Haptic touch modulates size adaptation aftereffects on the hand.

When we interact with objects using our hands, we derive their size through our skin. Prolonged exposure to an object leads to a perceptual size aftereffect: adapting to a larger/smaller object makes a subsequently perceived object to appear smaller/larger than its actual size. This phenomenon has been described as haptic as tactile sensations with kinesthetic feedback are involved. However, the exact role of different haptic components in generating this aftereffect remains largely underexplored. Here, we investigated how different aspects of haptic touch influence size perception. After adaptation to a large sphere with one hand and a small sphere with the other, participants touched two test spheres of equal or different sizes and judged which one felt larger. Similar haptic size adaption aftereffects were observed (a) when participants repeatedly grasped on and off the adapters, (b) when they simply continued to grasp the adapters without further hand movements, and (c) when the adapters were grasped without involving the fingers. All these conditions produced stronger aftereffects than a condition where the palms were simply resting on the adapter. Our findings suggest that the inclusion of grasp markedly increased the aftereffects, highlighting the pivotal role of haptic interactions in determining perceptual size adaptation. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Does Ipsilateral Remapping Following Hand Loss Impact Motor Control of the Intact Hand?

What happens once a cortical territory becomes functionally redundant? We studied changes in brain function and behavior for the remaining hand in humans (male and female) with either a missing hand from birth (one-handers) or due to amputation. Previous studies reported that amputees, but not one-handers, show increased ipsilateral activity in the somatosensory territory of the missing hand (i.e., remapping). We used a complex finger task to explore whether this observed remapping in amputees involves recruiting more neural resources to support the intact hand to meet greater motor control demands. Using basic fMRI analysis, we found that only amputees had more ipsilateral activity when motor demand increased; however, this did not match any noticeable improvement in their behavioral task performance. More advanced multivariate fMRI analyses showed that amputees had stronger and more typical representation-relative to controls' contralateral hand representation-compared with one-handers. This suggests that in amputees, both hand areas work together more collaboratively, potentially reflecting the intact hand's efference copy. One-handers struggled to learn difficult finger configurations, but this did not translate to differences in univariate or multivariate activity relative to controls. Additional white matter analysis provided conclusive evidence that the structural connectivity between the two hand areas did not vary across groups. Together, our results suggest that enhanced activity in the missing hand territory may not reflect intact hand function. Instead, we suggest that plasticity is more restricted than generally assumed and may depend on the availability of homologous pathways acquired early in life.

Gravitational and retinal reference frames shape spatial memory.

When reproducing the remembered location of dots within a circle, judgments are biased toward the center of imaginary quadrants formed by imaginary vertical and horizontal axes. This effect may result from the heightened precision in the visual system for these orientations in a retinotopic reference frame, or alternately on the internal representation of gravity. We dissociated reference frames defined by the retina and by gravity by having participants locate dots from memory in a circle when their head was upright (aligned with gravity) versus tilted 30° to the left (misaligned with gravity). We mapped the structure of spatial prototypes in a data-driven way using a novel "imaging" procedure. We calculated the rotation of the prototype maps which maximized the similarity between postures, letting us quantify the contribution of each reference frame. Spatial categories are determined by a combination of reference frames, with clear contributions from both gravitational and retinal factors. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Tilt adaptation aftereffects reveal fundamental perceptual characteristics of tactile orientation processing on the hand.

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural orientation selectivity has been reported in somatosensory cortices. However, little research has investigated the perceptual characteristics of the tactile TAE. The aim of the current study was to provide the first demonstration of a tactile TAE on the hand and investigate the perceptual nature of tactile TAE on the hand surface. We used a 2-point stimulation with minimal input for orientation. We found clear TAEs on the hand surface: Adaptation induced shifts in subjective vertical sensation toward the orientation opposite to the adapted orientation. Further, adaptation aftereffects were purely based on orientation processing given that the effects transferred between different lengths across adaptor and test stimuli and type of stimuli. Finally, adaptation aftereffects were anchored to the hand: tactile TAE occurred independently of hand rotation and transferred from palm to dorsum sides of the hand, while the effects did not transfer between hands. Our findings demonstrate the existence of hand-centered perceptual processing for basic tactile orientation information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

On the realness of people who do not exist: The social processing of artificial faces.

Today more than ever, we are asked to evaluate the realness, truthfulness and trustworthiness of our social world. Here, we focus on how people evaluate realistic-looking faces of non-existing people generated by generative adversarial networks (GANs). GANs are increasingly used in marketing, journalism, social media, and political propaganda. In three studies, we investigated if and how participants can distinguish between GAN and REAL faces and the social consequences of their exposure to artificial faces. GAN faces were more likely to be perceived as real than REAL faces, a pattern partly explained by intrinsic stimulus characteristics. Moreover, participants' realness judgments influenced their behavior because they displayed increased social conformity toward faces perceived as real, independently of their actual realness. Lastly, knowledge about the presence of GAN faces eroded social trust. Our findings point to potentially far-reaching consequences for the pervasive use of GAN faces in a culture powered by images at unprecedented levels.

Visceral politics: a theoretical and empirical proof of concept.

While the study of affect and emotion has a long history in psychological sciences and neuroscience, the very question of how visceral states have come to the forefront of politics remains poorly understood. The concept of visceral politics captures how the physiological nature of our engagement with the social world influences how we make decisions, just as socio-political forces recruit our physiology to influence our socio-political behaviour. This line of research attempts to bridge the psychophysiological mechanisms that are responsible for our affective states with the historical socio-cultural context in which such states are experienced. We review findings and hypotheses at the intersections of life sciences, social sciences and humanities to shed light on how and why people come to experience such emotions in politics and what if any are their behavioural consequences. To answer these questions, we provide insights from predictive coding accounts of interoception and emotion and a proof of concept experiment to highlight the role of visceral states in political behaviour. This article is part of the theme issue 'The political brain: neurocognitive and computational mechanisms'.

Reconstructing neural representations of tactile space.

Psychophysical experiments have demonstrated large and highly systematic perceptual distortions of tactile space. Such a space can be referred to our experience of the spatial organisation of objects, at representational level, through touch, in analogy with the familiar concept of visual space. We investigated the neural basis of tactile space by analysing activity patterns induced by tactile stimulation of nine points on a 3 × 3 square grid on the hand dorsum using functional magnetic resonance imaging. We used a searchlight approach within pre-defined regions of interests to compute the pairwise Euclidean distances between the activity patterns elicited by tactile stimulation. Then, we used multidimensional scaling to reconstruct tactile space at the neural level and compare it with skin space at the perceptual level. Our reconstructions of the shape of skin space in contralateral primary somatosensory and motor cortices reveal that it is distorted in a way that matches the perceptual shape of skin space. This suggests that early sensorimotor areas critically contribute to the distorted internal representation of tactile space on the hand dorsum.

Embodying an invisible face shrinks the cone of gaze.

The possibility of being invisible has long fascinated people. Recent research showed that multisensory illusions can induce experiences of bodily invisibility, allowing the psychological consequences of invisibility to be explored. Here, we demonstrate an illusion of embodying an invisible face. Participants received touches on their face and simultaneously saw a paintbrush moving synchronously in empty space and defining the shape of an invisible face. Using both explicit questionnaire measures (Experiment 1) and implicit physiological measures (Experiment 2), we show that such invisible enfacement induces a sense of ownership. We further demonstrate that embodying an invisible face shrinks the width of the cone of gaze (i.e., the range of eye deviations people judge as directed toward themselves; Experiments 3 and 4). These results suggest that the experience of invisibility affects the way in which we process the attention of others toward the self, starting from the perception of gaze direction. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Tactile distance adaptation aftereffects do not transfer to perceptual hand maps.

Recent studies have demonstrated that mental representations of the hand dorsum are distorted even for healthy participants. Perceptual hand maps estimated by pointing to specific landmarks (e.g., knuckles and tips of fingers) is stretched and shrunk along the medio-lateral and the proximo-distal axes, respectively. Similarly, tactile distance perception between two touches is longer along the medio-lateral axis than the proximo-distal axis. The congruency of the two types of distortions suggests that common perceptual and neural representations may be involved in these processes. Prolonged stimulation by two simultaneous touches having a particular distance can bias subsequent perception of tactile distances (e.g., adaptation to a long distance induces shorter stimuli to be perceived even shorter). This tactile distance adaptation aftereffect has been suggested to occur based on the modulations of perceptual and neural responses at low somatosensory processing stages. The current study investigated whether tactile distance adaptation aftereffects affect also the pattern of distortions on the perceptual hand maps. Participants localized locations on the hand dorsum cued by tactile stimulations (Experiment 1) or visually presented landmarks on a hand silhouette (Experiment 2). Each trial was preceded by adaptation to either a small (2 cm) or large (4 cm) tactile distance. We found clear tactile distance aftereffects. However, no changes were observed for the distorted pattern of the perceptual hand maps following adaptation to a tactile distance. Our results showed that internal body representations involved in perceptual distortions may be distinct between tactile distance perception and the perceptual hand maps underlying position sense.

Decoding stimulus identity in occipital, parietal and inferotemporal cortices during visual mental imagery.

In the absence of input from the external world, humans are still able to generate vivid mental images. This cognitive process, known as visual mental imagery, involves a network of prefrontal, parietal, inferotemporal, and occipital regions. Using multivariate pattern analysis (MVPA), previous studies were able to distinguish between the different orientations of imagined gratings, but not between more complex imagined stimuli, such as common objects, in early visual cortex (V1). Here we asked whether letters, simple shapes, and objects can be decoded in early visual areas during visual mental imagery. In a delayed spatial judgment task, we asked participants to observe or imagine stimuli. To examine whether it is possible to discriminate between neural patterns during perception and visual mental imagery, we performed ROI-based and whole-brain searchlight-based MVPA. We were able to decode imagined stimuli in early visual (V1, V2), parietal (SPL, IPL, aIPS), inferotemporal (LOC) and prefrontal (PMd) areas. In a subset of these areas (i.e., V1, V2, LOC, SPL, IPL and aIPS), we also obtained significant cross-decoding across visual imagery and perception. Moreover, we observed a linear relationship between behavioral accuracy and the amplitude of the BOLD signal in parietal and inferotemporal cortices, but not in early visual cortex, in line with the view that these areas contribute to the ability to perform visual imagery. Together, our results suggest that in the absence of bottom-up visual inputs, patterns of functional activation in early visual cortex allow distinguishing between different imagined stimulus exemplars, most likely mediated by signals from parietal and inferotemporal areas.

Culture modulates face scanning during dyadic social interactions.

Recent studies have revealed significant cultural modulations on face scanning strategies, thereby challenging the notion of universality in face perception. Current findings are based on screen-based paradigms, which offer high degrees of experimental control, but lack critical characteristics common to social interactions (e.g., social presence, dynamic visual saliency), and complementary approaches are required. The current study used head-mounted eye tracking techniques to investigate the visual strategies for face scanning in British/Irish (in the UK) and Japanese adults (in Japan) who were engaged in dyadic social interactions with a local research assistant. We developed novel computational data pre-processing tools and data-driven analysis techniques based on Monte Carlo permutation testing. The results revealed significant cultural differences in face scanning during social interactions for the first time, with British/Irish participants showing increased mouth scanning and the Japanese group engaging in greater eye and central face looking. Both cultural groups further showed more face orienting during periods of listening relative to speaking, and during the introduction task compared to a storytelling game, thereby replicating previous studies testing Western populations. Altogether, these findings point to the significant role of postnatal social experience in specialised face perception and highlight the adaptive nature of the face processing system.

Mapping visual spatial prototypes: Multiple reference frames shape visual memory.

Categories provide a fundamental source of information used to structure our perception of the world. For example, when people reproduce the remembered location of a dot in a circle, they implicitly impose vertical and horizontal axes onto the circle, and responses are biased towards the center of each of the resulting quadrants. Such results reveal the existence of spatial prototypes, which function as Bayesian priors and which are integrated with actual memory traces. Spatial prototypes have been extensively investigated and described in previous studies, but it remains unclear what type of information is used to create spatial categories. We developed a new approach that allowed to 'image' patterns of spatial bias in detail, and map the internal representational structure of objects and space. Previous studies, using circular shapes suggested that boundaries are established based on a viewer-based frame of reference, therefore using cues extrinsic to the object. Given that a circle has radial symmetry, the axes imposed cannot come from the shape itself. Here we investigated if the same applies for shapes with clearly-defined symmetry axes and thus intrinsic frames of reference. Using rotated shapes (squares and rectangles), where extrinsic and intrinsic cues are dissociated, we observed flexible usage of multiple reference frames. Furthermore, in certain contexts, participants relied mostly on cues intrinsic to the shape itself. These results show that humans divide visual space as a function of multiple reference frames, in a flexible, and context dependent manner.

The representational space of observed actions.

Categorizing and understanding other people's actions is a key human capability. Whereas there exists a growing literature regarding the organization of objects, the representational space underlying the organization of observed actions remains largely unexplored. Here we examined the organizing principles of a large set of actions and the corresponding neural representations. Using multiple regression representational similarity analysis of fMRI data, in which we accounted for variability due to major action components (body parts, scenes, movements, objects, sociality, transitivity) and three control models (distance between observer and actor, number of people, HMAX-C1), we found that the semantic dissimilarity structure was best captured by patterns of activation in the lateral occipitotemporal cortex (LOTC). Together, our results demonstrate that the organization of observed actions in the LOTC resembles the organizing principles used by participants to classify actions behaviorally, in line with the view that this region is crucial for accessing the meaning of actions.

MEG adaptation reveals action representations in posterior occipitotemporal regions.

When we observe other people's actions, a number of parietal and precentral regions known to be involved in the planning and execution of actions are recruited for example seen as power decreases in alpha and beta frequencies indicative of increased activation. It has been argued that this recruitment reflects the process of simulating the observed action, thereby providing access to the meaning of the action. Alternatively, it has been suggested that rather than providing access to the meaning of an action, parietal and precentral regions might be recruited as a consequence of action understanding. A way to distinguish between these alternatives is to examine where in the brain and at which time point it is possible to discriminate between different types of actions (e.g., pointing or grasping) irrespective of the way these are performed. To this aim, we presented participants with videos of simple hand actions performed with the left or right hand towards a target on the left or the right side while recording magnetoencephalography (MEG) data. In each trial, participants were presented with two subsequent videos (S1, S2) depicting either the same (repeat trials) or different (non-repeat trials) actions. We predicted that areas that are sensitive to the type of action should show stronger adaptation (i.e., a smaller decrease in alpha and beta power) in repeat in comparison to non-repeat trials. Indeed, we observed less alpha and beta power decreases during the presentation of S2 when the action was repeated compared to when two different actions were presented indicating adaptation of neuronal populations that are selective for the type of action. Sources were obtained exclusively in posterior occipitotemporal regions, supporting the notion that an early differentiation of actions occurs outside the motor system.

Beta band modulations underlie action representations for movement planning.

To be able to interact with our environment, we need to transform incoming sensory information into goal-directed motor outputs. Whereas our ability to plan an appropriate movement based on sensory information appears effortless and simple, the underlying brain dynamics are still largely unknown. Here we used magnetoencephalography (MEG) to investigate this issue by recording brain activity during the planning of non-visually guided reaching and grasping actions, performed with either the left or right hand. Adopting a combination of univariate and multivariate analyses, we revealed specific patterns of beta power modulations underlying varying levels of neural representations during movement planning. (1) Effector-specific modulations were evident as a decrease in power in the beta band. Within both hemispheres, this decrease was stronger while planning a movement with the contralateral hand. (2) The comparison of planned grasping and reaching led to a relative increase in power in the beta band. These power changes were localized within temporal, premotor and posterior parietal cortices. Action-related modulations overlapped with effector-related beta power changes within widespread frontal and parietal regions, suggesting the possible integration of these two types of neural representations. (3) Multivariate analyses of action-specific power changes revealed that part of this broadband beta modulation also contributed to the encoding of an effector-independent neural representation of a planned action within fronto-parietal and temporal regions. Our results suggest that beta band power modulations play a central role in movement planning, within both the dorsal and ventral stream, by coding and integrating different levels of neural representations, ranging from the simple representation of the to-be-moved effector up to an abstract, effector-independent representation of the upcoming action.

MEG Multivariate Analysis Reveals Early Abstract Action Representations in the Lateral Occipitotemporal Cortex.

Understanding other people's actions is a fundamental prerequisite for social interactions. Whether action understanding relies on simulating the actions of others in the observers' motor system or on the access to conceptual knowledge stored in nonmotor areas is strongly debated. It has been argued previously that areas that play a crucial role in action understanding should (1) distinguish between different actions, (2) generalize across the ways in which actions are performed (Dinstein et al., 2008; Oosterhof et al., 2013; Caramazza et al., 2014), and (3) have access to action information around the time of action recognition (Hauk et al., 2008). Whereas previous studies focused on the first two criteria, little is known about the dynamics underlying action understanding. We examined which human brain regions are able to distinguish between pointing and grasping, regardless of reach direction (left or right) and effector (left or right hand), using multivariate pattern analysis of magnetoencephalography data. We show that the lateral occipitotemporal cortex (LOTC) has the earliest access to abstract action representations, which coincides with the time point from which there was enough information to allow discriminating between the two actions. By contrast, precentral regions, though recruited early, have access to such abstract representations substantially later. Our results demonstrate that in contrast to the LOTC, the early recruitment of precentral regions does not contain the detailed information that is required to recognize an action. We discuss previous theoretical claims of motor theories and how they are incompatible with our data. SIGNIFICANCE STATEMENT: It is debated whether our ability to understand other people's actions relies on the simulation of actions in the observers' motor system, or is based on access to conceptual knowledge stored in nonmotor areas. Here, using magnetoencephalography in combination with machine learning, we examined where in the brain and at which point in time it is possible to distinguish between pointing and grasping actions regardless of the way in which they are performed (effector, reach direction). We show that, in contrast to the predictions of motor theories of action understanding, the lateral occipitotemporal cortex has access to abstract action representations substantially earlier than precentral regions.