The influence of visual and haptic material information on early grasping force.

In this paper, we assess the importance of visual and haptic information about materials for scaling the grasping force when picking up an object. We asked 12 participants to pick up and lift objects with six different textures, either blindfolded or with visual information present. We measured the grip force and estimated the load force from the object's weight and vertical acceleration.

A mass-density model can account for the size-weight illusion.

When judging the heaviness of two objects with equal mass, people perceive the smaller and denser of the two as being heavier. Despite the large number of theories, covering bottom-up and top-down approaches, none of them can fully account for all aspects of this size-weight illusion and thus for human heaviness perception. Here we propose a new maximum-likelihood estimation model which describes the illusion as the weighted average of two heaviness estimates with correlated noise: One estimate derived from the object's mass, and the other from the object's density, with estimates' weights based on their relative reliabilities.

Integrating force and position: testing model predictions.

In this study, we investigated the integration of force and position information in a task in which participants were asked to estimate the center of a weak force field. Two hypotheses, describing how participants solved this task, were tested: (1) by only using the position(s) where the force reaches the detection threshold, and (2) by extrapolating the force field based on perceived stiffness. Both hypotheses were also described formally, assuming a psychophysical function obeying a power law with an exponent smaller than one.

Correcting for Visuo-Haptic Biases in 3D Haptic Guidance.

Visuo-haptic biases are observed when bringing your unseen hand to a visual target. The biases are different between, but consistent within participants. We investigated the usefulness of adjusting haptic guidance to these user-specific biases in aligning haptic and visual perception.

The Effect of Global and Local Damping on the Perception of Hardness.

In tele-operation systems, damping is often injected to guarantee system stability during contact with hard objects. In this study, we used psychophysical experiments to assess the effect of adding damping on the user's perception of object hardness. In Experiments 1 and 2, combinations of stiffness and damping were tested to assess their effect on perceived hardness.

Haptic perception of force magnitude and its relation to postural arm dynamics in 3D.

In a previous study, we found the perception of force magnitude to be anisotropic in the horizontal plane. In the current study, we investigated this anisotropy in three dimensional space. In addition, we tested our previous hypothesis that the perceptual anisotropy was directly related to anisotropies in arm dynamics.

Expertise effects in cutaneous wind perception.

We examined whether expertise effects are present in cutaneous wind perception. To this end, we presented wind stimuli consisting of different wind directions and speeds in a wind simulator. The wind simulator generated wind stimuli from 16 directions and with three speeds by means of eight automotive wind fans.

Haptic exploratory behavior during object discrimination: a novel automatic annotation method.

In order to acquire information concerning the geometry and material of handheld objects, people tend to execute stereotypical hand movement patterns called haptic Exploratory Procedures (EPs). Manual annotation of haptic exploration trials with these EPs is a laborious task that is affected by subjectivity, attentional lapses, and viewing angle limitations. In this paper we propose an automatic EP annotation method based on position and orientation data from motion tracking sensors placed on both hands and inside a stimulus.

Target contact and exploration strategies in haptic search.

In a haptic search task, one has to detect the presence of a target among distractors using the sense of touch. A salient target can be detected faster than a non-salient target. However, little is known about the exploration strategies that are used, especially in 3D search tasks where items are held in the hand.

Tactual perception of liquid material properties.

In this paper, studies into the tactual perception of two liquid material properties, viscosity and wetness, are reviewed. These properties are very relevant in the context of interaction with liquids, both real, such as cosmetics or food products, and simulated, as in virtual reality or teleoperation. Both properties have been the subject of psychophysical characterisation in terms of magnitude estimation experiments and discrimination experiments, which are discussed.

Haptic discrimination of distance.

While quite some research has focussed on the accuracy of haptic perception of distance, information on the precision of haptic perception of distance is still scarce, particularly regarding distances perceived by making arm movements. In this study, eight conditions were measured to answer four main questions, which are: what is the influence of reference distance, movement axis, perceptual mode (active or passive) and stimulus type on the precision of this kind of distance perception? A discrimination experiment was performed with twelve participants. The participants were presented with two distances, using either a haptic device or a real stimulus.

Parallel processing of shape and texture in haptic search.

In a haptic search task, one has to determine the presence of a target among distractors. It has been shown that if the target differs from the distractors in two properties, shape and texture, performance is better than in both single-property conditions (Van Polanen, Bergmann Tiest, & Kappers, 2013). The search for a smooth sphere among rough cubical distractors was faster than both the searches for a rough sphere (shape information only) and for a smooth cube (texture information only).

Identifying haptic exploratory procedures by analyzing hand dynamics and contact force.

Haptic exploratory procedures (EPs) are prototypical hand movements that are linked to the acquisition of specific object properties. In studies of haptic perception, hand movements are often classified into these EPs. Here, we aim to investigate several EPs in a quantitative manner to understand how hand dynamics and contact forces differ between them.

Anisotropy in the haptic perception of force direction and magnitude.

Although force-feedback devices are already being used, the human ability to perceive forces has not been documented thoroughly. The haptic perception of force direction and magnitude has mostly been studied in discrimination tasks in the direction of gravity. In our study, the influence of physical force direction on haptic perception of force magnitude and direction was studied in the horizontal plane.

Bimanual integration of position and curvature in haptic perception.

For small stimuli, it has been shown that subjects are very accurate in distinguishing a cylinder with an elliptical cross section from one with a circular cross section. In such a task, both curvature and length are integrated effectively. Large cylinders are explored differently: either by one hand or by two hands sliding over the surface.

Bimanual and unimanual length perception.

From previous studies, it is unclear how bimanual length discrimination differs from unimanual length discrimination. To investigate the difference, we designed an experiment with four conditions. In the first two conditions, unimanual and bimanual discrimination thresholds are determined.

Contact force and scanning velocity during active roughness perception.

Haptic perception is bidirectionally related to exploratory movements, which means that exploration influences perception, but perception also influences exploration. We can optimize or change exploratory movements according to the perception and/or the task, consciously or unconsciously. This paper presents a psychophysical experiment on active roughness perception to investigate movement changes as the haptic task changes.

Influence of shape on the haptic size aftereffect.

Recently, we showed a strong haptic size aftereffect by means of a size bisection task: after adaptation to a large sphere, subsequently grasped smaller test spheres felt even smaller, and vice versa. In the current study, we questioned whether the strength of this aftereffect depends on shape. In four experimental conditions, we determined the aftereffect after adaptation to spheres and tetrahedra and subsequent testing also with spheres and tetrahedra.

Integration of length and curvature in haptic perception.

We investigated if and how length and curvature information are integrated when an object is explored in one hand. Subjects were asked to explore four types of objects between thumb and index finger. Objects differed in either length, curvature, both length and curvature correlated as in a circle, or anti-correlated.

Illusory rotation in the haptic perception of a moving bar.

Haptic matching of the orientation of bars separated by a horizontal distance leads to large systematic deviations. This finding leads to the following intriguing question which we investigated in this study: How will a bar moving from left to right in a fixed orientation be perceived by blindfolded observers? Interestingly, this previous finding predicts that the translating bar will cause the illusory perception of a rotation. In our experiment, we used psychophysical methods to determine the rotation needed to perceive the bar as non-rotating, for both rightward and leftward translations.

Integration and disruption effects of shape and texture in haptic search.

In a search task, where one has to search for the presence of a target among distractors, the target is sometimes easily found, whereas in other searches it is much harder to find. The performance in a search task is influenced by the identity of the target, the identity of the distractors and the differences between the two. In this study, these factors were manipulated by varying the target and distractors in shape (cube or sphere) and roughness (rough or smooth) in a haptic search task.

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.

Binding in haptics: integration of "what" and "where" information in working memory for active touch.

Information about the identity and the location of perceptual objects can be automatically integrated in perception and working memory (WM). Contrasting results in visual and auditory WM studies indicate that the characteristics of feature-to-location binding can vary according to the sensory modality of the input. The present study provides first evidence of binding between "what" and "where" information in WM for haptic stimuli.

Haptic discrimination and matching of viscosity.

In three experiments, viscosity perception of liquids using the sense of touch was studied. The first two were discrimination experiments in which Weber fractions were determined for a number of viscosities spanning the range of what is encountered in daily life, and for two ways of perceiving viscosity (stirring with a spatula or with the index finger). For high viscosities, Weber fractions were around 0.

Haptic search for hard and soft spheres.

In this study the saliency of hardness and softness were investigated in an active haptic search task. Two experiments were performed to explore these properties in different contexts. In Experiment 1, blindfolded participants had to grasp a bundle of spheres and determine the presence of a hard target among soft distractors or vice versa.