Examining the relationships between cognition and auditory hallucinations: A systematic review.

OBJECTIVE: Auditory hallucinations (hearing voices) have been associated with a range of altered cognitive functions, pertaining to signal detection, source-monitoring, memory, inhibition and language processes. Yet, empirical results are inconsistent. Despite this, several theoretical models of auditory hallucinations persist, alongside increasing emphasis on the utility of a multidimensional framework. Thus, clarification of current evidence across the broad scope of proposed mechanisms is warranted. METHOD: A systematic search of the Web of Science, PubMed and Scopus databases was conducted. Records were screened to confirm the use of an objective behavioural cognitive task, and valid measurement of hallucinations specific to the auditory modality. RESULTS: Auditory hallucinations were primarily associated with difficulties in perceptual decision-making (i.e. reduced sensitivity/accuracy for signal-noise discrimination; liberal responding to ambiguity), source-monitoring (i.e. self-other and temporal context confusion), working memory and language function (i.e. reduced verbal fluency). Mixed or limited support was observed for perceptual feature discrimination, imagery vividness/illusion susceptibility, source-monitoring for stimulus form and spatial context, recognition and recall memory, executive functions (e.g. attention, inhibition), emotion processing and language comprehension/hemispheric organisation. CONCLUSIONS: Findings were considered within predictive coding and self-monitoring frameworks. Of concern was the portion of studies which - despite offering auditory-hallucination-specific aims and inferences - employed modality-general measures, and/or diagnostic-based contrasts with psychologically healthy individuals. This review highlights disparities within the literature between theoretical conceptualisations of auditory hallucinations and the body of rigorous empirical evidence supporting such inferences. Future cognitive investigations, beyond the schizophrenia-spectrum, which explicitly define and measure the timeframe and sensory modality of hallucinations, are recommended.

Limited awareness of hallucinations in patients with Alzheimer's disease.

INTRODUCTION: We investigated the degree of cognitive insight in patients with Alzheimer's Disease (AD) regarding their hallucinations, aiming to elucidate the subjective experiences and perceptions associated with this phenomenon. METHODS: Using a cross-sectional design, we invited both AD patients (n = 31) and their informants to evaluate the occurrence of hallucinations. Degree of cognitive insight was based upon the discrepancy between the patients' and informants' evaluations. RESULTS: Analysis demonstrated that AD patients rated the occurrence of hallucinations lower than their informants, indicating that patients tended to underestimate the frequency of their hallucinations. The discrepancy between the ratings of patients and informants was negatively correlated with cognitive functioning, suggesting that a greater discrepancy (indicating poorer insight) was associated with lower cognitive functioning in patients. DISCUSSION: Our findings highlight the deficits in insight into hallucinations among AD patients, specifically indicating that AD patients have limited awareness of their own hallucinations. Furthermore, our findings support the idea that deficits in insight into hallucinations are associated with the progression of AD.

On hallucinations and memory: the relationship between hallucinations and autobiographical overgenerality in Alzheimer's Disease.

OBJECTIVES: Alzheimer's disease (AD) has been associated with autobiographical overgenerality (i.e. a tendency of patients to retrieve general rather than specific personal memories). AD has also been associated with hallucinations. We investigated the relationship between autobiographical overgenerality and hallucinations in AD. METHODS: We invited 28 patients with mild AD to retrieve autobiographical memories, and we also evaluated the occurrence of hallucinations in these patients. RESULTS: Analysis demonstrated significant correlations between hallucinations and autobiographical overgenerality in the patients. CONCLUSION: AD patients who are distressed by hallucinations may demonstrate autobiographical overgenerality as a strategy to avoid retrieving distressing information that may be related with hallucinations. However, hallucinations as observed in our study can be attributed to other factors such as the general cognitive decline in AD.

Examining the impact of experiencing auditory verbal hallucinations from a first-person perspective on the degree of empathy and stigmatization in a group of psychology students: A study using 360° immersive videos.

BACKGROUND: Stigmatization toward psychosis is persistent among mental health professionals (MHPs) and negatively impacts the patients' outcomes. One suggested way of reducing stigmatization is to expose MHPs to simulations of psychotic symptoms. This approach has been associated with an increase in empathy, but also with an increase in the desire of social distance. The addition of an empathic task (ET) has been suggested to neutralize this effect on social distance. The present study aims to (1) examine the effect of a remotely administered 360° immersive video (360IV) simulation on empathy and stigma among psychology students and (2) replicate the neutralizing effect of an ET on social distance. Finally, the potential role of immersive properties on changes will also be explored. METHODS: A 360IV simulating auditory hallucinations was constructed in collaboration with patient partners. 121 psychology students were allocated to one of three conditions: (i) exposure to the 360IV, (ii) exposure to the 360IV and to an ET (360IV + ET), and (iii) no exposure (control). Measures of empathy and stigma (stereotypes and social distance) were collected before and after the interventions. RESULTS: An increase of empathy was observed in the 360IV and 360IV + ET conditions compared to the control condition. There was an increase of stereotypes in all conditions and no effect on social distance. CONCLUSIONS: This study confirms the effectiveness of a 360IV simulation intervention in increasing empathy in psychology students but questions its efficacy in reducing stigma.

Anomalous self-experiences and neurocognitive functioning in adolescents at risk for psychosis: Still no significant associations found between these two vulnerability markers.

BACKGROUND: Anomalous self-experiences (ASEs) and neurocognitive impairments are considered essential domains of vulnerability for developing psychotic disorders. However, little research exists of possible associations between ASEs and neurocognitive functions in individuals at-risk for psychosis. The interconnections between ASEs and neurocognitive impairments should therefore be clarified as much as possible, especially in young individuals at risk. No previous studies have investigated these two fundamental domains in non-help-seeking adolescents at risk for developing psychosis. METHODS: This study is based on the Norwegian Mother, Father and Child Cohort Study (MoBa). Adolescents (N = 48, 94% females, mean age = 15.3) were invited to participate after completing a 14-year-old survey distributed by MoBA. At-risk adolescents were selected based on the 0.4% highest scores on 19 items assessing both psychotic-like experiences and ASEs. Five specifically selected and formulated items measuring ASEs were computed to an ASEs total score. Neurocognitive functioning was assessed using the MATRICS Consensus Cognitive Battery. RESULTS: Regression analyses revealed no significant relationships between ASEs and any neurocognitive domain. CONCLUSIONS: We did not find any significant associations between ASEs and neurocognitive functions in non-help-seeking adolescents at risk for psychotic disorders, which is in line with reports from other types of cohorts. Thus, ASEs and neurocognitive functions may be understood as two relatively separate domains that co-exist in at-risk states. These results underline the need for a wider scope when making predictions about future trajectories, e.g. the development of psychotic disorders. Including both ASEs and neurocognitive functioning in at-risk populations may increase the specificity of vulnerability criteria in this population and enhance our understanding of early psychosis psychopathology.

Using 360-degree immersive videos to assess multiple transdiagnostic symptoms: A study focusing on fear of negative evaluation, paranoid thoughts, negative automatic thoughts, and craving.

Over the last 20 years, virtual reality (VR) has gained a great interest for both assessment and treatment of various psychopathologies. However, due to high costs and material specificity, VR remains disadvantageous for clinicians. Adopting a multiple transdiagnostic approach, this study aims at testing the validity of a 360-degree immersive video (360IV) for the assessment of five common psychological symptoms (fear of negative evaluation, paranoid thoughts, negative automatic thoughts, craving for alcohol and for nicotine). A 360IV was constructed in the Darius Café and included actors behaving naturally. One hundred and fifty-eight adults from the general population were assessed in terms of their proneness towards the five symptoms, were then exposed to the 360IV and completed measures for the five state symptoms, four dimensions of presence (place, plausibility, copresence and social presence illusions) and cybersickness. Results revealed that the five symptoms occurred during the immersion and were predicted by the participants' proneness towards these symptoms. The 360IV was also able to elicit various levels of the four dimensions of presence while producing few cybersickness. The present study provides evidence supporting the use of the 360IV as a new accessible, ecological, and standardized tool to assess multiple transdiagnostic symptoms. Supplementary Information: The online version contains supplementary material available at 10.1007/s10055-023-00779-y.

Eliciting false auditory perceptions using speech frequencies and semantic priming: a signal detection approach.

INTRODUCTION: Individuals experiencing auditory hallucinations (AH) tend to perceive voices when exposed to random noise. However, the factors driving this tendency remain unclear. The present study examined the interaction of a top-down (expectations) and bottom-up (type of noise) process to better understand the mechanisms that underlie AH. METHODS: Fifty-two healthy individuals (29 with high proneness and 23 with low proneness to AH) completed a signal detection task, in which they listened to pre-recorded sentences. The last word was either masked by noise or only noise was presented without the word. Two types of noise existed (speech-related versus speech-unrelated frequencies) and words were characterised by either high or low levels of semantic expectation. RESULTS: Participants with high proneness to AH showed a more liberal decision bias (i.e., they were more likely to report having heard a word) and poorer discrimination ability as compared to participants with low proneness to AH - but only when the word was masked by speech-related noises and the level of expectation was high. Further, the more liberal decision bias correlated negatively with the tendency to experience AH. CONCLUSION: This novel paradigm demonstrated an interaction between top-down (level of expectation) and bottom-up (type of noise) processes, supporting current theoretical models of AH.

Correlates of Hallucinatory Experiences in the General Population: An International Multisite Replication Study.

Hallucinatory experiences can occur in both clinical and nonclinical groups. However, in previous studies of the general population, investigations of the cognitive mechanisms underlying hallucinatory experiences have yielded inconsistent results. We ran a large-scale preregistered multisite study, in which general-population participants (N = 1,394 across 11 data-collection sites and online) completed assessments of hallucinatory experiences, a measure of adverse childhood experiences, and four tasks: source memory, dichotic listening, backward digit span, and auditory signal detection. We found that hallucinatory experiences were associated with a higher false-alarm rate on the signal detection task and a greater number of reported adverse childhood experiences but not with any of the other cognitive measures employed. These findings are an important step in improving reproducibility in hallucinations research and suggest that the replicability of some findings regarding cognition in clinical samples needs to be investigated.

In the twilight zone: An epidemiological study of sleep-related hallucinations.

BACKGROUND: Few studies have investigated hallucinations that occur at the onset/offset of sleep (called hypnagogic/hypnopompic hallucinations; HHHs), despite the fact that their prevalence in the general population is reported to be higher than the prevalence of daytime hallucinations. We utilized data from an epidemiological study to explore the prevalence of HHHs in various modalities. We also investigated phenomenological differences between sleep-related (HHHs) and daytime hallucinations in the auditory modality. We hypothesized that individuals with only HHHs would not differ from controls on a range of mental health and wellbeing measures, but that if they occur together with daytime hallucinations will pose a greater burden on the individual experiencing them. We also hypothesize that HHHs are qualitatively different (i.e. less severe) from daytime hallucinations. METHODS: This study utilized data from a cross-sectional epidemiological study on the prevalence of hallucinations in the Norwegian general population. The sample (n = 2533) was divided into a control group without hallucinations (n = 2303), a group only experiencing sleep-related hallucinations (n = 62), a group only experiencing daytime hallucinations (n = 57), and a group experiencing both sleep-related as well as daytime hallucinations (n = 111). Prevalence rates were calculated and groups were compared using analyses of variance and chi-square tests where applicable. RESULTS: The prevalence for HHHs in the auditory domain was found to be 6.8%, whereas 12.3% reported multimodal HHHs, and 32.2% indicated out-of-body experiences at the onset/offset of sleep. Group comparisons of hallucinations in the auditory modality showed that individuals that experienced only auditory HHHs scored significantly (p < 0.05) lower than those who also experienced daytime auditory hallucinations on a range of variables including mental health, anxiety, childhood happiness, and wellbeing. In addition, individuals with only auditory HHHs reported significantly (p < 0.05) less frequent hallucinations, less disturbing hallucinations, more neutral (in terms of content) hallucinations, hallucinations with less influence over their behavior, and less hallucination-related interference with social life compared to those individuals that experience daytime hallucinations. We also found that purely auditory HHHs had a significantly higher age of first onset of hallucinations than the purely daytime and the combined daytime and auditory HHHs groups (28.2 years>20.9 > 19.1). CONCLUSIONS: Sleep-related hallucinations are common experiences in the general population, with the auditory modality being the least common. They occur mostly in combination with daytime hallucinations. However, some individuals (2.4%) experience only (auditory) sleep-related hallucinations and this group can be seen as more closely related, on a range of health-related factors, to non-hallucinating individuals than individuals who experience daytime hallucinations. Finally, there is a clear need for more research in this field, and ideas for future studies are presented.

Using 360° immersive videos to assess paranoia in a non-clinical population.

Introduction: For the past two decades, virtual reality (VR) has proven to be an innovative approach for the assessment of state paranoia. However, the use of VR remains costly, and avatars are still far from realistic in terms of facial and bodily expressions. The present study aimed to test the validity of three 360° immersive videos (360IVs) as an accessible and realistic alternative for the assessment of non-clinical state paranoia.Method: Three 360IVs were created (a Lift, a Library and a Bar) and included actors behaving naturally. One hundred and fifty healthy students were assessed in terms of their proneness towards trait paranoia, were then exposed to one of the three 360IVs, and finally completed measures of state paranoia, sense of presence and cybersickness.Results: Results revealed the presence of various interpretations about the actor's attitudes in the three 360IVs. Also, paranoid thoughts were predicted by proneness towards trait paranoia in two out of the three 360IVs. Furthermore, moderate levels of sense of presence and low levels of cybersickness were observed for each 360IV.Conclusion: The present study provides evidence in favour of the use of 360IVs as a new accessible, realistic, and standardised tool to assess state paranoia in non-clinical samples.

Mapping psychotic-like experiences: Results from an online survey.

Suggestions have been made that psychotic-like experiences (PLEs), such as hallucinatory and delusional experiences, exist on a continuum from healthy individuals to patients with a diagnosis of schizophrenia. We used the screening questions of the Questionnaire for Psychotic Experiences (QPE), an interview that captures the presence and phenomenology of various psychotic experiences separately, to assess PLEs in Norway. Based on data from an online survey in a sample of more than 1,400 participants, we demonstrated that the QPE screening questions show satisfactory psychometric properties. Participants with mental disorders reported more frequent lifetime and current hallucinatory experiences than participants without mental disorders. Childhood experiences were rather low and ranged from 0.7% to 5.2%. We further replicated findings that young age, illegal drug use, lower level of education, and having parents with a mental disorder are associated with higher endorsement rates of PLEs. Finally, a binomial regression revealed that the mere presence of PLEs does not discriminate between individuals with and without a mental disorder. Taken together, the findings of the present study support existing models that both hallucinations and delusions exist on a structural and phenomenological continuum. Moreover, we demonstrated that the QPE screening questions can be used by themselves as a complementary tool to the full QPE interview.

Olfactory hallucinations in Alzheimer's disease.

We assessed the frequency, duration, and degree of unpleasantness of olfactory hallucinations in Alzheimer's disease (AD). Informants of 31 AD patients were invited to rate the frequency, duration, and degree of unpleasantness of olfactory, auditory, and visual hallucinations. Analysis demonstrated little occurrence of olfactory hallucinations compared with auditory or visual hallucinations. Results also demonstrated that olfactory hallucinations span from a few seconds to one minute, a duration that was similar to that of auditory and visual hallucinations. Olfactory hallucinations were rated as unpleasant compared with auditory or visual hallucinations. Finally, olfactory hallucinations were significantly correlated with depression. Our findings demonstrate little occurrence of olfactory hallucinations but that when they occur, they are experienced as relatively unpleasant in AD patients. Our findings also demonstrate a relationship between olfactory hallucinations and psychiatric characteristics (i.e., depression) in AD.

Hallucinations and Covid-19: Increased Occurrence of Hallucinations in Patients with Alzheimer's Disease During Lockdown.

We investigated the effects of lockdown, as implemented by retirement homes to cope with the spread of Covid-19, on hallucinatory experiences in patients with Alzheimer's disease (AD). The study included 47 patients with AD living in retirement homes and who were already experiencing hallucinations prior to the lockdown. We invited caregivers to rate hallucinatory experiences in these patients during the lockdown, and compared this rating with that provided by the same caregivers prior to the lockdown. Results demonstrated increased hallucinatory experiences in patients with AD during the lockdown, compared with before the lockdown. The decrease in social and physical activities during the lockdown, and especially, the physical separation of residents from family members, might have led to decreased sensory stimulation and increased loneliness, and consequently, to the hallucinatory experiences in patients with AD living in retirement homes during the lockdown. While the restrictive measures were necessary to cope with the spread of Covid-19, these measures have increased hallucinations in patients with AD living in retirement homes, at least in those who were already experiencing hallucinations prior to the lockdown.

Idiographic analyses of motivation and related processes in participants with schizophrenia following a therapeutic intervention for negative symptoms.

BACKGROUND: Motivational negative symptoms hinder quality of life and daily functioning of individuals with schizophrenia spectrum disorders. A recently developed intervention, Switch, has shown promising effects on negative symptoms and functional outcomes. Switch targets multiple cognitive, emotional and behavioural processes associated with motivation and goal directed behaviours. We aimed to investigate its effects on motivation and associated processes in a naturalistic setting, and to explore the dynamics between the processes. METHODS: We used a single case approach (n = 3), with a pre-post and follow-up assessment design, which also included ambulatory assessments (experience sampling method, ESM; and step count). We computed autoregressive lag 1 models to evaluate the effects of the intervention on daily motivation levels and related processes, descriptive pie-charts, and vector autoregressive modelling to reveal the dynamics of the processes over time. RESULTS: The intervention was beneficial for each participant according to traditional evaluations of motivational negative symptoms, apathy, daily functioning and quality of life. The effects on the ESM variables revealed distinct outcomes for each individual. The dynamics between the various processes differed between participants, and fluctuated within participants (when comparing baseline, intervention phase, and follow-up). CONCLUSIONS: This study used an innovative approach to look at the effectiveness of an intervention. The intervention seems to lead to meaningful improvements in motivational negative symptoms and functional outcomes. The mechanisms of change need to be further investigated. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov, NCT04325100 . Registered 27 March 27, 2020 -retrospectively registered. REPORTING: Guidelines from the Transparent Reporting of Evaluations with Non-randomized Designs (TREND) statement were followed.

Hallucinations and source monitoring in Alzheimer's disease.

INTRODUCTION: the source monitoring account has been widely investigated for hallucinations in schizophrenia. According to this account, hallucinations are inner events that are misattributed to another source. Our paper investigated this account for Alzheimer's disease. METHOD: we investigated hallucination experiences in participants with Alzheimer's disease and age-matched healthy controls, as well as their source monitoring ability. The assessment of source monitoring included three conditions. In the first condition, participants had to remember whether objects were previously manipulated by themselves or by the experimenter (i.e. reality monitoring). In the second condition, they had to remember whether objects were previously manipulated by a black or white experimenter-gloved hand (i.e. external monitoring). In the third condition, participants had to remember whether they had previously manipulated objects or had imagined having done so (i.e. internal monitoring). RESULTS: relative to healthy control participants, participants with Alzheimer's disease experienced hallucinations more often and lower hits on source monitoring. Interestingly, significant correlations were only observed between hallucinations and the internal monitoring condition in participants with Alzheimer's disease. DISCUSSION: hallucinations in Alzheimer's disease seem to be related to the processes of making judgments about the (internal) context in which an event has occurred.

Psychometric investigation of the French version of the Aberrant Salience Inventory (ASI): differentiating patients with psychosis, patients with other psychiatric diagnoses and non-clinical participants.

During the prodromal phase of psychosis, individuals may experience an aberrant attribution of salience to irrelevant stimuli. The concept of aberrant salience has been hypothesized to be a central mechanism in the emergence and maintenance of psychosis. The 29-item Aberrant Salience Inventory (ASI) was designed to measure five aspects of aberrant salience. The aim of this study was to investigate the psychometric properties of the French version of the ASI comparing patients with psychosis, patients with other diagnosis and healthy, non-clinical participants. The French-language ASI was adapted using the back-translation procedure. Two hundred and eighty-two participants issued from the general population and 150 psychiatric patients were evaluated. Internal validity was assessed using a two-parameter logistic item response model. Reliability was estimated using a test-retest procedure. Convergent validity was estimated using correlations between the ASI scores and several other scales. Sensitivity was evaluated by comparing the scores of participants with a diagnosis of psychosis, patients with other diagnoses and the general population. The best model distinguished three factors: Enhanced Interpretation and Emotionality, Sharpening of Senses and Heightened Cognition. Reliability and convergent validity estimates were good in both groups. The Sharpening of Senses factor was able to discriminate between patients and the general population. Only the Heightened Cognition factor was able to discriminate patients with psychosis from the other psychiatric patients. The ASI is a valid and reliable tool to study not only the aberrant salience phenomenon in patients with psychosis, but also with other diagnoses and within the general population.

Switch, a new intervention that targets motivational negative symptoms in people with schizophrenia: An uncontrolled pilot study.

OBJECTIVE: People diagnosed with schizophrenia experience difficulties in their daily life, which is best explained by motivational negative symptoms. This study explores the feasibility, acceptability, and efficacy of Switch, a new multifactorial intervention that targets motivational deficits. METHOD: Eight participants with schizophrenia or schizoaffective disorder followed around 30 individual sessions of Switch over 12 months. Participants and their informants were interviewed at baseline (T0), at 6 months (T1), at the end of the intervention (T2), and at 6 months follow-up (T3). RESULTS: T0-T1 paired sample t tests showed large improvements on motivational deficits, general negative symptoms, and apathy and functional outcomes (both as rated by informants). At T2 and T3, moderate to large improvements were maintained. Switch was well accepted by participants. CONCLUSIONS: This preliminary investigation provides evidence that Switch may be a feasible, acceptable, and effective intervention specifically designed to target motivational deficits and improve daily functioning.

No sex difference in an everyday multitasking paradigm.

According to popular beliefs and anecdotes, females best males when handling multiple tasks at the same time. However, there is relatively little empirical evidence as to whether there truly is a sex difference in multitasking and the few available studies yield inconsistent findings. We present data from a paradigm that was specifically designed to test multitasking abilities in an everyday scenario, the computerized meeting preparation task (CMPT), which requires participants to prepare a room for a meeting and handling various tasks and distractors in the process. Eighty-two males and 66 females with a wide age range (18-60 years) and a wide educational background completed the CMPT. Results revealed that none of the multitasking measures (accuracy, total time, total distance covered by the avatar, a prospective memory score, and a distractor management score) showed any sex differences. All effect sizes were d ≤ 0.18 and thus not even considered "small" by conventional standards. The findings are in line with other studies that found no or only small gender differences in everyday multitasking abilities. However, there is still too little data available to conclude if, and in which multitasking paradigms, gender differences arise.

Testing a model of auditory hallucinations: the role of negative emotions and cognitive resources.

Introduction: Models of auditory hallucinations (AH) state that AH arise through an interaction between negative emotions and limited available cognitive resources. However, this hypothesis has never been directly tested. Methods: A two-by-two factorial design was used to examine the effect of emotions (neutral VS negative) and available cognitive resources (high VS low) on the elicitation of false alarms in an auditory signal detection paradigm. One hundred and seventy four healthy participants were assigned to one of the four experimental conditions. While participants were listening to white noise, their emotional state was manipulated using affective pictures and the level of available cognitive resources was manipulated using a visual N-back task. Results: Results revealed significant interaction effects between emotions and cognitive resources on the number of false alarms. In particular, participants with fewer available cognitive resources and at the same time who were in a negative emotional state, tended to hear significantly more false alarms. In addition, the degree of certitude was significantly correlated with a higher degree of hallucination proneness. Conclusions: Such results are in agreement with models of AH and they provide new data for the understanding of the emotional and cognitive mechanisms that underpin AH.

A look into hallucinations: the relationship between visual imagery and hallucinations in Alzheimer's disease.

Introduction: We investigated the relationship between visual hallucinations and vividness of visual imagery in patients with Alzheimer's disease (AD). Method: We recruited 28 patients with AD and 30 healthy control participants, matched for age and education. We evaluated proneness towards hallucinations with the Launay-Slade Hallucinations Scale, which includes items assessing visual and auditory hallucinations. We also evaluated vividness of visual imagery with the Vividness of Visual Imagery Questionnaire on which participants had to imagine four images (i.e., imagining the face of a friend, the rising sun, a familiar shop-front, and a country scene) and report the vividness of the images they generated. Results: Analysis demonstrated significant positive correlations between visual hallucinations and vividness of visual imagery in AD patients, however, no significant correlations were observed between auditory hallucinations and vividness of visual imagery in these participants. No significant correlations were observed between hallucinations and vividness of visual imagery in healthy control participants, probably due to the lack of hallucinations in these participants. Discussion: These results demonstrate a selective relationship between the occurrence of visual (but not auditory) hallucinations and the ability to generate vivid visual images in AD.