Original Research PaperSignature dynamics in Alzheimer's disease
Introduction
Forensic document examiners (FDEs) are often tasked with determining if a questioned signature is genuine or non-genuine. Such signatures may appear on documents such as wills, deeds, trusts, and contracts and the health of the signatory can be a pertinent factor [1]. In cases of suspected dementia, two questions are usually asked: (1) did the signatory execute the questioned signatures? and (2) did the signatory have the mental capacity to understand what they were signing? Given an adequate number of contemporaneous specimens, the FDE can answer the first questioned to some degree of certainty [2], [3], [4]. However, uncertainty creeps into this process in cases where the signatory's mental status declines or fluctuates making it difficult for the FDE to estimate the individual's natural variation [5].
Walton [6] cautioned that FDEs must be careful in the examination of writers with neurological diseases. She noted that line quality, tremor, retouching, pen pressure, and speed may be erratic, but this is not necessarily due to simulation, but may result from the effects of normal aging. Her study found that some people in their 90s and even centenarians wrote with normal speed and exhibited little deterioration in their handwriting. Earlier, Behrendt [7] suggested that the FDE should be aware of the writer's medical history and be cognizant of the effects of medication (especially on tremor) on a patient with AD. He warned that contemporaneous standards were a necessity and in late-stage AD, specimens written on the same day as the questioned signature may be necessary to prevent error.
Questionable levels of signature variation in a writer often raise concern of health change, reaction to prescribed medication, or substance use. Of concern to document examiners preparing testimony on signature authorship, the presence of features outside the range of natural variation may be indicative of a simulation. Documents such as wills that bear disputed signatures are frequently submitted to FDEs for examination. Dementia is not an uncommon explanation that is proffered to explain the presence of poor line quality in the testator's signature. However, data are lacking to inform the FDE on the impact of a dementing illness on a writer's natural signature variability. The purpose of this study was to provide estimates of feature variability derived from dynamic analyses of signatures written by individuals with AD compared with age-comparable healthy individuals.
Section snippets
Participants
Study subjects were recruited from volunteers participating in a large clinical research program at the University of California, San Diego Alzheimer’s Disease Research Center. Sixty-nine subjects meeting DSM-IV criteria for dementia as well as the Alzheimer's Disease and Related Disorders Association (ADRDA) criteria for probable AD [8] and 74 age-comparable healthy control (HC) subjects were included in the study. AD subjects had a mean (standard deviation) age of 75.56 (9.44) years; while HC
Results
The majority of subjects from both groups wrote signatures using text-based style, where every allograph was discernable from the signature. Ten AD (14.5%) and two HC subjects (2.7%) wrote signatures using mixed (8/10 AD) or stylized (2/10 AD and both HC) styles. The difference in proportion of non-text-based signatures between the two groups was statistically significantly (χ2 = 6.46; p = 0.01). For this reason, we report group differences in kinematic features and variability for text-based
Discussion
Several new findings emerged from the present study. First, dynamic signature features (including stroke duration, amplitude, velocity, smoothness, and pen pressure) for AD subjects did not differ from age-comparable healthy subjects. These findings from a relatively large sample of subjects suggest that the presence of moderate levels of dementia severity associated with AD appeared not to impact signature dynamics. For the FDE, this means that parameters such as stroke height, inferred speed
Summary and conclusions
Previously published empirical research on the impact of dementia on linguistic and motor aspects of handwriting offers little help to the forensic document examiner tasked with evaluating signature specimens. This study is one of few and perhaps the largest to address signature writing in individuals with Alzheimer's disease, the most common form of dementia. The study found that signatures written by individuals with AD show normal temporal, spatial, and fluency characteristics when subjected
Author contributions
Caligiuri: conceptualization; data curation; formal analysis; funding acquisition; investigation; methodology; project administration; resources; software; supervision; validation; visualization; roles/writing – original draft; writing – review & editing.
Mohammed: roles/writing – original draft; writing – review & editing.
Funding
This research was supported by a grant from National Institute on Aging (AG05131).
Acknowledgments
The author wishes to acknowledge Kelly Landy and Chi Kim for their assistance in data collection and Doug Galasko, M.D. and David Salmon, Ph.D., for their contribution to the diagnosis and scoring of the clinical assessments and leadership in making the ADRC facilities and patients available to this research.
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