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date: 20 November 2017

Aphasia from a Neurolinguistic Perspective

Summary and Keywords

Aphasia is an acquired language disorder subsequent to brain damage in the left hemisphere. It is characterized by diminished abilities to produce and understand both spoken and written language compared with the speaker’s presumed ability pre-cerebral damage. The type and severity of the aphasia depends not only on the location and extent of the cerebral damage but also the effect the lesion has on connecting areas of the brain. Type and severity of aphasia is diagnosed in comparison with assumed normal adult language. Language changes associated with normal aging are not classed as aphasia. The diagnosis and assessment of aphasia in children, which is unusual, takes account of age norms.

The most common cause of aphasia is a cerebral vascularaccident (CVA) commonly referred to as a stroke, but brain damage following traumatic head injury such as road accidents or gunshot wounds can also cause aphasia. Aphasia following such traumatic events is non-progressive in contrast to aphasia arising from brain tumor, some types of infection, or language disturbances in progressive conditions such as Alzheimer’s disease, where the language disturbance increases as the disease progresses.

The diagnosis of primary progressive aphasia (as opposed to non-progressive aphasia, the main focus of this article) is based on the following inclusion and exclusion criteria by M. Marsel Mesulam, in 2001. Inclusion criteria are as follows: Difficulty with language that interferes with activities of daily living and aphasia is the most prominent symptom. Exclusion criteria are as follows: Other non-degenerative disease or medical disorder, psychiatric diagnosis, episodic memory, visual memory, and visuo-perceptual impairment, and, finally, initial behavioral disturbance.

Aphasia involves one or more of the building blocks of language, phonemes, morphology, lexis, syntax, and semantics; and the deficits occur in various clusters or patterns across the spectrum. The degree of impairment varies across modalities, with written language often, but not always, more affected than spoken language. In some cases, understanding of language is relatively preserved, in others both production and understanding are affected. In addition to varied degrees of impairment in spoken and written language, any or more than one component of language can be affected. At the most severe end of the spectrum, a person with aphasia may be unable to communicate by either speech or writing and may be able to understand virtually nothing or only very limited social greetings. At the least severe end of the spectrum, the aphasic speaker may experience occasional word finding difficulties, often difficulties involving nouns; but unlike difficulties in recalling proper nouns in normal aging, word retrieval problems in mild aphasia includes other word classes.

Descriptions of different clusters of language deficits have led to the notion of syndromes. Despite great variations in the condition, patterns of language deficits associated with different areas of brain damage have been influential in understanding language-brain relationships. Increasing sophistication in language assessment and neurological investigations are contributing to a greater, yet still incomplete understanding of language-brain relationships.

Keywords: aphasia, acquired language disorder, brain damage, agrammatism, anomia, Broca’s area, Wernicke’s area

1. Historical Background and the “Standard Model” of Aphasia

Although descriptions of aphasic-like conditions can be found in ancient texts, the study of aphasia and the link to specific areas of the left hemisphere start in the 19th century with two eminent neurologists, Paul Broca and Carl Wernicke. Paul Broca, a surgeon in France, observed a patient, M. Leborgne, over a number of years. Leborgne appeared to understand but was unable to speak save for a meaningless repetition of “tan,” and over time, he developed paralysis of his right arm and leg. Following Leborgne’s death, an autopsy revealed extensive brain damage in the fronto-temporal area of the brain, probably caused by a cyst. Broca examined other similar cases, presenting his findings in 1861, and published his claim that “we speak with the left side of our brains” in 1865.

Nine years later, Carl Wernicke, a neuro-psychiatrist practicing in Germany, published descriptions of eight individuals who also had language disorders subsequent to brain damage. However, this language disorder was unlike that described by Broca. Although these individuals were able to hear, they had difficulty in understanding what they heard; and although they could speak fluently, their speech contained many lexical and semantic errors, and meaning was diminished. Based on post-mortem examinations, both physicians observed that the lesions were in the left cortex, but whereas Broca reported a lesion in the frontal lobe, the lesions observed by Wernicke were posterior to this. The distinction was not straightforward as patients described in Wernicke’s monograph had varied aetiologies and presented with differing language deficits (see Eggert, 1977), and subsequent examinations of Leborgne’s brain in the 20th century revealed that the lesion in Leborgne’s brain was extensive, extending beyond what is now considered Broca’s area of the brain (Dronkers, Plaisant, Iba-Zizen, & Canais, 2007).

These early seminal reports led to the notion of a main division within aphasia: Broca’s aphasia arising from frontal lobe lesions in the left hemisphere, characterized by relatively preserved understanding of language but impoverished output, and Wernicke’s aphasia characterized by fluent although often incoherent output and compromised understanding of language arising from damage to the left temporal lobe. Other terms were later coined to describe these or similar conditions including, “anterior,” “expressive,” or “motor” aphasia, which contrast to “posterior,” “sensory,” or “receptive” aphasia. Physicians working with brain injured individuals following both the first and second world wars, refined the descriptions of aphasia, and a number of further types of aphasia were described based on different language behavior and assumed sites of lesions (Grodzinsky & Amunts, 2006; Tesak & Code, 2008). Increasing interest resulted in a number of diagnostic schemes and clinical assessments. The most widely used scheme in both clinical and research environments in the English-speaking world was developed by Harold Goodglass and colleagues, in Boston MA. Their assessment (Boston Diagnostic Aphasia Examination) was first published in 1972 and was followed by further editions (Goodglass, Kaplan, & Barresi, 2001). In this scheme, two main types of aphasia, non-fluent and fluent aphasia, are identified by the ease of spoken language production as illustrated in the examples below. Non-fluent and fluent aphasia are further sub-divided into syndromes, listed here in decreasing severity: global, trans-cortical motor, and Broca’s aphasia are types of non-fluent aphasia, while Wernicke’s, trans-cortical sensory, conduction, and anomic aphasia are types of fluent aphasia. While anomic aphasia is a type of aphasia characterized by severe word finding difficulties, anomia is a key feature of all aphasia types. In non-fluent aphasia, retrieval of closed class words, verbs, in addition to other word classes and sentence structure, are problematic, while in fluent aphasia, retrieval of open class words, especially nouns, is problematic but sentence structure maybe retained. Repetition of language can be impaired in all aphasia types but characterizes conduction aphasia. Despite limitations to the syndromic approach, the main distinction between Wernicke and Broca type aphasia or between fluent and non-fluent aphasia remains a useful shorthand for superficial descriptions.

In primary progressive aphasia, a different classification has been proposed with three syndromes or variants (Gorno-Tempini et al., 2011): non-fluent agrammatic, semantic, and logopaenic. The semantic variant of primary progressive aphasia is also known as semantic dementia.

Here are two descriptions of the same picture: the first is by a speaker with Broca’s aphasia:

the woman is dishes ... I can dis ... the rest ... the dishes are filled with water ... the water floods ... the dishes or are floods ... the dishes are on ... the dishes are floods ... what’s it’s children children ... taking it the woman ... and the man children.

(Salis, 2006)

The second is a description by a speaker with Wernicke’s aphasia:

uh, we’re in the in the kermp kerken kitchen in in the kitchen and there’s a lady doing the slowing ... she’s got the pouring the plate watching it with with um ... the water is balancing in the sink the (unintelligible) of the sink and the water is pouring all over the bowing bowing all over it.

(Edwards, 2005)

The overlap of symptoms between syndromes and a poor fit of many patients to a syndrome led some researchers and clinicians to adopt assessments based on neuropsychological models of lexical and sentence processing. For example, Kay, Lesser, and Coltheart’s (1996) aphasia assessment approach assumes abstract cognitive levels of single word comprehensions and production, especially of nouns. Other theoretical neuropsychological models of language processing, which conceptualize lexical retrieval within the process of sentence production (e.g., Bock & Levelt, 1994) provide a way of mapping aphasic errors to stages of language production. Researchers working within a neurolinguistic tradition continued to examine sentence structure, verbs, verb inflection, and other grammatical aspects of aphasic language, and this led to the identification of a sub-group of Broca’s aphasia, a condition known as agrammatism. Individuals with agrammatism have typical non-fluent output, impoverished grammatical structure, as well as lexical retrieval difficulties. In addition, numerous studies have demonstrated that although these individuals have relatively good understanding and can interpret semantically reversible sentences with active canonical structure,

(1)

  • the mother hugs the child

they perform at chance level interpreting similar in meaning non-canonical sentences such as passive sentences

(2)

  • the child is hugged by the mother

In these conditions, word knowledge is insufficient for interpretation of the meaning of the sentence as both a child and a mother can hug, and thus either noun can have the agentive role. The agentive role is at the beginning of the sentence in (1) but at the end of the sentence in (2). These findings have led to strong claims about the nature of grammatical deficits in agrammatism (Grodzinsky, 2000): see sections 5.1 and 5.2 on sentence deficits. Descriptions and explanations of aphasic language continue to be developed with more sophisticated methods of examining the understanding and production of verbs, grammatical elements, anaphoric reference, negation, and inflectional morphology as well as the continuing exploration of impaired sentence production and comprehension. While it is widely acknowledged that aphasia is manifested in a variety of ways in individuals, the search for patterns of deficit across a number of individuals that can be related to a linguistic theory has been fruitful. Deficits that suggest “fault lines” in human grammar have driven much of the recent research. The search for underlying neurological correlates of syndromes has been largely overtaken by efforts to explore underlying cognitive processes associated with specific language deficits and to map highly specific linguistic phenomena onto increasingly discrete areas of the brain (Thompson et al., 2007).

Although publications of English studies of aphasia are numerous, there is considerable aphasic research in other languages: Finnish (Laine, Niemi, & Koivuselka-Sallinen, 1994); Hebrew (Friedmann & Grodzinsky, 1997); Italian (Luzzatti, Mondini, & Semenza, 2001) are some examples. Menn and Obler (1990) provide examples of agrammatism in a number of languages. Venkatesh, Edwards, and Saddy (2012) present a study on bilingual Hindi-English aphasia.

2. Neural Basis of Aphasia

Helm-Estabrooks, Albert, and Nicholas (2014) summarize three perspectives on the neural basis of aphasia: (a) language as related to highly specialized cortical areas or centers; (b) organization of language in a regional or zone-like pattern; (c) language involves widely distributed networks throughout the brain, functioning in series and in parallel.

The idea of specialized areas or centers originated in the work of Paul Broca and Carl Wernicke, culminating in the Wernicke-Lichtheim model in the late 19th century. In the early 20th century, Joseph Dejerine described the “zone of language” in the left hemisphere (Krestel, 2013). In particular, Dejerine described the arcuate fasciculus as an association fiber tract linking Broca’s area, Wernicke’s area, and the angular gyrus, a visual image center associated with reading functions. The anatomical description of arcuate fasciculus tracts in aphasic patients provided a foundation for the modern concepts of dorsal and ventral streams in language processing. A dorsal stream is thought to be involved in relating sound to articulation, and a ventral stream in sound to meaning.

Two main cortical areas or centers are implicated in aphasia, Broca’s and Wernicke’s areas. Broca’s area is located in the frontal lobe and, more specifically, the inferior frontal gyrus (Brodmann’s areas 44 and 45, pars opercularis and pars triangularis, respectively). However, the precise location of Broca’s area has been a matter of dispute. Brown and Hagoort (1999) remark that several distinct areas have been subsumed under Broca’s area. In reviewing the neuroanatomical literature, Uylings, Malofeeva, Bogolepova, Amunts, and Zilles (1999) point out the existence of three different anatomical definitions of Broca’s area: (a) area 44; (b) 44 and 45; and (c) 44, 45, and 47. Like Broca’s area, the exact location of Wernicke’s area has also been a matter of dispute. Wernicke’s area is located in the temporal lobe (Brodmann’s area 22, superior temporal gyrus) and has traditionally been associated with deficits in spoken comprehension (Robson, Sage, & Lambon Ralph, 2012). In the context of primary progressive aphasia, Mesulam, Thompson, Weintraub, and Rogalski (2015) note the lack of consensus on the exact boundaries of Wernicke’s area, but encompass the supramarginal and angular gyri of the inferior parietal lobule as well as the posterior parts of the superior, middle, and inferior temporal gyri.

Damage to Broca’s area has been associated with the agrammatic, dysprosodic, halted, and non-fluent speech output as well as deficits in understanding syntactically complex sentences. Dronkers, Wilkins, Van Valin, Redfern, and Jaeger (2004) conducted a lesion analysis study using magnetic resonance imaging (MRI) scans on sixty-four aphasic speakers. The locations of brain damage were correlated to a test of spoken sentence comprehension with a focus on syntactically complex sentences. Dronkers and colleagues did not find Broca’s area to contribute significantly to comprehension of syntactically complex sentences. In an analysis of 101 MRI scans, Bates et al. (2003) reported that spoken comprehension was most affected by lesions in the middle temporal gyrus, with contributions from dorsolateral prefrontal and parietal association cortices. The middle temporal gyrus was a significant factor in auditory comprehension after Wernicke’s area was factored out. However, after the middle temporal gyrus was factored out, the contribution of Wernicke’s area was no longer apparent. Such discrepant findings have been used to cast doubt on the notion of highly specialized areas for language functions and to bolster arguments for more distributed accounts of language representation in the brain (cf., Helm-Estabrooks, Albert, & Nichols, 2014). Another view of the non-specificity of functioning in particular areas espouses the notion of domain general processes such as working memory and attention, which support linguistic processing (Geranmayeh, Brownsett, & Wise, 2014).

The distributed network approach is based on a synthesis of diverse evidence going beyond the linguistic behavior-lesion association that has been the norm in aphasia. The distributed network approach draws on neuroimaging studies about behavior-lesion associations in aphasia and integrates findings from animal neuropsychology as well as neuroimaging findings from human neuropsychology. Ben Shalom and Poeppel (2008) present a unifying hypothesis, based on diverse neuroanatomical models from the 19th century, to contemporary thinking of brain-behavior relations. In their model, the temporal lobe is responsible for memorizing (learning new and retrieving stored information), the parietal lobe for analyzing (accessing subparts of stored information), and the frontal lobe for synthesizing verbal information (creating combinations of stored representations). The verbal information is divided into three core language functions, that is, phonology (speech sounds), semantics (word meaning), and syntactic (sentence structure).

The quest for a neural basis of aphasia began with autopsy studies as the only neuroimaging method available in the 19th century and has been refined with modern neuroimaging methods and sophisticated ways of analyzing the complexities of the data that these methods produce. While the search for mapping particular aspects of linguistic processing continues, there is an acknowledgement of the limitations and advantages of different neuroimaging methods and the synergy of diverse cortical areas.

3. Speech Sounds

Speech sound disorders in aphasia fall into two main categories: perceptual abilities that involve speech discrimination (input) and speech sound production (output).

Most aphasic speakers show difficulties in discriminating phonemes and other aspects of the sound structure of words (Blumstein, 1994). Difficulties emerge when speakers are asked to distinguish single syllables between “pa” vs. “ba” in categorical perception experiments (Basso, Casati, & Vignolo, 1977; Hickok, Costanzo, Capasso, & Miceli, 2011) or in tasks that require speakers to decide if the pictorial representations of the words “pear” and “bear” rhyme (Langland-Hassan, Faries, Richardson, & Dietz, 2015). Although phonological processing deficits do not severely affect understanding of spoken words and sentences (Blumstein, 1994), in some types of aphasia such as Wernicke’s aphasia, recent evidence suggests that a phonological deficit contributes to the spoken language deficits (Robson, Sage, & Lambon Ralph, 2012). In this study, the phonological deficit was associated with damage to the posterior superior temporal gyrus. Some studies investigated phonological processing in non-fluent, Broca’s aphasia, in an attempt to find out if Broca’s area is associated with phonological processing (Caplan, Gow, &, Makris, 1995; Hickok, Costanzo, Capasso, & Miceli, 2011). The conclusion was that Broca’s area is not critical for phonological processing.

There may be disruptions in sound production in aphasia. A phonological disorder in aphasia disrupts the ability to select and produce the phonemes that comprise individual words. If phonemes are not selected properly or not ordered correctly, phonological errors occur (phonemic paraphasias). For example, in a confrontation spoken naming task, whereby a person is shown a picture of a cat and the response is /tæk/, the error is a phonemic paraphasia.

In some aphasic speakers the phonological disorder is so severe that the spoken output does not resemble real words (neologisms). For example, if the response to a picture of a cat is /bren/, the error could be described as a neologism. The term jargon aphasia characterizes this type of speech output (Butterworth, 1992; Marshall, 2006). Marshall (2006) summarizes the cardinal features of jargon aphasia as follows: the phonological structure of neologisms usually adheres to the range of phonemes of the speaker’s language (rather than phonemes from other languages). Neologisms also follow phonotactic rules, with prevalence for the most frequently used phonemes in the speaker’s language. Neologisms can also be accompanied by other errors in the same speaker, notably, words that are close in meaning with an intended word (semantic paraphasias). Another feature in some cases of jargon aphasia, and indeed, other manifestations of aphasia, is the repeated attempts of a person to correct erroneous speech output. This behavior, known as conduit d’ approach, often results in either more recognizable words or even correct productions. In such cases the deficit could be in translating a phonological lexical representation into a phonetic speech plan. This behavior also shows that the person is aware of the erroneous speech and attempts to correct it through self-monitoring.

There is considerable debate as to whether sound production errors originate at phonological or phonetic levels (e.g., Galluzzi, Bureca, Guariglia, & Romani, 2015; Hardcastle & Edwards, 1992; Maas, Robin, Wright, & Ballard, 2008; Varley & Whiteside, 2001). This is important because it helps distinguish aphasia from apraxia of speech, which often co-occur in the same speakers. Apraxia of speech is an articulatory disorder disrupting motor speech programming of the sounds comprising words.

We should note that the ability to control with precision physical aspects of speech sound production is compromised in aphasia. Using instrumental speech sound analyses methods, Bose and van Lieshout (2008) studied five individuals with mild aphasia who did not present with speech or phonological processing deficits. Compared to healthy controls, the individuals with aphasia showed significantly longer movement duration and lower movement stability for longer speech strings (two and three syllables). Utterance length affected the lip movement patterns, in that the monosyllables had smaller peak velocities, smaller amplitudes, and shorter durations compared to two and three syllables. The authors argued that their findings provide support for the notion that linguistic changes have an impact on the characteristics of speech movements, and that individuals with aphasia are more affected by such changes than control speakers.

4. Words: Nouns and Verbs

4.1 Nouns

Word comprehension and word production deficits (anomia) are frequent in aphasia. In this section, we focus on semantic processing deficits that relate to extraction and production of meaning from two major grammatical classes of words: nouns (words usually denoting proper names and objects) and verbs (words denoting actions or states). The majority of research has focused on nouns, and, relatively recently, verbs.

Damage to the left temporo-parietal and/or prefrontal cortex is associated with semantic processing deficits (Jefferies, Patterson, & Lambon Ralph, 2008; Butler, Lambon Ralph, & Woollams, 2014; Walker et al., 2011).

Semantic errors in naming (semantic paraphasias) are usually indicative of semantic processing deficits. Semantic errors can be accompanied with errors in word comprehension, especially when words are close in meaning. While speakers presenting with a noun comprehension and production deficit can be sensitive in terms of the relative frequency of use of a word in the person’s language, in speakers presenting with semantic deficits variables such as concreteness, abstractness, and image ability could modify performance. Concrete and imageable words are usually easier to retrieve and understand in comparison to abstract and less imageable words (Whitworth, Webster, & Howard, 2014).

Empirical findings revealed a distinction between two broad types of semantic processing deficits, lexical-semantic (or verbal) and conceptual-semantic (or non-verbal). Lexical-semantic skills are evaluated with tasks that involve spoken or written language, while for conceptual-semantic skills, tasks do not involve language. A common task assessing conceptual-semantic skills is the picture-to-picture matching task, which is carried out silently. For example, the picture of a lemon has to be matched to a picture of a teapot, as opposed to a coffee pot (distractor picture). If a person presents with a lexical-semantic impairment, performance would be statistically better in this picture-to-picture matching task and worse in a similar verbal task that involves matching a spoken or written word, for example lemon, to the picture of a lemon, avoiding distractor pictures such as orange or banana. If performance is below norms in both tasks, the terms central semantic deficit (Whitworth et al., 2014) or semantic aphasia (Robson et al., 2012) are used to describe deficits extending to both lexical and conceptual-semantics. Conceptual-semantic deficits are particularly prevalent in the semantic variant of primary progressive aphasia.

Another type of lexical-semantic impairment is what has come to be known as category specific semantic deficit. The term “category specific” refers to a particular semantic category of the words that are impaired in relation to words and concepts that are spared. Most of these types of deficits involve the living/non-living distinction (a biological distinction), although other categories such as food, musical instruments, and body parts have also been reported. Category specific semantic impairments are rare.

4.2 Verbs

Research on verbs has its origins in older reports of greater preponderance of nouns over verbs in the spontaneous speech of aphasic speakers (Fillenbaum, Jones, & Wepman, 1961; Myerson & Goodglass, 1972). As a research topic, it gained increasing attention and popularity in the 1980s, with the advent of cognitive neuropsychology, a particular theoretical approach to studying brain-behavior relationships and cognition (Ellis & Young, 1988).

Comparative studies of differential performance in noun and verb comprehension and production revealed an organization of the lexical system along a verb-noun dichotomy. Another distinction that emerged was between comprehension and production processes for these word classes, which can be selectively impaired in a statistical sense, in some aphasic speakers. Berndt, Mitchum, Haendiges, and Sandson (1997) investigated understanding and production of nouns and verbs in single word contexts. In terms of understanding of nouns and verbs, only one person (of the eleven studied) was better able to understand nouns than verbs. All other participants were equally able to understand nouns and verbs, a finding corroborated by other researchers (Faroqi-Shah, Wood, & Gassert, 2010; Thompson, Lukic, King, Mesulam, & Weintraub, 2012).

In terms of spoken verb production, similar dissociations have also been reported. For example, in Berndt et al. (1997), some speakers had greater difficulty with verbs (as opposed to nouns), others had greater difficulty with nouns (as opposed to verbs), while others had equal difficulty with both words classes. The reverse pattern of greater difficulties with nouns over verbs has also been reported (Miozzo, Soardi, & Cappa, 1994).

Verbs play a crucial role in sentence comprehension and production (see section 5, “Sentences”). The reason for this is that verbs encode in their meaning not only the action or state they express as words in isolation (lexical meaning), but also the obligatory elements (known as arguments) that describe the event or state expressed by a particular verb. The term verb argument structure (also known as predicate argument structure) describes the relationship between verbs and the obligatory elements they must have for a sentence to be well formed in terms of sentence meaning. Verb argument structure dictates the structure of the sentence and, up to a point, the order of the obligatory elements (syntax). The examples in (3) show the three main types of verb argument structures in English, from the simplest to the more complex (arguments shown in italics).

(3)

a.

One argument

Julie laughed

b.

Two arguments

Bob pressed the button

c.

Three arguments

George gave Janet the stapler

Omission of an argument, a common difficulty in non-fluent aphasia, would result in an ungrammatical sentence, which would compromise the transmission of meaning. Substitution of an argument, a common difficulty in fluent aphasia, may retain the syntax of the sentence but the meaning would be compromised. The greater the verb argument structure, the greater the difficulty for the person with aphasia, especially to produce the verb and its associated arguments (Thompson, 2003).

5. Sentences

5.1. Understanding Sentences

Many individuals with aphasia have problems understanding spoken and written language. This is most apparent in people with Wernicke’s type aphasia, who have difficulty following instructions or conversations and have problems understanding single words, which can be demonstrated by a reduced ability to match sentences or object and action names to pictures. Lexical representation has been associated with the temporal parietal regions of the cortex (Dronkers et al., 2004), although studies in progressive aphasia suggest this area causes inconsistent problems with sentence comprehension (Mesulam, Thompson, Weintraub, & Rogalski, 2015). These researchers found the most severe sentence comprehension problems also involved Broca’s area and other anterior cortical areas. Broca’s area has long been associated with syntactic deficits and especially the combinatorial rules of grammar, hence the term agrammatism. The problems with sentence comprehension in Wernicke’s type aphasia may be explained as difficulty understanding individual words within a sentence, although in moderately impaired individuals, syntactic structure of a sentence may also impact on the ability to understand (Balogh & Grodzinsky, 2000). However, despite the recognized difficulty with understanding language, a syntactic deficit is not universally recognized. Blumstein and Milberg (2000) discuss contributions of lexical processing deficits, slow lexical activation, and inability to use and manipulate underlying semantic representations to understand different syntactic structures.

Whereas the problem understanding sentences is very obvious in Wernicke’s type aphasia, it is less obvious in Broca’s type aphasia and appears to be limited to interpreting sentences with complex or non-canonical word order. Despite seemingly good understanding of conversation, comprehension of semantically reversible non-canonical and other types of complex sentences can cause difficulties in aphasia (Mitchum & Berndt, 2008). A plethora of studies have reported on these phenomena in agrammatism (in some studies also referred to as Broca’s aphasia). Although simple semantically non-reversible active (4a) and non-reversible passive sentences (4b) may be interpreted correctly, problems arise interpreting reversible, non-canonical sentences such as reversible passives (5a), object clefts (5b), and some kinds of wh-questions (5c).

(4)

  1. a. Isaac ate the sandwich

  2. b. the sandwich was eaten by Isaac

(5)

  1. a. Isaac was hugged by Oscar

  2. b. the boy that the teacher saw was late

  3. c. which boy did the teacher see?

(6)

  • Oscar hugs Isaac

In semantically reversible sentences, either noun phrase (NP) could, semantically, be the agent of the verb, hence reversible. However, in (5a), because the agent is no longer the first NP as in active sentences (6), lexical knowledge and word order is insufficient for interpretation, and errors occur. When tested with, for example, a sentence-picture matching test, many participants with agrammatism will score at least above chance on the reversible active sentences but at chance on the reversible passives (Grodzinsky, 2000). This observation fueled claims that syntax is damaged and has led to explanations of the impairment based on linguistic concepts and especially the independence of syntax and lexical semantics. Thus, the argument is that errors in the interpretation of complex sentences involving movement of elements signify that grammar is disrupted in agrammatism: there is a syntactic deficit in understanding as well as producing sentences. However, because exceptions are found to this pattern of sentence comprehension, there is a debate as to whether this pattern of sentence comprehension is a defining feature of agrammatism. Further, some individuals with fluent aphasia may also show this pattern (Bastiaanse & Edwards, 2004).

Grodzinsky and his colleagues explain this pattern of sentence comprehension in agrammatism by claiming that if trace is deleted, moved constituents cannot be interpreted nor can the listener use animacy or an agent-first strategy, as either the NPs could be agent. This elegant explanation has opponents because not all agrammatic individuals show this pattern, and other factors are seen to be contributing to sentence comprehension deficits: see Grodzinsky (2000) for lead article and for commentaries arguing against his thesis with reference to English and other languages. While trace deletion may offer an explanation for declarative sentences, it is not sufficient to account for the difference in interpreting two types of wh-questions when there is a non-canonical order of thematic roles (7a and 7b).

(7)

Aphasia from a Neurolinguistic Perspective

Whereas both (7a) and (7b) involve movement of the wh-word (from post verb to sentence initial position), a difference between the understanding of canonical and non-canonical structures has been found only in the which questions. In the which questions, in addition to movement, the listener is required to link syntactic structure to previous discourse (Avrutin, 2000) or to select between semantic features of a group: the set hypothesis (Salis & Edwards, 2008).

Movement of constituents is not the only explanation; alternative or additional factors and resources underlying the comprehension deficit in agrammatism have been proposed, such as linking to discourse; the order of thematic roles; an agent first strategy; a deficit in the application of combinatorial rules rather than loss of representation (Burchert, Meissner, & De Bleser, 2008) or short-term memory. The role of short-term memory in sentence comprehension was considered in a detailed study of sixty-one people with aphasia using thirteen different sentences types (Caplan, Michaud, & Hufford, 2013). The researchers found a double dissociation between short-term memory (STM) and sentence comprehension. They concluded that although STM supports sentence comprehension, it is possible to have a low STM but perform with a normal level of accuracy on sentence comprehension tasks (one or single dissociation) and the reverse, that is, low accuracy on sentence comprehension but normal STM (double dissociation).

Queries about the strength of data sets have also arisen. For example, Burchert, Hanne, and Vasishth (2013) review the interpretation of chance performance on sentence comprehension tasks, comparing data gathered from on-line (eye-tracking) methods versus off-line methods to support their suggestion that problems comprehending non-canonical sentences arise as a result of intermittent deficiencies in the parsing mechanism rather than a syntactic deficit per se.

5.2 Producing Sentences

The ability to speak using well-formed grammatical structures is impaired in aphasia. Word finding difficulties, phonemic and lexical errors, neologisms (8)

(8)

  • in the kermp kerken kitchen

interfere with sentence structure in Wernicke type aphasia (see sample in the summary and in section 3, “Speech Sounds.” Broca’s aphasia is characterized by limited, hesitant utterances with curtailed or erroneous grammatical structure (also illustrated earlier in the summary). Difficulties with retrieving lexical verbs as in (9) are plenty, although noun retrieval is often more successful (also shown in 9).

(9)

  • the woman is dishes

Characteristically, there are problems with inflecting verbs for tense and sometimes number. In addition agrammatic speakers have problems using function or closed class words, as in determiners, pronouns, wh-words, and prepositions, which compound the difficulty in producing well-formed sentences. If sentences are produced, they are short and simple without embedded or relative clauses. These limitations cause the speaker a great deal of frustration and diminish communicative effectiveness. In addition to these problems, there may be accompanying problems with pronunciation as the lesion associated with Broca’s aphasia can extend into the pre-motor and motor strip (see section 3, “Speech Sounds”).

As with comprehension deficits, there are theoretically based claims about the underlying factors that cause difficulty constructing well-formed sentences in Broca’s type aphasia. These include short-term memory problems (Smith & Geva, 2000), slow activation of lexical items, and/or the motoric deficit, as well as claims that include deficits in syntactic structure or mapping between syntactic and semantic representations. Friedmann (2006), working with Hebrew data, produced an elegant account, of sentence errors, the Tree Pruning Hypothesis, in which tense but not agreement is damaged in Broca’s aphasia. Some adaptations have subsequently been developed around this idea, but essentially the claim is that syntactic concepts can be used to predict the grammatical errors found. Working within a generative linguistic tradition, errors arise because certain nodes of the syntactic tree are missing or under-specified, the syntactic tree is pruned at the tense node (10).

(10)

  • Complementizer -> Tense -> Negation -> Agreement -> Verb -> Noun

This predicts that an aphasic speaker who cannot project above tense will not be able to use tensed verbs and auxiliaries, copulas, subordinate clauses, complementizers formulate questions (neither yes/no or wh-questions). Thus the damaged grammar interferes with the ability to construct well-formed sentences. While it may be possible for an agrammatic speaker to name pictured actions, the ability to construct a sentence using tensed verbs, especially verbs with more than one argument (Thompson, 2003) is impaired. This research has galvanized work across many languages, and refinements proposed to this central claim have been developed. Despite much work in this field, the idea that deficits in sentence formulation arise from a syntactic impairment is not without dissenters. Criticism comes from those who eschew work within a broad generative school of linguistics, and they call upon notions of limited cognitive resources including short-term memory and general processing deficits (e.g., Kolk, 1998).

6. Discourse

The ability of people with aphasia to use connected speech for conversations or to relate narratives can be considered under the rather general term of discourse. In aphasiology, this can include observations about problems with interpretation and maintenance of monologic speech or conversation, and then broken down into consideration of problematic elements such as the use of cohesion, reference, or the range of speech acts used. Samples of connected speech are used for grammatical or lexical analysis, as language used in more naturalistic contexts may differ from that used in testing or experimental contexts (Beeke, Maxim, Best, & Cooper, 2011; Wilkinson, 1995). The study of conversational interaction focuses on details of interlocutory behavior, initiating, responding, and taking conversational turns using methods from conversational analysis. The focus of most aphasia studies has been on the levels of language covered in this encyclopedic entry. Studies of discourse deficits are fewer and less subject to theoretical debate. See Prins and Bastiaanse (2004) for a critical review of some methods of assessment of continuous speech samples.

Reported problems in discourse, pragmatics in particular, are more commonly a sequela of right hemispheric cortical damage, degenerative conditions such as Alzheimer’s disease (Cummings, 2014), or follow a traumatic brain injury: see Coelho, Liles, and Duffy (1995) for a review. However, in some cases, where left sided hemispheric damage does not result in aphasia, there may be a subtle disruption in managing narrative discourse. These may resolve over time (Ellis, Rosenbek, Rittman, & Bolsten, 2005) although Coelho and Flewellyn (2003) found that local and global coherence did not improve even though there were improvements at the micro-level of language. Global coherence refers to the whole text or story, while local level refers to a small part of the text, for example within or between sentences. Aphasia can have severe implications for a speaker’s ability to participate in and maintain conversation or produce narratives, and it is the lexical and syntactic difficulties inherent in aphasia that are the most obvious cause of problems with maintaining conversations or producing informative and coherent narratives.

6.1 Conversation

For those with Wernicke’s type aphasia, reduced understanding of their interlocutor will seriously interfere with their ability to sustain conversation. If the speaker with aphasia has partial understanding of what has been said, then non-sequiturs will arise and not be corrected. Below is an example of Dr. Wernicke talking with one of his patients (Eggert, 1977).

Dr. Wernicke: I would like to know how old you are

Mrs. A: Yes, that I don’t know at all. What my name? [...] what I am called here in Germany?

This example illustrates that, while Mrs. A retains some pragmatic abilities in that she recognizes that she is obliged to answer a question, the exchange collapses because she does not understand the question. Word finding difficulties, phonemic and lexical paraphasia, word omissions, and syntactic errors can add to the confusion as in (11). Asked how he was feeling, a person with Wernicke’s aphasia replied:

(11) I couldn’t walk quite quick on me foot one foot is a bit at night

(Edwards, 2005)

Again, this demonstrates that the aphasic speaker was aware of the type of answer required but lexical and sentence formulation problems result in a barely coherent answer.

While language comprehension of people with Broca’s aphasia is potentially adequate for participation in conversation, limitations in their ability to structure sentences and lexical retrieval difficulties can seriously interfere with conversation and the ability to retell stories or relate events. The following example (12) is an illustration of how labored conversation can be, even when the person with aphasia has relatively good comprehension. The example of conversation is of a person with a Broca’s type of aphasia, Barry (a pseudo name) trying to respond to questions from his partner Louise (also a pseudo name). The format is typical of a conversational analysis approach to examining aphasic data. Digits within brackets show length of pauses in seconds; attempts at lexical retrieval are shown in bracket (ella); overlapping utterances are marked with square brackets for example at lines 4 & 5.

(12) Conversation between a man with aphasia and his conversation partner.

(Beeke et al., 2014)

Louise we’ll go out today (.) yes?

Barry (0.8) yes (0.3) no it’s a go to (0.7) (um mum) eh no (o,8) ella Bella

Louise yeah   [we’ll g-    ]    [yes we’ll go and see Bella to      ]    day=

Barry      [Bella]          [(Bel) yeah]

Barry (1 syllable) and (2.7) it’s a (3.8) (amdea) Hamdean

Louise go to Ham     [dea- ] if we’ve got time

Barry        [no          ] no

Louise Galileo?

Barry (0.4) no

Louise no

6.2 Narrative Speech

The presence of aphasia interferes with a speaker’s ability to relate events within conversations. Research and clinical investigations of monologic speech use picture description or story (re-)telling tasks. These data are then scrutinized for lexical and/or grammatical errors using surface, descriptive grammars. A major issue is representation of the sample examined, as analyses tend to be time-consuming and, as a consequence, samples are small.

If a person with aphasia is asked to retell a story or relate an event, aphasic errors interfere with the task. While the speaker’s pragmatic awareness is usually intact, grammatical and lexical impairments impede the telling to a greater or lesser degree. Typically, a person with Wernicke’s aphasia will produce a lengthy yet barely coherent account. Here someone with Wernicke’s aphasia is telling a story depicted in a series of pictures (13). Without knowledge of the pictures, it is impossible to understand that the story is about a man and a woman preparing for a dinner party. There is use of pronouns without any referents; lexical errors (man > boy); neologisms (crup); unintelligible utterances (XX); verb omission (all sentences wonderful), all of which conspire to confuse the listener.

(13) and they said we’re writing and so they went the way and she was at the boy as he was telling it and must said and they went away and come on and they round [crup] at a XX and all sentence wonderful and she brings this lovely pig back ....

(Edwards, 2005)

In contrast, a person with Broca’s aphasia will often be able to convey some meaning despite problems with lexical retrieval and sentence structure, as in (14), which is an attempt to narrate a well known Aesop’s fable.

(14) rabbit and tortoise ... race ... rabbit ... faster ... tortoise walking ... rabbit sleeping ... and ...tortoise ... won ... won ... rabbit ... bad luck

(Salis, 2006)

Unlike the sample of Wernicke’s type aphasia in (13), despite the sparse output in (14), limited use of verbs and negligible grammatical structure, the speaker manages to convey the basic information of the story although were this not a familiar story, it might be less comprehensible.

It can be seen that problems of aphasic language above the sentential level usually arise from syntactic and lexical deficits in comprehension and production rather than an inability to sustain dialogue or monologue speech because of independent pragmatic or discourse impairments.

Further Reading

Caplan, D., Michaud, J., & Hufford, R. (2013). Short-term memory, working memory, and syntactic comprehension in aphasia. Cognitive Neuropsychology, 30, 77–109.Find this resource:

Dronkers, N. F., Plaisant, O., Iba-Zizen, M. T., & Canais, E. A. (2007). Paul Broca’s historic cases: High resolution MR imaging of the brains of Leborgne and Lelong. Brain, 130, 1432–1441.Find this resource:

Edwards, S. (2005). Fluent aphasia. Cambridge, U.K.: Cambridge University Press.Find this resource:

Geranmayeh, F., Brownsett, S. L. E., & Wise, R. J. S. (2014). Task-induced brain activity in aphasic stroke patients: What is driving recovery? Brain, 137, 2632–2648.Find this resource:

Grodzinsky, Y. (2000). The neurology of syntax: Language use without Broca’s area. Behavioral and Brain Sciences, 23, 1–21.Find this resource:

Grodzinsky, Y., & Amunts, K. (2006). Broca’s region. Oxford: Oxford University Press.Find this resource:

Hickok, G., Costanzo, M., Capasso, R., & Miceli, G. (2011). The role of Broca’s area in speech perception: Evidence from aphasia revisited. Brain and Language, 119, 214–220.Find this resource:

Mesulam, M-M., Thompson, C. K., Weintraub, S., & Rogalski, E. (2015). The Wernicke conundrum and the anatomy of language comprehension in primary progressive aphasia. Brain, 138, 2423–2437.Find this resource:

Robson, H., Sage, K., & Lambon Ralph, M. A. (2012). Wernicke’s aphasia reflects a combination of acoustic-phonological and semantic control deficits: A case-series comparison of Wernicke’s aphasia, semantic dementia and semantic aphasia. Neuropsychologia, 50, 266–275.Find this resource:

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