Capgras Delusion: Impaired Face Recognition Process
|✅ Paper Type: Free Essay||✅ Subject: Psychology|
|✅ Wordcount: 2122 words||✅ Published: 19th Apr 2018|
Capgras delusion, the belief that somebody is replaced by an imposer. First, this study examines whether Capgras patients, compared to controls, have an impaired face recognition process. Patients show to be hyporesponsive to familiar faces and show to have a decreased activity in brain areas, such as the prefrontal, lateral temporal and mesial temporal regions. The second part of this study examines the belief reasoning processes in patients compared to controls. Patients show an impairment in their belief reasoning process and this is linked to an impairment of the right lateral prefrontal cortex.
The goal is to see whether Capgras patients have an impaired face-recognition process and an impaired belief-evaluating process, associated with the brain activity, compared to control participants.
The main objectives
- Showing that Capgras patients have an impaired face recognition process because they are hyporesponsive to familiar faces, by measuring reaction times of the recognition of familiar and unfamiliar faces.
- Showing that, because certain areas in the brain are responsible for face recognition, Capgras patients have impairments in certain brain areas, such as the prefrontal, lateral temporal and mesial temporal regions (by measuring the BOLD activity in these areas), to experience Capgras delusions, because they are hyporesponsive to familiar faces.
- Showing that, because according to Coltheart’s two factor theory, Capgras patients have a decreased reasoning-evaluation process, Capgras patients have an impaired reasoning process. This study also wants to show that this reasoning process is associated with the right lateral prefrontal cortex (by measuring the BOLD activity in the right lateral prefrontal cortex) and that Capgras patients should show in impairment in this area.
This study is seeking to expand research on which processes are damaged in people who experience Capgras delusions, looking at two theories. Experiment 1 and 2 are about damage to the face recognition system. In experiment 1we argue that patients are hyporesponsive to familiar faces by looking at their reaction times in the recognition of familiar and unfamiliar faces. In experiment 2, an fMRI scan measures the brain activity while participants look at familiar and unfamiliar faces. It is predicted that Capgras patients will show impairments in areas that are involved in face recognition, such as the prefrontal, lateral temporal and mesial temporal regions. The second theory, the two factor theory, suggests that delusions are a result of an impairment of belief evaluation processes. Experiment 3 wants to link this impairment in belief reasoning to the right prefrontal lateral cortex. Capgras patients are expected to show a decreased activity, measured by an fMRI scan, in this area while they do a belief reasoning task. This will indicate that Capgras patients have impaired face recognition processes and impaired belief reasoning processes and these processes are linked to several impairments in the brain.
Delusional misidentification syndromes (DMS) are “psychiatric disorders distinguished by the fact that they all involve some deviation from normal processes of recognising people” (Ellis & Young, 1990, p239). A specific DMS is the Capgras syndrome. The Capgras syndrome is “characterized by the patient insisting that others, usually those quite close emotionally, have been replaced by doubles, impostors or robots” (Ellis et al., 1997, p 1058). For example, a man could think his mother is replaced by an imposer. Mostly the duplicated people, are people very close to the patients (Todd et al., 1981) and the patients often show conflicting feelings of love and hate for the duplicated relatives (Enoch & Trethowan, 1991). Most of the patients who are suffering from Capgras syndrome have some evidence of brain abnormalities (Joseph, 1985).
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Bauer (1984, 1986) introduced the dual recognition route. He suggests that there are two routes of facial recognition, the ventral and the dorsal route. The ventral route runs from the visual cortex to the temporal lobes and is the conscious recognition route. The dorsal route runs from the visual cortex to the limbic system and is the affective response route. Ellis & Young (1990) proposed that Capgras delusion is a mirror-image of prosopagnosia, the inability to recognise previous familiar faces, mostly following brain damage (Sorger et al., 2007). They suggested that in Capgras delusions, the affective response route is damaged, which means that patients will consciously recognise the person, but they won’t have an affective response that is associated with familiarity, but they do have an intact ventral route. In 1997 Ellis et al. did study on face recognition in Capgras patients. They found that unlike the control participants, who showed significant differences, that Capgras patients showed no difference in skin conductance response (SCR) to familiar and unfamiliar faces, which means that they are hyporesponsive to familiar faces and thus that Capgras patients have a breakdown in familiarity processing. Coltheart (2007) worked further on this idea and proposed that if you can answer the next two questions, we can have a possible explanation for the delusion. “Where did the delusion come from?” and “Why does the patient not reject the belief?” (Coltheart, 2007, p1044). This called this the two factor theory of delusions. He proposed that there had to be two neuropsychological deficits. First, what is responsible for the content of the delusion and secondly, what is responsible for the persistence of the belief, which means that there needs to be damage in the right hemisphere, because it is involved in belief evaluation. They argued that the right temporal-parietal regions and the right frontal lobe are very important in the belief evaluation. In 2011, Coltheart et al. explained that via abductive inference we make propositions. These propositions have to survive a belief-evaluation process to be adopted as a belief. According to Coltheart et al. (2011) this belief evaluation process is damaged in Capgras patients.
This study wants to look at both views, the impairments of face recognition and the impairments to belief evaluation processes.
Experiment 1 and 2 focuses on face recognition, whether experiment 3 focuses on the belief evaluation process. First of all, usually reaction times are significantly faster for familiar faces than for unfamiliar faces (Balas, Cox & Conwell, 2007). Because of the hyporesponsiveness to familiar faces (Ellis et al., 1997), Capgras patients are expected to have no significant difference in reaction time between familiar and unfamiliar faces. Secondly, according to Ellis et al. (1997), Capgras patients should have an impairment in their face recognition. One study found a reduced neural activity in the face recognition system in a case of Capgras delusion (Thiel et al., 2013). Another study found higher activity in the left superior parietal and biletral middle frontal gyrus in familiar faces (Rossion et al., 2001). Activations in the prefrontal, lateral temporal and mesial temporal regions were associated with recognition of famous faces (Leveroni et al., 2000). This would mean that Capgras patients, who are hyporesponsive to familiar faces (Ellis et al., 1997), would show an increased activity in these areas. In experiment 3, the belief evaluation process is tested. Coltheart et al. (2011) suggested that the impairment in Capgras patients in the belief evaluation process is associated with right lateral prefrontal cortex pathology. Evidence was found for a dynamic neural system for reasoning in the lateral/dorsal lateral prefrontal cortex (Goel & Dolan, 2003). In an fMRI study, they found a role of the lateral prefrontal cortex in modulation of reasoning by beliefs (Goel & Dolan, 2003). They found that correct logical reasoning showed an increased activity in the right lateral prefrontal cortex. This means that, according to Coltheart’s two factor theory (2010), that Capgras patient would show a decreased activity in this area, because of their impairments in the belief evaluation system.
Participants and design:
This study will recruit a sample of 10 Capgras patients and 10 healthy age-matched controls. Participants will receive fees for participating. They will be provided with an informed consent. This study exists out of two experiments. In the first task participants will be provided with pictures of familiar and unfamiliar faces (in Capgras patients familiar faces of the persons they replace with imposers and in controls with family members) while reaction time is measured and an fMRI scan is taken. In the second experiment, the right lateral prefrontal cortex activity is measured with an fMRI scan while the participants look at familiar and unfamiliar faces and at the same time are asked questions about these persons in a belief-reasoning task.
Stimulus materials and procedure:
In the first experiment, participants were asked to sit in 0.5 m in front of a screen. Each trial started with a cue image of a familiar or an unfamiliar face for 500 ms. After an interinterval of 500 ms, a picture that matched the cue image was shown together with a picture that didn’t match (left and right). The participants were asked via button presses to show which picture matched the cue image, as rapid and accurately as possible. All stimulus presentation responeses were analysed with the Matlab Psychophysics Toolbox. This task was taken from Balas, Cox & Conwell (2007).
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In the second experiment, before the participants will be asked to enter the fMRI, they will be instructed about the task. This study uses the task Ellis et al. (1997) used, for testing the identification of familiar faces. When they are in the fMRI, they will see pictures of their family members (for the Capgras patients, including the persons they think are replaced by imposers) or unfamiliar pictures. They got to see 10 familiar faces and 20 unfamiliar faces in random order. For each face the participant was asked to respond if the face was familiar to them or not, while the fMRI scan measured their blood-oxygen-level dependent (BOLD) activity in their brain. In experiment 3, the participants were asked again to enter the fMRI scan. We used the belief reasoning task (Appendix: Picture 1) of Sommer et al. (2007). In both of the conditions, the first four pictures are the same. In the true belief task the girl comes back in the room and sees that the boy puts the ball into the basket. In the false belief task, she comes back in the room after he putted the ball in the basket. The response picture (red) was the same in both condition. In 50% of the trials, the girl, based on her belief, looked for the ball in the expected box and in the other 50% in the unexpected box. The participants needed to decide if Betty, based on her belief, made the expected or unexpected choice by key pressing, while the BOLD activity in the right lateral prefrontal cortex was measured.
In experiment 1 we expect that Capgras patients will show no significant difference in reaction times to familiar or unfamiliar faces, because of their hyporesponsivess to familiar faces (Ellis et al., 1997), compared to normal controls who are expected to have reaction times faster for familiar faces than for unfamiliar faces (Balas, Cox & Conwell, 2007). In experiment 2 we expect Capgras patients to have a decreased activity in the prefrontal, lateral temporal and mesial temporal regions compared to controls, because of their impairment in face recognition (Ellis et al., 1997). In experiment 3, we expect patients to have a decreased activity in the right lateral prefrontal cortex while they do the belief reasoning task, because of Colthearts suggestion that Capgras patients have a damaged belief evaluation process.
This study will benefit psychologist who have studied Capgras delusion, because the causes are still very vague and not that many studies have been done on Capgras. It will also benefit Capgras patients. . It can be useful for patients suffering from schizophrenia and dementia because Capgras syndrome is often associated with these disorders. It can help create treatments by knowing the origins in the brain while patients experience these hallucinations. This study focus on more theories, which makes it easier to understand this delusion.
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