Effects of lighting variability on locomotion in posterior cortical atrophy

Abstract Introduction Clinical reports describe patients with Alzheimer's disease (AD) exhibiting atypical adaptive walking responses to the visual environment; however, there is limited empirical investigation of such behaviors or factors modulating their expression. We aim to evaluate effects of lighting‐based interventions and clinical presentation (visual‐ vs memory‐led) on walking function in participants with posterior cortical atrophy (PCA) and typical AD (tAD). Methods Participants with PCA (n = 10), tAD (n = 9), and healthy controls (n = 12) walked to visible target destinations under different lighting conditions within two pilot repeated‐measures design investigations (Experiment 1: 32 trials per participant; Experiment 2: 36 trials per participant). Participants walked to destinations with the floorpath interrupted by shadows varying in spatial extent (Experiment 1: no, medium, high shadow) or with different localized parts of the environment illuminated (Experiment 2: target, middle, or distractor illuminated). The primary study outcome for both experimental tasks was completion time; secondary kinematic outcomes were proportions of steps identified as outliers (Experiment 1) and walking path directness (Experiment 2). Results In Experiment 1, PCA participants overall demonstrated modest reductions in time taken to reach destinations when walking to destinations uninterrupted by shadows compared to high shadow conditions (7.1% reduction [95% confidence interval 2.5, 11.5; P = .003]). Experiment 2 found no evidence of differences in task performance for different localized lighting conditions in PCA participants overall. Neither experiment found evidence of differences in task performance between conditions in tAD or control participants overall. Completion time in both patient groups was longer relative to controls, and longer in PCA relative to tAD groups. Discussion Findings represent a quantitative characterization of a clinical phenomenon involving patients misperceiving shadows, implicating dementia‐related cortico‐visual impairments. Results contribute to evidence‐based design guidelines for dementia‐friendly environments.


BACKGROUND
The visual environment may play an elevated role mediating everyday function in Alzheimer's disease (AD) and other dementia syndromes.
This role is corroborated through clinical observations of patients overstepping perceptual variations in flooring, such as patterned carpeting or shadows, or being overly reliant on landmarks or conspicuous environmental features to support navigation. [1][2][3][4] Despite the promise of cost-effective environmental adaptations facilitating patient autonomy and safety, repeated calls for high-quality quantitative research in this area remain largely unmet, 2,5,6 and existing studies have given limited consideration to patient clinical presentation. 7 Posterior cortical atrophy (PCA) is the cardinal "visual dementia," a neurodegenerative syndrome characterized by progressive cortico-visual impairment and particular involvement of posterior parietal and occipito-temporal regions. [8][9][10][11] PCA is most commonly caused by AD and is often considered the most common atypical AD presentation. 12 PCA patients have relatively spared involvement of medial temporal regions, correspondingly demonstrating preserved episodic memory in early disease stages. 13,14 Corticovisual impairments arising in PCA, and to a lesser extent in typical, amnestic AD (tAD), include visuospatial and visuoperceptual deficits, diminished depth perception, and restrictions in the effective visual field. 9,15-18 PCA is associated with environmental disorientation and has profound implications for independence, safety, and care considerations. 19 At a relatively early stage, PCA patients may be unable to drive, read, dress independently, or reliably navigate familiar environments despite relatively preserved memory, language, and insight. 20 Environmental adaptations have been recommended to support individuals living with dementia, particularly for PCA patients and AD patients with memory and visuospatial presentations. 19,21,22 Recommendations based predominantly on professional guidance include strategic use of signage, contrast and salient visual features, patterned flooring, glare, and clutter. 2,19,[23][24][25] Lighting modulates contrast, perceived clutter, and visual saliency, factors particularly influencing object recognition and gaze location in PCA, 26,27 and lightingbased interventions may promote functional outcomes and fall reductions in patients with all-cause dementia. 23,28 Misperception of shadows has been reported in PCA and laterstage AD 19,24 and is associated with hesitation or disorientation during navigation. 4 Correspondingly, approaches to maintain uniformity of lighting and minimize shadows have been recommended in various forms. 23,24,29 Use of localized lighting has been proposed to emphasize stairways, distinguish environmental settings, or act as orientation cues, 29,30 and location-specific lighting to facilitate navigation has received limited support from one case study. 31

Participants
Ten PCA patients, 9 tAD patients, and 12 healthy controls were included. The number of PCA patients was limited owing to the low prevalence of PCA. PCA and tAD groups fulfilled clinical criteria for PCA-pure 11,32,33 and research criteria for probable AD, 34 respectively.

Procedure
The experimental setting was constructed at the Pedestrian Accessi-

Study outcomes
Statistical analyses were performed using Stata (v. 14.1). For statistical tests we reported a two-sided P-value (alpha level: P < .05).

Early visual processing
Visual acuity (CORVIST f ): Snellen 6/9 6/9 6/9 -- Measures are adopted from a standard published cognitive battery. 26 were iteratively identified as follows. 35 For each of the three groups, a three-level linear mixed model was fitted including random effects for participant, "room condition within participant," and "trial within participant and room condition." Outliers with long step times were defined as observations with a standardized residual >3; these were removed, the model refitted, and outlier removal repeated until no further outliers were identified. Numbers of outliers and total numbers of steps per person under each shadow condition were displayed in bar charts, without formal statistical analysis.

Experiment 2: Walking path straightness index
Walking paths were estimated using dead reckoning. IMU accelerations were converted to standard coordinates and integrated to calculate velocity. Velocity drift was corrected based on periods when feet were in contact with the ground, and corrected velocity integrated to estimate foot position. 35 Walking path straightness index (SI) was calculated as a ratio of the shortest possible path compared to the length of the path actually taken by a participant, with a range (0-1) for which 1 indicated maximum straightness. 36 As SI is a proportion   Table 2 shows comparisons of estimated completion times for different shadow conditions in PCA, tAD, and control groups. Figures 2 and 3 show step time outliers for participant groups under different shadow conditions.

Primary outcome: Completion time
Averaged over room conditions, overall task performance was slower in both the PCA (estimated geometric mean completion time: 9.9 seconds, 95% confidence interval [CI] 8.5, 11.7) and tAD groups (6.7 seconds, 95% CI 5.9, 7.5) relative to the control group (5.5 seconds, 95% CI 5.1, 5.9), and in the PCA relative to the tAD group. Between-group differences were statistically significant (pairwise comparisons all P ≤ .004).
Within the PCA group, the global test found evidence (P = .01) for an overall difference between shadow conditions. This was largely driven by a statistically significant (P = .003) but relatively modest 7.1% (95% CI 2.5%, 11.5%) reduction in geometric mean completion times for the no versus high shadow condition comparison. Completion times for the medium shadow condition were intermediate, and not statistically significantly different from those for either the no (P = .34) or high shadow (P = .08) conditions (Table 2).
Analogously, global tests of geometric means comparing shadow conditions within the tAD and control groups were not statistically significant (P = .77 and P = .33, respectively); therefore, no pairwise comparisons were carried out. Despite the differences between the participant groups in the statistical significance of the shadow effect comparisons, a global joint test found no evidence that shadow effects differed overall between participant groups (P = .15), although it should be noted that this test is not as highly statistically powered as those investigating effects within individual groups.

Secondary outcome: Step time outliers
Qualitatively, an increased proportion of outliers was observed as participants approached the shadow regions for the PCA group relative to tAD and control groups (Figure 2; Video in supporting information). tAD (N = 9) 6.6 (5.9, 7.5) 6.7 (6.0, 7.6) 6.6 (5.9, 7.5) P = .77 -2.1% (-8.9, 4.   Table 3 shows comparisons of estimated completion times and walking path SI for different localized lighting conditions in PCA, tAD, and control groups. Figure S1 in supporting information shows walking paths for participant groups under different localized lighting conditions.

Primary outcome: Completion time
Averaged over room conditions, overall task performance was slower in both PCA (estimated geometric mean completion time: 9.1 seconds, 95% CI 7.6, 10.9) and tAD groups (6.6 seconds, 95% CI 5.8, 7.5) relative to the control group (5.3 seconds, 95% CI 5.0, 5.7), and in the PCA relative to the tAD group. Between-group differences were statistically significant (pairwise comparisons all P ≤ .003).
Global tests found no evidence within any group for a difference in completion times between localized lighting conditions (PCA: P = .21; tAD: P = .91; controls: P = .76).

Secondary outcome: Walking path straightness index
Medians of observed person-specific median SI were slightly lower in Global tests found no evidence within any group for differences in SI between localized lighting conditions (Table 3B).

DISCUSSION
The current pilot investigation presents empirical evidence of lighting- Global test of the null hypothesis that within a participant group there is no difference between completion times under the three localized lighting conditions. c Walking path SI data were unavailable for one PCA participant owing to recording error, so N = 9 for SI analyses.
tendency for patients to exhibit more outliers when shadows interrupted floorpaths to destinations, the extent of heterogeneity and number of patients who did not exhibit outliers precluded formal assessment of differences between shadow conditions. Qualitative analysis of detected outliers suggested differing spatial profiles in the occurrence of hesitant steps between patient groups, likely relating to the principal differences in group presentation (visual versus memoryled). Taken altogether, results provide evidence for modest benefits of minimizing shadows on patient function in the PCA group, though findings may be relevant to a proportion of tAD patients exhibiting corticovisual impairment. 17,38 The second experiment investigated effects of localized lighting

CONFLICTS OF INTEREST
The authors have no conflicts of interest to declare.