Biology subjects

Sukumar, V.

Publications and source records attributed to Sukumar, V..

4 recordsLinked to original sources

bioRxiv2025

Speed-dependent modulation of tactile edge orientation discrimination

Previous studies investigating edge-orientation discrimination capacity either stimulated an immobilized finger at limited speeds, or did not manipulate movement speed during active exploration. Here we tested the effect of movement speed on edge-orientation discrimination, including very slow and fast speeds. Participants were instructed to move their finger across two pairs of edges while matching their speed to a visual cue. One edge pair was parallel and the other non parallel to varying degrees. Participants were asked to identify the non parallel pair of edges. We report three main findings. First, consistent with previous reports, when they were free to choose their movement speed, participants moved at an average speed of [~]29 mm/s (range: 15-52 mm/s). Second, there was no correlation between a participants natural speed and their edge orientation discrimination capacity. Third, participants got better at edge orientation discrimination at slower than average speeds (5mm/s), and worse at higher than average speeds (90 and 180 mm/s). This change in performance was correlated with their relative change in movement speed. New and NoteworthyHere we demonstrate speed-dependent variation in edge-orientation discrimination during active tactile exploration, with improved performance at very slow speeds. Changes in discrimination capacity as a function of speed are correlated with deviations from a participants natural speed.

neuroscience↗

bioRxiv2024

Unifying the analysis of bottom-up proteomics data with CHIMERYS

Proteomic workflows generate vastly complex peptide mixtures that are analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), creating thousands of spectra, most of which are chimeric and contain fragment ions from more than one peptide. Because of differences in data acquisition strategies such as data-dependent (DDA), data-independent (DIA) or parallel reaction monitoring (PRM), separate software packages employing different analysis concepts are used for peptide identification and quantification, even though the underlying information is principally the same. Here, we introduce CHIMERYS, a novel, spectrum-centric search algorithm designed for the deconvolution of chimeric spectra that unifies proteomic data analysis. Using accurate predictions of peptide retention time, fragment ion intensities and applying regularized linear regression, it explains as much fragment ion intensity as possible with as few peptides as possible. Together with rigorous false discovery rate control, CHIMERYS accurately identifies and quantifies multiple peptides per tandem mass spectrum in DDA, DIA and PRM experiments.

biochemistry↗

bioRxiv2022

Precise and stable edge orientation signaling by human first-order tactile neurons

Fast-adapting type 1 (FA-1) and slow-adapting type 1 (SA-1) first-order neurons in the human tactile system have distal axons that branch in the skin and form many transduction sites, yielding receptive fields with many highly sensitive zones or subfields. We previously demonstrated that this arrangement allows FA-1 and SA-1 neurons to signal the geometric features of touched objects, specifically the orientation of raised edges scanned with the fingertips. Here we show that such signaling operates for fine edge orientation differences (5-20{degrees}) and is stable across a broad range of scanning speeds (15-180 mm/s); that is, under conditions relevant for real-world hand use. We found that both FA-1 and SA-1 neurons weakly signal fine edge orientation differences via the intensity of their spiking responses and only when considering a single scanning speed. Both neuron types showed much stronger edge orientation signaling in the sequential structure of the evoked spike trains and FA-1 neurons performed better than SA-1 neurons. Represented in the spatial domain, the sequential structure was strikingly invariant across scanning speeds, especially those naturally used in tactile spatial discrimination tasks. This speed invariance suggests that neurons responses are structured via sequential stimulation of their subfields and thus links this capacity to their terminal organization in the skin. Indeed, the spatial precision of elicited action potentials rationally matched spatial acuity of subfield arrangements, which typically corresponds to the dimension of individual fingertip ridges. Significance StatementThe distal axons of human first-order tactile neurons branch and innervate many mechanosensitive end organs in the skin. For those neurons terminating in end organs associated with fingerprint ridges (Meissner and Merkel), this branching results in cutaneous receptive fields with multiple subfields spread across several ridges. Consequently, when a fingertip scans the surface of an object, the spatial coincidence between a neurons subfields and the tactile stimulus defines the sequential structure of the evoked spike train (i.e., the presence of action potential bursts and the gaps between them). Here we show that, for surfaces composed of oriented edges, this sequential structure signals information about edge orientation differences at the limit of what people can feel and that the spatial precision of the structuring is maintained across a broad range of speeds relevant for real-world hand use. We submit that, to be of human relevance, models of higher order tactile processing must consider the impact of multifocal receptive fields in the periphery. For example, the speed invariance of tactile fine-form/texture perception may arise simply because the same subsets of peripheral subfields in the population of first-order tactile neurons are stimulated together regardless of speed.

neuroscience↗

bioRxiv2018

Edge orientation perception during active touch

Previous studies investigating the perceptual attributes of tactile edge-orientation processing have applied their stimuli to an immobilized fingertip. Here we tested the perceptual attributes of edge orientation processing when participants actively touched the stimulus. Our participants moved their finger over two pairs of edges-one pair parallel and the other nonparallel to varying degrees-and were asked to identify which of the two pairs was nonparallel. In addition to the psychophysical estimates of edge orientation acuity, we measured the speed at which participants moved their finger and the forces they exerted when moving their finger over the stimulus. We report four main findings. First, edge orientation acuity during active touch averaged 12.4{degrees}, similar to that previously reported during passive touch. Second, on average, participants moved their finger over the stimuli at 23.9 mm/s and exerted contact forces of 0.47 N. Third, across participants, there was no clear relationship between how people moved their finger or how they pressed on the stimulus and their edge orientation acuity. However, within participants, there appeared to be a weak effect of speed on performance whereby error trials included slightly faster finger movements; no equivalent effect was found for contact force. Fourth, consistent with previous work testing spatial acuity, we found significant correlation between fingertip size and orientation acuity such that people with smaller fingertips tended to have better orientation acuity.

neuroscience↗