Madhur Mangalam

University of Nebraska at Omaha | UN Omaha · Division of Biomechanics and Research Development

Biological and psychological sciences have begun investigating whether random multiplicative cascade processes can support the capacity for an organism to perceive, act, and think. Random multiplicative cascades are nonlinear processes that repeatedly divide, branch, or aggregate structures across generations, resulting in multiplicative interactio...

When measuring physiological data, the central limit theorem typically implies a consistent variance, resulting in data that closely follows a Gaussian distribution. However, physiological measurements often deviate from this expectation, increasing variance due to nonlinear correlations across various scales. The challenge lies in testing these ta...

A rich and complex temporal structure of variability in postural sway characterizes healthy and adaptable postural control. However, neurodegenerative disorders such as Parkinson's disease, which often manifest as tremors, rigidity, and bradykinesia, disrupt this healthy variability. This study examined postural sway in young and older adults, incl...

Walking exhibits stride-to-stride variations. Given ongoing perturbations, these variations critically support continuous adaptations between the goal-directed organism and its surroundings. Here, we report that stride-to-stride variations during self-paced overground walking show cascade-like intermittency---stride intervals become uneven because...

Any reliable biomarker has to be specific, generalizable, and reproducible across individuals and contexts. The exact values of such a biomarker must represent similar health states in different individuals and at different times within the same individual to result in the minimum possible false-positive and false-negative rates. The application of...

Movement variability may reflect a fluid cascade of interactive factors. Instead of an assemblage of independent components recruited as needed in separate synergies, the movement system could embody a cascade of contingency, with contextual pressures at one scale shaping the degrees of freedom at another scale. Modeling cascades has been challengi...

A hallmark of dexterous, context-sensitive behavior is the capacity to blend and integrate information across various scales. Seamlessly pursuing multiple goals and navigating multiple task constraints involves a range of concerns across many scales: brief or bottom-up sensory corrections, long-term or top-down switches in intention and attention t...

We analyze the concept of "affordance" in ecological psychology and the concept of "Turing machine" drawn from computation. We propose that Turing's theory of computation supports Gibson's ecological theory of affordances as entities perceived directly—without invoking representations—as the configurations of Turing machines. Our arguments draw on...

Affordance has been a centerpiece of ecological approaches to psychology. Gibson developed this novel concept through the 1960s and 1970s, defining an "affordance" as an "opportunity for action" (Gibson, 1977). This concept offered novel means to understand the role of individual actors in constructing their experience. For explaining action and re...

An enduring controversy in biological and psychological sciences has centered on the tension between the role of random multiplicative cascade processes and the sometimes independent, additive effects of seemingly modular, scale-dependent component processes. The former supports the fluid interactivity of an organism's faculties for perception, act...

Individuals with Parkinson's disease exhibit tremors, rigidity, and bradykinesia, disrupting normal movement variability and resulting in postural instability. This comprehensive study aimed to investigate the link between the temporal structure of postural sway variability and Parkinsonism by analyzing multiple datasets from young and older adults...

Numerous natural growth processes exhibit allometric relationships among their respective traits, wherein one trait undergoes expansion as a power function of another, contingent upon certain physical constraints. For instance, the acknowledged consensus posits that tree height scales with the two-thirds power of stem diameter. In the context of hu...

Any reliable biomarker has to be specific, generalizable, and reproducible across individuals and contexts. The exact values of such a biomarker must represent similar health states in different individuals and at different times within the same individual to result in the minimum possible false-positive and false-negative rates. The application of...

Introduction: The seemingly periodic human gait exhibits stride-to-stride variations as it adapts to the changing task constraints. The optimal movement variability hypothesis (OMVH) states that healthy stride-to-stride variations exhibit “fractality”—a specific temporal structure in consecutive strides that are ordered, stable but also variable, a...

An ongoing thrust of research focused on human gait pertains to identifying individuals based on gait patterns. However, no existing gait database supports modeling efforts to assess gait patterns unique to individuals. Hence, we introduce the Nonlinear Analysis Core (NONAN) GaitPrint database containing whole body kinematics and foot placement dur...

When measuring physiological data, the central limit theorem suggests that a consistent variance confines the data within a narrow range resembling a Gaussian distribution. However, in the case of physiological measurements, the variance often increases due to cascade-like interactivity, resulting in distributions with heavier tails and nonlinear c...

Biological and psychological processes routinely break ergodicity, meaning they fail to have stable means ($Mean$) and independent variation over time that we might find in additive white Gaussian noise (awGn). One possible reason for this failure of ergodicity is the failure of biological and psychological processes to exhibit independence across...

Anomalous diffusion in various complex systems abounds in nature and spans multiple space and time scales. Canonical characterization techniques that rely upon mean squared displacement break down for nonergodic processes, making it challenging to characterize anomalous diffusion from an individual time-series measurement. Nonergodicity reigns when...

The seemingly periodic human gait exhibits stride-to-stride variations as it adapts to the changing task constraints. The optimal movement variability hypothesis (OMVH) states that healthy stride-to-stride variations exhibit ``fractality''---a specific temporal structure in consecutive strides that are ordered, stable but also variable, and adaptab...

After just months of simulated training, on January 19, 2019, a 23-year-old E-sports pro-gamer, Enzo Bonito, took to the racetrack and beat Lucas di Grassi, a Formula E and ex-Formula 1 driver with decades of real-world racing experience. This event raised the possibility that practicing in virtual reality can be surprisingly effective for acquirin...

Interference between a walking task (target speeds on a self-paced treadmill) and dual visual and tactile-visual response time task was investigated. Ambulatory dual-task scenarios reveal how attention is divided between walking and additional tasks, but the impact of walking speed and dual-task modality on gait characteristics and dual-task perfor...

Walking exhibits stride-to-stride variations. Given ongoing perturbations, these variations critically support continuous adaptations between the goal-directed organism and its surroundings. Here, we report that stride-to-stride variations during self-paced overground walking show cascade-like intermittency---stride intervals become uneven because...

Any reliable biomarker has to be specific, generalizable, and reproducible across individuals and contexts. The exact values of such a biomarker must represent similar health states in different individuals and at different times within the same individual. The application of standard cutoff points and risk scores across populations hinges upon the...

The task of grasping and manipulating virtual objects is expected to become perhaps one of the most fundamental actions in interactive Virtual Reality (VR), as it is in the real world. However, unnatural interactions of the virtual hand avatar with virtual objects and unnatural post-collision behavior of virtual objects severely limit the utility o...

Keywords: affordance bearded capuchin monkey body mass development learning nut cracking perceptioneaction Sapajus libidinosus skill tool Bearded capuchin monkeys at Fazenda Boa Vista, Piauí, Brazil older than 8 years routinely crack palm nuts with a stone hammer and anvil. An embodied, perceptioneaction stance hypothesizes that mon-keys' improving...

An ongoing thrust of research focused on human gait pertains to identifying individuals based on gait patterns. However, no existing gait database supports modeling efforts to assess gait patterns unique to individuals. Hence, we introduce the Nonlinear Analysis Core (NONAN) GaitPrint database that provides whole body kinematics and foot placement...

Anomalous diffusion in a variety of complex systems abounds in nature and spans multiple space and time scales. Canonical characterization techniques that rely upon mean squared displacement (MSD) break down for non-ergodic processes, making it challenging to characterize anomalous diffusion from an individual time-series measurement. Non-ergodicit...

The Bayesian Hurst-Kolmogorov (HK) method estimates the Hurst exponent of a time series more accurately than the age-old detrended fluctuation analysis (DFA), especially when the time series is short. However, this advantage comes at the cost of computation time. The computation time increases exponentially with N, easily exceeding several hours fo...

Detrended Fluctuation Analysis (DFA) is the most popular fractal analytical technique used to evaluate the strength of long-range correlations in empirical time series in terms of the Hurst exponent, H. Specifically, DFA quantifies the linear regression slope in log-log coordinates representing the relationship between the time series' variability...

Detrended Fluctuation Analysis (DFA) is the most popular fractal analytical technique used to evaluate the strength of long-range correlations in empirical time series in terms of the Hurst exponent, $H$. Specifically, DFA quantifies the linear regression slope in log-log coordinates representing the relationship between the time series' variabilit...

Increased fall risk in older adults and clinical populations is linked with increased amount and altered temporal structure of step width variability. One approach to rehabilitation seeks to reduce fall risk in older adults by reducing the amount of step width variability and restoring the temporal structure characteristic of healthy young adults....

An adaptive response to unexpected perturbations requires near-term and long-term adjustments over time. We used multifractal analysis to test how nonlinear interactions across timescales might support an adaptive response following an unpredictable perturbation. We reanalyzed balance data from 44 young and 24 older adults who performed a single-le...

Simpson’s paradox—also called the reversal paradox and amalgamation paradox—is a statistical phenomenon in which an apparent paradox arises because aggregate data at the group level (or at the level of a set of groups) can support a conclusion that is either not observed or is opposite from that suggested by the same data before aggregation at the...

Inference concerning cause-and-effect linkages in modern psychology and neuroscience follows the ergodic premise, which states that the mean response of representative samples allows predictions about the characteristics of specific sample members. However, emerging evidence suggests that empirical data in these fields often violate ergodic assumpt...

Turing inspired a computer metaphor of the mind and brain that has been handy and has spawned decades of empirical investigation, but he did much more and offered behavioral and cognitive sciences another metaphor—that of the cascade. The time has come to confront Turing’s cascading instability, which suggests a geometrical framework driven by powe...

Ergodicity breaking is a challenge for biological and psychological sciences. Ergodicity is a necessary condition for linear causal modeling. Long-range correlations and non-Gaussianity characterizing various biological and psychological measurements break ergodicity routinely, threatening our capacity for causal modeling. Long-range correlations (...

Adaptive response to unexpected perturbation requires balancing short- with long-scale behaviors. Multifractal analysis allows testing several expectations for how nonlinear interactions across timescales might support adaptive response following perturbation. We reanalyzed data from 40 young and 24 older adults performing a single-leg squat task,...

Increased fall risk in older adults and clinical populations is linked with increased amount and altered temporal structure of step width variability. Therefore, rehabilitation seeks to reduce fall risk in older adults by reducing the amount of step width variability and restoring the temporal structure characteristics of step width variability pre...

Biological and psychological processes routinely break ergodicity, meaning they fail to have stable means ($Mean$) and independent variation over time that we might find in additive white Gaussian noise (awGn). One possible reason for this failure of ergodicity is the failure of biological and psychological processes to exhibit independence across...

Ergodicity breaking is a challenge for biological and psychological sciences. Ergodicity is a necessary condition for linear causal modeling. Long-range correlations and non-Gaussianity characterizing various biological and psychological measurements break ergodicity routinely, threatening our capacity for causal modeling. Long-range correlations (...

The effectiveness of human-robot interactions critically depends on the success of computational efforts to emulate human inference of intent, anticipation of action, and coordination of movement. To this end, we developed two models that leverage a well described feature of human movement: Gaussian-shaped submovements in velocity profiles, to act...

After just months of simulated training, on January 19, 2019, a 23-year-old E-sports pro-gamer, Enzo Bonito, took to the racetrack and beat Lucas di Grassi, a Formula E and ex-Formula 1 driver with decades of real-world racing experience. This event raised the possibility that practicing in virtual reality can be surprisingly effective for acquirin...

The brain-as-computer metaphor has anchored the professed computational nature of mind, wresting it down from the intangible logic of Platonic philosophy to a material basis for empirical science. However, as with many long-lasting metaphors in science, the computer metaphor has been explored and stretched long enough to reveal its boundaries. Thes...

The creativity and emergence of biological and psychological behavior tend to be nonlinear—biological and psychological measures contain degrees of irregularity. The linear model might fail to reduce these measurements to a sum of independent random factors (yielding a stable mean for the measurement), implying nonlinear changes over time. The pres...

Turing inspired a computer metaphor of the mind and brain that has been handy and has spawned decades of empirical investigation, but he did much more and offered behavioral and cognitive sciences another metaphor—that of the cascade. The time has come to confront Turing’s cascading instability, which suggests a geometrical framework driven by powe...

The stochastic processes underlying the growth and stability of biological and psychological systems reveal themselves when far from equilibrium. Far from equilibrium, nonergodicity reigns. Nonergodicity implies that the average outcome for a group/ensemble (i.e., of representative organisms/minds) is not necessarily a reliable estimate of the aver...

The stochastic processes underlying the growth and stability of biological and psychological systems reveal themselves when far from equilibrium. Far from equilibrium, nonergodicity reigns. Nonergodicity implies that the average outcome for a group/ensemble (i.e., of representative organisms/minds) is not necessarily a reliable estimate of the aver...

Among primates, prehensile/semi-prehensile tails have evolved independently in the families Atelidae and Cebidae of the infraorder Platyrrhini (Neotropical monkeys). Prehensile/semi-prehensile tails facilitate maintenance of stability during locomotion on thin, flexible branches and while reaching for food on challenging substrates. How a prehensil...

Control of reach-to-grasp movements for deft and robust interactions with objects requires rapid sensorimotor updating that enables online adjustments to changing external goals (e.g., perturbations or instability of objects we interact with). Rarely do we appreciate the remarkable coordination in reach-to-grasp, until control becomes impaired by n...

Collaborative research that provides unprecedented opportunities to individuals with various capacities to contribute to scientific knowledge also encourages the practice of inflating credentials by serving as coauthors on papers, frequently with little to no contribution. A more systematic and consistent methodology for quantifying author contribu...

The ubiquity of tool use in human life has generated multiple lines of scientific and philosophical investigation to understand the development and expression of humans’ engagement with tools and its relation to other dimensions of human experience. However, existing literature on tool use faces several epistemological challenges in which the same...

We see the computer metaphor of the brain as a holdover from premodern scientific traditions hoping to anchor the mind’s computational ability in a material anatomical part. Despite having prompted decades of valuable empirical insights, the computer metaphor has likely outgrown its usefulness. Brains are context-sensitive and capable of adapting t...

Among primates, prehensile/semi-prehensile tails have evolved independently in the families Atelidae and Cebidae of the infraorder Platyrrhini (Neotropical monkeys). Prehensile/semi-prehensile tails facilitate maintenance of stability during locomotion on thin, flexible branches and while reaching for food on challenging substrates. How a prehensil...

The ubiquity of tool use in human life has generated multiple lines of scientific and philosophical investigation to understand the development and expression of humans’ engagement with tools and its relation to other dimensions of human experience. However, existing literature on tool use faces several epistemological challenges in which the same...

The COVID-19 pandemic has accelerated interest in virtual reality (VR) for education, entertainment, telerehabilitation, and skills training. As the frequency and duration of VR engagement increases — the number of people in the United States using VR at least once per month is forecasted to exceed 95 million — it is critical to understand how VR e...

The success of psychology and neuroscience depends on making causal inferences about a phenomenon that generalizes to new individuals in the long run. Typically, studies infer the cause from statistical tests conducted on aggregated data from a random sample to infer the cause. This policy assumes that the study phenomenon is ‘ergodic.’ Ergodicity...

Speech perception and memory for speech require active engagement. Gestural theories have emphasized mainly the effect of speaker's movements on speech perception. They fail to address the effects of listener movement, focusing on communication as a boundary condition constraining movement among interlocutors. The present work attempts to break new...

The embodied theory of tooling predicts that individuals accommodate their actions to manage the degrees of freedom (DoFs) in the body-plus-object system when using a grasped object as a tool. We tested predictions from this theory by studying how tufted capuchin monkeys (Sapajus spp.) and humans (Homo sapiens) used a hoe to retrieve a token. The h...

Simpson’s paradox — also called the reversal paradox and amalgamation paradox — is a statistical phenomenon in which an apparent paradox arises because aggregate data at the group level (or at the level of a set of groups) can support a conclusion that is either not observed or is opposite from that suggested by the same data before aggregation at...

Technological advancements and increased access have prompted the adoption of head mounted display-based virtual reality for neuroscientific research, manual skill training, and neurological rehabilitation. Applications that focus on manual interaction within the virtual environment, especially haptic-free virtual reality, critically depend on virt...

The creativity and emergence of biological and psychological behavior tend to be nonlinear—biological and psychological measures contain degrees of irregularity. The linear model might fail to reduce these measurements to a sum of independent random factors (yielding a stable mean for the measurement), implying nonlinear changes over time. The pres...

Virtual reality (VR) has garnered much interest as a training environment for motor skill acquisition, including for neurological rehabilitation of upper extremities. While the focus has been on gross upper limb motion, VR applications that involve reaching for, and interacting with, virtual objects are growing. The absence of true haptics in VR wh...

When humans handle a tool, such as a tennis racket or hammer, for the first time, they often wield it to determine its inertial properties. The mechanisms that contribute to perception of inertial properties are not fully understood. The present study’s goal was to investigate how proprioceptive afferents contribute to effortful perception of heavi...

Quiet standing exhibits strongly intermittent variability that has inspired at least two interpretations. First, variability can be intermittent through the alternating engagement and disengagement of complementary control processes at distinct scales. A second and perhaps deeper way to interpret this intermittency is through the possibility that p...

Speech perception and memory for speech require active engagement. Gestural theories have emphasized mainly the effect of the movements of the speaker on speech perception. They fail to address the effects of listener movement, focusing on communication as a boundary condition constraining movement among interlocutors. The present work attempts to...

Modern biomedical, behavioral and psychological inference about cause-effect relationships respects an ergodic assumption, that is, that mean response of representative samples allow predictions about individual members of those samples. Recent empirical evidence in all of the same fields indicates systematic violations of the ergodic assumption. I...