125,723 research outputs found
Tactual perception of material properties
No full textThis paper reviews tactual perception of material properties such as roughness, compliance, coldness and friction. Psychophysical functions relating physical properties to perception are discussed, as well as discrimination thresholds. Also, the neural codes mediating some of these sensations are discussed. Furthermore, we take a look into how sensation of these material properties can be induced artificially in haptic displays. Lastly, the interactions between perception of the different material properties are explored
Cues for haptic perception of compliance
No full textFor the perception of the hardness of compliant materials, several cues are available. In this paper, the relative roles of force/displacement and surface deformation cues are investigated. We have measured discrimination thresholds with silicone rubber stimuli of differing thickness and compliance. Also, the influence of the finger span is assessed. When compliance is expressed as the Young's modulus, the thresholds in the different conditions follow Weber's law with a Weber fraction of 15 percent. When the surface deformation cue was removed, thresholds more than trebled. Under the assumption of optimal cue combination, this suggests that a large fraction of the information comes from the surface deformation cue. Using a matching experiment, we found that differences in object thickness are correctly taken into account. When cues appear to contradict each other, the conflict is resolved by means of a compromis
Tactile perception of thermal diffusivity
No full textThe thermal diffusivity of an object is a parameter that controls the rate at which heat is extracted from the hand when it touches that object. It is an important feature for distinguishing materials by means of touch. In order to quantitatively describe the ability of human observers to discriminate between materials on the basis of heat extraction rate, we conducted an experiment in which this heat extraction was performed in a controlled way. In different conditions, subjects were repeatedly asked to select from two stimuli the one that cooled faster. The discrimination threshold was around 43% of the extraction rate. A rate that was twice as slow also yielded twice the absolute threshold. When we halved the temperature difference between the beginning and end of the stimulus, the threshold did not change as much. In separate experiments, we investigated the different cues that were available in the stimulus: initial cooling rate and end temperature. Both cues were used for discrimination, but cooling rate seemed to be the most important
Human middle temporal cortex, perceptual bias, and perceptual memory for ambiguous three-dimensional motion
No full textWhen faced with inconclusive or conflicting visual input human observers experience one of multiple possible perceptions. One factor that determines perception of such an ambiguous stimulus is how the same stimulus was perceived on previous occasions, a phenomenon called perceptual memory. We examined perceptual memory of an ambiguous motion stimulus while applying transcranial magnetic stimulation (TMS) to the motion-sensitive areas of the middle temporal cortex (hMT+). TMS increased the predominance of whichever perceptual interpretation was most commonly reported by a given observer at baseline, with reduced perception of the less favored interpretation. This increased incidence of the preferred percept indicates impaired long-term buildup of perceptual memory traces that normally act against individual percept biases. We observed no effect on short-term memory traces acting from one presentation to the next. Our results indicate that hMT+ is important for the long-term buildup of perceptual memory for ambiguous motion stimul
Illusory rotation in the haptic perception of a moving bar
No full textHaptic matching of the orientation of bars separated by a horizontal distance leads to large systematic deviations (eg Kappers and Koenderink, 1999 Perception 28 781–795). A bar on the right side has to be rotated clockwise in order to be perceived as parallel to a bar at the left side. This finding leads to the following intriguing question which we investigated in this study: Will a bar moving from left to right in a fixed orientation be perceived as rotating counterclockwise? Blindfolded subjects had to touch a bar that moved from left to right or from right to left while it was rotating clockwise or counterclockwise with di erent speeds or did not rotate. For each trial they had to decide whether the rotation was clockwise or counterclockwise. From psychometric curves fitted to the data, we could determine that the results were consistent with the findings in the static case: A bar moving from left to right has to rotate clockwise in order to be perceived as non-rotating (and vice versa). In other words, a translating bar causes the illusory perception of a rotation
Stochastic variations in sensory awareness are driven by noisy neuronal adaptation: evidence from serial correlations in perceptual bistability
No full textWhen the sensory system is subjected to ambiguous input, perception alternates between interpretations in a seemingly random fashion. Although neuronal noise obviously plays a role, the neural mechanism for the generation of randomness at the slow time scale of the percept durations (multiple seconds) is unresolved. Here significant nonzero serial correlations are reported in series of visual percept durations (to the author’s knowledge for the first time accounting for duration impurities caused by reaction time, drift, and incomplete percepts). Serial correlations for perceptual rivalry using structure-from-motion ambiguity were smaller than for binocular rivalry using orthogonal gratings. A spectrum of computational models is considered, and it is concluded that noise in adaptation of percept-related neurons causes the serial correlations. This work bridges, in a physiologically plausible way, widely appreciated deterministic modeling and randomness in experimental observations of visual rivalry
Haptic perception of mutiple objects
No full textIn this thesis a series of investigations into haptic (touch) perception of multiple objects is presented. When we hold a collection of objects in our hand, we can extract different types of information about these objects. We can, for instance, identify which objects we are holding. The first chapters of this thesis aim at providing insight into how fast humans can find a certain object among other objects using touch and which specific features make an object stand out among the other objects. To this end human subjects were instructed to respond as fast as possible whether a certain target item was present among a varying number of distractor items. This way response times were measured as a function of the number of items. In chapters 2 and 3 subjects were asked to search a plane on which items could be placed. The results show that a rough item is highly salient among less rough items (chapter 2) and that in this produces ‘pop-out’ effect. In chapter 3 it is shown that very poor visual information can already guide haptic exploration effectively. In chapters 4 and 5 items consisted of three-dimensional shapes (spheres, cubes, tetrahedrons, cylinders and ellipsoids) that could be grasped together in the hand. We show that shapes with edges are highly salient and that there is a whole range of search slopes depending on the target –distractor combination. In addition to identifying the object we may hold in our hand, we can also determine how many objects we are holding. In chapters 6 to 8 we investigated haptic numerosity judgement. From vision it is known that numerosity judgment is fast and error-free up to 3 or 4 items, while for larger numbers response times and error-rates increase rapidly. The process used for assessing small numerosities has been labeled ‘subitizing’, while the process for larger numerosities is referred to as ‘counting’. In chapter 6 we show that subitizing also occurs in haptics when subjects are asked to determine the number of spheres grasped in their hand. A visual study was conducted in chapter 7 to show that visual and haptic numerosity judgment is comparable. In chapter 8 we show that numerosity judgment can three times faster when the items are distributed over the two hands compared when they are all held in the same hand. Finally, in chapter 9 we show that numerosity judgement is not affected by size or shape differences between the objects in a set. The studies in this thesis show that haptic perception can be fast and that not all items have to be necessarily explored sequentially. Haptic information can be processed in parallel across the different items in a set when searching for a salient target item or when judging small numbers of items
A kinematic cue for active haptic shape perception
No full textThis study quantitatively investigates the actual movements that observers make when exploring a shape. It addresses the question of how the kinematics of these movements relate to and may affect perceived shape. It is one of the first studies to do so for real stimuli and for relatively unconstrained exploration. Observers discriminated the curvature of circularly shaped strips. We identify a kinematic cue for a single finger stroking across circular strips under conditions of slip. This cue consists of two terms that are related to the shift of the skin contact surface across the fingertip and the rotation angle of the finger. The rotation angle of the finger is found to increase linearly with the curvature of the stimulus. Observers rotated their finger less on a concave curvature by a constant amount, while at the same time they overestimated the radius of the concave strips compared to the convex ones. We show that responses were related to kinematic properties of the actual movements and we consider several mechanisms that could explain this findin
Psychophysical experiment on roughness perception considering bidirectionality in active touch
No full textIn active touch, tactile perception is bidirectionally related to the exploratory movements. This means that exploration influences perception, but also perception influences exploration. We can optimize/change the exploratory movements according to the perception and/or the task, consciously or unconsciously. In this paper, a psychophysical experiment on roughness perception is presented. Exerted normal force and velocity in different perceptual tasks (discrimination task and scaling task) using rough and smooth stimuli are collected. The results support that humans might adjust their way of touching (force, velocity, etc.) according to the task and their perception
The effect of changing size on vergence is mediated by changing disparity
No full textIn this study, we investigated the effect of changing size on vergence. Erkelens and Regan (1986) proposed that this cue to motion in depth affects vergence in a similar way as it affects perception. The measured effect on vergence was small and we wondered why the vergence system would use changing size as an additional cue to changing disparity. To elucidate the effect of changing size on vergence, we used an annulus carrying both changing size and changing disparity signals to motion in depth. The cues were either congruent or signaled a different depth. The results showed that vergence was affected by changing size, however in an opposite way than that perception was affected. These results were incongruent with those reported by Erkelens and Regan (1986). We therefore additionally measured the effects on vergence of the individual parameters associated with changing size, i.e., stimulus area, retinal eccentricity, and luminance. Stimulus (retinal) eccentricity was inversely related to vergence gain. Luminance, on the other hand, had a smaller but positive relation to vergence gain. Thus, changing size affected the disparity signal two-fold: it changed the retinal location of the disparity signal and it changed the strength of the disparity signal (luminance change). These effects of changing size on disparity can explain both our results (change in retinal location of the disparity signal) and those of Erkelens and Regan (1986; change in luminance). We thus conclude that changing size did not in itself contribute to vergence, rather its effect on vergence was mediated by disparit
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