Influence of Visual Feedback on Passive Tactile Perception of Speed and Spacing of Rotating Gratings
ABSTRACT We studied the influence of visual feedback on the tactual perception of both speed and spatial period of a rotating texture. Participants were placed in a situation of perceptual conflict concerning the rotation speed of a cylindrical texture. Participants touched a cylindrical texture of gratings rotating around its axis at a constant speed, while they watched a cylinder without gratings rotating at a different speed on a computer screen. Participants were asked to estimate the speed of the gratings texture under the finger and the spacing (or spatial period) of the gratings. We observed that the tactual estimations of both speed and spacing co-varied with the speed of the visual stimulus, although the cylinder perceived tactually rotated at a constant speed. The first effect (speed effect) could correspond to the resolution of the perceptual conflict in favor of vision. The second effect (spacing effect) is apparently surprising, since no varying information about spacing was provided by vision. However, the physical relation between spacing and speed is well established according to every day experience. Thus, the parameter extraneous to the conflict could be influenced according to previous experience. Such cross-modal effects could be used by designers of virtual reality systems and haptic devices to improve the haptic sensations they can generate using simple (constant) tactile stimulations combined with visual feedback.
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ABSTRACT: ABSTRACT This paper presents a survey of the main results obtained in the field of “pseudo-haptic feedback”: a technique meant to simulate haptic sensations in virtual environments using visual feedback and properties of human visuo-haptic perception. Pseudo-haptic feedback uses vision to distort haptic perception and verges on haptic illusions. Pseudo-haptic feedback has been used to simulate various haptic properties such as the stiffness of a virtual spring, the texture of an image, or the mass of a virtual object. This paper describes the several experiments inwhich,these haptic properties were simulated. It assesses the definition and the properties of pseudo-hapticfeedback. It also describes several virtual reality applications in which pseudo-haptic feedback has been successfully implemented, such as a virtual environment for vocational training of milling machine operations, or a medical simulator for training in regional anesthesia procedures. Pseudo-Haptic Feedback 3Presence Teleoperators & Virtual Environments 01/2009; 18:39-53. · 1.04 Impact Factor
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ABSTRACT: When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.Nature 02/2002; 415(6870):429-33. · 38.60 Impact Factor
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ABSTRACT: Optimal perception of surface roughness requires lateral movement between skin and surface, suggesting the importance of temporal cues. The roughness of periodic gratings is affected by changing either inter-element spacing (groove width, G) or element width (ridge width, R). Peripheral neural responses to gratings depend quantitatively on a spatial variable, G, and a temporal variable, grating temporal frequency (F(t)), with changes in R acting indirectly through concomitant changes in F(t). We investigated, psychophysically, the contribution of temporal cues to human tactile perception of roughness, using gratings varying in either R or G. Gratings were scanned across the immobile fingerpad with controlled movement speed (S) and contact force. In one experiment, we found that roughness magnitude estimates depended on both G and F(t). In a second experiment, discrimination of the roughness of gratings varying in either R or G was affected by manipulating F(t). Overall, the effect of G on roughness judgments was much stronger than that of F(t), probably explaining why many previous studies using surfaces that varied only in inter-element spacing led to the conclusion that temporal factors play no role in roughness perception. However, the perceived roughness of R-varying gratings was determined by F(t) and not spatial variables. Roughness judgments were influenced by G and F(t) in a manner entirely consistent with predicted afferent response rates. Thus perceived roughness, like peripheral afferent responses, depends in part on temporal variables.Journal of Neuroscience 08/2001; 21(14):5289-96. · 6.91 Impact Factor
Influence of Visual Feedback on Passive Tactile
Perception of Speed and Spacing of Rotating Gratings
Anatole Lécuyer1, Marco Congedo1, 2, Edouard Gentaz3,
Olivier Joly4, Sabine Coquillart5
1. INRIA Rennes, Campus de Beaulieu,
35042 Rennes Cedex, France, email@example.com.
2. ViBS Team, GIPSA-lab CNRS, Domaine Universitaire,
38402 Saint Martin d'Hères Cedex, France, firstname.lastname@example.org.
3. LPNC, CNRS and Université Pierre Mendès-France,
38040 Grenoble Cedex 9, France, email@example.com.
4. CEA LIST, 92265 Fontenay-Aux-Roses Cedex, France, firstname.lastname@example.org.
5. INRIA Rhône-Alpes-LIG, 655 avenue de l'Europe, Montbonnot,
38334 Saint Ismier Cedex, France, email@example.com.
Abstract. We studied the influence of visual feedback on the tactual perception
of both speed and spatial period of a rotating texture. Participants were placed
in a situation of perceptual conflict concerning the rotation speed of a
cylindrical texture. Participants touched a cylindrical texture of gratings rotating
around its axis at a constant speed, while they watched a cylinder without
gratings rotating at a different speed on a computer screen. Participants were
asked to estimate the speed of the gratings texture under the finger and the
spacing (or spatial period) of the gratings. We observed that the tactual
estimations of both speed and spacing co-varied with the speed of the visual
stimulus, although the cylinder perceived tactually rotated at a constant speed.
The first effect (speed effect) could correspond to the resolution of the
perceptual conflict in favor of vision. The second effect (spacing effect) is
apparently surprising, since no varying information about spacing was provided
by vision. However, the physical relation between spacing and speed is well
established according to every day experience. Thus, the parameter extraneous
to the conflict could be influenced according to previous experience. Such
cross-modal effects could be used by designers of virtual reality systems and
haptic devices to improve the haptic sensations they can generate using simple
(constant) tactile stimulations combined with visual feedback.
Keywords: Touch, Texture, Perception, Illusion, Speed effect, Spacing effect
Our everyday activities rely on the simultaneous and interactive involvement of
different senses. The exchanges between individuals and environment are mostly
multimodal. There has been increasing interest on multimodal integration and cross-
modal interaction, particularly on integration of vision and touch (Hatwell, Streri and
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Author manuscript, published in "EuroHaptics'10 - 2010 international conference on Haptics - generating and perceiving tangible
sensations: Part II Part II (2010) 978-3-642-14074-7"
Gentaz, 2003; Ernst and Banks, 2002; Lécuyer, 2009). Early studies on integration of
vision and touch used situations of sensory conflict and revealed a strong dominance
of vision for spatial properties (Rock & Victor, 1964). However, the notion of visual
dominance has been further modulated since, because other studies have shown a
“compromise” between the two conflicting values (Heller, 1983). It seems that in
spatial conflicts vision is usually dominant, but tactual information comes into play
abruptly when inter-modal coherence is broken. Moreover, results are different for
material properties, which are the domain favored by touch. For instance, tactual
perception of textures is as efficient as visual perception and sometimes, for fine
textures of abrasive papers, touch surpasses vision (Heller, 1989). Contrary to what
was found for spatial properties, Heller (1989) and Lederman (1974) observed no
difference between active exploration (participants rub the object with their fingers)
and passive one (the object is moved under the immobile fingers). Thus, perception of
textures might be less the result of kinesthetic than of cutaneous information. In a
conflicting situation on textures properties, with abrasive paper seen and touched, the
participants gave compromise responses (Lederman & Abbott, 1981). Their
evaluation of the conflicting texture was a mean of the visual and tactual values.
Lederman, Thorne and Jones (1986) dissociated two elements of textures: the notion
of “roughness” (a material property) and the spatial density of the grains (a geometric
property). A tactual-dominant compromise appeared when participants were
instructed to estimate roughness, whereas a visual capture appeared when participants
were instructed to evaluate the spatial density of the grains. Tactual dominance in the
estimation of roughness was also observed in passive exploration (Guest & Spence,
In few studies, the issue of how the perceptual influence on one parameter
influences other parameters physically related to it has been addressed (Lécuyer,
2009). To further investigate this issue, we set up an unusual situation of perceptual
conflict regarding the rotation speed of a cylindrical texture (a texture glued on a
rotating cylinder). Participants touched (without active movements) a cylindrical
texture made of gratings rotating around its axis at constant speed, while watching on
a computer screen a representation of a cylinder without gratings rotating at a
different speed. The rotation of the visual stimulus was sometimes largely accelerated
or decelerated when compared to the actual rotation of the gratings under the finger.
Participants were asked to estimate both the speed of the gratings texture under the
finger, and the spacing, i.e., spatial period, of the gratings. The reviewed literature
suggests that the visual perception of speed could dominate the tactual one. We then
expected the tactual perception of speed to be influenced by the visual speed. We also
studied the possible influence of the perceptual conflict on the tactual estimation of
the spatial period of the texture.
Population: Ten adults (6 men and 4 women) took part in this experiment. All
participants were right-handed.
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Experimental apparatus: The texture used as tactual stimulus was a cylindrical
texture of gratings (Figure 1-left). The gratings had a 1.5mm height (or amplitude)
and a 5mm spacing (or spatial period). The cylinder on which the texture was glued
had a 50mm diameter. The spacing of the gratings texture remained constant since the
same texture was used along the whole experiment. The texture was set in rotation by
an electrical motor. The texture was touched with the left index, perpendicularly to
the axis of the cylinder and thus to the texture. The texture rotated from the interior to
the exterior of the finger. The tactual stimulus was hidden to the participants’ view by
means of a box which enclosed both texture and participants’ left hand. The left index
rested on the gratings without any motion. As a consequence, the tactual perception of
gratings was passive and based exclusively on cutaneous information. A small screen
could be positioned between the index and the stimulus in order to enable or disable
the contact between the finger and the texture. It was removed when testing the
texture and immediately replaced after it.
Fig. 1. Experimental apparatus: (Left) Tactual texture of gratings; (right) Visual scene.
The visual scene was made of a rotating cylinder (Figure 1-right). This cylinder
had the same radius as the real cylindrical texture (i.e. 50mm) and was 10cm long.
The visual texture used and mapped on the cylinder on the screen was a standard
image (terra cotta) provided with the O2 graphic workstation of the SGI Company.
This texture was considered as “neutral”, as it did not provide meaningful information
in terms of spacing of the gratings. The visual stimulus was displayed on a computer
screen in monoscopic conditions. The participants were seated 30cm in front of the
screen. The eyes of the participant were at the same height as the display of the
cylinder on screen. The frame rate of the visual stimulus was of 15Hz.
Experimental procedure: During a test, participants were asked to touch the tactual
stimulus with their left index while looking at the computer screen. Participants were
told that the cylinder displayed on the computer screen was a representation of the
rotating shaft on which their finger rested. We used the magnitude estimation method
(Lederman, Thorne & Jones, 1986). During each trial, participant began to perceive
the speed and spacing of a first texture (reference condition). After a 2-second break,
they were asked to perceive the speed and spacing of a second texture (comparison
condition). Participants were allowed unlimited time needed to evaluate each texture,
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but they were asked to perform the trials as quickly as possible. After each trial, the
participants were asked to grade both the speed and the spacing of the comparison
texture located under the finger, as compared to the reference texture, using a 10-
based scale. For example, a speed –or spacing– of the comparison texture estimated as
two times faster –or wider– was graded with a 20 value. For the purpose of the
analysis, the estimations can be converted into rpm values for the speed and mm
values for the spacing.
The spacing of the gratings remained constant throughout the experiment and equal
to 5mm. The rotation speed of the texture remained also constant under the finger and
equal to 15rpm for both the reference and the comparison conditions. The linear speed
of the texture at the surface of the finger was thus equal to 39.27mm/s. In the
reference condition, the visual speed of the cylinder on the computer screen was also
equal to 15rpm. In the comparison condition, 7 different visual speeds were used
(smaller, equal or greater than the tactual one): 7.5, 10.5, 13.5, 15, 16.5, 19.5, and
22.5 rpm. Each comparison pair was tested 4 times, for a total of 4x7=28 trials per
participant. The 7 comparison pairs were presented randomly. The experiment lasted
around 40 minutes. The participants wore earphones to eliminate noise cues.
Fig. 2. Experimental results (black circle = one participant, black rhombus = average): (Left)
Estimated tactual speed of the texture ; (Right) Estimated spatial period of the texture.
Estimation of Speed: Figure 2-left shows individual estimations of the tactual speed
averaged across the four blocks of trials. The fitted line with all individual estimations
(N=70) has equation y=6.87x+0.61. The R-squared value is 0.53. The t-test for the
slope being different from zero is significant (t(68)=8.75; p<0.0001). The estimated
tactual speed seems thus positively correlated to the visual speed.
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Estimation of Spatial Period: Figure 2-right shows individual estimations of the
spatial period averaged across the four blocks (N=70). With spatial period data
converted to rpm values, so to allow comparison with results obtained with Speed
estimation, the obtained fitted line has equation y=4.68x+0.71. The R-squared value
is 0.67. The t-test for the slope being different from zero is significant (t(68)=11.74;
p<0.0001). The estimated spacing is positively correlated to the visual speed. Thus,
the tactual estimates of the spatial period of the texture seem also influenced by the
speed of the visual stimulus.
Summary of results: Our studies explored two cross-modal effects of vision on
tactual perception. The first effect, named the “speed effect”, concerned the visuo-
haptic perceptual estimation of the rotation speed of a cylinder. All participants
reported a change in the tactual speed although this speed remained constant during
all trials. If the visual and tactual percepts do not agree, the visual feedback was found
to influence the tactual perception of the constant stimulus. The second effect, named
the “spacing effect”, concerned the estimation of the spatial period (spacing) of the
gratings texture located on the cylinder. When the visual speed was greater than the
real one, the participants reported that the spacing of gratings increased, and when the
visual speed was smaller than the real one they reported that the spacing decreased. In
this case, no relevant information about spacing was provided by the visual stimulus,
but the tactual estimation of spacing was still influenced as for speed. Therefore this
experiment shows that when touching gratings which rotate at a constant speed, the
tactual perception of both the speed and spatial period of the gratings is influenced by
the visual perception of the rotation speed of a “neutral” texture rotating at different
speeds. The speed and spatial period of the texture perceived tactually tend to increase
(or decrease) when the rotation of the visual stimulus is accelerated (or decelerated).
Indeed, the varying visual stimuli influence the perception of the two constant tactual
parameters. A relation between stimuli coming from separate modalities is built by
the participants, and question of how this phenomenon operates remains open.
Discussion: The speed effect is in line with previous research showing that for spatial
properties vision dominates touch in the bimodal integration process. The spacing
effect is more surprising. No explicit relation existed in the experimental materials
between the parameter estimated tactually and the visual stimulus. There was indeed
no relevant information available on the visual scene to provide a notion of spatial
period of the gratings. However, a cross-modal association is arbitrarily established
between the two stimuli, as shown by Figure 2. An interpretation of the spacing effect
consists in considering a texture of rectangular gratings moving at the surface of a
finger. A relation does exist between three parameters: the speed of the texture, its
spatial period (spacing) and the resulting temporal frequency which corresponds to
the temporal activation of the surface of the finger at a single point (Cascio & Sathian,
2001). This relation ensures the physical homogeneity and is given by Equation 1,
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