Biology subjects

Johansson, R. S.

Publications and source records attributed to Johansson, R. S..

5 recordsLinked to original sources

bioRxiv2024

Adaptive Gaze and Hand Coordination while Manipulating and Monitoring the Environment in Parallel

Research on visually guided object manipulation has shown that participants fixate goal locations-such as objects to be grasped and locations where they are placed-prior to hand arrival, with gaze serving two primary functions: directing the hand (or object in hand) to the vicinity of the goal using peripheral vision and gaze related signals, and guiding the hand using central vision as it approaches the goal. However, in real world scenarios, manipulation tasks are often performed while concurrent monitoring of the environment, resulting in competition for gaze. Here we examined gaze-hand coordination under such conditions. Participants performed a manipulation task, that involved grasping balls and placing them at target locations, while concurrently monitoring a display to detect probabilistically occurring visual events, which required central vision. Participants managed gaze competition in two main ways. First, fixations allocated to the action task were brief and prioritized directing the hand towards the goal (object or target location); participants then relied on tactile feedback to complete the action (grasping or placing the object). When tactile feedback was reduced-by using a tool instead of the fingertips to perform the task-gaze additionally served the guiding function. Second, participant reduced gaze competition by exploiting temporal regularities of events in the monitoring task. Specifically, they adjusted both gaze allocation and hand movement timing to reduce the likelihood that action task fixations would coincide with visual events. These findings demonstrate how individuals flexibly integrate sensorimotor control with analysis of environmental statistics to manage competing visual demands. Significance StatementIn everyday behaviour, we often perform manual tasks while simultaneously monitoring the environment, creating competition for gaze. How the brain resolves this competition remains poorly understood. Using a novel paradigm combining an object manipulation task with visual event monitoring, we show that participants integrate knowledge of sensorimotor demands and temporal regularities in the monitoring task to manage gaze. Specifically, we found that participants preferentially allocated gaze to the action task when it is most critical for sensorimotor control and when the likelihood of a visual event was low. Additionally, participants adjusted their hand movement timing based on event statistics to reduce gaze competition. These findings reveal how the brain dynamically allocates gaze resources across competing sensorimotor and visual task demands.

neuroscience↗

bioRxiv2023

Memory at your fingertips: how viscoelasticity affects tactile neuron signaling

Human skin and its underlying tissues constitute a viscoelastic medium, implying that any deformation depends not only on the currently applied force, but also the recent loading history. The extent to which this physical memory influences the signaling of first-order tactile neurons during natural hand use is not well understood. Here, we examined the effect of past loading on the responses of fast-adapting (FA-1) and slowly-adapting (SA-1 and SA-2) first-order tactile neurons innervating the human fingertip to loadings applied in different directions representative of object manipulation tasks. We found that variation in the preceding loading affected neurons overall signaling of force direction. Some neurons kept signaling the current direction, while others signaled both the current and preceding direction, or even primarily the preceding direction. In addition, ongoing impulse activity in SA-2 neurons between loadings signaled information related to the fingertips viscoelastic deformation state. We conclude that tactile neurons at the population level signal continuous information about the fingertips viscoelastic deformation state, which is shaped by both its recent history and current loading. Such information might be sufficient for the brain to correctly interpret current force loading and help in computing accurate motor commands for interactions with objects in manipulation and haptic tasks.

neuroscience↗

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↗

bioRxiv2020

Human first-order tactile neurons can resolve spatial details on the scale of single fingerprint ridges

Fast-adapting type 1 (FA-1) and slow-adapting type 1 (SA-1) first-order tactile neurons provide detailed spatiotemporal tactile information when we touch objects with fingertips. The distal axon of these neuron types branches in the skin and innervates many receptor organs associated with fingerprint ridges (Meissner corpuscles and Merkel cell neurite complexes, respectively), resulting in heterogeneous receptive fields that include many highly sensitive zones or subfields. Using raised dots that tangentially scanned a neurons receptive field, here we examined the spatial resolution capacity of FA-1 and SA-1 neurons afforded by their heterogeneous receptive fields and its constancy across scanning speed and direction. We report that the resolution of both neuron types on average corresponds to a spatial period of [~]0.4 mm and provide evidence that a subfields spatial selectivity arises because its associated receptor organ measures mechanical events limited to a single fingerprint ridge. Accordingly, the sensitivity topography of a neurons receptive fields is quite stable over repeated mappings and over scanning speeds representative of real-world hand use. The sensitivity topography is substantially conserved also for different scanning directions, but the subfields can be relatively displaced by direction-dependent shear deformations of the skin surface. Significance StatementThe branching of the distal axon of first-order tactile neurons with receptor-organs associated with fingerprint ridges (Meissner and Merkel end-organs) results in cutaneous receptive fields composed of several distinct subfields spread across multiple ridges. We show that the spatial selectivity of the subfields typically corresponds to the dimension of the ridges ([~]0.4 mm) and that neurons subfield layout is well preserved across tangential movement speeds and directions representative of natural use of the fingertips. We submit that the receptor-organ underlying a subfield essentially measures mechanical events at an individual ridge. That neurons receive convergent input from multiple subfields does not preclude the possibility that spatial details can be resolved on the scale of single fingerprint ridges by a population code.

neuroscience↗

bioRxiv2017

Fast and accurate edge orientation processing during object manipulation

Quickly and accurately extracting information about a touched objects orientation is a critical aspect of dexterous object manipulation. However, the speed and acuity of tactile edge orientation processing with respect to the fingertips as reported in previous perceptual studies appear inadequate in these respects. Here we directly establish the tactile systems capacity to process edge-orientation information during dexterous manipulation. Participants extracted tactile information about edge orientation very quickly, using it within 200 ms of first touching the object. Participants were also strikingly accurate. With edges spanning the entire fingertip, edge-orientation resolution was better than 3{degrees} in our object manipulation task, which is several times better than reported in previous perceptual studies. Performance remained impressive even with edges as short as 2 mm, consistent with our ability to precisely manipulate very small objects. Taken together, our results radically redefine the spatial processing capacity of the tactile system.

neuroscience↗