Tactual picture identification by blind and sighted people: effects of providing categorical information

Recognition of facial expressions of emotions in tactile drawings by blind children, children with low vision and sighted children

In the context of blindness, studies on the recognition of facial expressions of emotions by touch are essential to define the compensatory touch abilities and to create adapted tools on emotions. This study is the first to examine the effect of visual experience in the recognition of tactile drawings of facial expressions of emotions by children with different visual experiences. To this end, we compared the recognition rates of tactile drawings of emotions between blind children, children with low vision and sighted children aged 6-12 years. Results revealed no effect of visual experience on recognition rates. However, an effect of emotions and an interaction effect between emotions and visual experience were found. Indeed, while all children had a low average recognition rate, the drawings of fear, anger and disgust were particularly poorly recognized. Moreover, sighted children were significantly better at recognizing the drawings of surprise and sadness than the blind children who only showed high recognition rates for joy. The results of this study support the importance of developing emotion tools that can be understood by children with different visual experiences.

Reconsidering Luria's speech mediation: Verbalization and haptic picture identification in children with congenital total blindness

Current accounts of behavioral and neurocognitive correlates of plasticity in blindness are just beginning to incorporate the role of speech and verbal production. We assessed Vygotsky/Luria's speech mediation hypothesis, according to which speech activity can become a mediating tool for perception of complex stimuli, specifically, for encoding tactual/haptic spatial patterns which convey pictorial information (haptic pictures). We compared verbalization in congenitally totally blind (CTB) and age-matched sighted but visually impaired (VI) children during a haptic picture naming task which included two repeated, test-retest, identifications. The children were instructed to explore 10 haptic schematic pictures of objects (e.g., cup) and body parts (e.g., face) and provide (without experimenter's feedback) their typical name. Children's explorations and verbalizations were videorecorded and transcribed into audio segments. Using the Computerized Analysis of Language (CLAN) program, we extracted several measurements from the observed verbalizations, including number of utterances and words, utterance/word duration, and exploration time. Using the Word2Vec natural language processing technique we operationalized semantic content from the relative distances between the names provided. Furthermore, we conducted an observational content analysis in which three judges categorized verbalizations according to a rating scale assessing verbalization content. Results consistently indicated across all measures that the CTB children were faster and semantically more precise than their VI counterparts in the first identification test, however, the VI children reached the same level of precision and speed as the CTB children at retest. Overall, the task was harder for the VI group. Consistent with current neuroscience literature, the prominent role of speech in CTB and VI children's data suggests that an underlying cross-modal involvement of integrated brain networks, notably associated with Broca's network, likely also influenced by Braille, could play a key role in compensatory plasticity via the mediational mechanism postulated by Luria.

Drawing as a tool for investigating the nature of imagery representations of blind people: The case of the canonical size phenomenon

Several studies have shown that blind people, including those with congenital blindness, can use raised-line drawings, both for "reading" tactile graphics and for drawing unassisted. However, research on drawings produced by blind people has mainly been qualitative. The current experimental study was designed to investigate the under-researched issue of the size of drawings created by people with blindness. Participants (N = 59) varied in their visual status. Adventitiously blind people had previous visual experience and might use visual representations (e.g., when visualising objects in imagery/working memory). Congenitally blind people did not have any visual experience. The participant's task was to draw from memory common objects that vary in size in the real world. The findings revealed that both groups of participants produced larger drawings of objects that have larger actual sizes. This means that the size of familiar objects is a property of blind people's mental representations, regardless of their visual status. Our research also sheds light on the nature of the phenomenon of canonical size. Since we have found the canonical size effect in a group of people who are blind from birth, the assumption of the visual nature of this phenomenon - caused by the ocular-centric biases present in studies on drawing performance - should be revised.

Size and Quality of Drawings Made by Adults Under Visual and Haptic Control

The aim of this study was twofold. First, our objective was to test the influence of an object’s actual size (size rank) on the drawn size of the depicted object. We tested the canonical size effect (i.e., drawing objects larger in the physical world as larger) in four drawing conditions — two perceptual conditions (blindfolded or sighted) crossed with two materials (paper or special foil for producing embossed drawings). Second, we investigated whether drawing quality (we analysed both the local and global criteria of quality) depends on drawing conditions. We predicted that drawing quality, unlike drawing size, would vary according to drawing conditions — namely, being higher when foil than paper was used for drawing production in the blindfolded condition. We tested these hypotheses with young adults who repeatedly drew eight different familiar objects (differentiated by size in the real world) in four drawing conditions. As expected, drawn size increased linearly with increasing size rank, whatever the drawing condition, thus replicating the canonical size effect and showing that this effect was not dependent on drawing conditions. In line with our hypothesis, in the blindfolded condition drawing quality was better when foil rather than paper was used, suggesting a benefit from haptic feedback on the trace produced. Besides, the quality of drawings produced was still higher in the sighted than the blindfolded condition. In conclusion, canonical size is present under different drawing conditions regardless of whether sight is involved or not, while perceptual control increases drawing quality in adults.

Touching and hearing the shapes: How auditory angular and curved sounds influence proficiency in recognising tactile angle and curve shapes when experienced and inexperienced in using haptic touch

This study investigated whether adding auditory angular and curved sounds to tactile angle and curve shapes – one unspecified sound to one unspecified shape – positively influences the accuracy and exploration time in recognising tactile angles and curves when experienced and inexperienced in using haptic touch. A within-participant experiment was conducted, with two groups of participants: experienced and inexperienced in using haptic touch, and with two conditions: congruous (e.g., angle shape and angular sound) and incongruous (e.g., angle shape and curved sound) tactile and auditory shape information. Adding congruous auditory angular and curved sounds to tactile angle and curve shapes positively influences the accuracy in recognising tactile angles and curves both when experienced and inexperienced in using haptic touch, and the exploration time on correct recognitions when experienced. People integrate tactile and auditory (angle; curve) shape information and this improves their proficiency in recognising tactile angles and curves.

Exploring 3D miniatures with action simulations by finger gestures: Study of a new embodied design for blind and sighted children

Tactile books for blind children generally contain tactile illustrations referring to a visual world that can be difficult to understand. This study investigates an innovative way to present content to be explored by touch. Following embodied approaches and evidence about the advantages of manipulations in tactile processing, we examined 3D miniatures that children explored using their middle and index fingers to simulate leg movements. This “Action simulations by finger gestures–ASFG” procedure has a symbolic relevance in the context of blindness. The aim of the present study was to show how the ASFG procedure facilitates the identification of objects by blind and sighted children. Experiment 1 examined the identification of 3D miniatures of action objects (e.g. the toboggan, trampoline) by 8 early blind and 15 sighted children, aged 7 to 12, who explored with the ASFG procedure. Results revealed that objects were very well identified by the two groups of children. Results confirmed hypotheses that ASFG procedures are relevant in the identification process regardless of the visual status of subjects. Experiment (control) 2 studied identification of tactile pictures of same action objects by 8 different early blind and 15 sighted children, aged 7 to 12. Results confirmed that almost all objects obtained lower recognition scores in tactile pictures than in 3D miniatures by both groups and showed surprisingly higher scores in blind children than in sighted children. Taken together, our study provides evidence of the contribution of sensorimotor simulation in the identification of objects by touch and brings innovative solutions in book design for blind people. Moreover, it means that only the ASFG procedure has a very inclusive potential to be relevant for a larger number of subjects, regardless of their visual skills.

Identification of Textured Tactile Pictures in Visually Impaired and Blindfolded Sighted Children

A high level of variability in the capacity of visually impaired children to accurately identify tactile images is reported in the literature, with on average rather low percentages of correct naming responses. However, most of these studies used raised-line drawings as stimuli to be explored and named. The present experiment investigated whether blind children of 3 to 8 years of age would demonstrate a satisfactory ability to name the elements making up tactile images when tested in an experimental setting similar to their natural reading conditions. Textured tactile images taken from genuine illustrated tactile books for young children were used, and the participants received information about the title of the book or listened the text that accompanied each picture before exploration, as it would occur in a natural reading setting. The results showed that their naming scores were indeed higher than previously reported at equivalent ages and did not differ from those of age-matched sighted children. These scores were positively impacted by haptic practice in blind children and correlated with the use of some specific exploratory procedures. The blind children benefited from information provided before exploration, as did their sighted counterparts. However, only in the former did the condition in which full information was provided influence the way the children organized their exploration. The haptic identification scores increased with age regardless of visual status, with the exploration times decreasing in the blind children, while the reverse trend was observed in the sighted children. These results are discussed at the light of the image-mediation model of haptics, suggesting that during the age period considered in the present experiment, blind children would progressively learn to process haptic information directly, thus leading to a decrease of exploration times, while sighted children would learn to translate haptic information into a visual image used to retrieve semantic information, involving an increase of their exploration times.

Testing Nonverbal Intelligence of Working-age Visually Impaired Adults: Evaluation of the Adapted Kohs Block Design Test

This article presents an initial empirical investigation of the Adapted Kohs Block Design Test with 78 working-age adults with visual impairments. The test is shown to have adequate reliability and initial concurrent validity. Construct validity within the limitations of the sample size was inconclusive, but indicated that further investigation of the test is warranted.

Weight-Discrimination Sensitivity in Congenitally Blind and Sighted Adults

This study compared the weight-discrimination sensitivity of 41 congenitally blind and 41 normally sighted adults. The superior weight-discrimination sensitivity of the congenitally blind subjects suggests that blindness from birth can cause compensatory adaptations within the cutaneous modality.

Comparing Haptic Pattern Matching on Tablets and Phones: Large Screens Are Not Necessarily Better

Touchscreen-based, multimodal graphics represent an area of increasing research in digital access for individuals with blindness or visual impairments; yet, little empirical research on the effects of screen size on graphical exploration exists. This work probes if and when more screen area is necessary in supporting a pattern-matching task.

PURPOSE

Larger touchscreens are thought to have distinct benefit over smaller touchscreens for the amount of space available to convey graphical information nonvisually. The current study investigates two questions: (1) Do screen size and grid density impact a user's accuracy on pattern-matching tasks? (2) Do screen size and grid density impact a user's time on task?

METHODS

Fourteen blind and visually impaired individuals were given a pattern-matching task to complete on either a 10.5-in tablet or a 5.1-in phone. The patterns consisted of five vibrating targets imposed on sonified grids that varied in density (higher density = more grid squares). At test, participants compared the touchscreen pattern with a group of physical, embossed patterns and selected the matching pattern. Participants were evaluated on time exploring the pattern on the device and their pattern-matching accuracy. Multiple and logistic regressions were performed on the data.

RESULTS

Device size, grid density, and age had no statistically significant effects on the model of pattern-matching accuracy. However, device size, grid density, and age had significant effects on the model for grid exploration. Using the phone, exploring low-density grids, and being older were indicative of faster exploration time.

CONCLUSIONS

A trade-off of time and accuracy exists between devices that seems to be task dependent. Users may find a tablet most useful in situations where the accuracy of graphic interpretation is important and is not limited by time. Smaller screen sizes afforded comparable accuracy performance to tablets and were faster to explore overall.

Bouba or kiki with and without vision: Shape-audio regularities and mental images

95% of the world's population associate a rounded visual shape with the spoken word 'bouba', and an angular visual shape with the spoken word 'kiki', known as the bouba/kiki-effect. The bouba/kiki-effect occurs irrespective of familiarity with either the shape or word. This study investigated the bouba/kiki-effect when using haptic touch instead of vision, including the role of visual imagery. It also investigated whether the bouba/kiki shape-audio regularities are noticed at all, that is, whether they affect the bouba/kiki-effect itself and/or the recognition of individual bouba/kiki shapes, and finally what mental images they produce. Three experiments were conducted, with three groups of participants: blind, blindfold, and vision. In Experiment 1, the participants were asked to pick out the tactile/visual shape that they associated with the auditory bouba/kiki. Experiment 1 found that the participants who were blind did not show an instant bouba/kiki-effect (in Trial 1), whereas the blindfolded and the fully sighted did. It also found that the bouba/kiki shape-audio regularities affected the bouba/kiki-effect when using haptic touch: Those who were blind did show the bouba/kiki-effect from Trial 4, and those who were blindfolded no longer did. In Experiment 2, the participants were asked to name one tactile/visual shape and a segment of audio together as either 'bouba' or 'kiki'. Experiment 2 found that corresponding shape and audio improved the accuracy of both the blindfolded and the fully sighted, but not of those who were blind - they ignored the audio. Finally, in Experiment 3, the participants were asked to draw the shape that they associated with the auditory bouba/kiki. Experiment 3 found that their mental images, as depicted in their drawings, were not affected by whether they had experienced the bouba/kiki shapes by haptic touch or by vision. Regardless of their prior shape experience, that is, tactile or visual, their mental images included the most characteristic shape feature of bouba and kiki: curve and angle, respectively, and typically not the global shape. When taken together, these experiments suggest that the sensory regularities and mental images concerning bouba and kiki do not have to be based on, or even include visual information.

Angle Discrimination in Raised-Line Drawings

We investigated the angular resolution subserving the haptic perception of raised-line drawings by measuring how accurately observers could discriminate between two angle sizes under various conditions. We found that, for acute angles, discrimination performance is highly dependent on exploration strategy: mean thresholds of 2.9° and 6.0° were found for two different exploration strategies. For one of the strategies we found that discriminability is not dependent on the bisector orientation of the angle. Furthermore, we found that thresholds almost double when the angular extent is increased from 20° to 135°. We also found that local apex information has a significant influence on discrimination for acute as well as obtuse angles. In the last experiment we investigated the influence of depiction mode but did not find any effect. Overall, the results tell us that the acuity with which angles in raised-line drawings are perceived is determined by the exploration strategy, local apex information, and global angular extent.

Haptic-2D: A new haptic test battery assessing the tactual abilities of sighted and visually impaired children and adolescents with two-dimensional raised materials

To fill an important gap in the psychometric assessment of children and adolescents with impaired vision, we designed a new battery of haptic tests, called Haptic-2D, for visually impaired and sighted individuals aged five to 18 years. Unlike existing batteries, ours uses only two-dimensional raised materials that participants explore using active touch. It is composed of 11 haptic tests, measuring scanning skills, tactile discrimination skills, spatial comprehension skills, short-term tactile memory, and comprehension of tactile pictures. We administered this battery to 138 participants, half of whom were sighted (n=69), and half visually impaired (blind, n=16; low vision, n=53). Results indicated a significant main effect of age on haptic scores, but no main effect of vision or Age × Vision interaction effect. Reliability of test items was satisfactory (Cronbach's alpha, α=0.51-0.84). Convergent validity was good, as shown by a significant correlation (age partialled out) between total haptic scores and scores on the B101 test (rp=0.51, n=47). Discriminant validity was also satisfactory, as attested by a lower but still significant partial correlation between total haptic scores and the raw score on the verbal WISC (rp=0.43, n=62). Finally, test-retest reliability was good (rs=0.93, n=12; interval of one to two months). This new psychometric tool should prove useful to practitioners working with young people with impaired vision.

Simultaneous Sketching Aids the Haptic Identification of Raised Line Drawings

Haptically identifying raised line drawings is difficult. We investigated whether a major component of this difficulty lies in acquiring, integrating, and maintaining shape information from touch. Wijntjes, van Lienen, Verstijnen, and Kappers reported that drawings which participants had failed to identify by touch alone could often subsequently be named if they were sketched. Thus, people sometimes needed to externalize haptically acquired information by making a sketch in order to be able to use it. We extended Wijntjes et al.'s task and found that sketching while touching improved drawing identification even more than sketching after touching, but only if people could see their sketches. Our results suggest that the slow, serial nature of information acquisition seriously hampers the haptic identification of raised line drawings relative to visually identifying line drawings. Simultaneous sketching may aid identification by reducing the burden on working memory and by helping to guide haptic exploration. This conclusion is consistent with the finding reported by Lawson and Bracken that 3-D objects are much easier to identify haptically than raised line drawings since, unlike for vision, simultaneously extracting global shape information is much easier haptically for 3-D stimuli than for line drawings.

The contributions of vision and haptics to reaching and grasping

This review aims to provide a comprehensive outlook on the sensory (visual and haptic) contributions to reaching and grasping. The focus is on studies in developing children, normal, and neuropsychological populations, and in sensory-deprived individuals. Studies have suggested a right-hand/left-hemisphere specialization for visually guided grasping and a left-hand/right-hemisphere specialization for haptically guided object recognition. This poses the interesting possibility that when vision is not available and grasping relies heavily on the haptic system, there is an advantage to use the left hand. We review the evidence for this possibility and dissect the unique contributions of the visual and haptic systems to grasping. We ultimately discuss how the integration of these two sensory modalities shape hand preference.

Designing Haptic Assistive Technology for Individuals Who Are Blind or Visually Impaired

This paper considers issues relevant for the design and use of haptic technology for assistive devices for individuals who are blind or visually impaired in some of the major areas of importance: Braille reading, tactile graphics, orientation and mobility. We show that there is a wealth of behavioral research that is highly applicable to assistive technology design. In a few cases, conclusions from behavioral experiments have been directly applied to design with positive results. Differences in brain organization and performance capabilities between individuals who are "early blind" and "late blind" from using the same tactile/haptic accommodations, such as the use of Braille, suggest the importance of training and assessing these groups individually. Practical restrictions on device design, such as performance limitations of the technology and cost, raise questions as to which aspects of these restrictions are truly important to overcome to achieve high performance. In general, this raises the question of what it means to provide functional equivalence as opposed to sensory equivalence.

Perception of tactile graphics: embossings versus cutouts

Graphical information, such as illustrations, graphs, and diagrams, are an essential complement to text for conveying knowledge about the world. Although graphics can be communicated well via the visual modality, conveying this information via touch has proven to be challenging. The lack of easily comprehensible tactile graphics poses a problem for the blind. In this paper, we advance a hypothesis for the limited effectiveness of tactile graphics. The hypothesis contends that conventional graphics that rely upon embossings on two-dimensional surfaces do not allow the deployment of tactile exploratory procedures that are crucial for assessing global shape. Besides potentially accounting for some of the shortcomings of current approaches, this hypothesis also serves a prescriptive purpose by suggesting a different strategy for conveying graphical information via touch, one based on cutouts. We describe experiments demonstrating the greater effectiveness of this approach for conveying shape and identity information. These results hold the potential for creating more comprehensible tactile drawings for the visually impaired while also providing insights into shape estimation processes in the tactile modality.

Grasping without sight: insights from the congenitally blind

We reach for and grasp different sized objects numerous times per day. Most of these movements are visually-guided, but some are guided by the sense of touch (i.e. haptically-guided), such as reaching for your keys in a bag, or for an object in a dark room. A marked right-hand preference has been reported during visually-guided grasping, particularly for small objects. However, little is known about hand preference for haptically-guided grasping. Recently, a study has shown a reduction in right-hand use in blindfolded individuals, and an absence of hand preference if grasping was preceded by a short haptic experience. These results suggest that vision plays a major role in hand preference for grasping. If this were the case, then one might expect congenitally blind (CB) individuals, who have never had a visual experience, to exhibit no hand preference. Two novel findings emerge from the current study: first, the results showed that contrary to our expectation, CB individuals used their right hand during haptically-guided grasping to the same extent as visually-unimpaired (VU) individuals did during visually-guided grasping. And second, object size affected hand use in an opposite manner for haptically- versus visually-guided grasping. Big objects were more often picked up with the right hand during haptically-guided, but less often during visually-guided grasping. This result highlights the different demands that object features pose on the two sensory systems. Overall the results demonstrate that hand preference for grasping is independent of visual experience, and they suggest a left-hemisphere specialization for the control of grasping that goes beyond sensory modality.

Neural correlates associated with superior tactile symmetry perception in the early blind

Symmetry is an organizational principle that is ubiquitous throughout the visual world. However, this property can also be detected through non-visual modalities such as touch. The role of prior visual experience on detecting tactile patterns containing symmetry remains unclear. We compared the behavioral performance of early blind and sighted (blindfolded) controls on a tactile symmetry detection task. The tactile patterns used were similar in design and complexity as in previous visual perceptual studies. The neural correlates associated with this behavioral task were identified with functional magnetic resonance imaging (fMRI). In line with growing evidence demonstrating enhanced tactile processing abilities in the blind, we found that early blind individuals showed significantly superior performance in detecting tactile symmetric patterns compared to sighted controls. Furthermore, comparing patterns of activation between these two groups identified common areas of activation (e.g. superior parietal cortex) but key differences also emerged. In particular, tactile symmetry detection in the early blind was also associated with activation that included peri-calcarine cortex, lateral occipital (LO), and middle temporal (MT) cortex, as well as inferior temporal and fusiform cortex. These results contribute to the growing evidence supporting superior behavioral abilities in the blind, and the neural correlates associated with crossmodal neuroplasticity following visual deprivation.

Tactile drawing aesthetics and a blind woman’s drawings of sounds

This article makes four points. First, in making raised, tangible outline pictures, blind people can invent sophisticated treatments for topics they select themselves. Second, their drawings can be realistic. Third, they can also be metaphoric, in showing sounds for example. Fourth, their outline drawings use line for surface edges, and they incorporate aspects of perspective such as profiles. These points are illustrated by three drawings by EW, a blind woman. They are sketches of a couple waltzing, a guitar player, and a samba band. The account of line and profiles given here for the blind, this article argues, applies also to Palaeolithic art, as in Herzog’s ‘Cave of forgotten dreams’ and Cook’s ‘Ice age art: the arrival of the modern mind’.

Haptic perception

Fueled by novel applications, interest in haptic perception is growing. This paper provides an overview of the state of the art of a number of important aspects of haptic perception. By means of touch we can not only perceive quite different material properties, such as roughness, compliance, friction, coldness and slipperiness, but we can also perceive spatial properties, such as shape, curvature, size and orientation. Moreover, the number of objects we have in our hand can be determined, either by counting or subitizing. All these aspects will be presented and discussed in this paper. Although our intuition tells us that touch provides us with veridical information about our environment, the existence of prominent haptic illusions will show otherwise. Knowledge about haptic perception is interesting from a fundamental viewpoint, but it also is of eminent importance in the technological development of haptic devices. At the end of this paper, a few recent applications will be presented. WIREs Cogn Sci 2013, 4:357-374. DOI: 10.1002/wcs.1238 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Tactile picture recognition: errors are in shape acquistion or object matching?

Numerous studies have demonstrated that sighted and blind individuals find it difficult to recognize tactile pictures of common objects. However, it is still not clear what makes recognition of tactile pictures so difficult. One possibility is that observers have difficulty acquiring the global shape of the image when feeling it. Alternatively, observers may have an accurate understanding of the shape but are unable to link it to a particular object representation. We, therefore, conducted two experiments to determine where tactile picture recognition goes awry. In Experiment 1, we found that recognition of tactile pictures by blindfolded sighted observers correlated with image characteristics that affect shape acquisition (symmetry and complexity). In Experiment 2, we asked drawing experts to draw what they perceived after feeling the images. We found that the experts produced three types of drawings when they could not recognize the tactile pictures: (1) drawings that did not look like objects (incoherent), (2) drawings that looked like incorrect objects (coherent but inaccurate) and (3) drawings that looked like the correct objects ( coherent and accurate). The majority of errors seemed to result from inaccurate perception of the global shape of the image (error types 1 and 2). Our results suggest that recognition of simplistic tactile pictures of objects is largely inhibited by low-level tactile shape processing rather than high-level object recognition mechanisms.

Prior visual experience, and perception and memory of shape in people with total blindness

The aim of this study was to explore the role of prior visual experience for tactile differentiation of object shapes. The study investigated whether people who lost their vision later in life were able to identify and recognize object shapes more accurately and faster than those who were blind from their birth. Four experiments were conducted. The first two were concerned with tactile shape differentiation, the second two with shape recognition. The hypotheses were only partially confirmed. The ‘late’ blind participants distinguished shapes more accurately than the congenitally blind (particularly in ‘simple’ perception tasks). This finding may suggest that people who have prior visual experience use an allocentric strategy when visualizing object shapes in their imagery. The ‘late’ blind participants performed the tasks more slowly than those who were congenitally blind. This may be explained by the complexity of the task, the time needed to create an allocentric representation, and discrepancy in the tactile experiences between the congenitally and late blind groups. A number of implications for further research are outlined.

Haptic Object Recognition: How Important are Depth Cues and Plane Orientation?

Raised-line drawings of familiar objects are very difficult to identify with active touch only. In contrast, haptically explored real 3-D objects are usually recognised efficiently, albeit slower and less accurately than with vision. Real 3-D objects have more depth information than outline drawings, but also extra information about identity (eg texture, hardness, temperature). Previous studies have not manipulated the availability of depth information in haptic object recognition whilst controlling for other information sources, so the importance of depth cues has not been assessed. In the present experiments, people named plastic small-scale models of familiar objects. Five versions of bilaterally symmetrical objects were produced. Versions varied only in the amount of depth information: minimal for cookie-cutter and filled-in outlines, partial for squashed and half objects, and full for 3-D models. Recognition was faster and much more accurate when more depth information was available, whether exploration was with both hands or just one finger. Novices found it almost impossible to recognise objects explored with two hand-held probes whereas experts succeeded using probes regardless of the amount of depth information. Surprisingly, plane misorientation did not impair recognition. Unlike with vision, depth information, but not object orientation, is extremely important for haptic object recognition.

Mechanisms of cross-modal plasticity in early-blind subjects

A variety of studies have demonstrated enhanced blood oxygenation level dependent responses to auditory and tactile stimuli within occipital cortex as a result of early blindness. However, little is known about the organizational principles that drive this cross-modal plasticity. We compared BOLD responses to a wide variety of auditory and tactile tasks (vs. rest) in early-blind and sighted subjects. As expected, cross-modal responses were larger in blind than in sighted subjects in occipital cortex for all tasks (cross-modal plasticity). Within both blind and sighted subject groups, we found patterns of cross-modal activity that were remarkably similar across tasks: a large proportion of cross-modal responses within occipital cortex are neither task nor stimulus specific. We next examined the mechanisms underlying enhanced BOLD responses within early-blind subjects. We found that the enhancement of cross-modal responses due to early blindness was best described as an additive shift, suggesting that cross-modal plasticity within blind subjects does not originate from either a scaling or unmasking of cross-modal responsivities found in sighted subjects.

Haptic recognition of two-dimensional raised-line patterns by early-blind, late-blind, and blindfolded sighted adults

We investigated the role of visual experience and visual imagery in the processing of two-dimensional (2-D) tactile patterns. The performance of early-blind (EB), late-blind (LB), and blindfolded sighted (S) adults in the recognition of 2-D raised-line patterns was compared. We also examined whether recognition of 2-D tactile patterns depends on the type of memory strategy (eg spatial, visuo-spatial, verbal, and kinesthetic) used by EB, LB, and S participants to perform the task. Significant between-group differences in the recognition performance have not been found despite significant between-group differences in self-reported memory strategies. Recognition performance does not vary significantly with the strategy, but correlates positively with visuo-spatial imagery abilities in the S participants. These findings may be taken to suggest that the difficulties some blind people experience with tactile pictures are not due to difficulties in processing 2-D tactile patterns.

Look what I have felt: unidentified haptic line drawings are identified after sketching

The difficulty that observers experience when trying to identify a raised line drawing by touch is still largely unexplained. In this article, we show that observers who are unable to haptically identify a raised line drawing are suddenly able to do so after they have sketched on paper what they have in their mind. We conducted three experiments: first of all we show that this effect is robust; in the second experiment, we show that identification-after-sketching is caused by visual inspection of the sketch, and not caused by feedback in general; and in the third we show that sketches which were identified by the observers who produced them, were also identified by completely naive viewers. These experiments demonstrate that during raised line drawing identification the mental capacities required to interpret the stimulus seem to be inadequate: although enough pictorial information was present to produce a sketch which could even be identified by naive viewers, the stimulus could not be identified by haptic and mental processing alone. Furthermore, we investigated whether increasing the haptic perceptual field by using two hands instead of one hand had an influence on identification performance. We did indeed find that using two hands significantly increased identification. We use both results to discuss the underlying mechanisms of haptic raised line drawing identification.

The Influence of Picture Size on Recognition and Exploratory Behaviour in Raised-Line Drawings

We demonstrate the influence of picture size on haptic recognition and exploratory behaviour. The stimuli were raised-line drawings of everyday objects. Participants were instructed to think aloud during haptic exploration of the pictures. We measured the delay between initial correct speculation and final correct response. The results indicate that picture size influences accuracy but not response latency: large drawings are recognised more often but not faster. By analysing video recordings of the experiment we found that two-handed exploration increases when picture size increases and that, on average, 83% of the exploration time involves the use of two hands. The thinking-aloud data showed that the average time difference between the initial correct speculation and final correct response amounted to 23% of the total reaction time. We discuss our results with respect to the design of tactile aids and the ecological validity of single-finger exploration.

Superior haptic perceptual selectivity in late-blind and very-low-vision subjects

Blindfolded sighted, congenitally blind, late-blind, and very-low-vision subjects were tested on a tangible version of the embedded-figures test. The results of ANOVAs on accuracy measures yielded superior performance by the very-low-vision and late-blind subjects compared with the blindfolded sighted and congenitally blind participants. Accuracy of the congenitally blind subjects was similar to that of the blindfolded sighted participants. However, all groups of blind subjects were significantly faster than the blindfolded sighted subjects. It is suggested that experience with pictures combined with haptic skill aid perceptual selectivity in touch.

Tactile picture perception in sighted and blind people

This paper reviews recent research on the perception of tangible pictures by sighted people and those who are blind or have extremely low vision. Raised-line pictures are useful for evaluating spatial cognition in congenitally blind people. The ease or difficulty of picture recognition is shown to vary with complexity, familiarity, and categorical information. Blind people are able to use pictorial displays effectively, but may benefit from instruction when complex depictions of three-dimensional objects involve foreshortening.

Tangible pictures: viewpoint effects and linear perspective in visually impaired people

Perception of raised-line pictures in blindfolded-sighted, congenitally blind, late-blind, and low-vision subjects was studied in a series of experiments. The major aim of the study was to examine the value of perspective drawings for haptic pictures and visually impaired individuals. In experiment 1, subjects felt two wooden boards joined at 45 degrees, 90 degrees, or 135 degrees, and were instructed to pick the correct perspective drawing from among four choices. The first experiment on perspective found a significant effect of visual status, with much higher performance by the low-vision subjects. Mean performance for the congenitally blind subjects was not significantly different from that of the late-blind and blindfolded-sighted subjects. In a further experiment, blindfolded subjects drew tangible pictures of three-dimensional (3-D) geometric solids, and then engaged in a matching task. Counter to expectations, performance was not impaired for the 3-D drawings as compared with the frontal viewpoints. Subjects were also especially fast and more accurate when matching top views. Experiment 5 showed that top views were easiest for all of the visually impaired subjects, including those who were congenitally blind. Experiment 5 yielded higher performance for 3-D than frontal viewpoints. The results of all of the experiments were consistent with the idea that visual experience is not necessary for understanding perspective drawings of geometrical objects.

Face recognition by hand

We investigated participants' ability to identify and represent faces by hand. In Experiment 1, participants proved surprisingly capable of identifying unfamiliar live human faces using only their sense of touch. To evaluate the contribution of geometric and material information more directly, we biased participants toward encoding faces more in terms of geometric than material properties, by varying the exploration condition. When participants explored the faces both visually and tactually, identification accuracy did not improve relative to touch alone. When participants explored masks of the faces, thereby eliminating material cues, matching accuracy declined substantially relative to tactual identification of live faces. In Experiment 2, we explored intersensory transfer of face information between vision and touch. The findings are discussed in terms of their relevance to haptic object processing and to the face-processing literature in general.

Haptic perception of the horizontal by blind and low-vision individuals

We examined haptic perception of the horizontal in visually impaired people. Blind people (late blind and congenitally blind), persons with very low vision, and blindfolded sighted individuals felt raised-line drawings of jars at four angles. They had to demonstrate their understanding that water remains horizontal, despite jar tilt, by selecting the correct raised-line drawing given four choices. Low-vision subjects, with near perfect scores, performed significantly better than the other groups of subjects. While the late-blind and blindfolded sighted subjects performed slightly better than the congenitally blind participants, the difference between the late-blind and congenitally blind groups was nonsignificant. The performance of the congenitally blind subjects indicates that visual experience is not necessary for the development of an understanding that water level stays horizontal, given container tilt.

Perception of the horizontal and vertical in tangible displays: minimal gender differences

A study is reported of gender differences in a haptic version of three Piagetian tests that assess understanding of Euclidian space. A raised-line drawing kit was used both for subject responses and for production of stimuli. To test understanding of the horizontal, subjects felt pictures of a jar at four tilts and were asked to draw the water line. Two methods were used to examine understanding of the vertical. First, subjects drew a hanging electrical cord and light bulb, attached to the ceiling of a bus, parked on hills of four different angles. Subsequently, subjects drew telephone poles (represented by a single line) on hills of four different angles. In the jar task, males and females showed comparable performance, both groups showing large errors. Judgments of the vertical were very similar for males and females in the bus task, but errors diminished considerably for both genders when subjects drew telephone poles on hills. It is suggested that better judgments of the vertical in the pole task probably derive from the use of body-centered spatial reference information.

The Tactile Depiction of Visual Conventions: The Advantage of Explicit Cues

The introduction of representational standards for tactile diagrams might improve their use. Two elements central to the design of visual diagrams are the relative positioning and movement of the objects yet no standard convention for representing either of these in tactile form has been established. Consequently, systems representing the movement and relative positioning of objects were developed with the Intention of producing design conventions for these elements. The method of depicting the element of movement was based on the concept that an object's movement is defined by changes between Its initial and final positions while the method of depicting relative positioning was based on a number of the principals underlying linear perspective, along with an additional texture-based cue. Tactile diagrams making use of these systems of representation were designed and produced for exploration by eight blind participants. They were confident and accurate in their Interpretations of diagrams that depicted relative positioning of objects and, on the basis of their comments on the diagrams depleting movement, a convention for the depletion of movement was proposed.

Haptic form perception: relative salience of local and global features

When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the hepatic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.

SOMESTHESIS

In this review we focus on the perceptual and psychophysical aspects of somesthesis, although some information on neurophysiological aspects will be included as well; we look primarily at studies that have appeared since 1988. In the section on touch, we cover peripheral sensory mechanisms and several topics related to spatial and temporal pattern perception, specifically measures of spatial sensitivity, texture perception with particular emphasis on perceived roughness, complex spatial-temporal patterns, and the use of touch as a possible channel of communication. Other topics under this section include the effects of attention on processing tactile stimuli, cortical mechanisms, and the effects of aging on sensitivity. We also deal with thermal sensitivity and some aspects of haptics and kinesthesis. In the section on pain, we review work on the gate-control theory, sensory fibers, and higher neural organization. In addition, studies on central neurochemical effects and psychophysics of pain are examined.

The haptic oblique effect in the perception of rod orientation by blind adults

The haptic perception of vertical, horizontal, +45 degrees oblique, and +135 degrees oblique orientations was studied in completely blind adults. The purpose was to determine whether the variations of the gravitational cues provided by the arm-hand system during scanning would affect the manifestation of the oblique effect (lower performance in oblique orientations than in vertical-horizontal ones) as they did in blindfolded sighted people (Gentaz & Hatwell, 1996). In blindfolded sighted adults, the oblique effect was reduced or absent when the magnitude of gravitational cues was decreased. If visual experience participated in the haptic oblique effect, we should observe no oblique effect in early blind subjects in the conditions of manual exploration where late blind and blindfolded sighted manifest this effect. The magnitude of gravitational cues was therefore varied by changing gravity constraints, whereas the variability of these cues was varied by changing the plane in which the task was performed: horizontal (low variability) and frontal (high variability). Early and late blind adults were asked to explore haptically a rod and then to reproduce its orientation ipsilaterally in one of two exploratory conditions in each plane. In the horizontal plane, the oblique effect was absent, whatever the gravity constraints, in both groups (early and late blind subjects). In the frontal plane, the oblique effect was present, whatever the gravity constraints, in both groups. Taken together, these results showed that, in blind people, the variability of gravitational cues played a role in the haptic oblique effect; no effect of previous visual experience was observed.

Production and interpretation of perspective drawings by blind and sighted people

In three experiments the production and interpretation of perspective drawings by blind and sighted subjects were examined. Blindfolded sighted, early-blind, and late-blind subjects first attempted to produce raised-line drawings of a surface at a number of angles-0 degree (panel horizontal), -22.5 degrees, -45 degrees, -67.5 degrees, and -90 degrees (vertical). Congenitally blind subjects did not show foreshortening in their naive raised-line drawings. However, the congenitally blind subjects were able to understand aspects of perspective, and performed as well as the blindfolded sighted and late-blind subjects in a subsequent multiple-choice task. Subjects in the multiple-choice task were required to match tangible perspective drawings to a slanted board. Although the three groups performed alike, both groups of blind subjects performed better than blindfolded sighted controls on judgments involving drawings of the vertical panel in the second experiment. In a final experiment, in which vision and touch were compared, sighted subjects were required to adjust the angle of the panel to match foreshortened, perspective drawings. This experiment yielded significantly better performance with vision than with touch, but only for drawings of the board at the vertical orientation. The results suggested that congenitally blind people may benefit from haptic exposure to raised-line configurations representing geometric perspective.