Jeroen B J Smeets

..We discuss the influence of scleral coils on saccade generation and suggest that a change in motor strategy due to the discomfort of wearing the coils might be the cause of the increased variability...

..Human behavior can show a reduction in context effects over time without assuming an underlying shift from illusory towards veridical size information...

..Subjects tended to approach the object's surfaces orthogonally, suggesting that they aim for an optimal precision of digit placement rather than simply closing their hand as it reaches the object...

..It did not influence the velocity of grip closure in the way that one would expect if size were mis-perceived. Thus there is no reason to assume that the perceived size guides the way that we reach and grasp an object...

..7), showing that the suboptimal grip orientations were planned that way. We conclude that subjects plan their grasps using information that is based on the misperceived shape...

..We found no direct relationship between the control of the reaching movement towards the object and the force applied at the surface of the object to pick it up. We conclude that the reaching and lifting movements are quite independent...

..They systematically tapped ahead of the position of the flash, in accordance with the above-mentioned perceptual mislocalisations. Thus the lack of systematic errors in Hansen's study is not a general property of fast motor responses...

..Because the flankers changed more than only the PGA, we conclude that the effect of the flankers on prehension cannot only be because of misjudgement of the size of the central disk...

..For targets moving at a velocity above average, or above 12 cm/s, the initial movement direction did not depend on the target's velocity. Similar behaviour is also known from pursuit eye movements...

..This was even so if the squares' luminances changed considerably at the moment that the subject's hand started to move. Thus, chromatic information can be used for the fast on-line control of action...

..We compared the direction of the mislocalization with the changes in gaze and in target position during different intervals relative to the flash. We found that the mislocalization is related to the change in gaze after the flash...

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..The digits' target positions change, both when object position and when object size change. A model in which the individual digits move smoothly to these new positions yields the same behaviour as is observed experimentally...

..Perhaps subjects nevertheless quickly respond in the direction of motion because this helps avoid collisions when pressed for time...

..This dichotomy corresponds to both to the distinction between magno-cellular and parvo-cellular pathways and to a dorsal-ventral distinction. The latency also differed systematically between subjects, independent of their reaction time...

..The conclusion that seeing one's hand does not lead to an alignment between vision and proprioception has important consequences for the interpretation of previous work on visuomotor adaptation...

..Illusions only affect those aspects of a task that are based on the spatial attributes that are affected by the illusion...

..As expected, the illusion only had a significant influence on the sagittal dimension. The size of this illusory effect was equal for perception and action...

..We conclude that the way that obstacles influence the movement time in reach-to-grasp movements is determined by the extent to which they limit the digits' paths...

..Pointing movements under different visual conditions were based on different relative contributions of position and vector coding. The contribution of vector coding was always rather modest...

..Thus although the adaptation closely matches the imposed distortion, it does not appear to be directly linked to the orientation of the eyes or of the exposed arm...

..Instead, this correlation is presumably implicitly considered in the way that the color contrast at borders is determined...

..The time of the maximum velocity did not differ, but the maximum velocity was higher in the one-target condition. Thus our hypothesis is rejected, favouring a non-mechanical explanation of the one-target advantage...

..This anatomic biomechanical study was undertaken to gain insight into the underlining mechanism of tipping of the maxillary segments during transverse expansion using tooth-borne and bone-borne distraction devices...

..We propose that relative disparities only guide parts of very slow movements that require extreme precision...

..The illusion influenced the two tasks to the same extent, suggesting that the visual information processing is the same for the two tasks...

..Thus, it is unlikely that both effects have a common origin in misjudging egocentric straight ahead...

..Our conclusion is that our actions are controlled by the judged positions of the end-effector and the target, even when the former is quite detached from the muscles and joints that are involved in the action...

..They even appear to vary the timing of release to compensate for the errors in the hand's movement. Thus timing does not appear to be the limiting factor...

..The extent to which the average colour of nearby surfaces influences the apparent colour of the target seems to depend on the average chromatic variability of the whole scene...

..The model that considers postural constraints does not perform better than the simple model. We conclude that such constraints are not responsible for the main characteristics of the reach-to-grasp movement...

..This indicates that influences of task history are limited to the use of information from preceding trials rather than to changes in how information is used (movement strategy)...

..Finally, we show that the model with relative damping can be used to model subtle differences between multi-joint interceptions. The model with relative damping fits the data much better than a version of the model with absolute damping...

..They conclude that this experiment cannot be regarded as firm support for the 2-visual-systems hypothesis (i.e., that the ventral stream is for perception and the dorsal stream is for visually guided actions)...

..The authors conclude that it is not possible to distinguish between the 3 components of noise reduction without knowing the controlled variables...

..Thus motion parallax is used to judge surface slant, even when one is under the impression of standing still...

..We conclude that neural latency differences of tens of milliseconds between cues are irrelevant because of the low temporal resolution of neural processing...

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..On many trials the window passed the target and returned, indicating that the next movement had been planned before identifying the item that was in view...

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..We conclude that subjects respond only to the changing target position. Target speed influences the direction in which the hand moves indirectly, possibly via a speed-related misperception of position...

..The jumping introduced uncertainty about where the target was at the indicated moment, giving room for biases to be expressed. Participants showed a clear preference to select positions that were nearer to where they were looking...

..Thus subjects did not aim further ahead when they hit more slowly. This supports our earlier suggestion that the acceleration of the hand and the direction in which it moves are controlled separately...

..However, the involved weights must be variable and depend systematically on parameters such as the luminance contrast at the surface's borders and other chromatic contrasts within the scene...

..The authors propose that these biases arise from a combination of a large temporal uncertainty, a temporal asymmetry related to sampling the moving object's position, and a bias toward believing that one is looking at what one sees...

..We found that the resulting taus of decreasing gaps were also related linearly. We conclude that this relationship cannot be considered as evidence for the tau-coupling theory...

..This suggests that the motion of an object is not broken down into speed components in different directions, but that speed and direction are perceived and used separately...

..Given the commonly observed movement deficits of the spastic arm, these results show that participants with spastic hemiparesis displayed a remarkable ability in adjusting movements quickly...

..Thus we show that adaptation to motion must (also) occur at a stage at which local motions have not yet been integrated to give a unified percept...

..These findings support the notion that the systematic mislocalisation of flashed targets is related to the way in which people intercept moving objects...

..We conclude that the adaptation to different kinds of perturbations not only differs in extent but also involves different (egocentric) mechanisms...

..We conclude that people do not consider an object's orientation to estimate the temporal demands of an interception task, but that they use the object's size and speed, and their experience from previous trials...

..Thus, if catchers use a strategy that involves combining vertical and horizontal estimates of the ball's speed, they do not obtain their estimates of the horizontal component from the rate of expansion alone...

..We conclude that the influence of the bar's orientation on the curvature of the hand's path is caused by a misperception of the initial direction in which the hand has to move to reach the target...

..We conclude that a spatial cue reduces the mislocalisation of targets that are flashed during pursuit eye movements. The cue does not have to be exactly at the same position as the flash...

..We conclude that actions are influenced by visual illusions, but that such influences are only apparent if the action is guided by the attribute that is fooled by the illusion...

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..We conclude that acceleration is not used in this simple manner to intercept moving targets...

..Therefore, the most important role for texture in everyday judgments of time to passage is probably that it helps one judge the object's shape and thereby estimate how its image will deform as it moves...