|The term Aphasia (also known as dysphasia) denotes a class of acquired language disorders, which includes the following:|
(1) Anomic Aphasia is characterized by an inability to recall proper names and names of objects. Speech is fluent and grammatical.
(2) Broca's Aphasia (or `Broca's Type Aphasia') is named after the French neurologist Paul Broca, who in the nineteenth century identified an area within the frontol lobe which is important in the control of speech. Broca's aphasia results from damage to this area and is characterized by slow, laborious, hesitant speech, with
little intonation and obvious articulation difficulties. Also identified by
impairments in word order. Generally, it is interpreted as a difficulty in
sequencing the units of language.
Ah ... Monday ... ah Dad and Paul ... and Dad ... hospital. Two ... ah ... doctors ... and ah ... thirty minutes ... and yes ... ah ... hospital. And er Wednesday ... nine o'clock. And er Thursday, ten o'clock ... doctors. Two doctors .. and ah ... teeth (taken from T. Harley The Psychology of Language.)
Broca's Aphasia is a form of agrammatism. Broca's type aphasics are studied by speech production researchers intersted in modeling both the processes of speech production and the underlying disruptions giving rise to such disorders.
|(3) Conduction aphasia is characterized by relatively impaired repetition of speech, accompanied by some difficulty in naming and some comprehension impairment. This is relevant to models of speech production, since it implies that there is a route between speech perception centers and speech production centers that can be selectively impaired.|
|(4) Global Aphasia is a linguistic disorder in which spontaneous speech, naming, and repetition are all severely impaired. (5) Transcortical Aphasia is characterized by various impairments consistent with the ability to repeat words relatively well. There are two types of transcortical aphasia dependent upon location of the lesion:|
|(6) Wernicke's Aphasia is caused by damage to the left temporal lobe just posterior to the primary auditory cortex and is characterized by defecits in speech comprehesions and meaningless, but somewhat grammatical, speech (known as word salad).|
|Apraxia refers to the impairment of the ability to produce purposeful or voluntary movements (such movements aren't restricted to those involved in speech); involuntary movements are unaffected. This inability cannot be explained by weakness of the muscles involved or difficulty in coordinating movements, as the patient can perform an activity automatically--just not when commanded to do so. Apraxia often occurs with and is difficult to distinguish from aphasia. Generally it is held that linguistic problems in aphasia involve damage to the phonological system itself, while linguistic problems in apraxia involve the inability to control the use of a phonological system which is intact. Apraxia may be developmental or aquired (i.e. not caused at birth).|
Dysarthia refers to a group of disorders, in acquired or developmental form, which result from damage to the movement control systems of the central or peripheral nervous system. Aspects of speech production affected in dysarthia include respiration, phonation, articulation and prosody. Unlike apraxia, dysarthia involves weakness of muscles and incoordination. There are four main types of dysarthia:|
(1) Dyskinetic dysarthia:
(a) Hyperkinetic: prosody is severely affected particularly in relation to rate and rhythm; deletion of sounds and segments; hypernasal resonance.
(b) Hypokinetic: occurs most frequently in Parkinson's Disease; poor articulation; deterioration in connected speech.
(2) Spastic dysarthia: all parameters of speech are affected; poor respiration, hoarseness, restricted intonation patterns, excessive stress.
(3) Peripheral dysarthia (also known as flaccid dysarthia): hypernasality, nasal emission of air, distorted consonants; speech occurs in short phrases.
(4) Mixed dysarthia: results from impairment in more than one motor system.
Dysfluency (also called non-fluency) refers to stammering/stuttering and cluttering (excessive speed of delivery of speech). (Arrhythmia and dysrhythmia are sometimes used to refer to phonetic interference with the normal rhythms of speech.) The characteristics that stutterers display can be grouped as follows:|
(1) Abnormal repetition of syllable, word or phrase.
(2) Obstructions to airflow (referred to as blocking.
(3) Abnormal prolongations of sound segments (e.g. s-s-s-sorry).
(4) Introduction of extra words or sounds.
(5) Erratic stress patterns.
(6) Words left unfinished.
(7) Awkward circumlocutions (avoiding words which cause problems and replacing them with awkward phrases).
(Some of these characteristics are also involved in cluttering.)
Causes of dysfluency difficult to discern. Organic theories relate dysfluency to some genetic or physical disposition which is triggered by environmental stress. Psychoneurotic theories relate dysfluency to some aspect of the subject's personality. Of course there is also the possibility that dysfluency is caused by a combination of organic and functional factors, thus it is difficult to decide between competing theories.
|Agnosia is a disorder, developmental or acquired, in which the ability to perceive sounds and objects is intact, while the ability to recognize them is impaired. Agnosia may be visual, acoustic (difficulty in sound discrimination in general), tactile or auditory (difficulty in understanding spoken language).|
|Aphonia is a voice disorder, i.e. it affects phonation (the source of sound vibration in the vocal tract--the larynx) and resonance (the modification of the vibration in the cavities contiguous to the larynx). Aphonia involves a complete loss of voice and may be organic or functional: in the former case, there is a clear anatomical, physiological or neurological cause; in the latter case, the cause is thought to be primarily psychological.|
Dyslexia refers to difficulty with reading, writing and spelling. It may be developmental or acquired. There are four types of acquired dyslexia:|
(1) Surface dyslexia is characterized by a selective impairment in the ability to read irregular (or exception) words. For example, patients will have no trouble with speak, but make errors with words like steak. When surface dyslexics make attempts at irregular words, they tend to make overregularization errors: e.g., pronounce steak as steek. Conversely, the ability to pronounce regular words and non-words is unimpaired. Moreover,word meanings are preserved; they can understand what an island is even if they cannot read it.(2) Deep Dyslexia. involves semantic errors, although other symptoms may also be present (e.g. word-substitution and derivational errors). That is, unlike surface dyslexia, deep dyslexia is manifested in the difficulty with word meanings, not syntactic structure. For example, low-imageability words are harder to read aloud than high-imageability words.
(3) Word-form dyslexia involves the ability to understand what is being read aloud by reading only one letter at a time.
(4) Phonological dyslexia patients have a selective impairment in the ability to read pronounceable nonwords or psuedowords, while the ability to read matched words is preserved. For example, they cannot read words like sleeb, while being able to read words like sleep. Irregular words are no more difficult than regular words for these patients. This suggests, according to the dual route model of reading, that such patients can only read by the lexical route (read directly at the word level) and symptoms reflect an impairment in the non-lexical route.