Frames of Reference for Human Perceptual-Motor Coordination: Space-Based Versus Joint-Based Adaptation

In this study, the authors addressed the issue of whether space-based motor planning occurs at a higher, equal, or lower level of central nervous system control than joint-based motor planning by using a computerized adaptation paradigm. Visual displays of participants' (N = 32) reaching movements to spatial targets were distorted either with respect to spatial hand displacements (space-based distortion) or with respect to joint angle displacements (joint-based distortion). Participants adapted more easily to space-based distortion than to joint-based distortion. The results suggest that when the participants were confronted with new visuomotor mappings, they aimed for virtual spatial targets whose positions were adjusted to compensate for the distortions associated with the new mappings. That strategy was preferred over a joint- or posture-based strategy, in which a posture is selected for the displayed spatial target and is then modified so that the new mapping between adopted and seen positions can be accommodated. The results support the widely held view that space-based planning occurs at a higher level than joint-based planning.     

Impact of action planning on spatial perception: Attention matters

Previous research suggested that perception of spatial location is biased towards spatial goals of planned hand movements. In the present study I show that an analogous perceptual distortion can be observed if attention is paid to a spatial location in the absence of planning a hand movement. Participants judged the position of a target during preparation of a mouse movement, the end point of which could deviate from the target by a varying degree in Exp. 1. Judgments of target position were systematically affected by movement characteristics consistent with perceptual assimilation between the target and the planned movement goal. This effect was neither due to an impact of motor execution on judgments (Exp. 2) nor due to characteristics of the movement cues or of certain target positions (Exp. 3, Exp. 5A). When the task included deployment of attention to spatial positions (former movement goals) in preparation for a secondary perceptual task, an effect emerged that was comparable with the bias associated with movement planning (Exp. 4, Exp. 5B). These results indicate that visual distortions accompanying manipulations of variables related to action could be mediated by attentional mechanisms.     

Object-based processes in the planning of goal-directed hand movements

Theories in motor control suggest that the parameters specified during the planning of goal-directed hand movements to a visual target are defined in spatial parameters like direction and amplitude. Recent findings in the visual attention literature, however, argue widely for early object-based selection processes. The present experiments were designed to examine the contributions of object-based and space-based selection processes to the preparation time of goal-directed pointing movements. Therefore, a cue was presented at a specific location. The question addressed was whether the initiation of responses to uncued target stimuli could benefit from being either within the same object (object based) or presented at the same direction (space based). Experiment 1 replicated earlier findings of object-based benefits for non-goal-directed responses. Experiment 2 confirmed earlier findings of space-based benefits for goal-directed hand pointing movements. In Experiments 3 and 4, space-based and object-based manipulations were combined while requiring goal-directed hand pointing movements. The results clearly favour the notion that the selection processes for goal-directed pointing movements are primarily object based. Implications for theories on selective attention and action planning are discussed.     

Perceived spatial organization of cutaneous patterns on surfaces of the human body in various positions

The perceived spatial organization of cutaneous patterns was examined in three experiments. People identified letters or numbers traced on surfaces of their body when the relative spatial orientations and positions of the body surfaces and of the stimuli were varied. Stimuli on the front or back of the head were perceived with respect to a frame of reference positioned behind those surfaces, independent of the surfaces' position and orientation. This independence may relate to the way in which the sensory apparatus on the front of the head is used in planning action. Stimuli on other surfaces of the head and body were perceived in relation to the position and orientation of the surface with respect to the whole body or trunk (most of which was usually upright). Stimuli on all transverse/horizontal surfaces were perceived with respect to frames of reference associated with the head/upper chest area. These frames were also used for stimuli on frontoparallel surfaces in front of the upper body. These observations may result from the use of "central" frames of reference that are independent of the head and are associated with the upper body. Stimuli on surfaces in other positions and orientations (with two exceptions) were perceived "externally"--that is, in frames of reference directly facing the stimulated surface. The spatial information processing we found may be fairly general because several of our main findings were also observed in very young children and blind adults and in paradigms studying perception by "active touch" and the spatial organization of the motor production of patterns.     

Spatial distortions induced by multiple visual landmarks: how local distortions combine to produce complex distortion patterns

Visual landmarks introduce systematic distortions into spatial short-term memory for single target positions, the exact form of the distortion depending on the spatial layout of the landmarks. In two experiments, we investigated how the combined effect of two landmarks can be predicted from the effects of individual landmarks. Participants used a mouse cursor to reproduce the positions of briefly presented targets in the context of one, the other, or both landmarks. We found that distortions near a landmark are independent of whether another landmark is present, so that remembered space is partitioned into regions dominated by single landmarks. Interestingly, the display midpoint behaves like a "virtual landmark," with its own pattern of distortion. Results are inconsistent with current models of spatial memory distortions but suggest that attentional processes can lead to enhanced fidelity of salient regions in topographical neural networks while also introducing some spatial biases.     

Memory for targets in a multilevel simulated environment: Evidence for vertical asymmetry in spatial memory

In two experiments, adult participants explored a symmetrical three-tiered computer-simulated building that contained six distinctive objects, two on each floor. Following exploration, the objects were removed, and the participants were asked to make direction judgments from each floor, indicating the former positions of the objects on that floor and on higher and lower floors. Relative tilt error scores indicated a bias, in that targets that were higher than the test location were judged as consistently lower than their actual positions and targets that were lower than the test location were judged as consistently higher than their actual positions. Absolute tilt errors revealed an asymmetry, with more accurate and less variable tilt errors for judgments directed to lower floors than for judgments directed to higher floors. Experiment 3 ruled out an account of the findings that does not relate them to spatial memory. The results suggest that the superiority of downward over upward spatial judgments, previously reported in two-dimensional visual-spatial tasks, extends to navigational spatial memory.     

Space- and object-based attention depend on motor intention

The authors investigated the impact of different motor demands on space- and object-based attention allocation. Responses to targets were either lifting a finger, or pointing to the target, or grasping a clay object placed on the target location. Reaction times and movement times were recorded to assess covert and overt attention, respectively. Both reaction times and movement times showed more space-based attention for pointing than for finger lifting and more object-based attention for grasping than for pointing. That result supports the view that visual selectivity is tuned to specific motor intentions (H. Bekkering & F. W. Neggers, 2002) and illustrates the tight coupling of perception and action.     

Aiming error under transformed spatial mappings suggests a structure for visual-motor maps

Transformed spatial mappings were used to perturb normal visual-motor processes and reveal the structure of internal spatial representations used by the motor control system. In a 2-D discrete aiming task performed under rotated visual-motor mappings, the pattern of spatial movement error was the same for all Ss: peak error between 90 degrees and 135 degrees of rotation and low error for 180 degrees rotation. A two-component spatial representation, based on oriented bidirectional movement axes plus direction of travel along such axes, is hypothesized. Observed reversals of movement direction under rotations greater than 90 degrees are consistent with the hypothesized structure. Aiming error under reflections, unlike rotations, depended on direction of movement relative to the axis of reflection (see Cunningham & Pavel, in press). Reaction time and movement time effects were observed, but a speed-accuracy tradeoff was found only for rotations for which the direction-reversal strategy could be used. Finally, adaptation to rotation operates at all target locations equally but does not alter the relative difficulty of different rotations. Structural properties of the representation are invariant under learning.     

Planning paths to multiple targets: memory involvement and planning heuristics in spatial problem solving

For large numbers of targets, path planning is a complex and computationally expensive task. Humans, however, usually solve such tasks quickly and efficiently. We present experiments studying human path planning performance and the cognitive processes and heuristics involved. Twenty-five places were arranged on a regular grid in a large room. Participants were repeatedly asked to solve traveling salesman problems (TSP), i.e., to find the shortest closed loop connecting a start location with multiple target locations. In Experiment 1, we tested whether humans employed the nearest neighbor (NN) strategy when solving the TSP. Results showed that subjects outperform the NN-strategy, suggesting that it is not sufficient to explain human route planning behavior. As a second possible strategy we tested a hierarchical planning heuristic in Experiment 2, demonstrating that participants first plan a coarse route on the region level that is refined during navigation. To test for the relevance of spatial working memory (SWM) and spatial long-term memory (LTM) for planning performance and the planning heuristics applied, we varied the memory demands between conditions in Experiment 2. In one condition the target locations were directly marked, such that no memory was required; a second condition required participants to memorize the target locations during path planning (SWM); in a third condition, additionally, the locations of targets had to retrieved from LTM (SWM and LTM). Results showed that navigation performance decreased with increasing memory demands while the dependence on the hierarchical planning heuristic increased.     

Cross-talk of instructed and applied arbitrary visuomotor mappings

Humans are able to perform any voluntary motor response to any environmental stimulus. This cornerstone of the flexibility of human behaviour has been investigated under the label of arbitrary visuomotor mapping. The focus of research has been the question as to how these mappings are executed once the subjects have been instructed appropriately. However, one question has been rather neglected thus far: what, in the first place, enables humans to instantaneously implement any arbitrary S-R mapping by mere instruction! We report an experiment assessing the cross-talk of arbitrary S-R mappings as a part of the instructed task representation, on the one hand, and the cross-talk of repetitively applied mappings, on the other hand. The results show a behavioural dissociation of the cross-talk elicited by instructed and applied mappings, suggesting that the first occurs on the level of task-set, whereas the latter occurs on the level of specific S-R associations.     

特征和位置信息在价值驱动注意捕获中的作用

本研究采用训练−测试范式考察颜色和位置信息在价值驱动注意捕获中的作用。实验1考察是否存在基于具体位置的价值驱动的注意捕获效应。在训练阶段, 被试对8个位置中两个位置出现的红色目标反应伴随着高奖励反馈, 而对另外两个位置出现的红色目标反应伴随着低奖励反馈, 其它4个位置为中性位置, 没有目标出现。在测试阶段, 一半试次中红色刺激作为分心物出现。结果发现, 只有当分心刺激出现在高奖励位置和两个高奖励位置之间的中性位置时才能够捕获注意; 实验2考察颜色和位置信息在价值驱动注意捕获中的交互作用。在训练阶段, 将颜色特征和位置信息联合起来进行学习。在测试阶段, 和高、低奖励相联结的颜色刺激各在1/3试次中作为分心物出现。结果发现, 只有当高奖励颜色出现在高奖励位置或出现在高奖励位置之间的中性位置时才能够捕获注意。研究结果表明：(1)位置联结的价值驱动的注意捕获效应能够泛化到特定邻近位置上; (2)个体在训练阶段将颜色和位置的联合特征与奖励建立联结, 训练阶段建立的联结不能泛化到部分特征上。价值驱动注意捕获效应的泛化具有选择性。     

You can detect the trees as well as the forest when adding the leaves: Evidence from visual search tasks containing three-level hierarchical stimuli

The present study investigated how multiple levels of hierarchical stimuli (i.e., global, intermediate and local) are processed during a visual search task. Healthy adults participated in a visual search task in which a target was either present or not at one of the three levels of hierarchical stimuli (global geometrical form made by intermediate forms themselves constituted by local forms). By varying the number of distractors, the results showed that targets presented at global and intermediate levels were detected efficiently (i.e., the detection times did not vary with the number of distractors) whereas local targets were processed less efficiently (i.e., the detection times increased with the number of distractors). Additional experiments confirmed that these results were not due to the size of the target elements or to the spatial proximity among the structural levels. Taken together, these results show that the most local level is always processed less efficiently, suggesting that it is disadvantaged during the competition for attentional resources compared to higher structural levels. The present study thus supports the view that the processing occurring in visual search acts dichotomously rather than continuously. Given that pure structuralist and pure space-based models of attention cannot account for the pattern of our findings, we discuss the implication for perception, attentional selection and executive control of target position on hierarchical stimuli.     

Gait symmetric adaptation: Comparing effects of implicit visual distortion versus split-belt treadmill on aftereffects of adapted step length symmetry

Understanding gait adaptation is essential for rehabilitation, and visual feedback can be used during gait rehabilitation to develop effective gait training. We have previously shown that subjects can adapt spatial aspects of walking to an implicitly imposed distortion of visual feedback of step length. To further investigate the storage benefit of an implicit process engaged in visual feedback distortion, we compared the robustness of aftereffects acquired by visual feedback distortion, versus split-belt treadmill walking. For the visual distortion trial, we implicitly distorted the visual representation of subjects’ gait symmetry, whereas for the split-belt trial, the speed ratio of the two belts was gradually adjusted without visual feedback. After adaptation, the visual feedback or the split-belt perturbation was removed while subjects continued walking, and aftereffects of preserved asymmetric pattern were assessed. We found that subjects trained with visual distortion trial retained aftereffects longest. In response to the larger speed ratio of split-belt walking, the subjects showed an increase in the size of aftereffects compared to the smaller speed ratio, but it steeply decreased over time in all the speed ratios tested. In contrast, the visual distortion group showed much slower decreasing rate of aftereffects, which was evidence of longer storage of an adapted gait pattern. Visual distortion adaptation may involve the interaction and integration of the change in motor strategy and implicit process in sensorimotor adaptation. Although it should be clarified more clearly through further studies, the findings of this study suggest that gait control employs distinct adaptive processes during the visual distortion and split-belt walking and also the level of reliance of an implicit process may be greater in the visual distortion adaptation than the split-belt walking adaptation.     

Understanding planning ability measured by the Tower of London: an evaluation of its internal structure by latent variable modeling

The Tower of London (TOL) is a widely used instrument for assessing planning ability. Inhibition and (spatial) working memory are assumed to contribute to performance on the TOL, but findings about the relationship between these cognitive processes are often inconsistent. Moreover, the influence of specific properties of TOL problems on cognitive processes and difficulty level is often not taken into account. Furthermore, it may be expected that several planning strategies can be distinguished that cannot be extracted from the total score. In this study, a factor analysis and a latent class regression analysis were performed to address these issues. The results showed that 4 strategy groups that differed with respect to preplanning time could be distinguished. The effect of problem properties also differed for the 4 groups. Additional analyses showed that the groups differed on average planning performance but that there were no significant differences between inhibition and spatial working memory performance. Finally, it seemed that multiple factors influence performance on the TOL, the most important ones being the score measurements, the problem properties, and strategy use.     

Reflexive shifts of covert attention operate in an egocentric coordinate frame.

Covert shifts of attention have been shown to improve detection and discrimination thresholds for a range of visual stimuli. Although there is some evidence to suggest that the allocation of attention to a particular region of interest occurs in a retinotopic frame of reference, the importance of an allocentric, or object-based, framework has gained widespread empirical support. The current experiment investigates the nature of the spatial representation in which covert shifts of attention occur in response to a reflexive prime. Primes and targets were presented in four conditions designed to vary systematically the validity of the spatial relationship between the prime and target in egocentric or allocentric coordinate frameworks. A significant advantage, in terms of reaction time and correct identification, was found for targets located in positions previously primed in an egocentric (but not allocentric) framework whereas there was no advantage for locations primed in an allocentric (but not egocentric) framework. These results suggest that the allocation of covert spatial attention within an egocentric framework may be more important than previously thought.     

Manual tapping enhances visual short‐term memory performance where visual and motor coordinates correspond

Visuo‐manual interaction in visual short‐term memory (VSTM) has been investigated little, despite its importance in everyday tasks requiring the coordination of visual perception and manual action. This study examines the influence of a manual action performed during stimulus learning on a subsequent VSTM test for object appearance. The memory display comprised a sequence of briefly presented 1/f noise discs (i.e., possessing spectral properties akin to natural images), wherein each new stimulus was presented at a unique screen location. Participants either did (or did not) perform a concurrent manual action (spatial tapping) task requiring that a hand‐held stylus be moved to a position on a touch tablet that corresponded (or did not correspond) to the screen position of each new stimulus as it appeared. At test, a single stimulus was presented, either at one of the original screen positions, or at a new position. Two factors were examined: the execution (or otherwise) of spatial tapping at a corresponding or non‐corresponding position, and the presentation of test stimuli either at their original spatial positions, or at new positions. We find that spatial tapping at corresponding positions elevates VSTM performance by more than 15%, but this occurs only when stimulus positions are matched from memory to test display. Our findings suggest that multimodal attentional focus during stimulus encoding (incorporating visual, spatial, and manual components) leads to stronger, more robust memory representations. We posit several possible explanations for this effect.     

Conceptual layers and strategies in tour planning

We present an exploratory study of an everyday navigation planning situation, addressing spatial planning strategies as well as cognitive shifts between the visually available map and the conceptualized real-world environment. Participants were asked to plan a diversified holiday route on an island, with the help of a map representing spatial as well as activity information. Following the task proper, they reported in written form about the problem-solving process. Route trajectories were analyzed with respect to their properties, and reports were analyzed with respect to the represented concepts and linguistic patterns. Results reveal that route trajectories tended to be circular rather than random, with relatively few detours or crossing lines. The underlying spatial planning strategies as represented in the written reports resembled earlier findings on the Traveling Salesperson Problem, providing insights into the extent to which this abstract task transfers to a naturalistic scenario. Most crucially, our linguistic analysis provides new results about the representation of conceptual layers when considering the real-world navigation domain of traveling in relation to the actual table-top map planning domain.     

Movement prediction and movement production

The prediction of future positions of moving objects occurs in cases of actively produced and passively observed movement. Additionally, the moving object may or may not be tracked with the eyes. The authors studied the difference between active and passive movement prediction by asking observers to estimate displacements of an occluded moving target, where the movement was driven by the observer's manual action or was passively observed. In the absence of eye tracking, they found that in the active condition, estimates are more anticipatory than in the passive conditions. Decreasing the congruence between motor action and visual feedback diminished but did not eliminate the anticipatory effect of action. When the target was tracked with the eyes, the effect of manual action disappeared. Results indicate distinct contributions of hand and eye movement signals to the prediction of trajectories of moving objects.     

Algorithmic responding on the radial maze in rats does not always imply absence of spatial encoding

Two experiments were conducted to determine whether consistent algorithmic response patterning on 8- and 10-arm versions of the radial maze is independent of spatial encoding. On the 8-arm version well-trained hooded rats were tested in darkness, after maze rotation that rendered room cues ambiguous with respect to arm positions, or with room cues unsystematically relocated. Ambiguous maze rotation was also used with well-trained subjects on the 10-arm version. If algorithmic patterning is a learned, non-spatial strategy, animals using it consistently ought not to have been affected by changes in the spatial layout of the test environment, and the type of pattern used by each subject would have remained constant. On the 8-arm radial maze, responses were most often made to arms 2 or 3 from that just visited. In many animals patterns were interchangeable, switching occurring between preferred angles of turn from day to day. Performance fell when animals were tested in darkness and upon ambiguous maze rotation early (but not later) in training. Testing in darkness increased the angle through which animals turned when responding, perhaps due to the disturbance of intramaze cue use. On the 10-arm maze the “consecutive arm” pattern was used persistently by several animals and appeared to protect their performance from disruption by ambiguous maze rotation. Animals not using rigid patterning were adversely affected. However, on both mazes animals using patterning correctly identified maze arms that had been omitted from otherwise patterned choice sequences. Animals adopted continuous patterning only when spatial encoding had been established. Response patterning appears to serve a mnemonic function and in rats complements rather than replaces the use of a spatial representation of the environment. It was concluded that a complex, flexible relationship exists between spatial functioning and its expression via motor responses.     

Properties of intermodal transfer after dual visuo- and auditory-motor adaptation

Previous work documented that sensorimotor adaptation transfers between sensory modalities: When subjects adapt with one arm to a visuomotor distortion while responding to visual targets, they also appear to be adapted when they are subsequently tested with auditory targets. Vice versa, when they adapt to an auditory-motor distortion while pointing to auditory targets, they appear to be adapted when they are subsequently tested with visual targets. Therefore, it was concluded that visuomotor as well as auditory-motor adaptation use the same adaptation mechanism. Furthermore, it has been proposed that sensory information from the trained modality is weighted larger than sensory information from an untrained one, because transfer between sensory modalities is incomplete. The present study tested these hypotheses for dual arm adaptation. One arm adapted to an auditory-motor distortion and the other either to an opposite directed auditory-motor or visuomotor distortion. We found that both arms adapted significantly. However, compared to reference data on single arm adaptation, adaptation in the dominant arm was reduced indicating interference from the non-dominant to the dominant arm. We further found that arm-specific aftereffects of adaptation, which reflect recalibration of sensorimotor transformation rules, were stronger or equally strong when targets were presented in the previously adapted compared to the non-adapted sensory modality, even when one arm adapted visually and the other auditorily. The findings are discussed with respect to a recently published schematic model on sensorimotor adaptation.