Biology subjects

Joiner, W. M.

Publications and source records attributed to Joiner, W. M..

5 recordsLinked to original sources

bioRxiv2025

Computational characterization of decision making during trans-saccadic visual perception

When viewing the environment, humans execute fast sequential saccadic eye movements that disrupt the flow of visual information, yet still preserve stability in their visual percept. At the time of the saccade subjects often experience saccadic suppression of displacement - a failure to notice changes in the location of visual objects slightly shifted during the eye movement. Although well studied, the weighing of sensory information and the extent to which this integration influences visual perceptual judgments is still poorly characterized and understood. Here we used a drift diffusion modeling (DDM) framework to systematically examine the extent to which sensory information biased perceptual judgments when detecting trans-saccadic shifts of visual targets. Healthy human participants (N = 29, 20 female) completed a visual perception task in which a visual target was shifted following a cued saccadic eye movement (4o or 8o). Trans-saccadic target displacements occurred up to +2.5o along the horizontal axis, and participants reported the shift direction with a button press response. We present a version of the DDM that takes the visual error as input to simulate offsets in evidence accumulation during decision-making. The model provides an explanatory framework for the integration of sensory information, capturing the temporal dynamics of evidence accumulation that explain the range of perceptual biasing and response timing effects observed across participants.

neuroscience↗

bioRxiv2024

A posture subspace in primary motor cortex

To generate movements, the brain must combine information about movement goal and body posture. Motor cortex (M1) is a key node for the convergence of these information streams. How are posture and goal information organized within M1s activity to permit the flexible generation of movement commands? To answer this question, we recorded M1 activity while monkeys performed a variety of tasks with the forearm in a range of postures. We found that posture- and goal-related components of neural population activity were separable and resided in nearly orthogonal subspaces. The posture subspace was stable across tasks. Within each task, neural trajectories for each goal had similar shapes across postures. Our results reveal a simpler organization of posture information in M1 than previously recognized. The compartmentalization of posture and goal information might allow the two to be flexibly combined in the service of our broad repertoire of actions.

neuroscience↗

bioRxiv2023

Tremors in Time: Mechanically Induced Motor Tremors Influence

Contemporary research has begun to show a strong relationship between movements and the perception of time. More specifically, concurrent movements serve to both bias and enhance time estimates. To explain these effects, we recently proposed a mechanism by which movements provide a secondary channel for estimating duration that is combined optimally with sensory estimates, in accordance with Bayesian cue combination. However, a critical test of this framework is that by introducing "noise" into movements, sensory estimates of time should similarly become noisier in a manner predicted by cue combination equations. To accomplish this, we had human participants move a robotic arm while estimating intervals of time in either auditory or visual modalities (n=24, ea.). Crucially, we introduced an artificial "tremor" in the arm while subjects were moving, that varied across three levels of amplitude (1-3 N) or frequency (4-12 Hz). The results of both experiments revealed that increasing the frequency of the tremor led to noisier estimates of duration, but in such a way that higher levels of noise saturated the impact, consistent with optimal integration. Further, the effect of noise varied with the base precision of the interval, such that a naturally less precise timing (i.e. visual) was more influenced by the tremor than a naturally more precise modality (i.e. auditory). To explain these findings, we fit the data with a recently developed drift-diffusion model of perceptual decision making, in which the momentary, within-trial variance was allowed to vary across conditions. Here, we found that the model could recapitulate the observed findings, further supporting the theory that movements influence perception directly. Overall, our findings support the proposed framework, and demonstrate the utility of inducing motor noise via artificial tremors, thus providing clinical utility in their connection to movement disorders characterized by tremors.

neuroscience↗

bioRxiv2018

Proprioceptive Sonomyographic Control: A novel method of intuitive proportional control of multiple degrees of freedom for upper-extremity amputees

Technological advances in multi-articulated prosthetic hands have outpaced the methods available to amputees to intuitively control these devices. Amputees often cite difficulty of use as a key contributing factor for abandoning their prosthesis, creating a pressing need for improved control technology. A major challenge of traditional myoelectric control strategies using surface electromyography electrodes has been the difficulty in achieving intuitive and robust proportional control of multiple degrees of freedom. In this paper, we describe a new control method, proprioceptive sonomyographic control that overcomes several limitations of myoelectric control. In sonomyography, muscle mechanical deformation is sensed using ultrasound, as compared to electrical activation, and therefore the resulting control signals can directly control the position of the end effector. Compared to myoelectric control which controls the velocity of the end-effector device, sonomyographic control is more congruent with residual proprioception in the residual limb. We tested our approach with 5 upper-extremity amputees and able-bodied subjects using a virtual target achievement and holding task. Amputees and able-bodied participants demonstrated the ability to achieve positional control for 5 degrees of freedom with an hour of training. Our results demonstrate the potential of proprioceptive sonomyographic control for intuitive dexterous control of multiarticulated prostheses.

bioengineering↗

bioRxiv2018

Reduced transfer of visuomotor adaptation is associated with aberrant sense of agency in Schizophrenia

One deficit associated with schizophrenia (SZ) is the reduced ability to distinguish sensations resulting from self-caused actions from those due to external sources. This reduced sense of agency (SoA, awareness of ownership over self-generated actions) is hypothesized to result from a diminished utilization of internal monitoring signals of self-movement (i.e., efferent copy) which subsequently impairs forming and utilizing sensory prediction errors (differences between the predicted and actual sensory consequences resulting from movement). Here, we investigated the connections between clinical SZ symptoms and motor adaptation, a process that uses sensory prediction errors to update motor output. Schizophrenia patients (SZP, N=30) and non-psychiatric healthy control subjects (HC, N=31) adapted to altered movement visual feedback, and then applied the motor recalibration to untested contexts (i.e., the spatial generalization to untrained targets). Although adaptation was similar for SZP and controls, the extent of generalization was significantly less for SZP; movement trajectories made by patients to the furthest untrained target (135{degrees}) before and after adaptation were largely indistinguishable. Interestingly, deficits in the generalization were correlated to positive symptoms of psychosis (e.g., hallucinations), but not negative symptoms. Generalization was also associated with subjective measures of SoA across both SZP and HC, emphasizing the major role action awareness plays in motor behavior, and suggesting that tendencies to misattribute agency, even in HC, manifest in abnormal motor performance. We discuss the possible link of these findings to cerebellar circuit abnormalities that may be a common source for deficits in the utilization of sensory prediction errors and aberrant SoA.

neuroscience↗