Biology subjects

Culham, J. C.

Publications and source records attributed to Culham, J. C..

7 recordsLinked to original sources

bioRxiv2026

Reaching movements in virtual reality depend on the seen avatar arm and not just the acting arm

Virtual reality (VR) offers unique opportunities to study behaviour by allowing the visual environment to be manipulated in ways otherwise impossible in the real world. A central theoretical question is how body-related visual information shapes movement control. Given right-handers' greater dexterity with the right arm, perhaps even seeing a right arm vs. a left arm may engage sensorimotor processes associated with more precise motor control. We examined reaching performance while participants used their own right or left arm to move the manipulandum of a KINARM robot to intercept static targets. Participants wore a VR head-mounted display, calibrated to the robot's physical workspace, in which they saw either the right or left arm holding and moving the manipulandum. The 2 x 2 design allowed for independent manipulation of the controlling arm and virtual arm displayed. As expected, reaches were faster and more accurate when controlled by the right arm. More interestingly, performance was also affected by the seen arm. Participants made straighter reaches when they saw a virtual right arm than a left arm, especially for the right controlling arm. These findings show that precise motor control relies not only on the arm that is actually moved and provides proprioceptive feedback, but also on the visual identity of the arm. The ability to modulate performance using visual features in VR opens new theoretical questions and opportunities for applications such as rehabilitation.

neuroscience↗

bioRxiv2026

fNIRS reveals that live social interactions and visual realism influence neural responses

The human face is central to social interactions, supporting the ability to interpret others' mental states using theory of mind (ToM). We examined whether functional near-infrared spectroscopy (fNIRS) would reveal brain-activation differences between live and pre-recorded social conversations in brain regions implicated in ToM. Furthermore, we examined whether activation depended on the visual realism of a social partner - viewed as a human or an animated avatar. By one view, social interactions may be dependent on how natural the social partner appears; by another view, social interactions may depend only upon the attribution of responses to a real human regardless of visual appearance. Neural activation for pre-recorded compared to live interactions was prolonged, consistent with extended cognitive effort. Activation patterns in the right temporoparietal junction differed between interacting with humans versus avatars, along with a stronger preference for looking at the eyes when interacting with a human (vs. avatar), underscoring the social relevance of real faces. Findings highlight the importance of both live interactions and facial realism in shaping social-cognitive processing, a finding with relevance for optimizing online social interactions.

neuroscience↗

bioRxiv2025

Distinct perceptual and conceptual representations of natural actions along the lateral and dorsal visual streams: an EEG-fMRI fusion study

Actions are the building blocks of our dynamic visual world, yet the neural computations supporting action perception are not well understood. How does perceptual and conceptual information unfold in the brain when we observe what others are doing? We collected EEG and fMRI data while participants viewed short videos and sentences depicting naturalistic actions. Using representational similarity analysis, we found a posterior-to-anterior gradient along the lateral pathway, from perceptual features to conceptual, modality-invariant representations. Among conceptual features, the target of actions (i.e. whether the action was directed at an object, a person, or the self) explained the most unique variance in EEG responses. In fMRI, we found distinct conceptual representations along the ventral, dorsal, and lateral pathways, with the target of actions specifically encoded in lateral occipitotemporal cortex (LOTC) and posterior superior temporal sulcus (pSTS). Finally, EEG-fMRI fusion revealed rapid processing along the lateral and dorsal pathways. Together, our results disentangle the perceptual and conceptual components of action understanding and characterize the underlying spatiotemporal dynamics in the human brain.

neuroscience↗

bioRxiv2025

Tool-use brain representations are independent of the acting body part and motor experience

The sensorimotor system is broadly organized somatotopically. However, an action-type organization has also been found: a division based on action-type independent of acting body parts has been shown for reaching and grasping actions. Does this generalization extend to non-ethological actions? Here, we examined fMRI responses for tool-use actions that participants performed with their hands or feet. We additionally tested individuals born without hands to control for hand motor imagery when performing foot actions. We show that the primary sensorimotor cortices have hand and foot selectivity, consistent with a somatotopic organization. In contrast, higher-level motor areas within the tool-use network, such as the premotor cortex, supplementary motor area, and superior parietal cortices, showed a shared preference for tool-use independent of the executing body part and sensorimotor experience. Multivariate decoding of action-type in these areas generalized between controls hand and foot and was successful in individuals born without hands. Finally, the temporal dynamics pattern in primary and association areas carried effector-specific and action-type information, respectively. Altogether, we show that the tool-use network in motor association areas represents higher-order action information beyond concrete motor parameters associated with specific effectors, and regardless of hand motor experience. This suggests that an action-type, effector-independent organization extends beyond ethological actions, supporting a hierarchical organization in the action domain. Further, it shows that functional organization in congenital handlessness is based on the hierarchical organization of the intact cortex.

neuroscience↗

bioRxiv2024

Target interception in virtual reality is better for natural versus unnatural trajectory shapes and orientations

Human performance in perceptual and visuomotor tasks is enhanced when stimulus motion follows the laws of gravitational physics, including acceleration consistent with Earths gravity, g. Here we used a manual interception task in virtual reality to investigate the effects of trajectory shape and orientation on interception timing and accuracy. Participants punched to intercept a ball moving along one of four trajectories that varied in shape (parabola or tent) and orientation (upright or inverted). We also varied the location of visual fixation such that trajectories fell entirely within the lower or upper visual field. Reaction times were faster for more natural shapes and orientations, regardless of visual field. Overall accuracy was poorer and movement time was longer for the inverted tent condition than the other three conditions, perhaps because it was imperfectly reminiscent of a bouncing ball. A detailed analysis of spatial errors revealed that interception endpoints were more likely to fall along the path of the final trajectory in upright vs. inverted conditions, suggesting stronger expectations regarding the final trajectory direction for these conditions. Taken together, these results suggest that the naturalness of the shape and orientation of a trajectory contributes to performance in a virtual interception task.

neuroscience↗

bioRxiv2023

Shared representations of human actions across vision and language

Humans can recognize and communicate about many actions performed by others. How are actions organized in the mind, and is this organization shared across vision and language? We collected similarity judgments of human actions depicted through naturalistic videos and sentences, and tested four models of action categorization, defining actions at different levels of abstraction ranging from specific (action verb) to broad (action target: whether an action is directed towards an object, another person, or the self). The similarity judgments reflected a shared organization of action representations across videos and sentences, determined mainly by the target of actions, even after accounting for other semantic features. Language model embeddings predicted the behavioral similarity of action videos and sentences, and captured information about the target of actions alongside unique semantic information. Together, our results show how action concepts are organized in the human mind and in large language model representations.

neuroscience↗

bioRxiv2023

Distinct neural components of visually guided grasping during planning and execution

Selecting suitable grasps on three-dimensional objects is a challenging visuomotor computation, which involves combining information about an object (e.g., its shape, size, and mass) with information about the actors body (e.g., the optimal grasp aperture and hand posture for comfortable manipulation). Here we used functional magnetic resonance imaging to investigate brain networks associated with these distinct aspects during grasp planning and execution. Human participants viewed and then executed preselected grasps on L-shaped objects made of wood and/or brass. By leveraging a computational approach that accurately predicts human grasp locations, we selected grasp points that disentangled the role of multiple grasp-relevant factors: grasp axis, grasp size, and object mass. Representational Similarity Analysis revealed that grasp axis was encoded along dorsal-stream regions during grasp planning. Grasp size was first encoded in ventral-stream areas during grasp planning, then in premotor regions during grasp execution. Object mass was encoded in ventral-stream and (pre)motor regions only during grasp execution. Premotor regions further encoded visual predictions of grasp comfort, whereas the ventral stream encoded grasp comfort during execution, suggesting its involvement in haptic evaluation. These shifts in neural representations thus capture the sensorimotor transformations that allow humans to grasp objects. Significance StatementGrasping requires integrating object properties with constraints on hand and arm postures. Using a computational approach that accurately predicts human grasp locations by combining such constraints, we selected grasps on objects that disentangled the relative contributions of object mass, grasp size, and grasp axis during grasp planning and execution in a neuroimaging study. Our findings reveal a greater role of dorsal-stream visuomotor areas during grasp planning, and surprisingly, increasing ventral stream engagement during execution. We propose that during planning, visuomotor representations initially encode grasp axis and size. Perceptual representations of object material properties become more relevant instead as the hand approaches the object and motor programs are refined with estimates of the grip forces required to successfully lift the object.

neuroscience↗