Most cash transactions occur quickly with people spending no more than a second or two looking at banknotes. How, then, do public users benefit from the considerable investment by Central Banks in banknote design and complex anti-counterfeit security features if they barely have time to notice them? Until recently, answers to this question were elusive, even though the notion that the public play a significant role in counterfeit detection is widely accepted. However, clear evidence has now emerged to show that accurate authentication of a banknote is well within human capability even when a banknote is seen for less than a second. Moreover, accurate authentication, especially when time is short, appears to be highly dependent on banknote design.

The research leading to these important findings was conducted by the Four Nations Group of Central Banks. In 2018 they commissioned Professor Jane Raymond at the University of Birmingham, UK to design and conduct an intensive research program to investigate the human cognitive processes underpinning banknote authentication by public consumers under a variety of conditions, including time pressure. The resulting ‘CogNote Project’ comprised multiple studies conducted in four different countries (Australia, Canada, England, United States) thereby advancing understanding of the underlying mechanisms and socio-geographic factors that underpin human authentication behaviours. Supported by an unprecedented level of investment and collaboration, the CogNote Project used a range of approaches that have extended understanding of banknote authentication well beyond simple banknote discrimination tasks. The project measured eye movements, brain activity levels, and socio-geographic habits. It applied artificial intelligence approaches to probe how banknote design guides the eye and brain to rapidly identify counterfeit. The targeted objectives of the project were to provide the Four Nations with an actionable analysis of human authentication behaviour as well as concrete guidelines to inform decision making on banknote design, security feature selection, and quality policies.

Cognitive Theory of Authentication

The highly structured design of the CogNote Project was based on well-developed theories from psychological science that speak directly to questions concerning banknote authentication under time pressure. Broadly speaking, these theories predict that accurate authentication should be possible with less than a second of viewing a banknote if, and only if, attention and eye movements are rapidly attracted to hard-to-mimic design elements, e.g., security features, as opposed to easily mimicked elements, e.g., signatures. The CogNote Project put this prediction to the test by asking members of the public to authenticate a series of banknotes while their eye movements were being monitored. Eight different banknotes from four currencies (AUD, CAD, GBP, and USD, including paper and polymer banknotes) were targeted for study. Genuine banknotes drawn from general circulation were mixed with counterfeit that had been either forensically recovered or specially manufactured. A total of 128 adults aged between 18 and 64 years from four different countries participated in this component of the Project.

The psychological science basis for predicting that banknote authentication should be possible with only a second to view a note is rooted in a notion known as ‘predictive coding’[1]. All sensory data obtained from the environment, including light patterns on a banknote, are initially processed by low level sensory systems in a non-conscious, rapid fashion. This takes a few tenths of a second at most and provides central brain areas with a flood of information. To avoid information overload, high-level areas of the brain attempt to predict what the sensory flood might yield, enabling the necessary high-level processing networks to be prepared. This process of ‘predictive coding’ creates a mental representation of expected of sensory events that can then be matched to actual sensory events when they occur. If sensory and predicted events match, then further processing of the current sensory data can proceed very quickly, and planned action can be rapidly executed. A mismatch, on the other hand, produces a ‘hiccup’ in the brain, causing it to alter course. Greater sensory analysis is instigated, planned action is halted, and slow conscious processing is engaged so that the source of the unexpected information can be analysed. For example, if you hear someone say, “I’ll pay with …”, your brain probably anticipates the word “cash” or “card” to follow, a prediction that sensibly eases the listening task. However, if, the word “paperclips” was spoken instead, your brain would register surprise, causing you to replay events and puzzle out what happened. This simple example illustrates how the human brain routinely relies on predictive coding to not only speed perception of the environment but also to efficiently detect unexpected events.

The basic notion of predictive coding has been applied to banknote authentication in a simple model called SIMBA (Suspicion Initiated Model of Banknote Authentication[2], Raymond et al. 2020), which served as the theoretical basis for the CogNote Project. It says that the first stage of banknote authentication involves rapid matching of the banknote’s sensory data with its expected look and feel. This involves collecting sensory data by using one or two eye movements to look at, or fixate, different spots on the banknote and can be completed in less than a second. If the sensory data obtained during these first few fixations is as expected, then no suspicion is raised and the transaction proceeds almost automatically without further visual or tactile analysis. However, if a mismatch arises during this first critical stage, then neural systems sound an ‘alarm’ and active a search for more information. Thus, the second stage of banknote authentication involves accrual of more information over a period of several seconds. This is used to support conscious, deliberate decision-making regarding the note’s authenticity. The important point here is that slow, conscious cognitive engagement with a banknote probably occurs only when suspicion is raised in the first, rapid stage of authentication.

This implies that where gaze is directed during the first second or so of viewing a banknote should directly determine authentication accuracy. If the location that attracts the eye contains high quality authentication information, as in a security feature, then sensory mismatch signals raised by counterfeit should be especially strong, leading to overt counterfeit detection. In contrast, if the eye is initially attracted to areas that are easy to mimic, e.g., a large image or signature, sensory mismatch signals raised by counterfeit might be small or undetectable, causing a person to accept a bad note. If security features are not directly looked at during the first stage of authentication, they may be of no assistance to the user even when they have been poorly imitated. In a nutshell, SIMBA makes the explicit prediction that authentication performance should be better when eye movements are quickly directed at security features than if they are captured by other design elements.

Up Next: Part 2 of this article series will explain what the CogNote Project revealed about authentication under time pressure and eye movements during authentication.


[1] Rao, R. P. & Ballard, D. H. Predictive coding in the visual cortex: a functional interpretation of some extra-classical receptive-field effects. Nat Neurosci. 2, 79-87 (1999).

2 Raymond, J. E., Dodgson, D.B. & Pearson, N. (2020). 3D Micro-Optics Enable Fast Banknote   Authentication by Non- Expert Users. Optical Document Security 2020 Proceedings, Reconnaissance International, ISBN 978-1-9163806-4-6.

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The Four Nations Group was founded in 1978 and consists of five central bank members – the Board of Governors of the Federal Reserve System, Bank of Canada, Reserve Bank of Australia, Bank of England and Banco de México. The group is a forum in which its members share information and experiences on banknote development, issuance and distribution, counterfeit deterrence, and relevant technical studies.

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