Bouba/Kiki Test for Patients with Behavioral and Psychological Symptoms of Dementia

In dementia patients likes and dislikes may change from time to time, and they are often clearly expressed without being restricted by the declining cognitive functions. Unlike healthy people, the emotional function of dementia patients is relatively easy to score, such as serious emotions with the Neuropsychiatric Inventory (NPI) [1] and favorable emotions being measured with the Delightful Emotional Index (DEI) [2]. Patients with high Behavioral and Psychological Symptoms of Dementia (BPSD) usually express anger, sorrow, violence but little joy and happiness. We wondered whether patients with high BPSD have favorable emotional sensitivities as well as serious negative sensitivities or not. It has not been reported whether opposing sensitivities exist simultaneously in patients with high BPSD. Here we address this issue. Furthermore, mechanisms of expressions of either serious or favorable emotions have not been well characterized. The Bouba/Kiki test [3] was developed to explore the influence of visual information on language processing. This test is a visual lexical decision task with the sharp-sounding and soft-sounding verbal stimuli presented within the spiky and curvy frames. It has been reported that in healthy persons about 95 to 98 % subjects answer appropriately to the Bouba/Kiki test, which suggests that both serious and favorable emotions may be sensitive simultaneously. We specifically wondered whether opposing emotional sensitivities can exist simultaneously in patients with BPSD or with high NPI scores. In the present study, we examined the Bouba/Kiki test in patients with high BPSD in a psychiatric dementia hospital and viewed potential mechanisms of explaining these sensitivities through the lens of and analogies to Quantum Mechanics (QM).

We showed dementia patients jagged shapes versus soft cloud-like shapes and asked, “Which shape corresponds to the names Kiki or Bouba [3]?”. Among 48 inpatients in Sendai Tomizawa Hospital, a psychiatric dementia hospital, 9 patients were excluded due to comorbidities (1 schizophrenia, 2 end stage of dementia, 3 difficult of hearing and 3 declining to participate). Finally, 39 patients with Alzheimer’s disease, vascular dementia, or Lewy body disease were included in the analysis. Over the period from April 2025 to August 2025, studies including the Mini-Mental State Examination (MMSE, 0-30) [4], NPI (0-144), and Barthel Index (0-100) [5] were cross sectionally performed in the morning. Answers for both round and spike shapes were all or nothing and appropriate answer means a correct answer for both shapes. Reproducibility was confirmed in all patients and they answered correctly and quickly once they understand the situation. All measurements were scored by a trained nurse who was blinded to treatment status. Written informed consent in this study was obtained from patients or their guardians.

Thirty-one of the 39 could answer this dichotomous question appropriately, even those with high BPSD (NPI =21±5, mean ±SD) and impaired cognitive function (MMSE =10±5, mean ±SD). The cumulative probability of this is  p≤∑_(k=0)^8 2^(-39) (39 k) , where (39 k)  is the binomial coefficient. Five covariates (sex, age, Barthel Index, MMSE, and NPI) were used for the multivariate regression analysis (Rcmdr Plugin. EZR, Japan) with each item as an explanatory variable and the positive or negative response to Bouba/Kiki test as an objective variable. All items showed no significant correlations (Table 1).

Table 1: Multivariate Logistic regeression analysis of Bouba/Kiki test (appropriate answer 31/ inppropriate answer 8).

The 5 covariates were used for the multivariate regression analysis (Rcmdr Plugin. EZR, Japan Significance was considered at P < 0.05.

Abbreviations: PRC, partial regression coefficient; OR, Odd's ratio: CI, cofidenence interval; BPSD, behavioral and psychological symptoms of dementia.

The present result suggests that opposing emotional sensitivities exist simultaneously in patients with decreased cognitive function nor increase of BPSD, and that if they are exposed to a Kiki environment, distressed emotions prevail, whereas if they are frequently exposed to a Bouba environment, happy emotions emerge. BPSD in dementia is a state in which distressing emotions are expressed, we suggest that by repeatedly inducing favorable emotions, BPSD will gradually decrease and the patient will be able to express favorable emotions. 

This study was approved by the ethics committee of Yamagata Kosei Hospital, in partnership with Sendai Tomizawa Hospital (2019-3).

One of us (JPB) would particularly like to thank the late Prof. Werner Heisenberg. I had the honor of a private meeting with him over tea more than 50 years ago. We met at a Harvard Physics Dept Colloquium, where Heisenberg was the Loeb Lecturer, and discussed parts of his lecturer which dealt with the Uncertainty Principle consequence that observations necessarily change the quantum states of the object observed. He had made a reference to this not applying in the biological world, to which I objected. His response was that while there is not a strict application of QM to biology (except through chemistry), there was indeed and definitely an almost exact parallel or analogy between QM and human interactions.

The authors declare no conflict of interest.

None.

All authors satisfy the four criteria for authorship based on the ICMJE recommendations, section 2: conception, analysis, interpretation; drafting for intellectual content; final approval; accountability. 

Approval code issued by IRB: (2025-1) granted by the Sendai Tomizawa Hospital.

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