasia) and with motor problems in the execution of speech movements (dysarthria).
The main difficulty of apraxia is movement planning. Why does this happen? There are basically three hypotheses:
- Hypothesis of damaged programs (Damaged Programs Hypothesis): representations relating to movements are impaired (at least partially)
- Program recovery deficit hypothesis (Program Retrieval Deficit Hypothesis): the problem is the activation of the correct program when other motor programs find themselves in competition (they are similar or have been activated recently)
- Hypothesis of reduced buffer capacity (Reduced Buffer Capacity Hypothesis): the motor planning buffer cannot contain more than one motor program at a time (whose size is that of a syllable)
A systematic review
A recent study by Mailend and colleagues (2019)  tried to compare the latter two hypotheses.
The participants were:
- 8 subjects with apraxia (six of them with associated aphasia)
- 9 subjects with aphasia, but without apraxia
- 25 control subjects
The task was to observe an initial word (prime) after which the word to be pronounced would appear (in white on a blue background). In some cases the word was identical, in others it was not (a rapid switching between the first and second stimulus was therefore necessary). The words were monosyllabic, with a CVC structure and 3-4 phonemes long.
Why monosyllabic words? To discriminate between the two hypotheses. Indeed:
- If the reduced buffer theory were true, we shouldn't see a particular slowdown, as words are monosyllabic
- If, on the other hand, the theory of activation of the correct program were true, there would be a slowdown due to the different competing programs
At the end, the results showed significant latency in patients with apraxia, in accordance with the program recovery hypothesis. The motor programs were therefore prepared, to some extent, at the time of the prime, but then had to be modified when a different word appeared.
Another very interesting aspect is that people with aphasia but without apraxia, they still made mistakes, but:
- Latency times were very similar to those of the control group (therefore, switching slowed only the subjects with apraxia)
- There were no significant differences between aphasic subjects and the control group when a word similar (but not identical) to that of the prime was proposed.
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Aphasia has not only an emotional but also an economic cost for the patient and his family. Some people, for economic reasons, limit their rehabilitation possibilities, despite the evidence supporting the need for intensive and constant work. For this reason, since September 2020, all our apps can be used for free online in GameCenter Aphasia and our activity sheets are all available here: https://www.trainingcognitivo.it/le-nostre-schede-in-pdf-gratuite/