Visuokinesthetic realignment in a video-controlled reaching task

The authors investigated the accuracy of horizontal pointing movements toward a visual target viewed on a vertical video monitor; the view included a directional distortion between perceptual and action spaces. Although accurate coding of the movement vector in a relative (visual) system of coordinates has been found to occur when there is a prismatic perturbation, provided that the hand and the target are continuously visible, such accurate performance has never been reported for video-controlled situations with larger deviations. To evaluate whether visual relative coding is task specific or depends on the magnitude of the induced misalignment, the authors manipulated the intensity of directional perturbation (10 degrees or 40 degrees) in a video-controlled task. Whatever the directional bias, participants (N = 40) were initially inaccurate but adapted quickly within a few trial rehearsals, with a concomitant recalibration of segmental proprioception. In contrast with prism studies, relative coding of the hand-to-target vector seemed not to be operative in video-controlled situations, suggesting that target location is specified in an egocentric system of reference that includes hand-related proprioceptive signals, despite the presence of a (consciously) detected misalignment between visual and kinesthetic systems.     

Early Huntington's disease affects movements in transformed sensorimotor mappings

This study examined the effect of transformed visual feedback on movement control in Huntington's disease (HD). Patients in the early stages of HD and controls performed aiming movements towards peripheral targets on a digitizing tablet and emphasizing precision. In a baseline condition, HD patients were slower but showed few precision problems in aiming. When visual feedback was inverted in both vertical and horizontal axes, patients showed problems in initial and terminal phases of movement where feedback is most critical. When visual feedback was inverted along a single axis as in a mirror-inversion, HD patients showed large deviations and over-corrections before adaptation. Adaptation was similar in both groups. These results suggest that HD impairs on-line error correction in novel movements.     

Laterality effects in the spinning dancer illusion: The viewing‐from‐above bias is only part of the story

The ‘silhouette illusion’, representing the silhouette of a female dancer pirouetting about her vertical axis, is a bistable stimulus created by Japanese web designer Nobuyuki Kayahara. Although the dancer can be perceived as spinning either clockwise or counterclockwise, the clockwise rotation is usually preferred. Troje and McAdam (i‐Perception, 2010, 1, 143) showed that this clockwise bias can be attributed to the tendency to assume a viewpoint from above rather than from below, given that the dancer is portrayed from a vantage point that is not perpendicular to the axis of rotation. Here, we tested whether another possible factor contributing to the observers’ interpretation of this bistable stimulus might be the tendency to perceive movements of the right rather than the left foot. We confirmed both the viewing‐from‐above bias and our hypothesis. The bias to perceive movements of the right leg might be a generalization to lower limbs of a perceptual frequency effect already observed for upper limbs. Such a perceptual and attentional bias towards the right hand/foot could account for the greater ability to predict the outcome of sport actions when observing right‐ rather than left‐limbed movements, and thus the left‐handers' and left‐footers' advantage observed in a variety of interactive sports.     

Visuokinesthetic Realignment in a Video-Controlled Reaching Task

The authors investigated the accuracy of horizontal pointing movements toward a visual target viewed on a vertical video monitor; the view included a directional distortion between perceptual and action spaces. Although accurate coding of the movement vector in a relative (visual) system of coordinates has been found to occur when there is a prismatic perturbation, provided that the hand and the target are continuously visible, such accurate performance has never been reported for video-controlled situations with larger deviations. To evaluate whether visual relative coding is task specific or depends on the magnitude of the induced misalignment, the authors manipulated the intensity of directional perturbation (10° or 40°) in a video-controlled task. Whatever the directional bias, participants (N = 40) were initially inaccurate but adapted quickly within a few trial rehearsals, with a concomitant recalibration of segmental proprioception. In contrast with prism studies, relative coding of the hand-to-target vector seemed not to be operative in video-controlled situations, suggesting that target location is specified in an egocentric system of reference that includes hand-related proprioceptive signals, despite the presence of a (consciously) detected misalignment between visual and kinesthetic systems.     

自由观看实景图片时注意的空间偏向

本研究采用眼动仪直接记录40名在校大学生及研究生（平均年龄21.9岁,SD=1.8）自由观看实景图片的眼动情况,考察自然状态下视觉注意在真实场景中的空间偏向。为了控制图片不同区域刺激特征显著性对结果的影响,将被试随机分为两组,一组观看正向图片,一组观看倒置图片。对图片四个象限上的首次注视概率、首次眼跳方向和注视时间百分比分别进行2（水平方向）×2（垂直方向）×2（呈现方式）的重复测量方差分析,结果表明,存在独立于刺激特征的空间注意偏向,表现在水平方向具有左侧注意偏向,垂直方向具有上侧注意偏向。     

Speed and accuracy of compensatory responses to limb disturbances

This study examines the speed and accuracy of compensatory responses to flexion-extension perturbations of the wrist in the horizontal plane. In Experiments 1 and 2 the subjects were required to establish an initial flexion or extension force of approximately 15% maximum at a prescribed initial muscle length. The perturbations changed the load force by +/-5% in both simple and choice reaction protocols. The results showed that the latencies to compensate for the perturbation were longer when the direction of disturbance was unknown (i.e., choice effect) and when the perturbation unloaded the muscle (i.e., directional effect). Accuracy constraints on the compensatory response increased movement time and reduced the variability of latency without affecting mean latency. In Experiment 3, a visual stimulus generated a comparable choice effect on latency to that produced by the perturbations, but no directional effect in relation to the preload was apparent. Our behavioral analysis of compensatory responses triggered by wrist perturbations confirms that these responses are susceptible to variables that influence the initiation of voluntary movements. Our analysis also demonstrates a directional preload effect that is stimulus specific.     

Spatial sonification of letters on tablets to stimulate literacy skills and handwriting in 5 y-o children: A pilot study

We evaluate the effects of multisensory training on letters, including sonification of graphic symbols. We used “spatial sonification” where letter handwriting movements recorded in a two dimensional plan, vertical and horizontal, are systematically assigned to two acoustic features, spectral composition for the horizontal axis and frequency for the vertical axis. Forty-six kindergarten children were recruited. They were randomly assigned to three multisensory training groups: with sonification (Son) of letters, with a melody unrelated to the shape of the letters (Mel) and without any sound (Sil). We observed a significant effect of training, with the Son group performing better than the other groups in the reading and spelling tasks. We also observed a modification of two kinematic cues (time and in-air time) during handwriting, also in the Son group. We conclude that letter sonification could act as a binder between the visual and auditory dimensions of the letter. The processes underlying this benefit are discussed in the light of the Act-In model, a cognition memory model.     

Manual localization of lateralized visual targets

The effects of visual field, responding limb and extrapersonal space on the ability to localize visual targets using slow positioning movements of the arm were examined. Special contact lenses were used to lateralize visual information and to make comparisons with localization under monocular control conditions. Subjects made slow positioning movements to place a cursor directly beneath target lights. They saw target lights but not the moving limb during the trial. For directional error, results indicated that subjects were more accurate localizing targets lateralized to the right hemisphere than targets lateralized to the left hemisphere, indicating right hemisphere superiority for localization of visual targets in grasping space. Localization performance was significantly better with the right hand than the left hand. the left hand demonstrated a directional bias to the right of the targets. Responding hand and visual field did not interact. Finally, contrary to subjects' awareness and verbal reports, target localization was not less accurate in lens than in monocular control conditions. This was true for both amplitude and directional error. This is consistent with other studies where visual information about limb position is not available.     

Graze: A program to analyze recordings of the jaw movements of ruminants

Graze is a user friendly, Microsoft Windows 95/NT program for analyzing jaw movement recordings taken with the IGER Behavior Recorder. The program displays a plot of the jaw movement amplitude (vertical axis) against time (horizontal axis). Individual jaw movements can be automatically identified, using amplitude and frequency criteria specified by the user. Bouts of jaw movements can then be analyzed and are automatically identified as either grazing or ruminating. Behaviors other than grazing and ruminating (such as drinking or eating supplements) can also be identified and marked by the user. Identified jaw movements and bouts of behavior are superimposed on the jaw data display. Finally, the user can perform a bout analysis, which discriminates between bites and chews during eating and generates a summary file.     

Watch out! Directional threat-related postures cue attention and the eyes

Previous work indicates that threatening facial expressions with averted eye gaze can act as a signal of imminent danger, enhancing attentional orienting in the gazed-at direction. However, this threat-related gaze-cueing effect is only present in individuals reporting high levels of anxiety. The present study used eye tracking to investigate whether additional directional social cues, such as averted angry and fearful human body postures, not only cue attention, but also the eyes. The data show that although body direction did not predict target location, anxious individuals made faster eye movements when fearful or angry postures were facing towards (congruent condition) rather than away (incongruent condition) from peripheral targets. Our results provide evidence for attentional cueing in response to threat-related directional body postures in those with anxiety. This suggests that for such individuals, attention is guided by threatening social stimuli in ways that can influence and bias eye movement behaviour.     

Top-down social modulation of interpersonal observation–execution

Cyclical upper limb movement can involuntarily deviate from its primary movement axis when the performer concurrently observes incongruent biological motion (i.e. interpersonal observation–execution). The current study examined the social modulation of such involuntary motor interference using a protocol that reflected everyday social interactions encountered in a naturalistic social setting. Eighteen participants executed cyclical horizontal arm movements during the observation of horizontal (congruent) or curvilinear (incongruent) biological motion. Both prior to, and during the interpersonal observation–execution task, participants also received a series of social words designed to prime a pro-social or anti-social attitude. The results showed greater orthogonal movement deviation, and thus interference, for the curvilinear compared to horizontal stimuli. Importantly, and opposite to most of the previous findings from work on automatic imitation and mimicry, there was a greater interference effect for the anti-social compared to pro-social prime condition. These findings demonstrate the importance of interpreting the context of social primes, and strongly support predictions of a comparison between the prime construct and the self-concept/-schema and the top-down response modulation of social incentives.     

虚拟场景中不同客体朝向条件对内在参照系建立的影响

通过眼动记录和部分场景再认两种方法,探讨了虚拟建筑物对称场景中物体朝向统一、凸显两种条件对内在参照系建立的影响。结果发现:(1)场景中均为有朝向建筑物且朝向统一时,被试选择物体朝向与对称轴建立内在参照系的可能性没有差异;(2)场景中只有一个有朝向建筑物,其余均为无朝向物体时,即朝向凸显条件下,被试倾向于选择对称轴来建立内在参照系。物体朝向对内在参照系建立的影响作用具有局限性和不稳定性。     

How providing more or less time to solve a cognitive task interferes with upright stance control; a posturographic analysis on healthy young adults

Contrasted postural effects have been reported in dual-task protocols associating balance control and cognitive task that could be explained by the nature and the relative difficulty of the cognitive task and the biomechanical significance of the force platform data. To better assess their respective role, eleven healthy young adults were required to stand upright quietly on a force platform while concomitantly solving mental-calculation or mental-navigation cognitive tasks. Various levels of difficulty were applied by adjusting the velocity rate at which the instructions were provided to the subject according to his/her maximal capacities measured beforehand. A condition without any concomitant cognitive task was added to constitute a baseline behavior. Two basic components, the horizontal center-of-gravity movements and the horizontal difference between center-of-gravity and center-of-pressures were computed from the complex center-of-pressure recorded movements. It was hypothesized that increasing the delay should infer less interaction between postural control and task solution. The results indicate that both mental-calculation and mental-navigation tasks induce reduced amplitudes for the center-of-pressure minus center-of-gravity movements, only along the mediolateral axis, whereas center-of-gravity movements were not affected, suggesting that different circuits are involved in the central nervous system to control these two movements. Moreover, increasing the delays task does not infer any effect for both movements. Since center-of-pressure minus center-of-gravity expresses the horizontal acceleration communicated to the center-of-gravity, one may assume that the control of the latter should be facilitated in dual-tasks conditions, inferring reduced center-of-gravity movements, which is not seen in our results. This lack of effect should be thus interpreted as a modification in the control of these center-of-gravity movements. Taken together, these results emphasized how undisturbed upright stance control can be impacted by mental tasks requiring attention, whatever their nature (calculation or navigation) and their relative difficulty. Depending on the provided instructions, i.e. focusing our attention on body movements or on the opposite diverting this attention toward other objectives, the evaluation of upright stance control capacities might be drastically altered.     

Vection in depth during consistent and inconsistent multisensory stimulation

We examined vection induced during physical or simulated head oscillation along either the horizontal or depth axis. In the first two experiments, during active conditions, subjects viewed radial-flow displays which simulated viewpoint oscillation that was either in-phase or out-of-phase with their own tracked head movements. In passive conditions, stationary subjects viewed playbacks of displays generated in earlier active conditions. A third control, experiment was also conducted where physical and simulated fore-aft oscillation was added to a lamellar flow display. Consistent with ecology, when active in-phase horizontal oscillation was added to a radial-flow display it modestly improved vection compared to active out-of-phase and passive conditions. However, when active fore-aft head movements were added to either a radial-flow or a lamellar-flow display, both in-phase and out-of-phase conditions produced very similar vection. Our research shows that consistent multisensory input can enhance the visual perception of self-motion in some situations. However, it is clear that multisensory stimulation does not have to be consistent (i.e., ecological) to generate compelling vection in depth.     

Modulation of the Directional Attention Deficit in Visual Neglect by Hemispatial Factors

Using a visuo-spatial cuing paradigm, Posner and collaborators (Posner, Cohen, & Rafal, 1982; Posner, Walker, Friedrich, & Rafal, 1984) reported that subjects with a parietal lobe lesion have difficulty in disengaging their visual attention from an invalidly precued location in the ipsilesional hemifield when the target they have to respond to is presented in the contralesional field. Later, these authors (Posner, Walker, Friedrich, & Rafal, 1987) proposed that this disengagement deficit is one involving spatial shifts of attention in a contralesional direction, irrespective of the visual hemifield in which the target is presented. This proposal of a directional disengagement deficit along the horizontal axis, present in either hemifield, contrasts with a report by Baynes, Holtzman, & Volpe (1986) showing, in right parietal subjects, a disengagement deficit for shifts of attention along the vertical axis that is only manifest in the contralesional hemifield. In the present report, we assessed the disengagement deficit of a neglect subject along the horizontal and vertical axes. Results show a disengagement deficit restricted to shifts of attention in the contralesional direction (horizontal axis), which is significant only in the contralesional visual hemifield. However, there is a clear trend for a directional disengagement deficit in the ipsilateral field. These observations indicate that the attention deficit present in neglect is directional and is modulated either by hemispatial factors or by the lateral target location in the visual field. On the basis of the present results, it is proposed that the deficit of parietal subjects may best be conceptualized as one of attentional capture for stimuli located on the contralesional side of the current focus of attention rather than one of disengagement.     

Changes in the dynamics of tremor during goal-directed pointing.

For successful performance of activities requiring a fine level of manipulative control and dexterity, precise control over the intrinsic oscillations (tremor) in each segment is essential. However, the question of how individuals control (minimize) their tremor during precise postural movements remains unresolved. The aim of this study was to investigate the changes observed in limb tremor during goal-directed postural pointing tasks. Seven subjects attempted to minimize limb tremor during a pointing task whereby progressively greater levels of accuracy were required. Subjects held a small lightweight laser pointer in their extended hand during all tasks, the goal being to maintain the laser emission within a specified target area. Frequency analysis showed that the tremor profile for the hand and index finger was characterized by two prominent frequency peaks, located between 2-4 and 8-12 Hz. When the accuracy requirement of the task increased, there was a significant increase in the amplitude of the 8-12 Hz peak for all segments. Analysis of the time series component of tremor revealed a similar trend with the root mean square (RMS) and approximate entropy (ApEn) of the finger tremor increasing as the accuracy requirement increased. This same pattern was not seen for hand tremor where a small but systematic decrease in both the tremor RMS and ApEn was observed. Overall, it would appear that subjects attempted to reduce tremor at the finger by exerting greater control over the hand (as evidenced by decreased tremor output and increased regularity in the tremor signal). Unfortunately, the consequence of this strategy was that the tremor in the distal effector actually increased. Changes in the tremor output observed as a result of defining an explicit external goal probably resulted from the enhanced visual information provided by the laser emission. However, it would appear that subjects were not able to utilize this feedback effectively to reduce their tremor during the targeting tasks.     

Effect of Hand Posture on the Temporal and Kinematic Properties of Pointing and Drawing Movements Executed by Healthy Subjects and by a Patient With Primary Writing Tremor

Healthy individuals (n = 6) and a patient with "pure" primary writing tremor executed pointing and drawing movements while adopting different hand postures. The control subjects and the patient exhibited similar kinematics for most conditions. The patient displayed a severe right hand 4- to 6-Hz tremor and prolonged movements only when drawing with his normal hand posture. His tremor was manifested after a ready cue, in anticipation of a go command. The premovement tremor was abolished when the authors simply eliminated the ready cue and instructed the patient to relax and not think about drawing until he heard the go cue. Thus, the patient's writing tremor depended not only upon the writing or drawing act but also upon the hand position adopted and the intent to write, even in the absence of movement. The present results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits are compatible with a higher motor defect in central nervous system structures involved in the control of pointing and drawing movements.     

Collisions between moving visual targets: what controls alternative ways of seeing an ambiguous display?

When identical visual targets move directly toward and then past one another, they appear either to stream past one another or to bounce off each other. Bertenthal et al (1993 Perception 22 193-207) accounted for the relative strengths of these two percepts by invoking a directional bias, arising from cooperative interactions within a network of motion detectors. We tested this explanation by devising conditions that would enhance or diminish the strength of such a directional bias. In separate experiments we varied (i) the presence or absence of temporal transients (pausing, disappearance, occlusion); (ii) the distances travelled by the targets; and (iii) their acceleration or deceleration before and after collision. The tendency to see the objects stream past one another was not related to the strength of an hypothesized directional bias, suggesting that the perception of this ambiguous motion display was not mediated by directional recruitment. Instead, the results suggest that perceived direction reflects the operation of neural constraints that mirror the constraints operating upon moving objects in the three-dimensional natural world.     

Vection during conflicting multisensory information about the axis, magnitude, and direction of self-motion

We examined the vection induced by consistent and conflicting multisensory information about self-motion. Observers viewed displays simulating constant-velocity self-motion in depth while physically oscillating their heads left-right or back-forth in time with a metronome. Their tracked head movements were either ignored or incorporated directly into the self-motion display (as an added simulated self-acceleration). When this head oscillation was updated into displays, sensory conflict was generated by simulating oscillation along: (i) an orthogonal axis to the head movement; or (ii) the same axis, but in a non-ecological direction. Simulated head oscillation always produced stronger vection than 'no display oscillation'--even when the axis/direction of this display motion was inconsistent with the physical head motion. When head-and-display oscillation occurred along the same axis: (i) consistent (in-phase) horizontal display oscillation produced stronger vection than conflicting (out-of-phase) horizontal display oscillation; however, (ii) consistent and conflicting depth oscillation conditions did not induce significantly different vection. Overall, orthogonal-axis oscillation was found to produce very similar vection to same-axis oscillation. Thus, we conclude that while vection appears to be very robust to sensory conflict, there are situations where sensory consistency improves vection.     

The Goldmeier effect in adults and children: environmental, retinal, and phenomenal influences on judgments of visual symmetry

Adults judge that patterns symmetrical about the vertical axis are more similar to standard patterns symmetrical about both major orthogonal axes than are patterns which are symmetrical only about the horizontal axis (the Goldmeier effect). Thus, symmetry about the vertical axis is more salient for adults than symmetry about the horizontal axis. Two experiments are reported in which subjects from three age groups (preschool, 8 years old, and adult) were given Goldmeier problems under different conditions. In experiment 1 three head-tilt conditions were used (0 degrees, 45 degrees, 90 degrees); in experiment 2 there were four conditions defined by head orientation (0 degrees, 90 degrees) and phenomenal instructions (top of figure at 0 degrees or at 90 degrees). In both experiments, increasing head tilt from 0 degrees decreased the consistency with which the environmentally vertical pattern was chosen. Noncorrespondence between the three spatial frameworks (environmental, retinal, and phenomenal) failed to produce biases in favor of either retinal-egocentric or phenomenal systems. For rotated adult subjects in experiment 2, 0 degrees phenomenal instructions strengthened an environmental bias, and 90 degrees phenomenal instructions shifted responses toward a retinal bias. These findings provide strong refutation of explanations for symmetry perception that are based solely upon the anatomical symmetry of the visual system. The data also fail to support arguments for environmental or phenomenal frameworks as singular influences. The results are best explained in terms of failure of constancy mechanisms to coordinate environmental and retinal information as a function of degree of head rotation and stimulus complexity.