Multifractal signatures of perceptual processing on anatomical sleeves of the human body

Abstract

Research into haptic perception typically concentrates on mechanoreceptors and their supporting neuronal processes. This focus risks ignoring crucial aspects of active perception. For instance, bodily movements influence the information available to mechanoreceptors, entailing that movement facilitates haptic perception. Effortful manual wielding of an object prompts feedback loops at multiple spatio-temporal scales, rippling outwards from the wielding hand to the feet, maintaining an upright posture and interweaving to produce a nonlinear web of fluctuations throughout the body. Here, we investigated whether and how this bodywide nonlinearity engenders a flow of multifractal fluctuations that could support perception of object properties via dynamic touch. Blindfolded participants manually wielded weighted dowels and reported judgements of heaviness and length. Mechanical fluctuations on the anatomical sleeves (i.e. peripheries of the body), from hand to the upper body, as well as to the postural centre of pressure, showed evidence of multifractality arising from nonlinear temporal correlations across scales. The modelling of impulse–response functions obtained from vector autoregressive analysis revealed that distinct sets of pairwise exchanges of multifractal fluctuations entailed accuracy in heaviness and length judgements. These results suggest that the accuracy of perception via dynamic touch hinges on specific flowing patterns of multifractal fluctuations that people wear on their anatomical sleeves.

Postural constraints recruit shorter-timescale processes into the non-Gaussian cascade processes

“…It can be no small coincidence that tensegrity and neuronal-avalanche models all converge on the same multifractal geometry [48] that inspired the development of multiscale PDF analysis. Indeed, estimates of multifractality along this physiological cascade well predict the flow of perceptual information through the body and the coordination of disparate body parts [49,50]. Further, we see direct evidence that multifractal signatures of nonlinearity across time through DFA have direct relationships to cascade structure as estimated through multiscale PDF analysis, suggesting convergence of evidence through different analytical sources.…”

Visual effort moderates postural cascade dynamics

“…But these cascades affecting a dynamic balance of forces across the body seem to be essential foundations for how the body reaches out beyond itself to engage with the environment. 2,4,32,33 So, the present findings show how vision plays not only upon the photoreceptors in the eyes but also across the full-body postural system.…”

“…37 The metaphor of 'cascades,' as in tumbling water that accelerates and splashed down a rockface, captures some critical aspects of the dynamics of emergent behavior. 21,33,35 Destabilizing posture emphasizes the postural cascade dynamics. 36,38 Here, we propose that perturbing the visual system has a similar effect of strengthening postural cascade dynamics, in which the optical flow varies with fixation distance, as a meandering stream joins other streams and gathers momentum into rushing rapids, becoming more turbulent along the way.…”

Perceiving and remembering speech depend on multifractal nonlinearity in movements producing and exploring speech

“…It addresses current calls in the literature for a straightforward multifractal extension of the notion that a speaker-listener dyad depends on 'complexity matching' between the respective movement systems [54][55][56][57]. It rests on a long history of investigating the multifractal support for coordinating perceptual information within and across organisms [46][47][48][49][50][51]73].…”