Cognitive neuropsychology explains patterns of impaired performance in brain-damaged patients in terms of damage to modules within a normal cognitive process (Ellis & Young, 2013). In turn, conclusions about the mental organisation of normal cognitive processes can be drawn. This report aims to convince committee members that cognitive neuropsychology has successfully contributed to the understanding of normal cognition. Firstly, this report will show that studying patients with aphasia have contributed to the understanding of the general organisation of the normal lexical (vocabulary) system. Aphasia is a neurological condition that results in difficulty with spoken language or understanding spoken language (Caramazza & Hillis, 1991). This report will evaluate cognitive neuropsychological research showing that the processing of different grammatical class forms (verbs and nouns) rely on separate components in the lexical system. Secondly, this report will show that by studying patients with anosognosia, the structure of the normal awareness system is understood. Anosognosia is a neurological condition defined by a lack of awareness of a specific motor, sensory or cognitive deficit (Orfei et al., 2007). This report will evaluate cognitive neuropsychological research that suggests that there are domain specific modules responsible for explicit awareness and different forms of residual awareness (implicit and emergent awareness). Therefore cognitive neuropsychology has contributed to the understanding of the normal language and consciousness cognitive processes.
Research on aphasic patients has contributed to the understanding of how nouns and verbs are processed in the normal lexical system. This is shown in Matzig, Druks, Masterson and Vigliocco’s (2009) review examining 25 years of studies investigating aphasic patient’s performance on noun and verb picture naming tasks. The task involves presenting photographs of objects and actions to patients with different forms of aphasia and instructing them to name the specific noun or verb elicited. Among 63 patients across studies, 14 had a disproportionate deficit in naming nouns and 49 had a disproportionate deficit in naming verbs. This double dissociation between grammatical classes suggests that lexical deficits are selective and the processing of nouns and verbs are mediated by separate components in the normal lexical processing system. However, although picture naming tasks are used to evaluate relative impairment of noun and verb processing, the task is intrinsically testing the participants’ ability to process words referring to objects and actions. It is therefore unclear whether the dissociation occurs due to a grammatical or semantic difference. It could be that that selective noun-verb impairment occurs as a result of damage to the cognitive processes underlying knowledge of objects or action concepts (Vigliocco, Vinson, Druks, Barber & Cappa, 2011). In contrast, it could be a result of damage to processes underlying grammatical knowledge of the different word form classes (Laiacona & Caramazza, 2004).
Assessing patients’ performance in tasks using pseudo-words attempts to separate the semantic and grammatical class of nouns and verbs (Shapiro & Caramazza, 2003). If aphasic patients show disproportionate difficulty with both real verbs and pseudo-verbs (or real nouns and pseudo-nouns) the deficit cannot be of semantic class as pseudo-words have no meaning. Shapiro and Caramazza (2003) reported cases of Patient RC and Patient JR who took part in a picture naming and morphological transformation task. The morphological transformation task involved displaying, one-by-one, a collection of short sentences and instructing participants to transform singular pseudo-nouns to plural (e.g., “a zug”, “many zugs”), and present pseudo-verbs to past tense (e.g., “he zug”, “they zug”), or the other way around. Patient RC was flawed in action naming and in transforming both pseudo-verbs and actual verbs. Patient JR was flawed in object naming and in transforming both pseudo-nouns and actual nouns. Thus, as pseudo-words have no meaning, this noun-verb deficit dissociation cannot be due to the damage of separate semantic processes.
Due to sentence context bias, the participants in Shapiro and Caramazza’s (2003) study could have possibly interpreted pseudo-words by attaching meaning to them. For instance, introducing pseudo-nouns by a quantifier (e.g., “many”) could be interpreted as object-like while introducing pseudo-verbs by a pronoun (e.g., “they”) could be interpreted as action-like. Vigliocco et al. (2011) investigated this by firstly asking a group of healthy English speakers to create a definition for 40 pseudo-words. Each pseudo-word was displayed in different sentence contexts whereby each participant only saw each pseudo-word in one context (verb or action context). The study secondly involved showing a new group of healthy English speakers the definitions created and instructing them to guess whether they referred to an object, action or abstract concept. Definitions of pseudo-words displayed in a noun context were considered objects 84% of the time. Definitions of pseudo-words displayed in a verb context were considered actions 83% of the time. Therefore, the double dissociation in noun-verb selective deficits displayed between JR and RC can be explained on a semantic basis. Specifically, as pseudo-words could have been interpreted semantically as a result of the sentence context. This tells us that in normal cognition, processing verbs and nouns are mediated by separate cognitive processes due to semantic differences and not in terms of lexical-grammatical class. These findings converge with imaging studies demonstrating that the production of nouns activates an occipital-temporal-parietal network (areas normally associated with visual processing, spatial attention & object recognition). Comparably, the production of verbs depended on a frontal network of structures (areas normally associated with motor programming and control) (Gleichgerrcht et al., 2016). Therefore, in normal cognition, producing words used to semantically represent nouns and verbs rely on two dissociable networks. In addition, these dissociable networks employ brain areas involved in cognitive and sensorimotor experiences that correspond to the function conveyed by each grammatical word class.
For cognitive neuropsychology to contribute to the understanding of normal verb and noun processing in the future, research should be designed that investigates the processing of abstract verbs (e.g., inspire) and nouns (e.g., intelligence). A study could investigate aphasic patients’ ability to describe a picture in comparison to telling a story. Storytelling stimuli enable abstract verbs and nouns to be elicited (Gleichgerrcht et al., 2016). As abstract nouns and verbs do not rely on action-object knowledge, any differences in processing impairment between these grammatical word forms support a grammatical explanation for noun-verb processing, instead of an object-action semantic explanation. These findings would further clarify the debate regarding the interpretation of the dissociation between noun and verb processing. However, regardless of the interpretation, the presence of a dissociation in cognitive neuropsychological research and imaging studies is useful as it suggests there are independent processing modules for lexical word types in the language system. It also demonstrates how neural processes have developed in the language system, whereby each speech component may recruit segregated neural networks that are also used by other cognitive processes.
Next, by studying anosognosic patients the composite structure of the consciousness system has been illustrated. Among researchers there is an emerging agreement that anosognosia is a multi-factorial phenomenon (Orfei et al., 2007). This suggests that different mechanisms could be responsible for lack of awareness. In turn, studying different aspects of the disorder on patients with anosognosia for hemiplegia (AHP) has assisted our understanding of multiple independent components underlying self-awareness. Hemiplegia is defined as paralysis to a body part on one side of a subject’s body (Spinazzola, Pia, Folegatti, Marchetti & Berti, 2008). When asking AHP patients about their deficit, they have been found to explicitly deny motor difficulties and hence are explicitly unaware of their deficit (Marcel, Tegnér & Nimmo-Smith, 2004). Cocchini, Beschin, Fotopoulou and Della Sala (2010) investigated whether AHP may however have some form of residual awareness for their deficit. Cocchini et al. (2010) examined explicit and implicit awareness for upper limb motor impairment in 30 right brain-damaged (RBD) patients. Controls included seven participants with motor disorders of the upper limb not caused by brain damage. Explicit awareness was measured using a questionnaire whereby patients rated their motor abilities. Implicit awareness was measured using a bimanual task where participants were asked to carry out eight simple tasks. The task could be carried out with one hand, but using two hands enables better task performance (e.g., holding a two-handled tray). If participants had implicit awareness of their motor deficit they would approach the simple task with the correct coping strategy (e.g., lifting the two-handled tray by positioning their hand beneath the centre of it). If they were not implicitly aware they would approach the task as if they have two able hands (e.g., place their hand at one end of the two-handled tray). Controls showed neither explicit nor implicit unawareness, eight RBD participants were explicitly unaware but implicitly aware and two RBD participants were explicitly aware but implicitly unaware of their motor deficit. This double dissociation suggests that in normal cognition, there are domain specific modules responsible for explicit and implicit awareness that can be selectively disrupted after brain injury. A critique of this study is that two different tasks were used to measure implicit and explicit awareness and tasks might have had across-task difficulty variance. In the future, implicit and explicit awareness should be assessed in AHP patients using identical stimuli to confirm our understanding of the organisation of the normal awareness system.
Research into AHP patients has also found that implicit awareness deficit is dissociable with emergent awareness deficit (deficit to another form of residual awareness). Emergent awareness is when a patient becomes aware of their deficit only when asked to execute an action with the paralysed body part (Moro, Pernigo, Zapparoli, Cordioli & Aglioti, 2011). Moro et al. (2011) investigated implicit and emergent awareness in 12 patients with AHP and 12 patients with hemiplegia without anosognosia. Participants were first asked to verbally respond to how many hands they would use to hold a given object in a horizontal position. If they declared they would use two, regardless of their paralysis (explicitly unaware), the examiner picked up the object with two hands and then instructed the participant to pick it up. The distance of where the participant placed their hand in relation to the midpoint provided the measure of implicit awareness. Five participants placed their hand towards the centre of the object, thus displaying a difference between verbal report and behaviour. This validates the implicit and explicit awareness dissociation found in Cocchini et al. (2011) study as the same test is used to measure both forms of awareness. The second task involved executing five bimanual actions (e.g., tying a knot) and judging how well they would perform each action before, during and after they attempted to do the action. Changes in the patient’s judgement of ability provided the measure of emergent awareness whereby the effort to perform actions improved motor awareness in three patients. Interestingly the patients who displayed emergent awareness were not the same patients that displayed implicit awareness in the first task. As some patients presented a selective deficit for implicit and emergent awareness, this is evidence that in normal cognition the awareness system is a multicomponent structure made up of independent processing modules. It also supports the development of individualised therapies in the future as for some patient attempting an action may accelerate their explicit awareness.
To conclude, the aim of this report was to convince committee members that cognitive neuropsychology has successfully contributed to the understanding of normal cognition. Therefore, the report critically evaluated cognitive neuropsychological research into two aspects of cognition, namely language and consciousness. Firstly, it analysed research in aphasic patients to show that in normal cognition, nouns and verbs are processed by separate neural mechanisms (Matzig et al., 2009). This neural separation has been interpreted by cognitive neuropsychologists as due to semantic differences (action/object) and not in terms of lexical-grammatical class (Vigliocco et al., 2011). However, future research needs to be carried out to investigate whether, in normal cognition, separate processing components are required to process other verbs and nouns that do not require an object or verb knowledge. The report then analysed research into AHP patients to show that in normal cognition, awareness is an information processing system, with many independent components (Cocchini et al., 2011; Moro et al., 2011).