Visual appearance modulates motor control in social interactions.

The goal of new adaptive technologies is to allow humans to interact with technical devices, such as robots, in natural ways akin to human interaction. Essential for achieving this goal, is the understanding of the factors that support natural interaction. Here, we examined whether human motor control is linked to the visual appearance of the interaction partner. Motor control theories consider kinematic-related information but not visual appearance as important for the control of motor movements (Flash & Hogan, 1985; Harris & Wolpert, 1998; Viviani & Terzuolo, 1982). We investigated the sensitivity of motor control to visual appearance during the execution of a social interaction, i.e. a high-five. In a novel mixed reality setup participants executed a high-five with a three-dimensional life-size human- or a robot-looking avatar. Our results demonstrate that movement trajectories and adjustments to perturbations depended on the visual appearance of the avatar despite both avatars carrying out identical movements. Moreover, two well-known motor theories (minimum jerk, two-thirds power law) better predict robot than human interaction trajectories. The dependence of motor control on the human likeness of the interaction partner suggests that different motor control principles might be at work in object and human directed interactions.

Are allocentric spatial reference frames compatible with theories of Enactivism?

Theories of Enactivism propose an action-oriented approach to understand human cognition. So far, however, empirical evidence supporting these theories has been sparse. Here, we investigate whether spatial navigation based on allocentric reference frames that are independent of the observer's physical body can be understood within an action-oriented approach. Therefore, we performed three experiments testing the knowledge of the absolute orientation of houses and streets towards north, the relative orientation of two houses and two streets, respectively, and the location of houses towards each other in a pointing task. Our results demonstrate that under time pressure, the relative orientation of two houses can be retrieved more accurately than the absolute orientation of single houses. With infinite time for cognitive reasoning, the performance of the task using house stimuli increased greatly for the absolute orientation and surpassed the slightly improved performance in the relative orientation task. In contrast, with streets as stimuli participants performed under time pressure better in the absolute orientation task. Overall, pointing from one house to another house yielded the best performance. This suggests, first, that orientation and location information about houses are primarily coded in house-to-house relations, whereas cardinal information is deduced via cognitive reasoning. Second, orientation information for streets is preferentially coded in absolute orientations. Thus, our results suggest that spatial information about house and street orientation is coded differently and that house orientation and location is primarily learned in an action-oriented way, which is in line with an enactive framework for human cognition.

Spatial memory for vertical locations.

Most studies on spatial memory refer to the horizontal plane, leaving an open question as to whether findings generalize to vertical spaces where gravity and the visual upright of our surrounding space are salient orientation cues. In three experiments, we examined which reference frame is used to organize memory for vertical locations: the one based on the body vertical, the visual-room vertical, or the direction of gravity. Participants judged interobject spatial relationships learned from a vertical layout in a virtual room. During learning and testing, we varied the orientation of the participant's body (upright vs. lying sideways) and the visually presented room relative to gravity (e.g., rotated by 90° along the frontal plane). Across all experiments, participants made quicker or more accurate judgments when the room was oriented in the same way as during learning with respect to their body, irrespective of their orientations relative to gravity. This suggests that participants employed an egocentric body-based reference frame for representing vertical object locations. Our study also revealed an effect of body-gravity alignment during testing. Participants recalled spatial relations more accurately when upright, regardless of the body and visual-room orientation during learning. This finding is consistent with a hypothesis of selection conflict between different reference frames. Overall, our results suggest that a body-based reference frame is preferred over salient allocentric reference frames in memory for vertical locations perceived from a single view. Further, memory of vertical space seems to be tuned to work best in the default upright body orientation. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Memory for navigable space is flexible and not restricted to exclusive local or global memory units.

Objects learned within single enclosed spaces (e.g., rooms) can be represented within a single reference frame. Contrarily, the representation of navigable spaces (multiple interconnected enclosed spaces) is less well understood. In this study we examined different levels of integration within memory (local, regional, global), when learning object locations in navigable space. Participants consecutively learned two distinctive regions of a virtual environment that eventually converged at a common transition point and subsequently solved a pointing task. In Experiment 1 pointing latency increased with increasing corridor distance to the target and additionally when pointing into the other region. Further, when pointing within a region alignment with local and regional reference frames, when pointing across regional boundaries alignment with a global reference frame was found to accelerate pointing. Thus, participants memorized local corridors, clustered corridors into regions, and integrated globally across the entire environment. Introducing the transition point at the beginning of learning each region in Experiment 2 caused previous region effects to vanish. Our findings emphasize the importance of locally confined spaces for structuring spatial memory and suggest that the opportunity to integrate novel into existing spatial information early during learning may influence unit formation on the regional level. Further, global representations seem to be consulted only when accessing spatial information beyond regional borders. Our results are inconsistent with conceptions of spatial memory for large scale environments based either exclusively on local reference frames or upon a single reference frame encompassing the whole environment, but rather support hierarchical representation of space. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The Object Orientation Effect in Exocentric Distances.

The object orientation effect describes shorter perceived distances to the front than to the back of oriented objects. The present work extends previous studies in showing that the object orientation effect occurs not only for egocentric distances between an observer and an object, but also for exocentric distances, that are between two oriented objects. Participants watched animated virtual humans (avatars) which were either facing each other or looking away, and afterward adjusted a bar to estimate the perceived length. In two experiments, participants judged avatars facing each other as closer than avatars facing away from each other. As the judged distance was between two objects and did not involve the observer, results rule out an explanation that observers perceive object fronts as closer to prepare for future interaction with them. The second experiment tested an explanation by predictive coding, this is the extrapolation of the current state of affairs to likely future states here that avatars move forward. We used avatars standing on bridges either connecting them or running orthogonal to the inter-avatar line thus preventing forward movement. This variation of walkability did not influence participants' judgments. We conclude that if predictive coding was used by participants, they did not consider the whole scene layout for prediction, but concentrated on avatars. Another potential explanation of the effect assumes a general asymmetrical distribution of inter-person distances: people facing each other might typically be closer to each other than when facing away and that this asymmetry is reflected as a bias in perception.

Body-relative horizontal-vertical anisotropy in human representations of traveled distances.

A growing number of studies investigated anisotropies in representations of horizontal and vertical spaces. In humans, compelling evidence for such anisotropies exists for representations of multi-floor buildings. In contrast, evidence regarding open spaces is indecisive. Our study aimed at further enhancing the understanding of horizontal and vertical spatial representations in open spaces utilizing a simple traveled distance estimation paradigm. Blindfolded participants were moved along various directions in the sagittal plane. Subsequently, participants passively reproduced the traveled distance from memory. Participants performed this task in an upright and in a 30° backward-pitch orientation. The accuracy of distance estimates in the upright orientation showed a horizontal-vertical anisotropy, with higher accuracy along the horizontal axis compared with the vertical axis. The backward-pitch orientation enabled us to investigate whether this anisotropy was body or earth-centered. The accuracy patterns of the upright condition were positively correlated with the body-relative (not the earth-relative) coordinate mapping of the backward-pitch condition, suggesting a body-centered anisotropy. Overall, this is consistent with findings on motion perception. It suggests that the distance estimation sub-process of path integration is subject to horizontal-vertical anisotropy. Based on the previous studies that showed isotropy in open spaces, we speculate that real physical self-movements or categorical versus isometric encoding are crucial factors for (an)isotropies in spatial representations.

No advantage for remembering horizontal over vertical spatial locations learned from a single viewpoint.

Previous behavioral and neurophysiological research has shown better memory for horizontal than for vertical locations. In these studies, participants navigated toward these locations. In the present study we investigated whether the orientation of the spatial plane per se was responsible for this difference. We thus had participants learn locations visually from a single perspective and retrieve them from multiple viewpoints. In three experiments, participants studied colored tags on a horizontally or vertically oriented board within a virtual room and recalled these locations with different layout orientations (Exp. 1) or from different room-based perspectives (Exps. 2 and 3). All experiments revealed evidence for equal recall performance in horizontal and vertical memory. In addition, the patterns for recall from different test orientations were rather similar. Consequently, our results suggest that memory is qualitatively similar for both vertical and horizontal two-dimensional locations, given that these locations are learned from a single viewpoint. Thus, prior differences in spatial memory may have originated from the structure of the space or the fact that participants navigated through it. Additionally, the strong performance advantages for perspective shifts (Exps. 2 and 3) relative to layout rotations (Exp. 1) suggest that configurational judgments are not only based on memory of the relations between target objects, but also encompass the relations between target objects and the surrounding room-for example, in the form of a memorized view.

A catch-up illusion arising from a distance-dependent perception bias in judging relative movement.

The perception of relative target movement from a dynamic observer is an unexamined psychological three body problem. To test the applicability of explanations for two moving bodies participants repeatedly judged the relative movements of two runners chasing each other in video clips displayed on a stationary screen. The chased person always ran at 3 m/s with an observer camera following or leading at 4.5, 3, 1.5 or 0 m/s. We harmonized the chaser speed in an adaptive staircase to determine the point of subjective equal movement speed between runners and observed (i) an underestimation of chaser speed if the runners moved towards the viewer, and (ii) an overestimation of chaser speed if the runners moved away from the viewer, leading to a catch-up illusion in case of equidistant runners. The bias was independent of the richness of available self-movement cues. Results are inconsistent with computing individual speeds, relying on constant visual angles, expansion rates, occlusions, or relative distances but are consistent with inducing the impression of relative movement through perceptually compressing and enlarging inter-runner distance. This mechanism should be considered when predicting human behavior in complex situations with multiple objects moving in depth such as driving or team sports.

A systematic investigation of navigation impairment in chronic stroke patients: Evidence for three distinct types.

OBJECTIVE: In a recent systematic review, Claessen and van der Ham (2017) have analyzed the types of navigation impairment in the single-case study literature. Three dissociable types related to landmarks, locations, and paths were identified. This recent model as well as previous models of navigation impairment have never been verified in a systematic manner. The aim of the current study was thus to investigate the prevalence of landmark-based, location-based, and path-based navigation impairment in a large sample of stroke patients. METHOD: Navigation ability of 77 stroke patients in the chronic phase and 60 healthy participants was comprehensively evaluated using the Virtual Tübingen test, which contains twelve subtasks addressing various aspects of knowledge about landmarks, locations, and paths based on a newly learned virtual route. Participants also filled out the Wayfinding Questionnaire to allow for making a distinction between stroke patients with and without significant subjective navigation-related complaints. RESULTS: Analysis of responses on the Wayfinding Questionnaire indicated that 33 of the 77 participating stroke patients had significant navigation-related complaints. An examination of their performance on the Virtual Tübingen test established objective evidence for navigation impairment in 27 patients. Both landmark-based and path-based navigation impairment occurred in isolation, while location-based navigation impairment was only found along with the other two types. CONCLUSIONS: The current study provides the first empirical support for the distinction between landmark-based, location-based, and path-based navigation impairment. Future research relying on other assessment instruments of navigation ability might be helpful to further validate this distinction.

Learning New Sensorimotor Contingencies: Effects of Long-Term Use of Sensory Augmentation on the Brain and Conscious Perception.

Theories of embodied cognition propose that perception is shaped by sensory stimuli and by the actions of the organism. Following sensorimotor contingency theory, the mastery of lawful relations between own behavior and resulting changes in sensory signals, called sensorimotor contingencies, is constitutive of conscious perception. Sensorimotor contingency theory predicts that, after training, knowledge relating to new sensorimotor contingencies develops, leading to changes in the activation of sensorimotor systems, and concomitant changes in perception. In the present study, we spell out this hypothesis in detail and investigate whether it is possible to learn new sensorimotor contingencies by sensory augmentation. Specifically, we designed an fMRI compatible sensory augmentation device, the feelSpace belt, which gives orientation information about the direction of magnetic north via vibrotactile stimulation on the waist of participants. In a longitudinal study, participants trained with this belt for seven weeks in natural environment. Our EEG results indicate that training with the belt leads to changes in sleep architecture early in the training phase, compatible with the consolidation of procedural learning as well as increased sensorimotor processing and motor programming. The fMRI results suggest that training entails activity in sensory as well as higher motor centers and brain areas known to be involved in navigation. These neural changes are accompanied with changes in how space and the belt signal are perceived, as well as with increased trust in navigational ability. Thus, our data on physiological processes and subjective experiences are compatible with the hypothesis that new sensorimotor contingencies can be acquired using sensory augmentation.

Qualitative differences in memory for vista and environmental spaces are caused by opaque borders, not movement or successive presentation.

Two classes of space define our everyday experience within our surrounding environment: vista spaces, such as rooms or streets which can be perceived from one vantage point, and environmental spaces, for example, buildings and towns which are grasped from multiple views acquired during locomotion. However, theories of spatial representations often treat both spaces as equal. The present experiments show that this assumption cannot be upheld. Participants learned exactly the same layout of objects either within a single room or spread across multiple corridors. By utilizing a pointing and a placement task we tested the acquired configurational memory. In Experiment 1 retrieving memory of the object layout acquired in environmental space was affected by the distance of the traveled path and the order in which the objects were learned. In contrast, memory retrieval of objects learned in vista space was not bound to distance and relied on different ordering schemes (e.g., along the layout structure). Furthermore, spatial memory of both spaces differed with respect to the employed reference frame orientation. Environmental space memory was organized along the learning experience rather than layout intrinsic structure. In Experiment 2 participants memorized the object layout presented within the vista space room of Experiment 1 while the learning procedure emulated environmental space learning (movement, successive object presentation). Neither factor rendered similar results as found in environmental space learning. This shows that memory differences between vista and environmental space originated mainly from the spatial compartmentalization which was unique to environmental space learning. Our results suggest that transferring conclusions from findings obtained in vista space to environmental spaces and vice versa should be made with caution.

Multiple Strategies for Spatial Integration of 2D Layouts within Working Memory.

Prior results on the spatial integration of layouts within a room differed regarding the reference frame that participants used for integration. We asked whether these differences also occur when integrating 2D screen views and, if so, what the reasons for this might be. In four experiments we showed that integrating reference frames varied as a function of task familiarity combined with processing time, cues for spatial transformation, and information about action requirements paralleling results in the 3D case. Participants saw part of an object layout in screen 1, another part in screen 2, and reacted on the integrated layout in screen 3. Layout presentations between two screens coincided or differed in orientation. Aligning misaligned screens for integration is known to increase errors/latencies. The error/latency pattern was thus indicative of the reference frame used for integration. We showed that task familiarity combined with self-paced learning, visual updating, and knowing from where to act prioritized the integration within the reference frame of the initial presentation, which was updated later, and from where participants acted respectively. Participants also heavily relied on layout intrinsic frames. The results show how humans flexibly adjust their integration strategy to a wide variety of conditions.

The Influence of Human Body Orientation on Distance Judgments.

People maintain larger distances to other peoples' front than to their back. We investigated if humans also judge another person as closer when viewing their front than their back. Participants watched animated virtual characters (avatars) and moved a virtual plane toward their location after the avatar was removed. In Experiment 1, participants judged avatars, which were facing them as closer and made quicker estimates than to avatars looking away. In Experiment 2, avatars were rotated in 30 degree steps around the vertical axis. Observers judged avatars roughly facing them (i.e., looking max. 60 degrees away) as closer than avatars roughly looking away. No particular effect was observed for avatars directly facing and also gazing at the observer. We conclude that body orientation was sufficient to generate the asymmetry. Sensitivity of the orientation effect to gaze and to interpersonal distance would have suggested involvement of social processing, but this was not observed. We discuss social and lower-level processing as potential reasons for the effect.

How to Best Name a Place? Facilitation and Inhibition of Route Learning Due to Descriptive and Arbitrary Location Labels.

Establishing verbal memory traces for non-verbal stimuli was reported to facilitate or inhibit memory for the non-verbal stimuli. We show that these effects are also observed in a domain not indicated before-wayfinding. Fifty-three participants followed a guided route in a virtual environment. They were asked to remember half of the intersections by relying on the visual impression only. At the other 50% of the intersections, participants additionally heard a place name, which they were asked to memorize. For testing, participants were teleported to the intersections and were asked to indicate the subsequent direction of the learned route. In Experiment 1, intersections' names were arbitrary (i.e., not related to the visual impression). Here, participants performed more accurately at unnamed intersections. In Experiment 2, intersections' names were descriptive and participants' route memory was more accurate at named intersections. Results have implications for naming places in a city and for wayfinding aids.

Not all memories are the same: Situational context influences spatial recall within one's city of residency.

Reference frames in spatial memory encoding have been examined intensively in recent years. However, their importance for recall has received considerably less attention. In the present study, passersby used tags to arrange a configuration map of prominent city center landmarks. It has been shown that such configurational knowledge is memorized within a north-up reference frame. However, participants adjusted their maps according to their body orientations. For example, when participants faced south, the maps were likely to face south-up. Participants also constructed maps along their location perspective-that is, the self-target direction. If, for instance, they were east of the represented area, their maps were oriented west-up. If the location perspective and body orientation were in opposite directions (i.e., if participants faced away from the city center), participants relied on location perspective. The results indicate that reference frames in spatial recall depend on the current situation rather than on the organization in long-term memory. These results cannot be explained by activation spread within a view graph, which had been used to explain similar results in the recall of city plazas. However, the results are consistent with forming and transforming a spatial image of nonvisible city locations from the current location. Furthermore, prior research has almost exclusively focused on body- and environment-based reference frames. The strong influence of location perspective in an everyday navigational context indicates that such a reference frame should be considered more often when examining human spatial cognition.

Reference frames in learning from maps and navigation.

In everyday life, navigators often consult a map before they navigate to a destination (e.g., a hotel, a room, etc.). However, not much is known about how humans gain spatial knowledge from seeing a map and direct navigation together. In the present experiments, participants learned a simple multiple corridor space either from a map only, only from walking through the virtual environment, first from the map and then from navigation, or first from navigation and then from the map. Afterwards, they conducted a pointing task from multiple body orientations to infer the underlying reference frames. We constructed the learning experiences in a way such that map-only learning and navigation-only learning triggered spatial memory organized along different reference frame orientations. When learning from maps before and during navigation, participants employed a map- rather than a navigation-based reference frame in the subsequent pointing task. Consequently, maps caused the employment of a map-oriented reference frame found in memory for highly familiar urban environments ruling out explanations from environmental structure or north preference. When learning from navigation first and then from the map, the pattern of results reversed and participants employed a navigation-based reference frame. The priority of learning order suggests that despite considerable difference between map and navigation learning participants did not use the more salient or in general more useful information, but relied on the reference frame established first.

When in doubt follow your nose-a wayfinding strategy.

Route selection is governed by various strategies which often allow minimizing the required memory capacity. Previous research showed that navigators primarily remember information at route decision points and at route turns, rather than at intersections which required straight walking. However, when actually navigating the route or indicating directional decisions, navigators make fewer errors when they are required to walk straight. This tradeoff between location memory and route decisions accuracy was interpreted as a "when in doubt follow your nose" strategy which allows navigators to only memorize turns and walk straight by default, thus considerably reducing the number of intersections to memorize. These findings were based on newly learned routes. In the present study, we show that such an asymmetry in route memory also prevails for planning routes within highly familiar environments. Participants planned route sequences between locations in their city of residency by pressing arrow keys on a keyboard. They tended to ignore straight walking intersections, but they ignored turns much less so. However, for reported intersections participants were quicker at indicating straight walking than turning. Together with results described in the literature, these findings suggest that a "when in doubt follow your nose strategy" is applied also within highly familiar spaces and might originate from limited working memory capacity during planning a route.

Local and global reference frames for environmental spaces.

Two experiments examined how locations in environmental spaces, which cannot be overseen from one location, are represented in memory: by global reference frames, multiple local reference frames, or orientation-free representations. After learning an immersive virtual environment by repeatedly walking a closed multisegment route, participants pointed to seven previously learned targets from different locations. Contrary to many conceptions of survey knowledge, local reference frames played an important role: Participants performed better when their body or pointing targets were aligned with the local reference frame (corridor). Moreover, most participants turned their head to align it with local reference frames. However, indications for global reference frames were also found: Participants performed better when their body or current corridor was parallel/orthogonal to a global reference frame instead of oblique. Participants showing this pattern performed comparatively better. We conclude that survey tasks can be solved based on interconnected local reference frames. Participants who pointed more accurately or quickly additionally used global reference frames.

Verbal shadowing and visual interference in spatial memory.

Spatial memory is thought to be organized along experienced views and allocentric reference axes. Memory access from different perspectives typically yields V-patterns for egocentric encoding (monotonic decline in performance along with the angular deviation from the experienced perspectives) and W-patterns for axes encoding (better performance along parallel and orthogonal perspectives than along oblique perspectives). We showed that learning an object array with a verbal secondary task reduced W-patterns compared with learning without verbal shadowing. This suggests that axes encoding happened in a verbal format; for example, by rows and columns. Alternatively, general cognitive load from the secondary task prevented memorizing relative to a spatial axis. Independent of encoding, pointing with a surrounding room visible yielded stronger W-patterns compared with pointing with no room visible. This suggests that the visible room geometry interfered with the memorized room geometry. With verbal shadowing and without visual interference only V-patterns remained; otherwise, V- and W-patterns were combined. Verbal encoding and visual interference explain when W-patterns can be expected alongside V-patterns and thus can help in resolving different performance patterns in a wide range of experiments.

Psychological influences on distance estimation in a virtual reality environment.

Studies of embodied perception have revealed that social, psychological, and physiological factors influence space perception. While many of these influences were observed with real or highly realistic stimuli, the present work showed that even the orientation of abstract geometric objects in a non-realistic virtual environment could influence distance perception. Observers wore a head mounted display and watched virtual cones moving within an invisible cube for 5 s with their head movement recorded. Subsequently, the observers estimated the distance to the cones or evaluated their friendliness. The cones either faced the observer, a target behind the cones, or were oriented randomly. The average viewing distance to the cones varied between 1.2 and 2.0 m. At a viewing distance of 1.6 m, the observers perceived the cones facing them as closer than the cones facing a target in the opposite direction, or those oriented randomly. Furthermore, irrespective of the viewing distance, observers moved their head away from the cones more strongly and evaluated the cones as less friendly when the cones faced the observers. Similar distance estimation results were obtained with a 3-dimensional projection onto a large screen, although the effective viewing distances were farther away. These results suggest that factors other than physical distance influenced distance perception even with non-realistic geometric objects in a virtual environment. Furthermore, the distance perception modulation was accompanied by changes in subjective impression and avoidance movement. We propose that cones facing an observer are perceived as socially discomforting or threatening, and potentially violate an observer's personal space, which might influence the perceived distance of cones.