Haptic perception in anorexia nervosa before and after weight gain

Haptic perception of patients with anorexia nervosa (n = 10) was analyzed in a longitudinal study (T0-T1). The haptic explorations consisted of palpating the structure of 12 sunken reliefs in sequence with both hands, eyes closed. After each exploration the structure was reproduced on a piece of paper. In the anorexia group, mean exploration time was significantly shorter than in healthy control subjects. However, the reproductions of complex stimuli submitted by the anorexia group were of notably poorer quality than those of the healthy controls. This was also observed after weight gain (T1). The results of the haptic explorations can be interpreted as a cortical dysfunction and deficits in somatosensorical integration processing in patients with anorexia nervosa. This may be due to a disorder of tactual-spatial processing in the right parieto-occipital regions.

Oral stereognosis in stroke and Parkinson's disease: a comparison of partially dentate and edentulous individuals

Oral stereognosis was measured in partially dentate and edentulous patients with stroke, Parkinson's disease, and an age and gender-matched control group. Stereognostic tests involving conventional free intra-oral manipulation of test objects were undertaken in the partially dentate and edentulous with and without complete dentures. Comparisons were made using the unpaired t-test and ANOVA. Edentulous stroke patients without dentures had significantly greater error scores and fewer correct identifications compared with partially dentate stroke patients. Stereognostic measures were similar in the partially dentate and edentulous with dentures, within experimental groups. In the partially dentate, there were no differences in stereognostic measures between the three groups. Stereognostic measures were poorer in edentulous stroke patients with and without dentures compared with the edentulous control group. Partially dentate stroke patients are less likely to have impaired oral stereognosis than edentulous stroke patients.

Responses in primary somatosensory cortex of rhesus monkey to controlled application of embossed grating and bar patterns

Responses of 66 neurons in primary somatosensory cortex (SI) of three anesthetized monkeys (Macaca mulatta) were characterized with grating patterns of 550- to 2900-mm groove width (Gw) and 250-mm ridge width, and/or pairs of 3-mm-wide ridges (bars) spaced 1-20 mm apart. Surfaces were stroked across single fingertips at parametrically varied levels of force (25-150 g) and velocity (25-100 mm/sec). The average firing rates (AFRs) of many cells varied with Gw, but force and velocity altered response functions (e.g., from linear to plateau or inverted). Slowly adapting (SA) cells were more sensitive to force, rapidly adapting (RA) cells to velocity. Force and velocity affected all cells sensitive to Gw, which suggests that response independence (e.g., AFR correlated with Gw but not force or velocity) may require active touch. Discharge intervals of many cells replicated stimulus temporal period. This temporal fidelity in SAs far exceeded examples reported for active touch. However, discharge burst duration and AFR increased with Gw, supporting a neural rate rather than temporal code for roughness. Force and velocity altered the Gw at which some cells fired once in phase to stimulus cycle ("tuning point"). Responses to bar edges suggest cortical replication of peripheral mechanoreceptor sensitivity to skin curvature, leading to this temporal fidelity in some cortical cells. Graded RA responses to Gw without obvious stimulus temporal replication may reflect early stages of integrative processing in supra- and infragranular layers that blur obvious temporal patterning and lead to a rate code correlated with spatial variation and proportional to perceived roughness.

Differences in the oral size illusions produced by cross-modality matching of peg and hole stimuli by the tongue and fingers in humans

Individuals overestimate the diameter of 1-mm-deep stimulus holes presented to the tongue when they use their fingers to select a hole of matching diameter. The aim here was to determine whether the oral size illusion evident for 1-mm-deep holes would also occur with 1-mm-high pegs of similar diameters. The illusion was studied in 24 individuals who were blindfolded during the trials. The two sets of test stimuli were (a) 5 cylindrical pegs (1 mm high) and (b) five circular holes (1 mm deep), each of 2.5, 5.0, 7.5, 10.0, 12.5 mm dia. The stimuli were held to the mouth with one hand, while the fingers of the free hand were used to select a matching object from a comparator series of either 1-mm-deep holes or 1-mm-high pegs ranging from 2.0 to 18 mm dia. Each stimulus was presented four times in a random order. The participants overestimated the diameter of the 1-mm-deep stimulus holes when these were matched with 1-mm-deep comparator holes. However, there was no illusion with four out of five 1-mm-high stimulus pegs when matched with 1-mm-high comparator pegs. In the 'reverse' experiment, there was no illusion with four out of five stimulus holes when these were matched with 1-mm-high comparator pegs. However, an illusion was evident for all the 1-mm-high stimulus pegs when these were matched with the 1-mm-deep comparator holes. Regardless of the nature of the stimulus ('hole' or 'peg'), a mismatch between the stimulus and comparator was consistently seen only when the fingers probed comparator holes. The oral size illusion is not due to any intrinsic differences in the sensitivities of the tongue or fingers. Rather, the illusion is due to the inability of the fingertip to access small comparator holes.

Theta power in the EEG of humans during ongoing processing in a haptic object recognition task

Dynamic changes in spectral theta power (TP) in the EEG over frontal regions were reported previously during the processing of visually presented spatial and verbal tasks [Cereb. Cortex, 7 (1997) 374-385]. Lower TP was found at the beginning compared to the end of processing. In order to test another modality, we examined theta power during the exploration of haptic stimuli with different complexity. A linear correlation between theta power and mean exploration time (as a measure of stimulus complexity) was found at the end of exploration but not at its beginning. These data are in line with our hypothesis since one could expect minimal load of working memory independent of stimulus complexity at the beginning of exploration whereas working memory would have integrated the stimuli of differing complexity into a perceptual model at the end of exploration.

Comparison of oral sensory function in complete denture and implant-supported prosthesis wearers

In order to compare the differences of part of the oral sensory functions among natural dentition, complete denture wearers and implant-supported prostheses wearers, tactile and pressure awareness was measured. Tactile sense was estimated by the thickness perception threshold between upper and lower dentition. Sensibility of pressure feeling was evaluated by threshold of lateral loading on tooth. Within this limited experiment, it could be concluded that an osseointegrated root form implant helped towards restoration of oral sensory functions.

Visuo-haptic object-related activation in the ventral visual pathway

The ventral pathway is involved in primate visual object recognition. In humans, a central stage in this pathway is an occipito-temporal region termed the lateral occipital complex (LOC), which is preferentially activated by visual objects compared to scrambled images or textures. However, objects have characteristic attributes (such as three-dimensional shape) that can be perceived both visually and haptically. Therefore, object-related brain areas may hold a representation of objects in both modalities. Using fMRI to map object-related brain regions, we found robust and consistent somatosensory activation in the occipito-temporal cortex. This region showed clear preference for objects compared to textures in both modalities. Most somatosensory object-selective voxels overlapped a part of the visual object-related region LOC. Thus, we suggest that neuronal populations in the occipito-temporal cortex may constitute a multimodal object-related network.

Visual and tactile information about object-curvature control fingertip forces and grasp kinematics in human dexterous manipulation

Most objects that we manipulate have curved surfaces. We have analyzed how subjects during a prototypical manipulatory task use visual and tactile sensory information for adapting fingertip actions to changes in object curvature. Subjects grasped an elongated object at one end using a precision grip and lifted it while instructed to keep it level. The principal load of the grasp was tangential torque due to the location of the center of mass of the object in relation to the horizontal grip axis joining the centers of the opposing grasp surfaces. The curvature strongly influenced the grip forces required to prevent rotational slips. Likewise the curvature influenced the rotational yield of the grasp that developed under the tangential torque load due to the viscoelastic properties of the fingertip pulps. Subjects scaled the grip forces parametrically with object curvature for grasp stability. Moreover in a curvature-dependent manner, subjects twisted the grasp around the grip axis by a radial flexion of the wrist to keep the desired object orientation despite the rotational yield. To adapt these fingertip actions to object curvature, subjects could use both vision and tactile sensibility integrated with predictive control. During combined blindfolding and digital anesthesia, however, the motor output failed to predict the consequences of the prevailing curvature. Subjects used vision to identify the curvature for efficient feedforward retrieval of grip force requirements before executing the motor commands. Digital anesthesia caused little impairment of grip force control when subjects had vision available, but the adaptation of the twist became delayed. Visual cues about the form of the grasp surface obtained before contact was used to scale the grip force, whereas the scaling of the twist depended on visual cues related to object movement. Thus subjects apparently relied on different visuomotor mechanisms for adaptation of grip force and grasp kinematics. In contrast, blindfolded subjects used tactile cues about the prevailing curvature obtained after contact with the object for feedforward adaptation of both grip force and twist. We conclude that humans use both vision and tactile sensibility for feedforward parametric adaptation of grip forces and grasp kinematics to object curvature. Normal control of the twist action, however, requires digital afferent input, and different visuomotor mechanisms support the control of the grasp twist and the grip force. This differential use of vision may have a bearing to the two-stream model of human visual processing.

Perceptual processing at adjacent locations on a single finger: masking and response competition

When target patterns and nontarget patterns are presented either to the same or to adjacent locations on the distal pad of the index finger, the amount of interference in identifying targets depends on both the shape and the location of the nontarget (Horner, 1997). In the present study, the question of whether such interference is caused by masking (the masker in some way distorts the initial representation of the target) or by response competition (the observer mistakenly responds with the masker, rather than with the target) was investigated. A 4-to-2 paradigm was used (Craig, 1995), in which four stimuli were mapped to only two responses. Targets and nontargets were randomly selected from the set of four stimuli and presented to the same or adjacent locations on the same fingerpad. Both the distal pad and the medial pad of the index finger were tested, because innervation density varies proximodistally on the distal pad, but not on the medial pad. The results indicated that response competition was an important factor limiting perception. Furthermore, perception was affected by varying location on the distal pad, but not on the medial pad. Finally, varying location on the distal pad affected perception only when responses were based on pattern shape, not when responses were based on direction of motion. The results are discussed in terms of differences in innervation density between adjacent locations and possible resultant differences in the spatial filtering properties of the skin.

Somesthetic disconnection syndromes in patients with callosal lesions

Somesthetic disconnection syndromes were investigated in relation to the sites of lesions in the corpus callosum in 3 patients with callosal lesions, in order to identify the callosal regions responsible for the interhemispheric transfer of somesthetic information. Cases 1 and 2 with lesions in the posterior truncus exhibited transfer deficits of discriminative sensations between the left and right hands, left-sided tactile anomia and left-sided somesthetic alexia. Case 3 with lesions in the posteroventral part of the posterior truncus showed no signs of somesthetic disconnection syndromes. The results suggest the importance of the anterior and/or dorsal part of the posterior truncus of the corpus callosum for interhemispheric transfer of the discriminative sensations and integrated somesthetic information necessary for tactile naming and somesthetic reading.

Oral perception in tongue thrust and other oral habits

Oral stereognosis is the ability of the mouth to recognize shape and texture. Oral shape recognition is sensitive to repetition and to topical mucosal anesthesia. Age, upper and lower arch perimeter, and labiolingual dysfunction also interact with oral stereognosis. The purpose of this investigation was to define the influence of age, arch size, and oral dysfunction on oral stereognosis when submitted to repeated trials. Fifty subjects were selected before orthodontic treatment. Each subject underwent 4 trials: T1 and T4 without anesthesia and strictly similar, T2 with topical anesthesia of the tongue, and T3 with topical anesthesia of the palate. Five test pieces or stimuli were used. The recognition time (RT) of each stimulus, the perimeter of upper and lower anterior dental arch, and the labiolingual dysfunction index (LLDI) were the main variables statistically evaluated. Subjects with a mild degree of dysfunction needed more time to recognize the stimuli in T3 when compared with T2. The number of RT3 > RT2 was 2.5 +/- 1.12 in the group with a low LLDI (12 +/- 1.5), and 1.57 +/- 0.63 in the group with an LLDI of 16 +/- 2.5 (P >.05). This may be attributed to different manipulation of the test pieces between the 2 groups, which could have been modified through sensory deprivation. Bolus recognition before the swallowing act needs to be paralleled to stereognostic performance.

Assessment of spatial acuity at the fingertip with grating (JVP) domes: validity for use in an elderly population

JVP domes are of a set of small grating surfaces recently introduced for cutaneous spatial resolution measurement. The gratings are placed on the skin and subjects are required to identify the orientation of grooves and bars. The finest grating whose orientations are discriminated reliably (75% correct) provides an estimate of the spatial resolution limit in the tested area. In the present study, we sought to determine the capacity of elderly subjects to resolve such grating stimuli in order to obtain normative data for this population. Thirty-two elderly individuals in good health (range: 60-88 years) were assessed for their ability to perceive grating orientation at the tip of the dominant index finger. Testing proceeded from the widest grating dome (3 mm) to the next (e.g., 2 mm), until the performance level dropped below 75% correct discrimination. The grating orientation task proved to be very difficult for most subjects and only a minority (14/32) was able to provide reliable reports of grating orientation even with presentation of the widest dome available (3 mm). Accordingly, individual grating resolution thresholds were often considerably higher (> 2.5 mm, n = 26) than values previously reported in young adults for the fingertip region (approximately 1 mm). These results suggest that the current set of grating domes may not be adequate for spatial acuity measurement at the fingertip of older adults. New larger grating dimensions should be added to the set presently available to improve their sensitivity for an older population.

Tactual Performance Test: internal consistency reliability of the memory and location scores

Internal consistency reliabilities were computed for the Tactual Performance Test Memory and Location scores (N=602). After adjusting for unequal item difficulty, the reliabilities for Memory and Location were .69 and .79, respectively.

Complete denture wearers: electromyography of mastication and texture perception whilst eating meat

This study was undertaken to evaluate the sensitivity of denture wearers to different food textures and to follow masticatory pattern adaptation with variation in texture using electromyography (EMG) recordings. Nine patients with complete dentures and 9 dentate control patients without any oro-dental pathology were studied. Six different samples of beef were obtained from the same muscle by altering the state of the muscle fibres and by variation of the cooking temperature. The variations in texture were mechanically controlled. Electromyographic activity was recorded during chewing. The patients' subjective appreciation of texture was reported using a 10-cm non-structured analogue scale. The following parameters were analysed: muscle work, number of masticatory cycles, number of rejected samples, initial tenderness, overall tenderness, juiciness, and duration of chewing for each sample in the mouth. Muscle activity was less for the edentulous group, particularly that of the masseter muscles. The masticatory pattern of complete denture wearers was less adapted to each sample texture than was that of the control group. Both groups perceived differences in texture of the samples. It was concluded that although texture perception is little altered, muscular adaptation to the bolus is reduced in patients with complete dentures.

The functional anatomy of visual-tactile integration in man: a study using positron emission tomography

The integration of neural signals from different sensory modalities is a prerequisite for many cognitive and behavioural functions. In this study, we have mapped the functional anatomy of the integration of sensory signals across the tactile and visual modalities. Using the PET radiotracer H2(15)O, regional cerebral blood flow (rCBF) changes were measured in eight normal volunteers performing crossmodal recognition of simultaneously presented visual and tactile stimuli using a modified version of the 'arc-circle test'. Whilst intramodal matching within the visual modality led to relative rCBF increases in the visual association cortex, crossmodal matching (visual-tactile), when compared to intramodal matching, was accompanied by relative rCBF increases in the anterior cingulate cortex, inferior parietal lobules, the left dorsolateral prefrontal cortex (DLPFC) and the left claustrum/insular cortex. The pattern of brain activation is congruent with areas of heteromodal and supramodal cortex and indicates that activation of multimodal areas is required to solve the crossmodal problem.

[Haptic perception and EEG changes in anorexia nervosa]

OBJECTIVES

We predicted that due to diminished somatosensory integrative ability, the anorectic patients would have problems reproducing haptic stimuli. In addition we sought to determine whether EEGs from anorectic patients (AN) and the healthy controls (CO) would show discrepancies between the two groups during haptic explorations in theta-power over the right parietal region.

METHOD

EEG power (theta-power) data of AN (n = 13) and CO (n = 13) were analyzed during haptic exploration tasks and rest intervals. The haptic explorations consisted of palpating the structure of six sunken reliefs in sequence with both hands, eyes closed. After each exploration the structure was drawn on a piece of paper.

RESULTS

The reproductions of haptic stimuli submitted by the anorectic patients were of notably poorer quality than those of the healthy controls. During rest intervals and haptic explorations, spectral power was generally lower in the AN group in comparison to the healthy controls. Significant theta-power differences between groups showed over the right parietal cortex during haptic explorations. The decrease in EEG power in the anorectic patients in the theta bands across the right parietal region during haptic exploration tasks could be interpreted as a minor activation of visuo-spatial regions. The results of the haptic explorations as well as the EEG-power changes indicate a cortical dysfunction and deficits in somatosensory integration processing in anorexia nervosa patients.

Deterioration of intraoral hole size identification after treatment of oral and pharyngeal cancer

Thirty-one patients with a diagnosed malignant tumour of the oral cavity or pharynx were tested in hole size identification on four test occasions: before all treatment, after radiotherapy and 6 months and 1 year after surgical treatment. They were compared within groups as well as with a group of healthy reference individuals of the same age who underwent the same test procedure at a 2 months' interval. The oral group did not decline in hole size identification after radiotherapy, but did after surgery. The deterioration was persistent 1 year after surgery. The pharyngeal group did not change performance in hole size identification after radiotherapy, nor after surgery. It is obvious that surgery of the oral structures causes the deterioration. No correlation with damage to the lingual nerve could be registered. The oral cavity reacts as one unit, despite sensory input from two sides. The non-operated side does not compensate for the operated side. It is plausible that decreased oral sensory acuity, in recognizing hole size of the bolus, contributes to postoperative swallowing problems.

Relation between clinical measures and fine manipulative control in children with hemiplegic cerebral palsy

The present investigation examines the relation between various clinical measures and the performance of a functional precision grip-lift task. Fifteen children with hemiplegic cerebral palsy (CP), aged 8 to 14 years, and 15 age-matched control children grasped and lifted an object whose surface texture was varied while their fingertip forces were recorded. The force coordination was compared with tactile sensibility, grip strength, manual dexterity, and spasticity using correlational and regression analyses. The findings highlight the importance of tactile sensibility in this task. However, the manner in which sensibility was related varied for the sensory adaptation of fingertip forces, the anticipatory scaling of the force increase, and the smooth transitions between the temporal phases comprising the grip-lift task. The findings also indicate that spasticity affects some measures of the task, but not others, suggesting that the relation between spasticity and motor performance may not be absolute. The results further suggest that the impairments in grasping in children with hemiplegic CP are largely but not exclusively due to disturbed sensory mechanisms which may have direct implications for therapeutic intervention.

Tactile morphagnosia secondary to spatial deficits

A 73-year old man showed visual and tactile agnosia following bilateral haemorrhagic stroke. Tactile agnosia was present in both hands, as shown by his impaired recognition of objects, geometrical shapes, letters and nonsense shapes. Basic somatosensory functions and the appreciation of substance qualities (hylognosis) were preserved. The patient's inability to identify the stimulus shape (morphagnosia) was associated with a striking impairment in detecting the orientation of a line or a rod in two- and three-dimensional space. This spatial deficit was thought to underlie morphagnosia, since in the tactile modality form recognition is built upon the integration of the successive changes of orientation in space made by the hand as it explores the stimulus. Indirect support for this hypothesis was provided by the location of the lesions, which could not account for the severe impairment of both hands. Only those located in the right hemisphere encroached upon the posterior parietal cortex, which is the region assumed to be specialised in shape recognition. The left hemisphere damage spared the corresponding area and could not, therefore, be held responsible for the right hand tactile agnosia. We submit that tactile agnosia can result from the disruption of two discrete mechanisms and has different features. It may arise from a parietal lesion damaging the high level processing of somatosensory information that culminates in the structured description of the object. In this case, tactile recognition is impaired in the hand contralateral to the side of the lesion. Alternatively, it may be caused by a profound derangement of spatial skills, particularly those involved in detecting the orientation in space of lines, segments and complex patterns. This deficit results in morphagnosia, which affects both hands to the same degree.

Failure to recognise objects by active touch (astereognosia) results from lesion of parietal-cortex representation of finger kinaesthesis

The inability to identify objects by manipulation with eyes closed (astereognosia) results from a focal cortical lesion of the second order parietal area 2, which integrates inputs from finger joints with tactile information.

'Putting your foot in it'! A window into clumsy behaviour

Intra-modal matching by 7-year-old children diagnosed as having hand-eye co-ordination problems (HECP) and a control group of children without such problems was tested using a target location and matching task. The 'foot-hand' task required the children to locate a target pin with the 'big-toe' (felt target) and match the located target position with the hand, without vision. There were four conditions: location via right foot-matching the located target with the right hand (RfRh) and left hand (RfLh) and location via left foot-matching the located target with the left hand (LfLh) and right hand (LfRh). Both groups demonstrated better performance in the intra- as compared to the inter-hemispheric conditions, suggesting that the corpus callosum is not yet fully mature at this age. The HECP children showed inferior performance to the control children in three of the four conditions, the conditions where the right hemisphere was involved and/or information had to be transported across the corpus callosum (RfLh; LfLh; LfRh). Two possible explanations of these findings are put forward and discussed: right hemisphere insufficiency with or without dysfunctional corpus callosum.

Osseoperception: sensory function and proprioception

Tooth loss and its replacement have significant functional and psychosocial consequences. The removal of intra-dental and periodontal mechanoreception accompanying tooth loss changes the fine proprioceptive control of jaw function and influences the precision of magnitude, direction, and rate of occlusal load application. With the loss of all teeth, complete denture restoration is a compromise replacement which only partially restores function. Implant-supported prostheses restore jaw function more appropriately, with improved psychophysiological discriminatory ability and oral stereognosis. Osseoperception is defined as depending on central influences from corollary discharge from cortico-motor commands to jaw muscles, and contributions from peripheral mechanoreceptors in orofacial and temporomandibular tissues. The processing of central influences is considered with the recognition of the plasticity of neuromotor mechanisms that occurs to accommodate the loss of dental and periodontal inputs.

Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem concerning tactile pictorial perception by the blind. The aim of the experiments reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute values of 3-D properties from 2-D patterns read by the finger pads, the abilities of participants to perceive gradients lying between known maxima and minima were assessed. Experiment 1 involved blindfolded sighted participants making verbal magnitude estimations of texture-gradient magnitudes corresponding to plane surfaces at different slants. In experiment 2 the participants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind participants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for learning. Texture gradients appear as informative to the blind as they do to the sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigated.

The influence of stimulus tilt on haptic curvature matching and discrimination by dynamic touch

We investigated whether haptic comparison of the curvature of strips is influenced by the tilt (the average slope relative to the horizontal) of the curved strips. This particular stimulus manipulation was chosen to decide between two broad ways in which dynamic curvature comparison might be done: on the basis of the attitude (slope) differences over the surfaces or on the basis of the attitude (slope) differences between successively presented surfaces. For this purpose we conducted matching and discrimination experiments in which strips of constant curvature 9 cm long were touched dynamically and the tilts of the strips were varied. The results of the matching experiment showed some influence of tilt: the strips were judged to be slightly more curved if the tilt was nonzero than if it was zero. The results of the discrimination experiment did not show an effect of tilt. Because the attitude (slope) differences over the surfaces were independent of the tilt it is concluded that curvature comparison is based primarily on attitude differences over the curved surfaces.

[Haptic form discrimination. Group comparison of children with normal speech development and former speech development disordered patients]

The importance of the neurobiological basis of developmental language disorders includes somatosensory modalities. Twenty-five children were diagnosed as having specific language-impairment at preschool age. All were examined with regard to their manual haptic form discrimination without visual control at a mean age of 8.7 years +/- 7.1 months. This study group was compared to age- and gender-matched normal children of equal non-verbal intelligence (control group). Haptic discrimination was measured with the Seguin formboard on which the children were required to place ten geometrical forms in appropriate holes. Both groups differed significantly in their mean quantitative performances in favor of the control group (P < 0.05). The difference in their mean performance and their mean discrimination times did not reach statistical significance. All results were not age-dependent. The control group on average performed significantly better with their left hands than the study group (P < 0.05). Qualitative analysis revealed a significant difference in haptic discrimination of the pointed forms and was probably caused by inadequate exploration procedures and/or cognitive representation deficits. The results of the children with previous developmental language disorders were interpreted as an expression of an impaired cerebral maturation.