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1

Psychophysical Dimensions of
Tactile Perception of Textures
Shogo Okamoto, Hikaru Nagano, and Yoji Yamada, Member, IEEE
Abstract—This article reviews studies on the tactile dimensionality of physical properties of materials in order to determine a common
structure for these dimensions. Based on the commonality found in a number of studies and known mechanisms for the perceptionof physical properties of textures, we conclude that tactile textures are composed of three prominent psychophysical dimensions
that are perceived as roughness/smoothness, hardness/softness, and coldness/warmness. The roughness dimension may be divided
into two dimensions: macro and fine roughness. Furthermore, it is reasonable to consider that a friction dimension that is related tothe perception of moistness/dryness and stickiness/slipperiness exists. Thus, the five potential dimensions of tactile perception aremacro and fine roughness, warmness/coldness, hardness/softness, and friction (moistness/dryness, stickiness/slipperiness). We also
summarize methods such as psychological experiments and mathematical approaches for structuring tactile dimensions and theirlimitations.
Index Terms—Factor analysis, Multidimensional scaling, Sensory evaluation✦

1

I NTRODUCTION

H

UMANS perceive the physical properties of materials
or textures by touching their surfaces. Thus far, theperceptions of properties such as surface roughness andelasticity have been summarized in review articles [1], [2],[3], [4] from a psychophysical and neurophysiological pointof view. However, a thorough discussion of the perceptual
dimensionality does not exist in the literature. The dimensional
structure of the perceptual space has attracted the interests ofresearchers in haptics, and many studies have been conductedattempting to specify this structure. However, the structures
reported by these studies have varied, depending on the methodof psychological experiment, the mathematical approach, thestimuli used in the experiments, and other differences in themethodology. For example, one research team asserted thatthe perception of texture was constructed by three dimensions
i.e., roughness, hardness, and slipperiness, however, anotherteam demonstrated that four dimensions were involved. Thesestudies have not been comprehensively investigated after their
publication. Furthermore, the experimental methods and analytical approaches employed in each study suffer from significant drawbacks and as a result the dimensionality constructedin each individual study is incomplete. The objective of thisarticle is to investigate as many related works as possible andcompensate for their individual incompleteness in order tofind the common structure of perceptual dimensions. We also
summarize experimental and analytical methods for structuring
such dimensions along with their limitations for the benefit ofthose who attempt to develop perceptual dimensions.

• The authors are with the Department of Mechanical Science and Engineering, Nagoya University, Japan.
E-mail: see http://www.mech.nagoya-u.ac.jp/asi/• This study was supported in part by MEXT KAKENHI (23135514).

Digital Object Indentifier 10.1109/ToH.2012.32

Definition of psychophysical dimension: We define
tactile perception as the perception of the qualities and properties of material surfaces by touch. The shapes of objects
are of no concern of this article. Because the dimensionalityof the perception of tactile surfaces is still contentious, it
is reasonable to focus only on surface perceptions, althoughhaptic dimensions involving surface and shape perceptions
would be more intriguing (and also more complicated). In
general, human perception can be described by a hierarchy,
which also holds for tactile perceptions. Following the studies
by Chen et al. [5], [6], we assume that tactile perception
is composed of psychophysical and affective layers. The
psychophysical layer determines the perception of physicalproperties, such as surface roughness or the elasticity ofmaterials. The affective layer is mediated by a mental process
and includes perceptions such as richness, cleanliness, andkindness. In this article, we address the psychophysical layer.
The psychophysical layer is more fundamental, and a common
understanding or standardization of this layer will be useful for
haptic researchers. For example, an understanding of humantactile dimensions is helpful in the design of tactile displays
and sensors. The developers of these systems aim to extend
their systems to make them multimodal. The generalizationof tactile dimensionality indicates which dimension should beconsidered.

2

M ETHODOLOGY FOR S PECIFYING P ERCEP TUAL D IMENSIONS

Here, we describe methodologies used for specifying thedimensions of tactile perception. In general, we first need tocollect subjective data for various materials. Typical subjective
data are the perceptual ratings of material properties using
adjective labels or perceptual similarities between materials.
Multivariate analyses are then applied to the collected subjective data in order to extract potential perceptual factors and1939-1412/12/$31.00 © 2012 IEEE

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TABLE 1
Combination of mathematical and experimental methods
for structuring perceptual dimensions
Semantic differential method
Similarity estimation method
Classification method

Factor or principal
component analysis
Multidimensional scalingCircle or triangle indicates more or less frequently used approaches, respectively.

dimensions. We summarize psychological experiments used
for data collection and multivariate analyses in this section.
Table 1 shows the combinations of psychological experiments
and multivariate analyses that have been used in related
works. A circle or triangle indicates that the corresponding
combination has been used more frequently or less frequently,
respectively.
2.1

Collection of Subjective Data

In this section, we introduce the semantic differential (SD),similarity estimation, and classification methods, which areused for acquiring subjective data. In the SD method, subjective data are collected using adjective labels such as rough or
hard. Subjective data collected by SD methods are analyzed bya factor or principal component analysis. In the similarity estimation and classification methods, gross perceptual distances
between two materials are acquired while the participants are
asked to ignore certain types of physical material properties
such as the roughness or elasticity. Perceptual distances areanalyzed by multidimensional scaling (MDS) methods.
2.1.1 Semantic differential (SD) method
SD methods were originally established by Osgood et al. [7],and first applied to the study of the dimensionality of tactile
perception by Yoshida [8] in 1968. Since then, a numberof researchers employed this method. In an SD method,
participants rate materials one by one using scales whoseends represent the two adjectives in an opposing pair such as“rough” and “smooth,” as criteria for evaluation. Five or sevengrades were used in many cases. SD methods were used mostfrequently by researchers, including the authors of [8], [9],[10], [11], [12], [13], [14]. Instead of adjective labels, someresearchers used onomatopoeic expressions [11], [12].
Strength & limitation: SD methods allow us to interpretfundamental tactile factors without additional experiments thatare typically required for other methods because each factor
is explained by a combination of adjective words. In contrast,
fundamental factors extracted through SD methods are limitedby the adjective pairs used in experiments. If adjective labelsthat represent a certain perceptual dimension are not involved,that dimension remains unextracted. Thus, the labels should
be chosen such that they cover all potential dimensions.
2.1.2 Similarity estimation method
In many studies, participants rated the similarity of paired
materials. Although various methods exist for rating the similarity, most of the similarity estimation methods fall into one

2of three groups: ratio judgment, grading, and visual analog
scaling. In the ratio judgment method, participants estimate
the relative perceptual distance of materials in a pair using
arithmetic values. Ratio judgment methods were used in [15].
In the grading method, the similarity between two materials isgraded using, for example, a seven-point scale. This method
was used in [16], [17]. In the visual analog scaling method,
participants rate the relative distance by placing a mark on adrawn line. For example, a line with “dissimilar” and “similar”
labels on both poles can be used. Visual analog scaling
methods were used in [18], [19].
Strength & limitation: Unlike SD methods, the numberof dimensions constructed by this method is not affected by
adjective words because it does not involve specific adjectives.
The similarity data acquired by this method is analyzed by
a MDS method. Hence, the drawbacks of MDS, which will
be discussed in sec. 2.2.2, should also be considered. The
main drawback of similarity estimation methods relates to thenumber of trials. The similarity between all possible pairs of
stimuli needs to be tested in order to use classic MDS methods.
Hence, researchers who use paired comparison methods tend
to limit the number of texture stimuli. From limited types oftextures, limited numbers of dimensions are revealed.

2.1.3 Classification method
In the classification method, participants classify many materials that are simultaneously presented to them into groups basedon the similarities of the materials. Materials in the same groupare supposed to be perceptually similar. Dissimilarity scores
between materials are computed based on the classification.
For example, the materials in the same group are assigned dissimilarity scores of 0, whereas the dissimilarity score between
two materials in different groups is set to 1. The results from a
sufficient number of participants produce similarity distancesamong the materials. Classification methods were used in [20],[21], [22], [23].
In the free arrangement classification method, which wasused in [24], participants locate materials on a plane such thatthe geometric distances of materials accurately represent theperceptual distances of materials. The geometric distances areused to calculate the perceptual distances between materials.
This method tends to limit the perceptual space to twodimensions because the space is constructed based on thestimuli spread on a plane.
Strength & limitation: This method is participantfriendly in terms of time required for experiments, whichallows us to test a sufficient number of textures. It is notpossible to discuss the classification method in detail due tounsatisfactory literature relating to comparative research on
the experimental methodology. However, one may consider
that it is extreme to assume textures belonging to the samegroup have no dissimilarity. Furthermore, this method typicallydoes not assume subclasses. Each stimulus belongs to only
one class. These assumptions may lead to the loss of somedistinctions between textures.

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2.2

3

Multivariate analyses for subjective data

2.2.1 Factor analysis (FA)In factor analysis, inherent factors are extracted from multivariate data after testing for correlations between variables.
The number of factors is lower than the number of variables,
whereas the factors represent a large portion of the variancein the original data. This analysis is applied to data acquired
by SD methods. Let x i (i = 1, ..., n) represent subjective datacollected for n materials using p adjective pairs. x i can thenbe represented by the scores of m factors f i , a factor loading
matrix A , and a unique factor e i . x i can be written as follows:
xi = Ap×1

f i + eip×m m×1
p×1(i = 1, · · · , n).

(1)Each of the m factors is considered an independent factor
that constitutes a perceptual dimension. Principal component
analysis is also applied to data collected by SD methods. This
analysis is similar to factor analysis in that the variation oforiginal variables is represented by fewer factors.
2.2.2 Multidimensional scaling (MDS)
A multidimensional scaling method places materials on an rdimensional space such that the perceptual distances between
the materials are optimally maintained. Perceptual distances
determined by similarity estimation or classification methods
are often used to set the separation distances of materials.
Some researchers selected the subjective distances between
materials using data acquired by SD methods [8], [9].
When the perceptual similarities between materials j andk for all material pairs are given as E = (e jk | j = k), ( j, k =1, ..., n), the coordinates of n materials on an r-dimensional
space are determined by minimizing the following function:nn

Q = − ∑ ∑ e jk  y j − y k 2 ,(2)

j=1 k=1

where y j is the coordinate of material j. Each of the r dimensions is considered to be a potential perceptual dimension.
Limitation: The drawback of the MDS method is thatthe orthogonal rotation of the constructed space is indeterminate. An individual axis never corresponds to an individual
psychophysical dimension. Many researchers have noted the
difficulties of interpreting results from an indeterminate axis
system. Thus far, methods for this interpretation have varied
between researchers. Even worse, in some literature, thisinconvenient nature of the MDS method is almost entirely
neglected.
2.2.3 Imbalanced textures: limitations common to bothanalytical methods
Both analytical methods reveal a lower number of variables
than is required to accurately describe the variations in theoriginal data. If the original data is imbalanced in its density,then the characteristics of less dense data are unlikely to be
detected. For example, moist or adhesive sample materials
are less frequently used, whereas paper, fabric, rubber, stone,or leather materials, which are easily stored and prepared inlaboratories, are often adopted. When using these common

sample materials, factors representative of moist or adhesivematerials are unlikely to be detected. An imbalance in therange of materials used is a problem common to most studies.
None of the studies balanced or determined stimuli sets after
a satisfactory discussion of the issue. A simple increase in
the number of stimuli is not recommended because without
careful consideration of the properties, this may not balance
the range of materials. The balance of stimuli in the sample
set should be considered rather than the quantity of stimuli.
2.3 Post hoc validation of dimensionality
The interpretation of factors or dimensions extracted by theabove multivariate analyses is sometimes problematic. For
example, we cannot judge with certainty whether a specificfactor represents a perceived surface smoothness or elasticity
in some cases. In other cases, it is virtually impossible to interpret and name a dimension even when its contribution ratio
is large. An intuitive interpretation of factors and dimensions
was used in some research studies. Thus, a validation of thisinterpretation is necessary. Validation is especially requiredfor dimensions determined by MDS methods. In SD methods,
the characteristics of individual factors can be estimated tosome extent using the factor loadings of adjective labels. There
are two methods for validating the interpretation. One method
uses adjective labels, whereas the other exploits the physicalproperties of materials.
During validation using adjective labels, participants ratematerials using adjectives. The properties of the dimensions
are validated mainly based on the correlations between theadjective ratings and the scores of individual dimensions. For
example, when the scores on a specific dimension have strong
correlation with the ratings of “rough,” we interpret this tomean that this dimension is related to roughness perception.
Validation using adjective labels was performed in [19], [20],[21], [25].
During validation using the physical properties of materials,
correlations between the scores of individual dimensions orfactors and physical values such as the average roughness
or Young’s modulus are considered. For example, when thescores on a specific dimension have a strong correlation
with the average roughness of materials, this dimension isconsidered to be related to roughness perception. Validation
using physical properties was performed in [15], [18], [23].
2.4 Limitations of adjective labels
As described thus far, adjective labels are often used for thedetection and validation of perceptual dimensionality. Hence,these methods suffer from the difficulties associated withselecting appropriate adjectives.
One problem is a limited vocabulary, i.e., when there is not
an appropriate adjective to describe a certain dimension or
factor. For example, some researchers attempted to separate
the macro and fine roughness dimensions, and a few of themsucceeded. The problem here is that adjectives indicating the
opposite poles of macro and fine roughness are semanticallysimilar: they are “flat,” “smooth,” and “even.” Furthermore,when it comes to tactile perception, the vocabulary relatingThis article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.

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to physical properties of materials is limited. Hence, verbal
methods always restrict the structuring of dimensionality. One
comprehensive list of possible adjective terms relating to touch
can be found in [26].
Another problem is a consensus among participants. Soufflet et al. found a case in which the consensus of adjective
terms became a problem [27]. In their research using verbal
labels, women tended to classify fabrics into smaller subgroups
than men. Also, the majority of those who were working in
the textile industry used “nervous” as a sensory property offabrics, which did not correspond to any words used by thenon experts.

3 S TUDIES ON S TRUCTURING P ERCEPTUAL
D IMENSIONSWe searched for studies on psychophysical dimensions oftactile perception using scientific archives including Science
direct, SpringerLink, google scholar, and Web of Science
with the keywords such as “tactile,” “texture,” “dimension,”“factor,” “multidimensional scaling method (MDS),” “factor
analysis,” “principle component analysis,” and “correspondence analysis.” Among potential candidates, we selected ones
investigating the dimensional structures of tactile perception.
Those focusing on specific single dimensions such as roughness were excluded.
Table 2 lists several studies on the structuring of perceptual
dimensions and the materials used in each experiment. The
names of dimensions may differ from those in the original papers summarizing these studies. We qualitatively summarized
the names by taking into account how they were discovered.
The individual studies are described in detail in this section.
Yoshida 1968 (Roughness, hardness, warmness & moistness): In this experiment, 25 materials including silver, aluminum, vinyl, nylon, silk, and linen were used, and subjective
data was collected using an SD method in which 20 adjective
pairs were rated [8]. Twenty-five participants freely exploredthe materials with vision. Compared with the participants inother related works, they were allowed more freedom to touch
the materials, so they could pinch and hold the materials.
Using a factor analysis, four factors were extracted.
The first factor was described by “painful or not painful,”“hard-soft,” “cold-warm,” and “rough-smooth” scores in descending order. It should be noted that “pain” does not fit
the definition of a psychophysical dimension. As a result,
we assume that the first factor was a mixture of hard/soft,
cold/warm, and rough/smooth dimensions.
The second factor loaded “wet-dry,” “heavy-light,” “substantial or empty and hollow,” and “smooth-rough.” “Substantial or empty and hollow” was possibly connected withthe weight or density of materials because its scores andthose for “heavy-light” were highly correlated. We exclude
the properties related to weight from the surface properties oftextures. Hence, the second factor was a mixture of moist/dry
and rough/smooth.
The third factor was strongly associated with “sharp-dull.”This adjective pair was almost ignored without reason, andthe dimension was called “hard-soft” that exhibited the second

4highest load even though it was half the load of “sharp-dull.”
It is not clear how participants interpreted the terms “sharp”
and “dull.”
The fourth factor was related to “elastic or not elastic.”
We assume that “elastic” represented the bending stiffnessof materials, because the participants could hold and bend
the materials. However, in most of the other studies, theparticipants were allowed to touch only the surface of thematerial, and some of these studies separated the properties
related to the bending stiffness or thickness of materials fromthe perception of surfaces. We also follow the latter concept
and focus on surface properties only.
Lyne 1984 (Hardness & roughness): Lyne et al. structured
the perceptual space of eight types of tissue papers and paper
towels using a similarity estimation method and MDS [18]. In
their experiment, forty participants rated pieces of paper withvisual and haptic perceptions.
They extracted and named three dimensions based on thecorrelationship between physical parameters: namely, surface softness, rigidity, and embossed properties. The surface
softness dimension corresponded to hardness/softness. The
perceived rigidity was strongly correlated with the bending
stiffness, which we exclude from the surface properties oftextures. The embossed dimension accurately represented theembossed patterns of paper surfaces. Pieces of paper embossedwith a large square were located on one pole, and piecesof paper embossed with a small circle were located on the
opposite pole. From reviewing the experimental data, it is clearthat this dimension is related to macro surface patterns or paperroughness.
Hollins 1993 and 2000 (Roughness, hardness & slipperiness): Hollins et al. investigated the perceptual dimensionsof 17 materials, including paper, plastic, and velvet [20].
In their experiment, twenty participants passively exploredmaterials where the material beneath a finger pad moved.
Participants conducted classification tasks, and subjective data
were analyzed using a MDS method. As a result, three factors
were extracted. By comparing the correlations between thefactor scores and ratings acquired by adjective scales, they
named each factor. The first factor was correlated mostly
with smooth/rough, then with flat/bumpy, slippery/sticky, andcool/warm in descending order. Smooth/rough and flat/bumpy
were regarded as semantically identical due to the high correlation between their results. The second factor was highly
correlated with soft/hard. The third factor did not show strong
correlations with any adjective scales and was slightly correlated with sticky/slippery (r = 0.43) and bumpy/flat (r = 0.37).
They named this factor the “elastic factor” mainly becausematerials with prominent compressive properties were locatedalong this factor, however, the definition of this factor was
fairly unspecific.
Later, Hollins et al. re-investigated the structure of perceptual dimensions using a similarity estimation method [19].
They focused on personal differences of dimensionality
rather than on its general structure. As a result, participants demonstrated two- or three-dimensional structures.
The two-dimensional spaces were robustly constructed byrough/smooth and soft/hard scales. For some participants,

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5TABLE 2
Reference table of studies on perceptual dimensions of tactile textures
AuthorYear

TextureYoshida [8]1968

25 materials

Lyne [18]1984

8 tissues &paper towels

Hollins [20]1993

17 materials

Hollins [19]2000

17 materials

Tamura [13]2000

15 materials

Picard [21]2003

24 car seats

Picard [25]2004

40 fabrics

Soufflet [27]2004

26 fabrics

2005

20 materials

Rough/smoothHard/soft

Slippery/sticky

2005
2005
2006

20 materials
7 raised dots
124 materials

2006

13 fabrics

Yoshioka [15]Summers [29]Guest [30]
Guest [26]

2007
2008
2011
2011

16 materials
10 papers
15 fluids
5 fabrics

Cold/warm
Rough/smooth
Smooth/roughHard/soft,
Cold/warm
Rough/smooth

Moist/dryFine roughness
Not named

Tanaka [11]Rough/smooth
Macro roughness
Hard/soft
Moist/dry,Rough/smoothHard/soft
Rough/smooth
Slippery/sticky
Rough/smoothRough/smooth
Moist/dryOily
Hard/soft

Ballesteros[22], [24]Shirado [12]Gescheider [28]Bergmann Tiest [23]Dimension 1
Hard/soft,
Cold/warm,
Rough/smoothHard/soft
Rough/smooth,
Warm/cold,
Sticky/slippery,
Rough/smoothRough/smoothHard/soft
Hard/soft,
Rough(Fine roughness)
Hard/soft
Rough/smoothHard/softrough/smooth was strongly correlated with sticky/slippery.
For those who demonstrated the three-dimensional spaces,rough/smooth and sticky/slippery were associated with different dimensions. This study concluded that the importance of
sticky/slippery dimension varies between individuals.
Tamura 2000 (Roughness, hardness, warmness, & moistness): Tamura et al. acquired subjective data from participants
using an SD method [13]. They used 15 materials, includingaluminum, duralumin, rubber, and wood. Eleven adjective
pairs were used and 20 participants joined the study. It
was not clear whether participants were blindfolded. As aresult of their factor analysis, Tamura et al. constructed three
dimensions. The first dimension was correlated with hard/softand rough/smooth ratings. The second dimension showed astrong correlation with warm/cold ratings. The third dimension
was correlated with moist/dry ratings.
Picard 2003 and 2004 (Hardness, fine & macro roughness): In experiments conducted by Picard et al., twenty participants classified 24 materials on the basis of similarity [21].
Then, these similarities were analyzed by a MDS method.
Four dimensions were extracted and specified by verbal labels
applied to the materials. The materials were those used for carseats, such as velvet, plastic, and artificial suede.
The first dimension was frequently described by the labelsof soft, mellow, smooth, and pleasant on the one side andharsh, rough, and hard on the other side. “Harsh” and “rough”
are semantically close and exhibited similar correlation coefficients with the first dimension. Similarly, “mellow” and “soft”

Dimension 2
Moist/dry,
Smooth/roughDimension 3

Dimension 4

Hard/soft

Visuo-hapt.

Embossed(Roughness)
Hard/soft

Modality

Visuo-hapt.
HapticHard/soft

Not specified(Stiff)Sticky/slippery

Warm/cold

Moist/dry

Unknown

Relief(Macro roughness)

Hard/soft

Haptic

HapticRough/smooth

HapticWarm/cold

Haptic
HapticHard/soft
Not named

HapticUnknown
Haptic
HapticSticky/slippery

Haptic
Haptic
Haptic
Hapticwere close in terms of correlation coefficients. Hence, we consider that this dimension was a mixture of the rough/smoothand hard/soft dimensions.
The second dimension was mainly described by the terms
thin and thick and was slightly correlated with the relief andsmooth scales. We exclude the thickness of materials from thesurface properties.
The third dimension was correlated with relief scales. The
other side of the “relief” was “smooth,” but these were notcompletely aligned.
The fourth dimension was slightly correlated with the hardand mellow scales. This was not identical to the first dimension
because the fourth dimension was not correlated with therough and smooth scales at all.
We consider that two types of roughness should be considered: macro and fine roughness. The features of macroand fine roughness were explained by “relief,” and “rough,”
respectively. However, the opposing term for both these two
types of roughness could be “smooth.” “Smooth” was not rated
as the exact opposite of “rough,” or “relief,” and it tended tobe better aligned with “relief.” This clearly demonstrates a
vocabulary problem, i.e., it is not easy to assign appropriate
opposing terms to two types of roughness.
Considering all the results, the dimensions were interpreted
as follows. The first was mediated by the terms rough/smooth
as well as hard/soft. The second was represented by thin/thick.
The third and fourth were the macro-roughness (relief/smooth)and hard/soft dimensions, respectively.

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Picard et al. also conducted similar studies involving fabrics [25]. Twenty blindfolded participants performed a classification task using twenty types of fabrics. Another twenty
participants performed the same task using twenty different
types of fabrics. The results from the two groups were separately analyzed using MDS methods. The dimensions werethen interpreted using unipolar adjectives that were attached
to clusters of similar fabrics by the participants. One slightly
minor and two major dimensions were found for both groups.
The perceptual spaces of the two groups were a fair match,and it was concluded that the space was constructed with thefollowing three salient dimensions–rough/smooth, hard/soft(although it was stated that harsh/soft was more appropriate
for these analyses), and thin/thick. Furthermore, it was suggested that, as dimensions, slippery/sticky and relief/silky wereelicited by specific materials and were not salient.
Soufflet 2004 (Roughness, hardness, & warmness): Soufflet et al. constructed the perceptual dimensions of 26 fabrics
using a classification method. Then, they extracted threepotential dimensions. Eleven industrial experts and 40 novices
joined the experiments. Participants were allowed to hold thefabrics in a dark room that moderated the effects of vision.
According to the correspondence between the adjective
labels and fabrics, the first dimension was related with thelabels “harsh,” “rough,” and “stiff.” The label “soft” was placedat the other extreme of this dimension. This dimension isconsidered to be a mixture of hard/soft and rough/smooth,noting that the “smooth” label was not clearly align with thisdimension.
The second dimension was represented by the thin/thicklabels. Near the “thin” label, “smooth,” “slippery” and “cool”
labels were observed. “Warm” and “wooly” labels were placednear the “thick” label. This dimension is therefore considered
to be a mixture of thin/thick and cool/warm dimensions. Also,
non wooly fabrics may have tended to be slippery and smooth.
Soufflet et al. wrote that the interpretation of the third
dimension was not easy, however, based on the corresponding
adjective labels, they specified this dimension as stiff/supple:
it represents the bending stiffness of fabrics.
Ballesteros 2005 (Roughness, slipperiness, & hardness):
Ballesteros et al. investigated the perceptual space of 20
materials including tile, soap, adhesive tape, and a sponge [22],[24]. They used free classification and spatial arrangement
methods in order to collect data for a MDS method. In [22],they reported a two-dimensional model from 16 participants.
They named the factors from the characteristics of materials
distributed on the constructed perceptual space. The first
dimension was named the rough/smooth factor. The second
dimension was named the slippery/sticky and hard/soft factor.
In [24], they proposed a three-dimensional structure in which
the three dimensions were rough/smooth, slippery/sticky, andhard/soft.
Shirado 2005 (Roughness, warmness, moistness, & hardness): Shirado et al. acquired subjective ratings of 20 materials
such as metal, textile and wood using an SD method [12].
Thirty participants explored the materials without vision. They
used 13 adjective and Japanese onomatopoeia label pairs
such as sara-sara/nuru-nuru and zara-zara/sube-sube. The

6four factors were referred to as rough/smooth, cold/warm,
moist/wet, or hard/soft based on the combination of factor
loadings.
Gescheider 2005 (Macro & fine roughness): Gescheider et al. investigated the perceptual dimensions of raised-dot
textures using the adaptation of Pacinian channels [28]. They
prepared plastic trapezoidal dots that were arranged with interdot spaces ranging from 1.34 mm to 5.93 mm. Nineteen participants rated inter-texture differences using 15-grade scales.
In order to reduce the stickiness of textures, talcum powder
was rubbed on fingers of participants. Gescheider et al. used
the adapted and unadapted conditions of Pacinian channels
because their major objective was to investigate the roleof Pacinian corpuscles on roughness coding. The adaptation
was realized by 250 Hz vibration stimuli. The inter-texture
difference data were analyzed by a MDS method, and three
dimensions were extracted. The attributes of each dimension
were predicted based on interviews with participants.
The first dimension was termed the blur dimension, whichindicates “a degree to which individual dots cannot be felt,
but instead blur together.” The second dimension was termed
the roughness dimension. The third dimension was termed
clarity, which was defined as “a contrast between the dots
and background.” Later, these attributes were successfully
validated through a magnitude estimation method, in which
participants rated textures using three criteria: blur, roughness,and clarity.
Macro roughness (Pacinian-independent): The blur androughness dimensions were both functions of dot spacings,
whereas their profiles were clearly different. The scores in theblur dimension monotonically decreased with increasing dot
spacing. On the other hand, the scores in the roughness dimension fell along an inverted u-shaped curve that was similar
to profiles observed for the curve of the perceived roughnessof gratings (e.g. [31]). The adaptation did not influence theblur and roughness dimensions. Hence, we speculate that blur
represented Pacinian-independent macro roughness.
Fine roughness (Pacinian-dependent): The clarity dimension
was affected by the adaptation of Pacinian channels, but not by
the dot spacing. In additional experiments, it was found thatthe clarity dimension was related to the roughness of individual
dots rather than the spaces between dots. Hence, the clarity
dimension represented Pacinian-dependent fine roughness.
Gescheider et al. separately extracted the macro and fineroughness dimensions. Interestingly, when the participants
were explicitly asked to rate the overall roughness of textured
surfaces, these two dimensions were integrated. This study
suggested that the attention or instruction given to participants
could modify the constructed perceptual dimensions.
Bergmann Tiest 2006 (Roughness & hardness):
Bergmann Tiest et al. investigated the perceptual space of 124
materials using a classification method involving twenty blindfolded participants [23]. The materials included wood, glass,paper, rubber, cloth, and plastic. The perceptual dimensions
were constructed by a MDS method, and four dimensions wereextracted.
The first and second dimensions were specified by hard/softand rough/smooth factors, respectively, based on the correla-This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.

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tions between relevant physical values. The other two factors
were not clearly interpreted.
Tanaka 2006 (Roughness, moistness, hardness, & warmness): Tanaka et al. constructed the perceptual space of
13 textiles, including cotton, silk, and satin, using an SD
method [11]. Twenty-one blindfolded participants rated textiles
using seven adjective pairs. They extracted two potential factors using a factor analysis. The first factor was described by
the labels moist/dry and rough/smooth. The second factor was
described by the labels hard/soft, flat/downy, and cold/warm.
Because all materials were textiles attached on flat boards, thelabels flat/downy were considered to be semantically similar
to hard/soft.
Yoshioka 2007 (Roughness, hardness, & slipperiness):
Yoshioka et al. structured the perceptual dimensions of 16
materials, such as paper, rubber, denim, and suede, using
a similarity estimation method [15]. They applied a MDS
method to the dissimilarity scores acquired from eight participants. They extracted three dimensions and specified them bycomparing the results of adjective ratings given to each material. According to the adjective ratings, these dimensions were
described by rough/smooth, hard/soft, and sticky/slippery.
Summers 2008 (Roughness): Summers et al. constructed
the perceptual space of ten types of paper that could be
used for banknotes [29]. Using haptic cues without vision,
participants selected one of three samples. Two of the samples
were made of the same material. They were instructed to pickup the pieces of paper using one hand and pass it to the otherhand. From the answer ratios of this task, d  between materials
was calculated. Summers et al. then applied a MDS method
to these d  values and extracted two potential dimensions.
The first and second dimensions were predicted to be therough and stiff dimensions, respectively. These dimensions
were validated by ranking tasks in which participants ranked
materials in order of their perceived roughness and stiffness.
These ranks agreed well with the ranked scores of materials
for individual dimensions. In addition, the ranked averageroughness of a material’s surface was consistent with theperceptual ranks. Their bending stiffness was consistent withthe perceptual ranks of stiffness; hence, the stiffness dimension
originated purely from the bending stiffness of paper, which
we exclude from the surface properties of materials.
Guest 2011 (fluids) (Slipperiness, roughness, & oily):
Guest et al. investigated the tactile perception of fluids suchas oil, water, and cream, involving twenty participants [30].
Using index fingers, twenty participants explored fluids spreadover plastic sheet, forearm, and thumb. They applied a factor
analysis to scores given to 28 adjective labels and discovered
five factors. Because they did not use semantically opposed
pairs, but unipolar scorings, the factors were also unipolar.
The first factor, namely the watery factor, loaded “wet,”“flowing,” “slippery,” “damp,” “thin,” and “cold” labels. The
possible opposing factor was represented by the “thick,” “rubbery,” “draggy,” and “sticky” labels. These two factors correspond to slippery/sticky. Furthermore, the cold/warm label
may have been included although warm sample textures were
not used. Thin/thick appeared in this dimension, but, it was notclear how participants interpreted this label. This factor did not

7

TABLE 3
Number of reports of tactile dimensions in 16 studies
Rough/smooth
17
Macro
Fine
2
2

Hard/soft
14

Cold/warm
6

Frictional
10
Moist/dry
Slipp./sticky
5
5

literally indicate the thickness of textures because participants
touched flat plates or skins on which the fluids were spread.
The second factor was named textured and mostly describedby “gritty,” “bumpy,” “dry,” and “rough” labels. This factor
was interpreted as roughness factor. The opposing factor was
described by the labels “smooth,” “silky,” “soft,” “velvety,”and “creamy” labels, and was therefore called the silken
factor. These two factors represent rough/smooth, and possibly
hard/soft, although “hard” label was not used in the experiments.
The last factor highly loaded “oily,” “greasy,” and “slimy”
labels, and was clearly distinguished from the first factor. Thisfactor was named oily.
Guest 2011 (fabric) (Roughness, moistness, & hardness):
Guest et al. analyzed the tactile dimensions of five types of fabrics using a factor analysis [26]. The fabrics included cotton,
latex, hessian, and silky and textured polyester. The numberof materials was very small, and their aim was to determine
whether tactile dimensionality depended on the location on the
body contacting the surface. Thirty-five participants rated thematerials using 33 unipolar adjective words. As a result similardimensions were discovered for the different body sites.
The first factor positively loaded the labels “rough,”“bumpy,” and “prickly”, and negatively “smooth.” This factor
was assumed the rough/smooth dimension.
The remaining three factors were unipolar. The second
factor was associated with the labels “wet,” “damp,” “cold,”and “greasy.” A possible opposing factor was associated with“fuzzy,” “fluffy,” and “dry.” These two factors indicated the
moist/dry dimension. Further, they may have included theslippery/sticky and cold/warm dimensions, but these characteristics were not prominent.
The last factor was also unipolar, and described by thelabels “hard,” “firm,” and “sharp.” This factor may have been
the opponent of “fuzzy,” “fluffy,” and “dry” factor mentioned
above, and collectively represent the hard/soft dimension.
It is difficult to interpret the unipolar factors as bipolar ones,
however, we consider that the extracted dimensions were therough/smooth, moist/dry, and hard/soft dimensions in terms ofbipolar dimensions.

4

F IVE P ERCEPTUAL D IMENSIONS

The above mentioned studies clearly do not share a common
tactile dimension structure. They are complementary because
each individual study was incomplete due to limitations of
the methods or due to the imbalanced textures used in experiments. Here, we construct the commonality of dimensions
taking into account the reasons for the variety of dimensions
found in the above studies.

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4.1

Three fundamental dimensions

Table 3 shows the number of reports of tactile dimensions orfactors in related studies. For a broader category of materials,
roughness (rough/smooth), hardness (hard/soft), and warmness(cold/warm) dimensions were very frequently observed. These
three dimensions were consistently extracted. In addition,
the perceptual mechanisms of these dimensions are clearly
different (as described later in sec. 5). It is reasonable to referto these dimensions as the fundamental dimensions of tactile
perception.
When it comes to the magnitude of the contribution ofthese three dimensions, dimension 1 in Table 2 shows themost prominent dimensions or factors found in each study.
According to the table, roughness or hardness was potentiallythe most prominent dimension. Furthermore, Bensmaı̈a et al.
reported that roughness and friction rather than the warmness
factor contributed to the perceived dissimilarities between
materials [32]. It seems that among the three fundamental
dimensions, hardness or roughness is more prominent thanwarmness, although their contributions vary across studies.
4.2

Dimensions of macro and fine roughness

Roughness perception can be divided into two dimensions. A
few studies extracted separately the macro roughness, which
was represented by the “uneven,” “relief,” or “voluminous”
labels, and the fine roughness, which was mainly represented
by the “rough” labels. Gescheider et al. clearly separated thefine and coarse roughness dimensions through experiments
using the adaption of Pacinian corpuscles [28]. Picard et al.
uncovered macro roughness referred to as relief, and fineroughness, which they referred to as roughness [21]. When we
consider whether or not these two types of roughness dimension exist, it is helpful to focus on the perceptual mechanisms.
As described in sec. 5, perception of macro and fine roughness
perceptions are mediated by different mechanisms, and this
supports the presence of two types of roughness dimension.
Thus, we regard the perception of fine and macro roughness
as belonging to different dimensions. Nonetheless, we should
remark that the separation of perceptual mechanisms does notnecessarily mean the separation of recognizable perceptual
dimensions.
Why macro and fine roughness factors are hardly
detectable: We consider here the major reasons that make it
difficult to extract the macro and fine roughness dimensions
separately. First, there is a significant overlap between theperception of fine roughness and macro roughness. (see sec. 5).
Second, the rough/smooth adjective label, which has been mostfrequently used in related works, can be interpreted as both
macro and fine roughness. Also, in describing the roughness
with bipolar adjective pairs, similar words such as “smooth,”“even,” or “flat” can be substituted for the other poles. Thus,
the specification of dimensions using adjective labels may
obscure the existence of two types of roughness dimensions.
Using appropriate attention and well described scales, themacro and fine roughness dimensions can be separated. For
example, Gescheider et al. used scales with descriptions in

8order to maintain consistency with the words in their post hoc
validation phases [28].
4.3 Frictional dimension
Slippery/sticky and moist/dry dimensions are mediated by friction: Possibly the most controversial dimension comes from friction. Several studies reported dimensions described by moist/dry [11], [12], [13], [30] andsticky/slippery [19], [15], [22], [30]. We consider that these dimensions come from the dimensions that are related to friction.
Some studies reported that the perception of sticky/slipperyand moist/dry was mainly attributed to friction forces orfriction coefficients [33], [34], [15], [30], although otherphysical properties such as the elasticity and surface roughness
also collectively determine the perception of moistness andstickiness [5], [6], [35], [36]. We focus on the fact that the
sticky/slippery and moist/dry dimensions have never been
extracted independently through a single experiment. It isreasonable to conclude that these two dimensions originate
from a single dimension. We call this dimension the frictional
dimension.
Frictional dimension tends to hide in therough/smooth dimension: Some studies suggest a correlation
between friction and roughness perception [37], [38], [39],whereas lubrication did not affect the perception of fineroughness [40]. Furthermore, Skedung et al. demonstratedusing coated paper that perceived roughness was based on thesurface roughness rather than finger friction [41]. We consider
that the roughness and frictional dimensions are different
partly because many studies extracted the sticky/slippery or
moist/dry dimension and the rough/smooth dimension as
different dimensions in a single study [13], [19], [12], [15],[22], [30].
The frictional dimension tends to be hidden in the roughness
dimension because changes in surface roughness influence thefrictional properties of textures. For example, Smith et al.
showed the relationships between the roughness perceptionof raised dots and the variations of tangential forces (stickslip effects) applied to them when a finger traversed raised
dots [38]. When the surface roughness and friction were dependent, the roughness perception and friction showed strong
correlations. In addition, in most of the studies considered,
the number of sample textures that represent the frictional
dimension was relatively small. Wet textures in particularwere rarely used. From multivariate analyses, the frictional
dimension is regarded as a minor dimension particularly inthe case of imbalanced sample textures.
Oily and Watery: Finally, Guest et al. [30] suggested
the possibility of two types of sub-dimensions, i.e., watery andoily, in the frictional dimension as a result of their researchusing plates covered with watery, oily, and creamy fluids.
Because most researchers did not use such a wide range ofoily or watery textures in their experiments, we do not havesatisfactory information to discuss whether these are different
dimensions. One possibility is that these are clearly differentiated by the presence of frictional vibration, namely stickslip phenomena. Both watery and oily textures are slippery;

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9

dimensions should be used.

5 P ERCEPTUAL M ECHANISMS OF I NDIVIDUALTACTILE D IMENSIONS

Fig. 1. Five psychophysical dimensions of tactile perception for materials/textures
however, watery ones causes the vibration whereas oily ones
do not [30], [42]. Another possibility is that watery and oily
dimensions align on the same dimension because the opposing
adjective terms for these terms could be identical: “sticky”
and “dry.” Oily textures are very slippery and viscous; hence,
they are placed on the extreme of slippery/sticky dimension.
In contrast, watery textures are placed in the neutral position
along this dimension.
4.4

Five dimensions of tactile perception

Based on the considerations in the above sections, we summarize here the five possible psychophysical dimensions of tactile
perception. These are the macro and fine roughness, warmness,hardness, and friction (wetness and stickiness) dimensions(Fig. 1). This dimensional structure is similar to the categorization that has been considered thus far. Bergmann Tiest, in his
review article on perceptual mechanisms, classified tactile perceptions into four categories: roughness, compliance, coldness
and slipperiness [4]. Bensmaı̈a also reviewed related studies
on these four dimensions in his review article [3]. However,
the reasons for this categorization were not highlighted; thepresent review underlies their categorization.
It is difficult to discover all five dimensions in a single study.
Hollins et al. attempted to specify the perceptual dimensions
using five adjective labels: rough/smooth (fine roughness),flat/bumpy (macro roughness), hard/soft, slippery/sticky, andwarm/cool. However, their study ended in the extraction of
only two or three of these five potential dimensions partly
because of the limited number of textures involved [20]. In
addition, in a subsequent study using virtual textures presented
by a force feedback device, Hollins et al. failed to separate theperceptual dimensions of four physical stimuli: spring constant(hardness), kinetic friction coefficient, sinusoidal bump size
(roughness), and vibration at 115 Hz [43]. The five perceptual
dimensions listed above have not yet been extracted in a single
experiment. Finding these dimensions in a single experimentis a task for future research studies. Factor analyses andmultidimensional scaling methods reduce the likelihood of
detecting weak dimensions; thus, the number of materials
that represent individual dimensions should be balanced. In
a semantic differential method and in the post hoc validationof dimensions, suitable adjective labels that describe the five

The mechanisms of tactile perception have been studied indepth, although some aspects are still not well understood. The
progress of studies in this area will elucidate the perceptual
dimensions because the perceptual mechanisms are intimately
related to the tactile dimensions. Here, we briefly introduce
the perceptual mechanisms of individual tactile dimensions inorder to underlie the classification of five tactile dimensions.
Further details and a discussion on related controversial issues
are included in the review articles by Jones and Lederman [1],Lederman and Klatzky [2], Bensmaı̈a [3], and Bergmann
Tiest [4].
5.1 Roughness/Smoothness (Macro and Fine)
The perceptual mechanisms of surface roughness vary depending on the fineness of the roughness. Many researchers pointed
out that mechanisms are different above grating wavelengthsof 1 mm and below grating wavelengths of hundreds ofmicrometers. For coarse surface roughness, it is known fromneurophysiology studies that the spatial distribution of SAI
units contributes to roughness perception [44], [45], [31]whereas the temporal information on skin vibration that iscaused by exploring rough textures has an insignificant effecton the perception [46], [47]. In contrast, for finer surface
roughness, the contribution of the vibratory information isclearer [48], [49]. Thus, FAI and FAII units are related tothe perception of fine roughness.
5.2 Friction
Friction perception is mediated by the skin of the finger pad,although it tends to be categorized into force or proprioception. The perceptual mechanism of friction has not yet
been elucidated. Skin stretch or adhesion of a finger pad totextures has been considered to mediate the perception offriction, and one remarkable suggestion is that the stick-slip
phenomenon between a finger pad and a frictional texture
influences the friction perception [50], [42]. Zigler consideredthat the perception of stickiness and wetness was attributed tothe adhesion of finger pad skin to textures that were scannedby a finger [51], [52]. This idea is consistent with a report
indicating that the magnitude of finger pad skin stretch iscorrelated to the perception of friction [53]. For such dynamic
skin stretch caused by friction, all receptor classes could be
activated [54], [55]. One may doubt that the frictional andfine roughness dimensions are the same. However, it appears
reasonable that the perception of friction is based mainlyon skin stretch related to textures, whereas the perceptionof fine roughness is based on vibration of the finger pad.
Two interesting studies support this assumption. Taylor andLederman investigated the perception of fine roughness using
lubricant soap [40]. They concluded that roughness perception was insensitive to the frictional status of the surfaces.
Nonomura et al. investigated friction perception of a flat

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surface using a variety of lubricant oils with different frictional
properties [42]. For the flat surface, they used a fairly flat glassthat did not cause skin vibration due to its surface patterns.
They concluded that humans could estimate the magnitude offriction under such conditions. Finally, although the perceptionof slipperiness in prehension and the frictional property of
textures should not be confused, there are numerous studies
on slipperiness in grasping [56], [57], [58].
5.3

Warmness/Coldness

In material recognition, the importance of heat transfer during
the contact of the finger pad with a material has long beenrecognized [59]. The perception of warmness and coldness ofmaterials is attributed to the heat transfer property between
textures and finger skin [6], [12], [60], [61], [62], [63]. The
receptors of heat stimuli were not understood until recently,
although the warm and cold points on skin and the warm andcold fibers in skin have been known for a long time. These
points and fibers selectively respond to cold or hot stimuli.
Recently, TRP ion-channels on free nerve endings have been
identified as heat and coldness receptors [64], [65]. For instance, TRPV1 responds to heat stimuli above approximately
43◦ C. TRPV2, TRPV3, and TRPV4 also respond to stimuli
that are warmer than human body temperature. These ionchannels are activated in different temperature bands. The
perception of temperatures below human body temperature ismediated by receptors, such as TRPA1 and TRPM8.
5.4

Hardness/Softness

The perception of softness or elasticity is attributable to tactile
cues [66], [67], although we tend to consider the perception of
the spring constant of materials to be related to force information. In the mechanism for the tactile perception of softness,the contact area between the finger pad and the target object isimportant. In [68], [69], the researchers demonstrated tactile
softness displays that controlled the contact area between theircontactor and finger pad. However, it is not clear whether thepressure distribution in the contact area, the history of areachanges, or another type of information is dominant.

6

D IFFERENCES BETWEEN MODALITIES

6.1

Vision and touch

The structures of perceptual dimensions should be different
in the visual and haptic modes. Comprehension of thesedifferences will benefit designers of websites and catalogues.
According to our classification of the five dimensions oftactile perception, the visual and haptic dimensions are notsignificantly different. However, there exist dimensions thatare unique to visual perception, such as those relating toglossiness, contrast, and patterns of surface textures, whereas
no dimensions clearly specific to tactile perception have beenreported. The details of these dimensions are described in thefollowing sections.

10

6.1.1 Five dimensions are shared between vision andtouch
Three articles introduced in sec. 3 also compared the dimensionality between touch and vision. All of these agreed withthe similarities of the tactile and visual dimensions.
Yoshida [17] and Picard [70] constructed the perceptual
dimensions under haptic-only, visual-only, and visuo-haptic
conditions for comparison. Both studies observed similar
structures using the three conditions although some textures
were significantly impacted by the variation of modality [70].
For example, a type of velvet was perceived as more uneven
under the visual-only than under the haptic-only condition.
A certain type of denim was evaluated as harder when only
visual cues were available. Similarly, Ballesteros et al. reported
that they acquired analogous dimensional structures whenthe materials were explored using haptic-only or visuo-haptic
cues. For both conditions, they detected three dimensions:rough/smooth, hard/soft, and slippery/sticky. They also confirmed that the preferences of textures were very similar
between haptic-only and visuo-haptic conditions. According
to the above mentioned studies, perceptual dimensions constructed by haptic cues are also observed in those constructedby visuo-haptic and visual-only cues. Some textures could bemapped differently in these perceptual spaces.
6.1.2 Dimensions unique to vision
Some studies on the visual dimensions of textures suggested
the existence of dimensions specific to vision. In particular, theglossy/glossless (bright/dark) dimensions can be concluded as
unique to visual perception.
Glossiness (brightness): Some studies reported that thedimensions of glossiness and brightness were revealed invisual texture perception. Cho et al. extracted the brightness
dimension from perceptual dissimilarity data using 60 types ofmaterial pictures [16]. Lee et al. [10] and Nagano et al. [71]constructed perceptual dimensions using SD methods involving visual cues only, and detected those represented by glossless/glossy (dark/bright) dimension. The dimension of gloss
or brightness is clearly independent of the five psychophysicaldimensions of tactile perception. For example, even hard andcold metal, smooth and soft satin, and slippery oil can beglossy.
Contrast & regularity (simplicity): Contrast- or regularityrelated dimensions have been reported in the literature; these
are uniquely visual dimensions. Rao et al. determined thedimensional structure of visual textures using 56 material
pictures [9]. Three dimensions were discovered; namely,
regular/irregular, high contrast/low contrast, and fine/coarse.
Cho et al. reported four dimensions, which were associatedwith coarseness, regularity, contrast, and brightness [16].
These two studies discovered the contrast dimensions mentioned above. Furthermore, Nagano et al. detected simple/complex dimension, which corresponds to the visual regularity of surfaces. Hence, contrast and regularity appear
to be unique to visual perception. However, unlike theglossy/glossless dimension, the classification of these properties as visual-specific is contentious because they are relatedwith surface roughness. Contrast is affected by the shadowsThis article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.

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created by surface roughness. Regularity and complexity are
related by the forms and patterns of surfaces. In order toconclude whether or not they fit into the tactile dimensional
space, further cross-modal research is needed.
6.2 Concept and touch
Interestingly, a few research groups investigated the differences in dimensionality between touch and concept wherevisual or haptic stimuli were not used, and instead only words
were used (referred to as the conceptual condition). As well as
vision and touch, touch related dimensions were also observedin the dimensionality constructed by the conceptual condition.
Yoshida compared the perceptual dimensions between thetactile and conceptual conditions using a similarity estimation
method [17]. His participants only listened to the names ofmaterials. He then found similar distributions of materials
on two-dimensional spaces, of which the first dimension wascharacterized by rough/smooth and hard/soft, and the second
dimension was characterized by sticky/slippery. Guest et al.
examined the dimensionality of 33 adjectives using a similarity
estimation method [26]. They chose adjectives that could be
used for the tactile assessment of the physical propertiesof materials. Three dimensions were detected, namely, therough/smooth, moist/dry and warm/cold dimensions. These
dimensions are consistent with those frequently observed fortactile perception. The rough/smooth dimension also included
labels such as “sharp,” “jagged,” “bumpy,” and “hard” on therough pole, and “silky” on the smooth pole. On the dry pole,“wooly,” “fuzzy,” “hairy,” and “fluffy” labels were used. On
the moist pole, “wet,” “damp,” “greasy,” and “slippery” labels
were observed.

7

C ONCLUSION

We reviewed studies on the psychophysical dimensions, whichwere related to the perception of physical properties of materials, i.e., of tactile perception. The psychological experimentsin each study were limited by an unsatisfactory adjective label
vocabulary, an unbalanced or small number of materials, andother issues. Furthermore, mathematical approaches based ona factor analysis and multidimensional scaling method neverensure that all potential factors or dimensions are revealed.
Hence, we constructed a reliable common dimensionality by
investigating related studies in a complementary manner.
The roughness, warmness, and hardness dimensions wereconsistently extracted. A few studies reported that roughness
perception could be divided into macro and fine roughness
dimensions. These two types of roughness perception can be
regarded as separate dimensions from the point of view of
the neurophysiological mechanisms involved. Many studies
extracted dimensions related to moist/dry and sticky/slipperylabels. We summarized these dimensions as a single dimensionthat is mediated primarily by the friction of materials. Thus,
it is reasonable to conclude that the tactile perception ofmaterials is composed of five dimensions, namely, macro andfine roughness, warmness (warm/cold), hardness (hard/soft),and friction (moist/dry and sticky/slippery). Further studies
on the perceptual mechanisms of each tactile dimension will
confirm the classification.

11

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JOURNAL OF IEEE TRANSACTIONS ON HAPTICS, VOL. X, NO. X, 201X

Shogo Okamoto (M’ 06) received a B.S. degree
in engineering from Kobe University in 2005, and
M.S. and Ph.D. degrees in information sciencesin 2007 and 2010, respectively, from the Graduate School of Information Sciences, Tohoku
University. Since 2010, he has been an assistantprofessor at the Graduate School of Engineering, Nagoya University. His research interests
include haptic interfaces and human factors.

Hikaru Nagano (M’ 11) received B.S. and M.S.
degrees in engineering from Nagoya University,
Japan in 2010. Currently, he is a Ph.D. candidatein the Department of Mechanical Science andEngineering, Nagoya University. His researchinterests include human perception.

Yoji Yamada (M’ 91) received an M.S. degree inengineering from both Nagoya University, Japan,
and the University of Texas in 1983. He also
received Ph.D. degree from the Tokyo Instituteof Technology, Japan, in 1990. He had beenan Associate Professor at Toyota Technological
Institute. In 2004, he joined the National Instituteof Advanced Industrial and Science Technology(AIST) as a group leader of Safety Intelligence
Research Group, Intelligent Systems ResearchInstitute. In 2009, he joined the Department of
Mechanical Science and Engineering, Graduate School of Engineering,
Nagoya University as a Professor. His current research interests include
safety and intelligence technologies in human/machine systems, andtheir robotic sensing and control.

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