Tracking the Decline of Implicit Awareness in Early-Stage Dementia

An emotional Stroop test is a variation of the classic Stroop task that measures interference in reaction times when color-naming emotionally salient words.

It assesses attentional biases and implicit emotional processing by having participants rapidly name the ink color of neutral vs. emotional words.

Slower response times to the emotional words indicates attentional capture by their meaning, reflecting an emotional interference effect at a pre-conscious level.

Martyr, A., Nelis, S. M., Morris, R. G., Marková, I. S., Roth, I., Woods, R. T., & Clare, L. (2023). Exploring longitudinal changes in implicit awareness of dementia: An investigation of the emotional Stroop effect in healthy aging and mild dementia. Journal of Neuropsychology. https://doi.org/10.1111/jnp.12344 

Implicit and explicit awareness

Implicit awareness refers to an unconscious, automatic form of knowledge that exists below the surface of deliberate conscious understanding.

People may retain implicit awareness of deficits even after explicit, self-reported awareness of their condition fades.

In contrast, explicit awareness represents conscious, declarative knowledge of one’s status.

Tests like the emotional Stroop task can uncover these implicit cognition traces by tapping into rapid, pre-attentive processing.

Key Points

• The study investigated implicit awareness of dementia over time in people with early-stage dementia using an emotional Stroop task.
• Healthy older adults and people with early-stage dementia showed longer response times to dementia-relevant words compared to neutral words, indicating emotional interference and implicit awareness.
• Over a 20-month period, people with dementia showed a decline in emotional interference to dementia words on the Stroop task, suggesting a fading of implicit awareness.
• A decline in implicit awareness was independent of changes in scores on the MMSE cognitive screening tool.
• There was no significant change in ratings of explicit awareness in people with dementia over time.
• Implicit and explicit awareness were not associated with each other based on emotional Stroop and interview data.

Rationale

Prior research shows that many people with dementia retain some functional abilities despite reduced explicit awareness, suggesting an unconscious or implicit understanding of their condition (Weinstein, 1991).

Cognitive models propose mechanisms that allow implicit awareness to separate from explicit awareness in dementia (Geurten et al., 2021; Lenzoni et al., 2020; Morris & Mograbi, 2013).

Emotional Stroop tasks elicit responses at an automatic, pre-attentive level (Mogg et al., 1993; Ohman et al., 2001), providing a way to gauge implicit awareness.

A prior cross-sectional study found an emotional Stroop effect for dementia-relevant words, indicating implicit awareness even in subgroups with limited explicit awareness (Martyr et al., 2011).

Changes over time in implicit awareness of dementia have not been examined longitudinally. Emotional Stroop effects occur in caregivers (Martyr et al., 2011), but it is unknown if healthy older adults show similar emotional interference.

Method

• Emotional Stroop task using dementia-relevant and neutral words, with color-naming responses
• Longitudinal data collection at baseline (T1), 12 months (T2), and 20 months (T3) for group with early-stage dementia (n=24)
• Cross-sectional emotional Stroop data for healthy older adult controls (n=24)
• Interview ratings of explicit awareness collected at T1 and T2 for dementia group
• Compared response times for dementia-relevant vs neutral words
• Analyzed changes in Stroop responses and interview ratings over time

Sample

• 24 people with early-stage dementia
• 24 healthy older adult controls

Statistical Analysis

• Repeated-measures ANOVAs
• Paired-samples t-tests

Results

• At T1, people with dementia showed significantly slower responses to dementia-relevant words compared to neutral words on the emotional Stroop task.
• Healthy controls also demonstrated emotional interference for dementia words.
• People with dementia did not show emotional interference for dementia words at T3.
• The decline in emotional Stroop effect from T1 to T3 was not related to changes in MMSE scores.
• Interview ratings of explicit awareness did not change significantly over time in the dementia group.

Insight

Findings suggest that implicit awareness is present in early dementia but appears to fade over the course of the disease, independently of overall cognitive decline.

Explicit awareness remains stable, indicating a dissociation and lack of association between implicit and explicit awareness in dementia.

Healthy older adults also show emotional responses to dementia-related content, possibly reflecting fears about developing dementia.

Further research could explore reasons for declining implicit awareness in dementia using neuroimaging or test interventions aimed at supporting awareness.

Strengths

• The longitudinal design tracking both implicit and explicit awareness over 20 months provides richer data than cross-sectional studies. It enables analysis of trajectories over time.
• Using an emotional Stroop task to tap into automatic pre-conscious processing levels provides a nuanced picture of implicit cognition separate from deliberate self-reflections on awareness.
• Contrasting emotional Stroop performance and explicit awareness ratings between people with early-stage dementia and healthy older adults sheds light on both pathological and normal aging.
• The study collected detailed explicit awareness data through interviews at multiple timepoints, allowing comparison to emerging Stroop patterns.
• Rigorous repeated-measures statistics quantified emotional interference effects. Paired t-tests zeroed in on awareness changes within patients.

Limitations

• Small sample sizes (n=24) for both the early-stage dementia and healthy control groups limit statistical power to detect smaller effects and generalizability.
• The homogeneous white British sample additionally restricts generalizability to the UK population and beyond. Cultural factors may influence awareness.
• The study did not explore neural mechanisms behind declining implicit awareness over time in dementia, such as functional or structural brain changes.
• Additional baseline neuropsychological tests beyond the MMSE could aid understanding of links between fading awareness and cognitive profile.
• The correlational design cannot confirm causal directions between dementia progression and implicit awareness loss.
• There may have been uncontrolled factors between the 12-month and 20-month reassessments affecting Stroop performance.

Implications

• Supports separate implicit and explicit awareness systems in dementia, informing models. Implicit knowledge may persist past accurate self-appraisals.
• Declining implicit cognition likely impacts decision-making, behavior regulation, and safety. Further awareness research should inform optimized supports.
• Clinicians cannot assume their dementia patients’ awareness is static over time. Care plans may need continual adjustment as unconscious self-monitoring changes.
• Public health agencies should take care not to provoke unhealthy anxiety about dementia in older adults when combatting stereotypes about the disease.
• Study replication with larger, more diverse samples would boost generalizability of the patterns regarding declining unconscious cognition and stable self-ratings.

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Keep Learning

• How might we reconcile the dissociation between implicit and explicit awareness seen in the study? Could they represent parallel knowledge streams, with implicit fading faster?
• Should clinicians and caregivers try to reinforce explicit awareness if implicit awareness is declining continually? What are the ethics here?
• How could healthy older adults’ emotional reactions to dementia-related content be addressed? Is there a role for public awareness campaigns?
• If implicit awareness fades due to dementia pathology, would we expect to see similar patterns in other neurodegenerative diseases like Parkinson’s disease?
• Could pharmacologic interventions target the preservation of implicit awareness pathways in dementia? If so, what might be the benefits and risks?
• How might fMRI or other neuroimaging methods further illuminate the neural correlates of declining implicit awareness over disease stages?