The structure of frontoparallel haptic space is task dependent

In three experiments, we investigated the structure of frontoparallel haptic space. In the first experiment, we asked blindfolded participants to rotate a matching bar so that it felt parallel to the reference bar, the bars could be at various positions in the frontoparallel plane. Large systematic errors were observed, in which orientations that were perceived to be parallel were not physically parallel. In two subsequent experiments, we investigated the origin of these errors. In Experiment 2, we asked participants to verbally report the orientation of haptically presented bars. In this task, participants made errors that were considerably smaller than those made in Experiment 1. In Experiment 3, we asked participants to set bars in a verbally instructed orientation, and they also made errors significantly smaller than those observed in Experiment 1. The data suggest that the errors in the matching task originate from the transfer of the reference orientation to the matching-bar position

Illusory rotations in the haptic perception of moving spheres and planes

Recently, we have shown that a translating bar on which blindfolded participants position their hand is perceived as also rotating. Here, we investigated whether such an illusory rotation would also be found if a sphere or a plane (i.e. a stimulus without a clear orientation) was used as translating stimulus. We indeed found similar rotation biases: on average a stimulus that translates over a distance of 60cm has to rotate 25 degrees to be perceived as non-rotating. An additional research question was whether the biases were caused by the same underlying biasing egocentric reference frame. To our surprise, the correlations between the sizes of the biases of the individual participants in the various conditions were not high and mostly not even significant. This was possibly due to day-to-day variations, but clearly, more research is needed to answer this second research question

Haptic perception

Fueled by novel applications, interest in haptic perception is growing. This paper provides an overview of the state of the art of a number of important aspects of haptic perception. By means of touch we can not only perceive quite different material properties, such as roughness, compliance, friction, coldness and slipperiness, but we can also perceive spatial properties, such as shape, curvature, size and orientation. Moreover, the number of objects we have in our hand can be determined, either by counting or subitizing. All these aspects will be presented and discussed in this paper. Although our intuition tells us that touch provides us with veridical information about our environment, the existence of prominent haptic illusions will show otherwise. Knowledge about haptic perception is interesting from a fundamental viewpoint, but it also is of eminent importance in the technological development of haptic devices. At the end of this paper, a few recent applications will be presented

Anchoring In Action: Manual Estimates Of Slant Are Powerfully Biased Toward Initial Hand Orientation And Are Correlated With Verbal Report

People verbally overestimate hill slant by approximately 15 degrees to 25 degrees, whereas manual estimates (e. g., palm board measures) are thought to be more accurate. The relative accuracy of palm boards has contributed to the widely cited theoretical claim that they tap into an accurate, but unconscious, motor representation of locomotor space. In the current work, 4 replications (total N = 204) carried out by 2 different laboratories tested an alternative anchoring hypothesis that manual action measures give low estimates because they are always initiated from horizontal. The results of all 4 replications indicate that the bias from response anchoring can entirely account for the difference between manual and verbal estimates. Moreover, consistent correlations between manual and verbal estimates given by the same observers support the conclusion that both measures are based on the same visual representation. Concepts from the study of judgment under uncertainty apply even to action measures in information rich environments

Doctor of Philosophy

dissertationThe study of haptic interfaces focuses on the use of the sense of touch in human-machine interaction. This document presents a detailed investigation of lateral skin stretch at the fingertip as a means of direction communication. Such tactile communication has applications in a variety of situations where traditional audio and visual channels are inconvenient, unsafe, or already saturated. Examples include handheld consumer electronics, where tactile communication would allow a user to control a device without having to look at it, or in-car navigation systems, where the audio and visual directions provided by existing GPS devices can distract the driver's attention away from the road. Lateral skin stretch, the displacement of the skin of the fingerpad in a plane tangent to the fingerpad, is a highly effective means of communicating directional information. Users are able to correctly identify the direction of skin stretch stimuli with skin displacements as small as 0.1 mm at rates as slow as 2 mm/s. Such stimuli can be rendered by a small, portable device suitable for integration into handheld devices. The design of the device-finger interface affects the ability of the user to perceive the stimuli accurately. A properly designed conical aperture effectively constrains the motion of the finger and provides an interface that is practical for use in handheld devices. When a handheld device renders directional tactile cues on the fingerpad, the user must often mentally rotate those cues from the reference frame of the finger to the world-centered reference frame where those cues are to be applied. Such mental rotation incurs a cognitive cost, requiring additional time to mentally process the stimuli. The magnitude of these cognitive costs is a function of the angle of rotation, and of the specific orientations of the arm, wrist and finger. Even with the difficulties imposed by required mental rotations, lateral skin stretch is a promising means of communicating information using the sense of touch with potential to substantially improve certain types of human-machine interaction

Facteurs influencing haptic shape perception

Le but de cette étude était de déterminer la contribution de plusieurs facteurs (le design de la tâche, l’orientation d’angle, la position de la tête et du regard) sur la capacité des sujets à percevoir les différences de formes bidimensionnelles (2-D) en utilisant le toucher haptique. Deux séries d'expériences (n = 12 chacune) ont été effectuées. Dans tous les cas, les angles ont été explorés avec l'index du bras tendu. La première expérience a démontré que le seuil de discrimination des angles 2-D a été nettement plus élevé, 7,4°, que le seuil de catégorisation des angles 2-D, 3,9°. Ce résultat étend les travaux précédents, en montrant que la différence est présente dans les mêmes sujets testés dans des conditions identiques (connaissance des résultats, conditions d'essai visuel, l’orientation d’angle). Les résultats ont également montré que l'angle de catégorisation ne varie pas en fonction de l'orientation des angles dans l'espace (oblique, verticale). Étant donné que les angles présentés étaient tous distribués autour de 90°, ce qui peut être un cas particulier comme dans la vision, cette constatation doit être étendue à différentes gammes d'angles. Le seuil plus élevé dans la tâche de discrimination reflète probablement une exigence cognitive accrue de cette tâche en demandant aux sujets de mémoriser temporairement une représentation mentale du premier angle exploré et de la comparer avec le deuxième angle exploré. La deuxième expérience représente la suite logique d’une expérience antérieure dans laquelle on a constaté que le seuil de catégorisation est modifié avec la direction du regard, mais pas avec la position de la tête quand les angles (non visibles) sont explorés en position excentrique, 60° à la droite de la ligne médiane. Cette expérience a testé l'hypothèse que l'augmentation du seuil, quand le regard est dirigé vers l'extrême droite, pourrait refléter une action de l'attention spatiale. Les sujets ont exploré les angles situés à droite de la ligne médiane, variant systématiquement la direction du regard (loin ou vers l’angle) de même que l'emplacement d'angle (30° et 60° vers la droite). Les seuils de catégorisation n’ont démontré aucun changement parmi les conditions testées, bien que le biais (point d'égalité subjective) ait été modifié (décalage aux valeurs inférieurs à 90°). Puisque notre test avec le regard fixé à l’extrême droite (loin) n'a eu aucun effet sur le seuil, nous proposons que le facteur clé contribuant à l'augmentation du seuil vu précédemment (tête tout droit/regard à droite) doit être cette combinaison particulière de la tête/regard/angles et non l’attention spatiale.The purpose was to determine the contribution of several factors (design of the task, angle orientation, head position and gaze) to the ability of subjects to perceive differences in twodimensional (2-D) shape using haptic touch. Two series of experiments (n=12 each) were carried out. In all cases the angles were explored with the index finger of the outstretched arm. The first experiment showed that the mean threshold for 2-D angle discrimination was significantly higher, 7.4°, than for 2-D angle categorization, 3.9°. This result extended previous work, by showing that the difference is present in the same subjects tested under identical conditions (knowledge of results, visual test conditions, angle orientation). The results also showed that angle categorization did not vary as a function of the orientation of the angles in space (oblique, upright). Given that the angles presented were all distributed around 90°, and that this may be a special case as in vision, this finding needs to be extended to different ranges of angles. The higher threshold with angle discrimination likely reflects the increased cognitive demands of this task which required subjects to temporarily store a mental representation of the first angle scanned, and to compare this to the second scanned angle. The second experiment followed up on observations that categorization thresholds are modified with gaze direction but not head position when the unseen angles are explored in an eccentric position, 60° to the right of midline. This experiment tested the hypothesis that the increased threshold when gaze was directed to the far right might reflect an action of spatial attention. Subjects explored angles located to the right of midline, systematically varying the direction of gaze (away from or to the angles) along with angle location (30° and 60° to the right). Categorization thresholds showed no change across the conditions tested, although bias (point of subjective equality) was changed (shift to lower angle values). Since our testing with far right gaze (away) had no effect on threshold, we suggest that the key factor contributing to the increased threshold seen previously (head forward/gaze right) must have been this particular combination of head/gaze/angles used and not spatial attention

Where Are Your Fingers?

How do we know how our fingers are oriented in space? Contributions to limb and finger perception include afferent sensory signals from the muscles, joints, skin, as well as vision and other senses, and top-down assumptions about the bodys dimensions. A growing body of literature has examined the perception of finger and hand position and dimensions in a bid to understand how the limbs are represented in the brain. However, no studies have examined perception of the orientation of the fingers. A comprehensive model of highly articulated body parts must include perception of their orientation as well as their position. This dissertation seeks to fill an existing gap in the literature by exploring contributions to finger orientation perception, using a novel line-matching task. In Chapter 3 I provide evidence that vestibular disruption using galvanic vestibular stimulation (GVS) leads to an inward rotation of perceived finger orientation, and provide some evidence that finger orientation perception may not be accurate at baseline. In Chapter 4 I show that left- and right-handers may have differ- ent strategies for finger orientation perception, and provide evidence for an outward rotational bias that increases as the hands are placed further laterally from the body midline. In Chapter 5, I show that the way the probe line is initially displayed has a significant impact on performance, specifically on asymmetries of responses for the two hands and the compression of responses across the test range. I further show that the outward bias observed in Chapter 4 might be due to order of hand placement and differences in muscle strain across conditions. In Chapters 6 and 7, I show no difference in orientation perception for the ring and index fingers, but find an overall inward rotation of orientation estimates for palm-down hand postures, compared to palm-up postures. My research clearly shows that perceived finger orientation, as measured in my line-matching paradigm, is highly context-dependent. I discuss this in the greater context of the limb perception literature and outline some of the questions which much still be addressed in order to arrive at a comprehensive model of hand and finger perception

Activity in area V3A predicts positions of moving objects

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