In everyday life, individuals frequently face preferential choices that involve weighing risks and rewards between various options or courses of action. Whether deciding between faster but more expensive air travel versus slower, more economical driving, or choosing between a risky medical procedure and managing a chronic condition, these decisions are ubiquitous and carry significant consequences. Understanding the cognitive processes that underpin these risk-reward evaluations has been a central focus of research. A common experimental method for studying preferential choice is the lottery gamble task, where participants must choose between options defined by potential outcomes and their associated probabilities. Each gamble represents a decision-making scenario where an individual can gain or lose a certain amount of money (V) with a known probability (p), for example, gamble1 = <V1, p1> and gamble2 = <V2, p2>. These tasks are designed to mirror real-life decisions that balance potential rewards against associated risks. Two dominant theoretical approaches have emerged to explain decision-making in these contexts. The first, grounded in rational choice theory, centers on the concept of utility. This approach posits that individuals assign psychological value to observed properties, integrating these into a single metric—utility—that guides decision-making. According to this model, a decision-maker compares the utility values of different options, such as evaluating whether the potential benefits of a medical procedure outweigh the risks, and selects the option with the higher utility1,2.
Utility-based models have profoundly influenced decision-making research, forming the foundation of many subsequent computational models. These models share key premises:
- Psychological utility is an integral concept, where properties are multiplicatively combined into a single dimension, rendering the original attributes inseparable once the utility is calculated.
- The scope of information search is unrestricted, allowing all relevant properties to be integrated into a single utility value.
- These models typically do not specify the order in which properties are processed, leaving it unclear whether attributes are combined sequentially or in parallel when determining utility.
In contrast, the second major theoretical approach is rooted in the concept of heuristics—mental shortcuts or simple decision-making strategies. Far from being mere practical tools, heuristics address the limitations of human cognition, which often deviate from the principles of rationality2,3. Heuristics, such as the Take-The-Best (TTB) heuristic4, involve sequentially comparing attributes based on their importance, stopping as soon as a decisive difference is found. For instance, when deciding on surgery, a patient might first compare the potential outcomes and, if a clear difference emerges, make a decision without considering other factors.
Heuristic-based models adopt the following core premises:
- The properties of gambles, such as p and V, are independent, meaning they can be separated and individually assessed during decision-making.
- The scope of information search is often limited, with not all properties being considered.
- Attribute comparisons typically occur in a strict serial order.
These contrasting approaches—utility-based and heuristic-based—have shaped our understanding of decision-making processes, each offering unique insights into how individuals navigate complex choices involving risk and reward. This research aims to further explore and clarify these cognitive processes, providing a deeper understanding of how people make decisions in real-world scenarios.
Model validation and falsifiability and its challenges
Both classes of models, heuristic- and utility-based, are grounded on strong and falsifiable premises, which means that their predictions are constrained by critical assumptions, ensuring model validity and identifiability. Consequently, falsification of any of these premises would directly falsify one class of models and could be utilized to validate the other class. For instance, if it can be demonstrated that cognitive processes only consider one attribute in a decision-making task while disregarding other attributes, it would directly falsify the utility-based models in relation to premises 1 and 2. In contrast, the theoretical stance regarding premise 3 differs asymmetrically between proponents of the utility-based and heuristic-based approaches. While this premise is seldom explicitly stated in the theoretical framework, the proponents of fast and frugal heuristics (such as TTB4) offer a notable exception by clearly defining the serial property (referred to as lexicographic property) in attribute inspection4. Falsifying the third premise, by revealing a sequential processing order of attributes, may not provide strong evidence for falsifying utility-based models, but it can serve as robust evidence supporting heuristic-based approaches.
Three Key Challenges
Despite decades of research, the field of decision-making continues to grapple with significant challenges, particularly in achieving clear model identifiability. These challenges stem from several factors:
First, much of the historical research on preferential choices has focused primarily on predicting outcomes rather than dissecting the cognitive processes underlying these decisions. This "outcome-based" approach has prioritized forecasting behavior over understanding the mental mechanisms at play. By emphasizing the relationship between input variables and output decisions, these models often treat the cognitive system as a "black box," neglecting the intricacies of the mental processes that drive decisions. This has led to the development of what Gigerenzer terms "As-If" models—models that predict decision outcomes without fully exploring the cognitive systems responsible for generating them, thereby limiting their falsifiability and explanatory power5. However, the past two decades have seen considerable progress in investigating the mental processes involved in decision-making. This progress includes the development of sophisticated methodologies such as hierarchical Bayesian modeling and individual subject analysis. These advancements go beyond mere outcome prediction, enabling more precise predictions of joint response times and choice preferences. Additionally, process tracing methods have become increasingly refined, offering deeper insights into the covert cognitive processes that underlie decision-making6,7,8.
Second, the challenge of model mimicking presents a significant obstacle to distinguishing between competing decision-making models. Model mimicking occurs when different models predict identical outcomes, whether at the choice level or across both choice and response time distributions. This complicates the task of differentiating between models, even when additional variables like response times are considered. For example, Fifić, Houpt, and Rieskamp demonstrated that two distinct models could yield identical response time distributions, underscoring the difficulty of distinguishing between them9.
Third, there is a notable lack of a unified theoretical framework that integrates the diverse processes underlying these models. Both utility-based and heuristic-based approaches are often used interchangeably, as highlighted by Lee and Gluck and Diederich10,11. This aligns with the concept of hierarchical representations, a dominant paradigm in perception and neural organization12,13,14. Within this framework, decision-making attributes can be hierarchically structured, allowing decision-makers to access both individual properties and their combinations, such as utility and separate attributes. This hierarchical flexibility enables decision-makers to apply heuristic approaches when appropriate, while also leveraging utility-based representations for more comprehensive analyses when needed.
The solution to the challenges: Modular Serial-Parallel Networks (MSPN) as a Full Computational Processing Model for Cognitive and Perceptual Operations
In summary, the MSPN model is a powerful tool that addresses the key challenges in decision-making research. It moves beyond outcome-based models by offering a detailed analysis of cognitive processes, mitigates model mimicking by integrating multiple cognitive approaches, and provides a unified theoretical framework that can incorporate both heuristic and utility-based strategies. Through its modular and hierarchical organization, MSPN enhances our understanding of the cognitive mechanisms underlying decision-making and offers a versatile platform for exploring and validating different cognitive theories.
The Modular Serial-Parallel Network (MSPN) computational model serves as a comprehensive stochastic framework that can accurately account for both response accuracy (choice preferences) and response times in binary task conditions. The model is built around four core components: (a) representational, (b) decisional, (c) logical-rule implementation, and (d) modular stochastic accrual of information. The formal mathematical representation is provided in Supplementary Appendix A. Detailed parametric properties of the MSPN’s computational framework are provided in Supplementary Appendix B. The structure and flow of the MSPN model are visually presented in Figure 1.
(a) Representational Level: Memory plays a pivotal role in cognitive and perceptual processes at this level, where the properties of various decision-making scenarios are stored and organized. These properties include the basic features and attributes of the stimuli, represented as point values (M) on independent stimulus dimensions, with associated internal noise N(M, σ) (see Figure 1, Left). Understanding this foundational representation is crucial, as it influences higher-order cognitive operations. Each attribute is encoded as an independent feature, allowing the cognitive system to process and manipulate them individually. The presence of perceptual noise in these representations highlights the complexities of memory encoding, reflecting the inherent variability in our perceptual experiences. Similar to how neurons in the brain are tuned to specific features, this perceptual noise stems from the dynamic and context-dependent nature of cognitive processes12,13.
(b) Decisional Level: At this stage, the cognitive system establishes stimulus-response associations and determines how to classify property representations based on task requirements. In the MSPN model, a decision rule is represented by a single criterion value that divides a property dimension into two response regions, each corresponding to a different binary decision outcome. For example, in the stimulus scenario illustrated in Figure 1, if a property activation is observed to the right of the decision value on the V1 dimension (dotted line), it generates evidence favoring Gamble A (Decision A); otherwise, it supports Gamble B (Decision B). When a property is activated in memory, it automatically produces evidence that is labeled according to the decision rule, supporting one of the two binary outcomes.
(c) Logical Rule Implementation:In this stage, the system determines how to combine multiple sources of independently stored properties activated by the task15,16. The decision-making process involves logically integrating these activated properties, considering the scope of evidence from various attributes. This integration allows the system to make well-informed decisions. If all attributes need to be analyzed, the cognitive system employs a conjunctive rule (AND gate), requiring exhaustive evidence collection. If only one attribute is necessary, a disjunctive rule (OR gate) is used, allowing the decision to be made based on a single attribute, regardless of others.
(d) Modular Stochastic Accrual of Information:The MSPN model integrates two successful approaches to modeling response time (RT) data and choice outcomes: the random-walk and mental-architecture approaches16,17. The random walk is a stochastic process that accumulates noisy evidence over discrete time steps, with the observer setting criteria that determine the amount of evidence needed to choose either Gamble A or Gamble B. The sampling process continues until one of the criteria is reached, with the number of steps determining the decision time, as shown on Fig.1, the boxes at the top right.
Figure 1. A schematic illustration of the stimulus structure in a binary gamble task and the MSPN model. The stimuli consist of two dimensions: X (v1, the maximum gain value in Euros) and p1 (the probability of maximum gain). These dimensions are orthogonally combined to produce 16 different gamble sets. In this task, Gamble A = <vA1, pA1; 0, 1-pA1> and Gamble B = <200€, 1>. To make a preferential choice for Gamble A, participants must consider both v1 and p1, representing a classification problem where membership in category A follows a conjunctive rule (both v1 and p1 must exceed certain criterion values). In contrast, membership in category B follows a disjunctive rule, where at least one property is below its criterion. The decision boundaries for these rules are illustrated as dotted lines. The marginal dimensions depict the memory status of the gamble properties, represented as normal distributions of activation. In a single trial, two gambles are displayed (e.g., v1=700 and p1=0.9 for the gamble A and v2=200 and p=1.0 for the gamble B). To determine the preferential choice, the system accesses the underlying perceptual representations on each property dimension, sampling noisy evidence bounded by the decision criteria. Before evidence accumulation, the system decides to use either the serial or parallel modular system, with the modular gate probabilistically switching between them on a trial-by-trial basis, as governed by the pMod parameter, indicated by the three circles and arrow. In the example, the parallel interactive model is selected, where evidence is exchanged between two concurrent random walks, resulting in joint accumulation. This interaction, driven by the pCross parameter, allows the two random walks to act as a third combined process, facilitating a faster response by reaching the decision boundary more quickly, as shown by the superimposed random walk (bolded random walk) in the accumulation box belonging to the parallel module. At the bottom right, popular schematics of serial and parallel systems are shown to illustrate the information processing flow for decision-making, highlighting where pCross parameter influences the process, indicated as the “Process communication gate”.
The overall response is determined by the mental architecture, which governs the processing order of multiple random walks, each analyzing a different property. The serial and parallel processing modules are separated at the module gate, depicted in the middle of Fig. 1, indicated by the circles and the arrow. In serial processing, properties are analyzed sequentially, with the total response time being the sum of the accumulation times for each random walk (AND rule) or the time taken by the first random walk to reach a criterion (OR rule). In parallel processing, properties are analyzed simultaneously, with the response time being determined by the longest (AND rule) or shortest (OR rule) random walk.
The MSPN model also accounts for process dependency, where the time needed to process one attribute depends on the time needed to process others. This concept has been explored in various cognitive models18. The nature and extent of interaction in these models are often determined by free parameters, such as in the stochastic General Recognition Theory18. Other models fix the type of interaction based on assumptions, such as the relationship between facilitatory inputs and inhibitory lateral connections between accumulators19. In this model, the two parallel random walks exchange sampled evidence toward one of the two response boundaries at each step during accumulation. The concept of cross-channel interaction is implemented as a lateral connection between the two random walk accumulators, serving as a gate that allows the processes to share evidence. When the gate is open, both channels exchange their accumulated evidence at that time step.
When the random walks exchange congruent evidence, the accumulation rate for each channel increases, potentially leading to faster boundary crossing—this is identified as a facilitatory process interaction. Conversely, when they exchange incongruent evidence, the accumulation rate decreases, potentially slowing the boundary crossing—this is identified as an inhibitory process interaction. The example of two random walks exchanging information in a parallel system during accumulation can be represented as a superimposed random walk. This is depicted in Fig. 1 as a third, bolded accumulation line, which results from summing the evidence from the two parallel random walk accumulators, as displayed in the last to the right rectangular area of the parallel interactive module.
Interpreting MSPN Model Parameters and Validating/Falsifying Heuristic and Utility Approaches
The Modular Serial Parallel Network (MSPN) model offers a robust framework for interpreting decision-making strategies by evaluating specific model parameters. These parameters provide insight into whether a decision-making process aligns more closely with heuristic-based or utility-based approaches. The detailed parameter formalization of MSPN is described in Supplementary Appendix B.
- Process Interdependence (pCross):The interdependence of gamble properties—such as values v1, v2 and probabilities p1, p2—is assessed using the parameter pCross within the parallel processing module. A pCross value greater than zero (pCross > 0) indicates process dependency, suggesting that the properties are being combined during a single trial. This interdependence strongly supports utility-based models, which rely on the integration of multiple attributes to form a single decision metric.
- Scope of Information Search:The scope of information search is explored by comparing different variants of the MSPN model that engage stopping rules consistent with either limited or unlimited search scopes. This allows for the evaluation of whether a decision-making process is exhaustive—considering all available information—or self-terminating, focusing only on key attributes before making a decision. The scope of search can differentiate between strategies that are more heuristic-based (limited scope) versus those that are more utility-based (unlimited scope).
- The modularity gate parameter (pMod):The processing module used to combine retrieved individual task properties from memory, using the serial or processing, order is evaluated using the parameter pMod. A pMod value of 0 indicates a pure heuristic-based approach, where properties are processed sequentially and often independently, while the value of 1 indicates pure parallel processing, and thus more utility based. Values between 0 and 1 (0 ≤ pMod < 1) suggest a combination of heuristic and utility-based processing, with the degree of utility-based processing increasing as pMod approaches 1. This parameter helps in determining whether the decision-making process relies more on quick, rule-based judgments or on the comprehensive integration of information.
To assess these components, we designed a study using the MSPN model to analyze decision-making in a gambling task. By manipulating the values of two key attributes and collecting data on both response times and preferential choices, we aim to uncover the underlying cognitive mechanisms at play.