Functional versus effector-specific organization of the human posterior parietal cortex: revisited

Heed T, Leone FTM, Toni I, Medendorp WP. Functional versus effector-specific organization of the human posterior parietal cortex: revisited. Journal of Neurophysiology. 2016;116(4):1885-1899

Brief Communication Gaze-Centered Updating of Visual Space in Human Parietal Cortex

Single-unit recordings have identified a region in the posterior parietal cortex (PPC) of the monkey that represents and updates visual space in a gaze-centered frame. Here, using event-related functional magnetic resonance imaging, we identified an analogous bilateral region in the human PPC that shows contralateral topography for memory-guided eye movements and arm movements. Furthermore, when eye movements reversed the remembered horizontal target location relative to the gaze fixation point, this PPC region exchanged activity across the two cortical lobules. This shows that the human PPC dynamically updates the spatial goals for action in a gaze-centered frame

Spatial constancy mechanisms in motor control

The success of the human species in interacting with the environment depends on the ability to maintain spatial stability despite the continuous changes in sensory and motor inputs owing to movements of eyes, head and body. In this paper, I will review recent advances in the understanding of how the brain deals with the dynamic flow of sensory and motor information in order to maintain spatial constancy of movement goals. The first part summarizes studies in the saccadic system, showing that spatial constancy is governed by a dynamic feed-forward process, by gaze-centred remapping of target representations in anticipation of and across eye movements. The subsequent sections relate to other oculomotor behaviour, such as eye–head gaze shifts, smooth pursuit and vergence eye movements, and their implications for feed-forward mechanisms for spatial constancy. Work that studied the geometric complexities in spatial constancy and saccadic guidance across head and body movements, distinguishing between self-generated and passively induced motion, indicates that both feed-forward and sensory feedback processing play a role in spatial updating of movement goals. The paper ends with a discussion of the behavioural mechanisms of spatial constancy for arm motor control and their physiological implications for the brain. Taken together, the emerging picture is that the brain computes an evolving representation of three-dimensional action space, whose internal metric is updated in a nonlinear way, by optimally integrating noisy and ambiguous afferent and efferent signals

State Estimation in Posterior Parietal Cortex: Distinct Poles of Environmental and Bodily States.

Medendorp WP, Heed T. State Estimation in Posterior Parietal Cortex: Distinct Poles of Environmental and Bodily States. Progress in neurobiology. 2019;183: 101691.Posterior parietal cortex (PPC) has been implicated in sensory and motor processing, but its underlying organization is still debated. Sensory-based accounts suggest that PPC is mainly involved in attentional selection and multisensory integration, serving novelty detection and information seeking. Motor-specific accounts suggest a parietal subdivision into lower-dimensional, effector-specific subspaces for planning motor action. More recently, function-based interpretations have been put forward based on coordinated responses across multiple effectors evoked by circumscribed PPC regions. In this review, we posit that an overarching interpretation of PPC's functional organization must integrate, rather than contrast, these various accounts of PPC. We propose that PPC's main role is that of a state estimator that extends into two poles: a rostral, body-related pole that projects the environment onto the body and a caudal, environment-related pole that projects the body into an environment landscape. The combined topology interweaves perceptual, motor, and function-specific principles, and suggests that actions are specified by top-down guided optimization of body-environment interactions. Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved

Panoramic Uncertainty in Vertical Perception

Judgments of the orientation of a visual line with respect to earth vertical are affected by panoramic visual cues. This is illustrated by the rod-and-frame effect (RFE), the finding that the perceived orientation of a luminous rod is biased by the orientation of a surrounding squared frame. In this study, we tested how the uncertainty of frame orientation affects the RFE by asking upright or tilted participants to psychometrically judge the orientation of a briefly flashed rod contained within either a circular frame, a squared frame, or either of two intermediate frame forms, called squircles, presented in various orientations. Results showed a cyclical modulation of frame-induced bias across the range of the square and squircular frame orientations. The magnitude of this bias increased with increasing squaredness of the frame, as if the more unequivocal the orientation cues of the frame, the larger the reliance on them for rod orientation judgments. These findings are explained with a Bayesian optimal integration model in which participants flexibly weigh visual panoramic cues, depending on their orientation reliability, and non-visual cues in the perception of vertical