Aging and the Visual, Haptic, and Cross-Modal Perception of Natural Object Shape

Perceptuo-affective organization of touched materials in younger and older adults

In everyday interaction we touch different materials, which we experience along a limited number of perceptual and emotional dimensions: For instances, a furry surface feels soft and pleasant, whereas sandpaper feels rough and unpleasant. In a previous study, younger adults manually explored a representative set of solid, fluid and granular materials. Their ratings were made along six perceptual dimensions (roughness, fluidity, granularity, deformability, fibrousness, heaviness) and three emotional ones (valence, arousal, dominance). Perceptual and emotional dimensions were systematically correlated. Here, we wondered how this perceptuo-affective organization of touched materials depends on age, given that older adults show decline in haptic abilities, in particular detail perception. 30 younger participants (~22 years, half females) and 15 older participants (~66 years) explored 25 materials using 18 perceptual and 9 emotional adjectives. We extracted 6 perceptual and 2 emotional dimensions. Older and younger adults showed similar dimensions. However, in younger participants roughness and granularity judgments were done separately, while they were collapsed in a single dimension in older people. Further, age groups differed in the perception of roughness, granularity and valence, and older people did not show a positive correlation between valence and granularity as did younger people. As expected, control analyses between young males and females did not reveal similar gender differences. Overall, the results demonstrate that older people organize and experience materials partly differently from younger people, which we lead back to sensory decline. However, other aspects of perceptual organization that also include fine perception are preserved into older age.

Multisensory perception constrains the formation of object categories: a review of evidence from sensory-driven and predictive processes on categorical decisions

Although object categorization is a fundamental cognitive ability, it is also a complex process going beyond the perception and organization of sensory stimulation. Here we review existing evidence about how the human brain acquires and organizes multisensory inputs into object representations that may lead to conceptual knowledge in memory. We first focus on evidence for two processes on object perception, multisensory integration of redundant information (e.g. seeing and feeling a shape) and crossmodal, statistical learning of complementary information (e.g. the 'moo' sound of a cow and its visual shape). For both processes, the importance attributed to each sensory input in constructing a multisensory representation of an object depends on the working range of the specific sensory modality, the relative reliability or distinctiveness of the encoded information and top-down predictions. Moreover, apart from sensory-driven influences on perception, the acquisition of featural information across modalities can affect semantic memory and, in turn, influence category decisions. In sum, we argue that both multisensory processes independently constrain the formation of object categories across the lifespan, possibly through early and late integration mechanisms, respectively, to allow us to efficiently achieve the everyday, but remarkable, ability of recognizing objects. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Aging and temporal integration in the visual perception of object shape

It has been known for more than 160 years that highly occluded objects that would normally be visually unrecognizable can be successfully identified when they move. This anorthoscopic perception relies on the visual system's ability to integrate information over time to complete the perception of an entire object's shape. In this experiment, 16 younger and older adults (mean ages were 20.5 and 74.6 years, respectively) were familiarized with the (unoccluded) shapes of five naturally-shaped objects (bell peppers, Capsicum annuum) until they could be easily identified (i.e., with accuracies of at least 90 percent correct). All observers then viewed the stimulus objects anorthoscopically as they moved behind narrow slits; only small object fragments could be seen at any given time, because the objects were almost totally occluded from view. Even though the object identification performance for all observers was equivalent when whole object shapes were visible, a large age-related deficit in object identification emerged during anorthoscopic viewing such that the younger adults' identification performance was 45.4 percent higher than that of the older adults. This first ever study of aging and anorthoscopic perception demonstrates that there is an age-related deficit in performing the temporal integration needed for successful object recognition.

Crossmodal associations between visual textures and temperature concepts

Visual textures are critical in how individuals form sensory expectations about objects, which include somatosensory properties such as temperature. This study aimed to uncover crossmodal associations between visual textures and temperature concepts. In Experiment 1 (N = 193), we evaluated crossmodal associations between 43 visual texture categories and different temperature concepts (via temperature words such as cold and hot) using an explicit forced-choice test. The results revealed associations between striped, cracked, matted, and waffled visual textures and high temperatures and between crystalline and flecked visual textures and low temperatures. In Experiment 2 (N = 247), we conducted six implicit association tests (IATs) pairing the two visual textures most strongly associated with low (crystalline and flecked) and high (striped and cracked) temperatures with the words cold and hot as per the results of Experiment 1. When pairing the crystalline and striped visual textures, the results revealed that crystalline was matched to the word cold, and striped was matched to the word hot. However, some associations found in the explicit test were not found in the IATs. In Experiment 3 (N = 124), we investigated how mappings between visual textures and concrete entities may influence crossmodal associations with temperature and these visual textures. Altogether, we found a range of association strengths and automaticity levels. Importantly, we found evidence of relative effects. Furthermore, some of these crossmodal associations are partly influenced by indirect mappings to concrete entities.

Aging and the detection of moving objects defined by common fate

Grouping by common fate plays an important role in how human observers perceive environmental objects. In this study, the effect of aging upon the ability to utilize common fate was evaluated. Twenty-two younger and older adults (mean ages were 23.4 and 74.7 years, respectively) participated in two experiments. On any given trial, the participants sequentially viewed two apparent motion sequences and were required to indicate which temporal interval contained a coherently moving dotted line embedded in noisy random background motion. In Experiment 1, the number of dots defining the target was varied, while in Experiment 2, the target interpoint spacing was varied. The younger adults outperformed the older adults by 19.4 percent in Experiment 1 and 50.5 percent in Experiment 2. The older and younger adults were similarly affected by variations in the number of target dots and the target interpoint spacing. The individual older participants' object detection accuracies were highly correlated with their individual chronological ages, such that the performance of the younger old participants was much higher than that exhibited by the older old. Increases in age systematically affect the ability of older adults to detect and visually perceive objects defined by common fate.

Aging and the visual perception of object size

An experiment evaluated the ability of 30 younger and older adults to visually judge object size under three conditions: (1) full cue, (2) in the dark, with linear perspective, and (3) in complete darkness. Each observer made repeated judgments for the same square stimuli (the task was to adjust a separation until it matched the perceived size of the squares), enabling an evaluation of precision as well as accuracy. The judgments were just as accurate in the dark with linear perspective condition as in the full cue condition, indicating that linear perspective serves as an important source of optical information to support the perception of object size). In contrast, in complete darkness (where linear perspective information was unavailable), the accuracy of the observers' judgments was poor. Finally, there was no difference in either the accuracy or the precision of the observers' judgments between the two age groups, despite the fact that the older adults were more than 50 years older than the younger adults (mean age of the younger and older adults was 22.3 and 74.1 years, respectively). The ability to visually perceive object size is well maintained with increasing age, unlike a number of other important visual abilities.

Cross-Modal Interactions of the Tactile System

The sensory systems responsible for perceptions of touch, vision, hearing, etc. have traditionally been regarded as mostly separate, only converging at late stages of processing. Contrary to this dogma, recent work has shown that interactions between the senses are robust and abundant. Touch and vision are both commonly used to obtain information about a number of object properties, and share perceptual and neural representations in many domains. Additionally, visuotactile interactions are implicated in the sense of body ownership, as revealed by powerful illusions that can be evoked by manipulating these interactions. Touch and hearing both rely in part on temporal frequency information, leading to a number of audiotactile interactions reflecting a good deal of perceptual and neural overlap. The focus in sensory neuroscience and psychophysics is now on characterizing the multisensory interactions that lead to our panoply of perceptual experiences.

Multi-modal self-adaptation during object recognition in an artificial cognitive system

The cognitive connection between the senses of touch and vision is probably the best-known case of multimodality. Recent discoveries suggest that the mapping between both senses is learned rather than innate. This evidence opens the door to a dynamic multimodality that allows individuals to adaptively develop within their environment. By mimicking this aspect of human learning, we propose a new multimodal mechanism that allows artificial cognitive systems (ACS) to quickly adapt to unforeseen perceptual anomalies generated by the environment or by the system itself. In this context, visual recognition systems have advanced remarkably in recent years thanks to the creation of large-scale datasets together with the advent of deep learning algorithms. However, this has not been the case for the haptic modality, where the lack of two-handed dexterous datasets has limited the ability of learning systems to process the tactile information of human object exploration. This data imbalance hinders the creation of synchronized datasets that would enable the development of multimodality in ACS during object exploration. In this work, we use a multimodal dataset recently generated from tactile sensors placed on a collection of objects that capture haptic data from human manipulation, together with the corresponding visual counterpart. Using this data, we create a multimodal learning transfer mechanism capable of both detecting sudden and permanent anomalies in the visual channel and maintaining visual object recognition performance by retraining the visual mode for a few minutes using haptic information. Our proposal for perceptual awareness and self-adaptation is of noteworthy relevance as can be applied by any system that satisfies two very generic conditions: it can classify each mode independently and is provided with a synchronized multimodal data set.

Ageing and multisensory integration: A review of the evidence, and a computational perspective

The processing of multisensory signals is crucial for effective interaction with the environment, but our ability to perform this vital function changes as we age. In the first part of this review, we summarise existing research into the effects of healthy ageing on multisensory integration. We note that age differences vary substantially with the paradigms and stimuli used: older adults often receive at least as much benefit (to both accuracy and response times) as younger controls from congruent multisensory stimuli, but are also consistently more negatively impacted by the presence of intersensory conflict. In the second part, we outline a normative Bayesian framework that provides a principled and computationally informed perspective on the key ingredients involved in multisensory perception, and how these are affected by ageing. Applying this framework to the existing literature, we conclude that changes to sensory reliability, prior expectations (together with attentional control), and decisional strategies all contribute to the age differences observed. However, we find no compelling evidence of any age-related changes to the basic inference mechanisms involved in multisensory perception.

Aging and haptic shape discrimination: the effects of variations in size

Seventy-two older and younger adults haptically discriminated the solid shape of natural objects (bell peppers, Capsicum annuum). Plastic copies of the original-sized fruits were used as experimental stimuli, as well as copies that were reduced in size to 1/8th and 1/27th of the original object volumes. If haptic object shape is represented in a part-based manner, then haptic shape discrimination performance should be at least partly size invariant, since changes only in scale do not affect an object’s constituent parts. On any given trial, participants sequentially explored two bell pepper replicas and were required to judge whether they possessed the same shape or had different shapes. For some participants, the objects to be discriminated possessed the same size, while for others, the two objects had different sizes. It was found that variations in scale did significantly reduce the participants’ haptic sensitivities to shape. Nevertheless, the discrimination performance obtained for large variations in size was no lower than that obtained for smaller variations in size. The results also demonstrated that increases in age modestly affect haptic shape discrimination performance: the d′ values of the older participants were 15.5% lower than those of the younger participants.

The effect of sensory-motor training on hand and upper extremity sensory and motor function in patients with idiopathic Parkinson disease

STUDY DESIGN

Blinded randomized controlled trial.

INTRODUCTION

Patients with Parkinson disease (PD) have sensory problems, but there is still no accurate understanding of the effects of sensory-motor interventions on PD.

PURPOSE OF THE STUDY

To investigate the effects of sensory-motor training (SMT) on hand and upper extremity sensory and motor function in patients with PD.

METHODS

Forty patients with PD were allocated to the SMT group or the control group (CG) (mean ages ± standard deviation: SMT, 61.05 ± 13.9 years; CG, 59.15 ± 11.26 years). The CG received the common rehabilitation therapies, whereas the SMT group received SMT. The SMT included discrimination of temperatures, weights, textures, shapes, and objects and was performed 5 times each week for 2 weeks.

RESULTS

Significantly reducing the error rates in the haptic object recognition test (dominant hand [DH]: F = 15.36, P = .001, and effect size [ES] = 0.29; nondominant hand [NDH]: F = 9.33, P = .004, and ES = 0.21) and the error means in the wrist proprioception sensation test (DH: F = 9.11, P = .005, and ES = 0.19; NDH: F = 13.04, P = .001, and ES = 0.26) and increasing matched objects in the hand active sensation test (DH: F = 12.15, P = .001, and ES = 0.24; NDH: F = 5.03, P = .03, and ES = 0.12) founded in the SMT. Also, the DH (F = 6.65, P = .01, and ES = 0.15), both hands (F = 7.61, P = .009, and ES = 0.17), and assembly (F = 7.02, P = .01, and ES = 0.15) subtests of fine motor performance, as well as DH (F = 10.1, P = .003, and ES = 0.21) and NDH (F = 8.37, P = .006, and ES = 0.18) in upper extremity functional performance, were improved in the SMT.

DISCUSSION

SMT improved hand and upper extremity sensory-motor function in patients with PD.

CONCLUSION

The SMT group showed improved sensory and motor function. But these results were limited to levels 1 to 3 of the Hoehn and Yahr Scale.

Aging and the Perception of Motion-Defined Form

A single experiment required 26 younger and older adults to discriminate global shape as defined only by differences in the speed of stimulus element rotation. Detection of the target shape required successful perceptual grouping by common fate. A considerable adverse effect of age was found: In order to perceive the target and discriminate its shape with a d’ value of 1.5, the older observers needed target element rotational speeds that were 23.4% faster than those required for younger adults. In addition, as the difference between the rotation speeds of the background and target stimulus elements increased, the performance of the older observers improved at a rate that was only about half of that exhibited by the younger observers. The results indicate that while older adults can perceive global shape defined by similarity (and differences) in rotational speed, their abilities are nevertheless significantly compromised.

Haptic Distance Ratio Estimation: The Geometry of Space Within the Hands

In the current study of haptic distance perception, 20 younger (median age: 22 years) and 20 older adults (median age: 72 years) used active touch to estimate distance ratios(one length relative to another). Nine tactile stimuli were created from wooden dowels; each consisted of two perpendicular dowels. The stimulus distance ratios ranged from 1.0 to 5.0. Each participant used both hands (without vision) to actively explore (30 s) a single stimulus object on every trial. The task was to numerically estimate the distance ratio. Overall, the participants’ judgments were precise; the overall magnitude of the Pearson r correlation coefficient was 0.943 and did not differ for younger and older adults. While the participants’ judgments were precise, they were not completely accurate: The average slope (of the relationship between actual and judged distance ratios) for all participants was significantly greater than 1.0 (1.15). Surprisingly, differences in manual dexterity had no apparent effect on distance ratio estimates. Older adults apparently retain an excellent ability to perceive distances using their sense of touch. Our results also demonstrate that the geometry of haptic space (at the scale of the hand) is approximately Euclidean in nature (and certainly not merely topological, projective, or affine).

Age Effects on Visuo-Haptic Length Discrimination: Evidence for Optimal Integration of Senses in Senior Adults

Demographic changes in most developed societies have fostered research on functional aging. While cognitive changes have been characterized elaborately, understanding of perceptual aging lacks behind. We investigated age effects on the mechanisms of how multiple sources of sensory information are merged into a common percept. We studied visuo-haptic integration in a length discrimination task. A total of 24 young (20-25 years) and 27 senior (69-77 years) adults compared standard stimuli to appropriate sets of comparison stimuli. Standard stimuli were explored under visual, haptic, or visuo-haptic conditions. The task procedure allowed introducing an intersensory conflict by anamorphic lenses. Comparison stimuli were exclusively explored haptically. We derived psychometric functions for each condition, determining points of subjective equality and discrimination thresholds. We notably evaluated visuo-haptic perception by different models of multisensory processing, i.e., the Maximum-Likelihood-Estimate model of optimal cue integration, a suboptimal integration model, and a cue switching model. Our results support robust visuo-haptic integration across the adult lifespan. We found suboptimal weighted averaging of sensory sources in young adults, however, senior adults exploited differential sensory reliabilities more efficiently to optimize thresholds. Indeed, evaluation of the MLE model indicates that young adults underweighted visual cues by more than 30%; in contrast, visual weights of senior adults deviated only by about 3% from predictions. We suggest that close to optimal multisensory integration might contribute to successful compensation for age-related sensory losses and provides a critical resource. Differentiation between multisensory integration during healthy aging and age-related pathological challenges on the sensory systems awaits further exploration.

Aging and visual 3-D shape recognition from motion

Two experiments were conducted to evaluate the ability of younger and older adults to recognize 3-D object shape from patterns of optical motion. In Experiment 1, participants were required to identify dotted surfaces that rotated in depth (i.e., surface structure portrayed using the kinetic depth effect). The task difficulty was manipulated by limiting the surface point lifetimes within the stimulus apparent motion sequences. In Experiment 2, the participants identified solid, naturally shaped objects (replicas of bell peppers, Capsicum annuum) that were defined by occlusion boundary contours, patterns of specular highlights, or combined optical patterns containing both boundary contours and specular highlights. Significant and adverse effects of increased age were found in both experiments. Despite the fact that previous research has found that increases in age do not reduce solid shape discrimination, our current results indicated that the same conclusion does not hold for shape identification. We demonstrated that aging results in a reduction in the ability to visually recognize 3-D shape independent of how the 3-D structure is defined (motions of isolated points, deformations of smooth optical fields containing specular highlights, etc.).

SPATIAL UPDATING OF HAPTIC ARRAYS ACROSS THE LIFE SPAN

Background/Study Context: Aging research addressing spatial learning, representation, and action is almost exclusively based on vision as the input source. Much less is known about how spatial abilities from nonvisual inputs, particularly from haptic information, may change during life-span spatial development. This research studied whether learning and updating of haptic target configurations differs as a function of age.

METHODS

Three groups of participants, ranging from 20 to 80 years old, felt four-target table-top circular arrays and then performed several tasks to assess life-span haptic spatial cognition. Measures evaluated included egocentric pointing, allocentric pointing, and array reconstruction after physical or imagined spatial updating.

RESULTS

All measures revealed reliable differences between the oldest and youngest participant groups. The age effect for egocentric pointing contrasts with previous findings showing preserved egocentric spatial abilities. Error performance on allocentric pointing and map reconstruction tasks showing a clear age effect, with the oldest participants exhibiting the greatest error, is in line with other studies in the visual domain. Postupdating performance sharply declined with age but did not reliably differ between physical and imagined updating.

CONCLUSION

Results suggest that there is a general trend for age-related degradation of spatial abilities after haptic learning, with the greatest declines manifesting in all measures in people over 60 years of age. Results are interpreted in terms of a spatial aging effect on mental transformations of three-dimensional representations of space in working memory.

Effects of Aging in Multisensory Integration: A Systematic Review

Multisensory integration (MSI) is the integration by the brain of environmental information acquired through more than one sense. Accurate MSI has been shown to be a key component of successful aging and to be crucial for processes underlying activities of daily living (ADLs). Problems in MSI could prevent older adults (OA) to age in place and live independently. However, there is a need to know how to assess changes in MSI in individuals. This systematic review provides an overview of tests assessing the effect of age on MSI in the healthy elderly population (aged 60 years and older). A literature search was done in Scopus. Articles from the earliest records available to January 20, 2016, were eligible for inclusion if assessing effects of aging on MSI in the healthy elderly population compared to younger adults (YA). These articles were rated for risk of bias with the Newcastle-Ottawa quality assessment. Out of 307 identified research articles, 49 articles were included for final review, describing 69 tests. The review indicated that OA maximize the use of multiple sources of information in comparison to YA (20 studies). In tasks that require more cognitive function, or when participants need to adapt rapidly to a situation, or when a dual task is added to the experiment, OA have problems selecting and integrating information properly as compared to YA (19 studies). Additionally, irrelevant or wrong information (i.e., distractors) has a greater impact on OA than on YA (21 studies). OA failing to weigh sensory information properly, has not been described in previous reviews. Anatomical changes (i.e., reduction of brain volume and differences of brain areas' recruitment) and information processing changes (i.e., general cognitive slowing, inverse effectiveness, larger time window of integration, deficits in attentional control and increased noise at baseline) can only partly explain the differences between OA and YA regarding MSI. Since we have an interest in successful aging and early detection of MSI issues in the elderly population, the identified tests form a good starting point to develop a clinically useful toolkit to assess MSI in healthy OA.

Aging and Haptic-Visual Solid Shape Matching

A total of 36 younger (mean age = 21.3 years) and older adults (mean age = 73.8 years) haptically explored plastic copies of naturally shaped objects (bell peppers, Capsicum annuum) one at a time for 7 s each. The participants' task was to then choose which of 12 concurrently visible objects had the same solid shape as the one they felt. The younger and older participants explored the object shapes using either one, three, or five fingers (there were six participants for each combination of number of fingers and age group). The outcome was different from that of previous research conducted with manmade objects. Unlike Jansson and Monaci (2006) , we found that for most objects, our participants' performance was unaffected by variations in the number of fingers used for haptic exploration. While there was no significant overall effect of the number of fingers, there was a significant main effect of age. The younger adults' shape matching performance was 48.6% higher than that of the older adults. When perceiving naturally shaped objects such as bell peppers, it appears that the usage of a single finger can be as effective as haptic exploration with a whole complement of five fingers.

A contribuição do sistema âncora em diferentes segmentos corporais para o controle da postura em idosos

RESUMO O sistema âncora é uma ferramenta não rígida que fornece informação háptica adicional, consistindo de dois cabos maleáveis com 125 g de massa repousando no solo, devendo-se segurar a outra extremidade com as mãos (âncora-mão). Considerando que o toque leve em diferentes partes do corpo reduz a oscilação corporal, é possível, da mesma forma, que o uso do sistema âncora em diferentes partes do corpo seja efetivo. Portanto, o objetivo deste estudo foi investigar o efeito do uso do sistema âncora em diferentes segmentos corporais sobre a oscilação corporal de idosos. Trinta idosos participaram do presente estudo. Eles ficaram na postura ereta com os pés na posição semi-tandem sobre uma plataforma de força para a obtenção do deslocamento do centro de pressão (CP). Cinco condições experimentais foram realizadas: sem âncora, âncora-mão, âncoras nas mãos presas com presilhas, âncoras nos antebraços presas com presilhas e âncoras nos ombros presas com presilhas. Os resultados mostraram uma redução da área da elipse ajustada ao deslocamento do CP e na amplitude média de oscilação na direção anteroposterior nas condições com as âncoras posicionadas nas mãos (âncora-mão e presilha) e antebraços em comparação à condição sem âncora. Assim, o uso do sistema âncora foi efetivo quando as âncoras foram posicionadas no antebraço da mesma forma que quando foram seguras pelas mãos. A melhora observada com o uso das âncoras parece não estar relacionada com a quantidade de receptores táteis no ponto de contato dos cabos das âncoras.

Aging and the Haptic Perception of Material Properties

The ability of 26 younger (mean age was 22.5 years) and older adults (mean age was 72.6 years) to haptically perceive material properties was evaluated. The participants manually explored (for 5 seconds) 42 surfaces twice and placed each of these 84 experimental stimuli into one of seven categories: paper, plastic, metal, wood, stone, fabric, and fur/leather. In general, the participants were best able to identify fur/leather and wood materials; in contrast, recognition performance was worst for stone and paper. Despite similar overall patterns of performance for younger and older participants, the younger adults’ recognition accuracies were 26.5% higher. The participants’ tactile acuities (assessed by tactile grating orientation discrimination) affected their ability to identify surface material. In particular, the Pearson r correlation coefficient relating the participants’ grating orientation thresholds and their material identification performance was −0.8: The higher the participants’ thresholds, the lower the material recognition ability. While older adults are able to effectively perceive the solid shape of environmental objects using the sense of touch, their ability to perceive surface materials is significantly compromised.

Dynamic cutaneous information is sufficient for precise curvature discrimination

Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants’ thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement.

Perceiving Object Shape from Specular Highlight Deformation, Boundary Contour Deformation, and Active Haptic Manipulation

It is well known that motion facilitates the visual perception of solid object shape, particularly when surface texture or other identifiable features (e.g., corners) are present. Conventional models of structure-from-motion require the presence of texture or identifiable object features in order to recover 3-D structure. Is the facilitation in 3-D shape perception similar in magnitude when surface texture is absent? On any given trial in the current experiments, participants were presented with a single randomly-selected solid object (bell pepper or randomly-shaped "glaven") for 12 seconds and were required to indicate which of 12 (for bell peppers) or 8 (for glavens) simultaneously visible objects possessed the same shape. The initial single object's shape was defined either by boundary contours alone (i.e., presented as a silhouette), specular highlights alone, specular highlights combined with boundary contours, or texture. In addition, there was a haptic condition: in this condition, the participants haptically explored with both hands (but could not see) the initial single object for 12 seconds; they then performed the same shape-matching task used in the visual conditions. For both the visual and haptic conditions, motion (rotation in depth or active object manipulation) was present in half of the trials and was not present for the remaining trials. The effect of motion was quantitatively similar for all of the visual and haptic conditions-e.g., the participants' performance in Experiment 1 was 93.5 percent higher in the motion or active haptic manipulation conditions (when compared to the static conditions). The current results demonstrate that deforming specular highlights or boundary contours facilitate 3-D shape perception as much as the motion of objects that possess texture. The current results also indicate that the improvement with motion that occurs for haptics is similar in magnitude to that which occurs for vision.

Short-term visual deprivation, tactile acuity, and haptic solid shape discrimination

Previous psychophysical studies have reported conflicting results concerning the effects of short-term visual deprivation upon tactile acuity. Some studies have found that 45 to 90 minutes of total light deprivation produce significant improvements in participants' tactile acuity as measured with a grating orientation discrimination task. In contrast, a single 2011 study found no such improvement while attempting to replicate these earlier findings. A primary goal of the current experiment was to resolve this discrepancy in the literature by evaluating the effects of a 90-minute period of total light deprivation upon tactile grating orientation discrimination. We also evaluated the potential effect of short-term deprivation upon haptic 3-D shape discrimination using a set of naturally-shaped solid objects. According to previous research, short-term deprivation enhances performance in a tactile 2-D shape discrimination task – perhaps a similar improvement also occurs for haptic 3-D shape discrimination. The results of the current investigation demonstrate that not only does short-term visual deprivation not enhance tactile acuity, it additionally has no effect upon haptic 3-D shape discrimination. While visual deprivation had no effect in our study, there was a significant effect of experience and learning for the grating orientation task – the participants' tactile acuity improved over time, independent of whether they had, or had not, experienced visual deprivation.

Haptic guidance of overt visual attention

Research has shown that information accessed from one sensory modality can influence perceptual and attentional processes in another modality. Here, we demonstrated a novel crossmodal influence of haptic-shape information on visual attention. Participants visually searched for a target object (e.g., an orange) presented among distractor objects, fixating the target as quickly as possible. While searching for the target, participants held (never viewed and out of sight) an item of a specific shape in their hands. In two experiments, we demonstrated that the time for the eyes to reach a target-a measure of overt visual attention-was reduced when the shape of the held item (e.g., a sphere) was consistent with the shape of the visual target (e.g., an orange), relative to when the held shape was unrelated to the target (e.g., a hockey puck) or when no shape was held. This haptic-to-visual facilitation occurred despite the fact that the held shapes were not predictive of the visual targets' shapes, suggesting that the crossmodal influence occurred automatically, reflecting shape-specific haptic guidance of overt visual attention.

The effects of perceptual priming on 4-year-olds' haptic-to-visual cross-modal transfer

Four-year-old children often have difficulty visually recognizing objects that were previously experienced only haptically. This experiment attempts to improve their performance in these haptic-to-visual transfer tasks. Sixty-two 4-year-old children participated in priming trials in which they explored eight unfamiliar objects visually, haptically, or visually and haptically together. Subsequently, all children participated in the same haptic-to-visual cross-modal transfer task. In this task, children haptically explored the objects that were presented in the priming phase and then visually identified a match from among three test objects, each matching the object on only one dimension (shape, texture, or color). Children in all priming conditions predominantly made shape-based matches; however, the most shape-based matches were made in the Visual and Haptic condition. All kinds of priming provided the necessary memory traces upon which subsequent haptic exploration could build a strong enough representation to enable subsequent visual recognition. Haptic exploration patterns during the cross-modal transfer task are discussed and the detailed analyses provide a unique contribution to our understanding of the development of haptic exploratory procedures.

The visual discrimination of negative facial expressions by younger and older adults

Previous research has demonstrated that older adults are not as accurate as younger adults at perceiving negative emotions in facial expressions. These studies rely on emotion recognition tasks that involve choosing between many alternatives, creating the possibility that age differences emerge for cognitive rather than perceptual reasons. In the present study, an emotion discrimination task was used to investigate younger and older adults' ability to visually discriminate between negative emotional facial expressions (anger, sadness, fear, and disgust) at low (40%) and high (80%) expressive intensity. Participants completed trials blocked by pairs of emotions. Discrimination ability was quantified from the participants' responses using signal detection measures. In general, the results indicated that older adults had more difficulty discriminating between low intensity expressions of negative emotions than did younger adults. However, younger and older adults did not differ when discriminating between anger and sadness. These findings demonstrate that age differences in visual emotion discrimination emerge when signal detection measures are used but that these differences are not uniform and occur only in specific contexts.

Aging and curvature discrimination from static and dynamic touch

Two experiments evaluated the ability of 30 older and younger adults to discriminate the curvature of simple object surfaces from static and dynamic touch. The ages of the older adults ranged from 66 to 85 years, while those of the younger adults ranged from 20 to 29 years. For each participant in both experiments, the minimum curvature magnitude needed to reliably discriminate between convex and concave surfaces was determined. In Experiment 1, participants used static touch to make their judgments of curvature, while dynamic touch was used in Experiment 2. When static touch was used to discriminate curvature, a large effect of age occurred (the thresholds were 0.67 & 1.11/m for the younger and older participants, respectively). However, when participants used dynamic touch, there was no significant difference between the ability of younger and older participants to discriminate curvature (the thresholds were 0.58 & 0.59/m for the younger and older participants, respectively). The results of the current study demonstrate that while older adults can accurately discriminate surface curvature from dynamic touch, they possess significant impairments for static touch.

Aging and weight-ratio perception

Past research has provided evidence that older adults have more difficulty than younger adults in discriminating small differences in lifted weight (i.e., the difference threshold for older adults is higher than that of younger adults). Given this result, one might expect that older adults would demonstrate similar impairments in weight ratio perception (a suprathreshold judgment) compared to younger adults. The current experiment compared the abilities of younger and older adults to perceive weight ratios. On any given trial, participants lifted two objects in succession and were asked to provide an estimate of the objects' weight ratio (the weight of the heavier object relative to the lighter). The results showed that while the older participants' weight ratio estimates were as reliable as those of the younger participants, they were significantly less accurate: the older participants frequently perceived the weight ratios to be much higher than they actually were.

Solid shape discrimination from vision and haptics: natural objects (Capsicum annuum) and Gibson's "feelies"

A set of three experiments evaluated 96 participants' ability to visually and haptically discriminate solid object shape. In the past, some researchers have found haptic shape discrimination to be substantially inferior to visual shape discrimination, while other researchers have found haptics and vision to be essentially equivalent. A primary goal of the present study was to understand these discrepant past findings and to determine the true capabilities of the haptic system. All experiments used the same task (same vs. different shape discrimination) and stimulus objects (James Gibson's "feelies" and a set of naturally shaped objects--bell peppers). However, the methodology varied across experiments. Experiment 1 used random 3-dimensional (3-D) orientations of the stimulus objects, and the conditions were full-cue (active manipulation of objects and rotation of the visual objects in depth). Experiment 2 restricted the 3-D orientations of the stimulus objects and limited the haptic and visual information available to the participants. Experiment 3 compared restricted and full-cue conditions using random 3-D orientations. We replicated both previous findings in the current study. When we restricted visual and haptic information (and placed the stimulus objects in the same orientation on every trial), the participants' visual performance was superior to that obtained for haptics (replicating the earlier findings of Davidson et al. in Percept Psychophys 15(3):539-543, 1974). When the circumstances resembled those of ordinary life (e.g., participants able to actively manipulate objects and see them from a variety of perspectives), we found no significant difference between visual and haptic solid shape discrimination.

Cognitive and tactile factors affecting human haptic performance in later life

BACKGROUND

Vision and haptics are the key modalities by which humans perceive objects and interact with their environment in a target-oriented manner. Both modalities share higher-order neural resources and the mechanisms required for object exploration. Compared to vision, the understanding of haptic information processing is still rudimentary. Although it is known that haptic performance, similar to many other skills, decreases in old age, the underlying mechanisms are not clear. It is yet to be determined to what extent this decrease is related to the age-related loss of tactile acuity or cognitive capacity.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the haptic performance of 81 older adults by means of a cross-modal object recognition test. Additionally, we assessed the subjects' tactile acuity with an apparatus-based two-point discrimination paradigm, and their cognitive performance by means of the non-verbal Raven-Standard-Progressive matrices test. As expected, there was a significant age-related decline in performance on all 3 tests. With the exception of tactile acuity, this decline was found to be more distinct in female subjects. Correlation analyses revealed a strong relationship between haptic and cognitive performance for all subjects. Tactile performance, on the contrary, was only significantly correlated with male subjects' haptic performance.

CONCLUSIONS

Haptic object recognition is a demanding task in old age, especially when it comes to the exploration of complex, unfamiliar objects. Our data support a disproportionately higher impact of cognition on haptic performance as compared to the impact of tactile acuity. Our findings are in agreement with studies reporting an increase in co-variation between individual sensory performance and general cognitive functioning in old age.

Aging and the haptic perception of 3D surface shape

Two experiments evaluated the ability of older and younger adults to perceive the three-dimensional (3D) shape of object surfaces from active touch (haptics). The ages of the older adults ranged from 64 to 84 years, while those of the younger adults ranged from 18 to 27 years. In Experiment 1, the participants haptically judged the shape of large (20 cm diameter) surfaces with an entire hand. In contrast, in Experiment 2, the participants explored the shape of small (5 cm diameter) surfaces with a single finger. The haptic surfaces varied in shape index (Koenderink, Solid shape, 1990; Koenderink, Image and Vision Computing, 10, 557–564, 1992) from −1.0 to +1.0 in steps of 0.25. For both types of surfaces (large and small), the participants were able to judge surface shape reliably. The older participants’ judgments of surface shape were just as accurate and precise as those of the younger participants. The results of the current study demonstrate that while older adults do possess reductions in tactile sensitivity and acuity, they nevertheless can effectively perceive 3D surface shape from haptic exploration.

Aging and the discrimination of object weight

A single experiment was carried out to evaluate the ability of younger and older observers to discriminate object weights. A 2-alternative forced-choice variant of the method of constant stimuli was used to obtain difference thresholds for lifted weight for twelve younger (mean age = 21.5 years) and twelve older (mean age = 71.3 years) adults. The standard weight was 100 g, whereas the test weights ranged from 85 to 115 g. The difference thresholds of the older observers were 57.6% higher than those of the younger observers: the average difference thresholds were 10.4% and 6.6% of the standard for the older and younger observers, respectively. The current findings of an age-related deterioration in the ability to discriminate lifted weight extend and disambiguate the results of earlier research.

Perceptual equivalence between vision and touch is complexity dependent

We experience the shape of objects in our world largely by way of our vision and touch but the availability and integration of information between the senses remains an open question. The research presented in this article examines the effect of stimulus complexity on visual, haptic and crossmodal discrimination. Using sculpted three-dimensional objects whose features vary systematically, we perform a series of three experiments to determine perceptual equivalence as a function of complexity. Two unimodal experiments--vision and touch-only, and one crossmodal experiment investigating the availability of information across the senses, were performed. We find that, for the class of stimuli used, subjects were able to visually discriminate them reliably across the entire range of complexity, while the experiments involving haptic information show a marked decrease in performance as the objects become more complex. Performance in the crossmodal condition appears to be constrained by the limits of the subjects' haptic representation, but the combination of the two sources of information is of some benefit over vision alone when comparing the simpler, low-frequency stimuli. This result shows that there is crossmodal transfer, and therefore perceptual equivalency, but that this transfer is limited by the object's complexity.

The perception of 3-D shape from shadows cast onto curved surfaces

In a natural environment, cast shadows abound. Objects cast shadows both upon themselves and upon background surfaces. Previous research on the perception of 3-D shape from cast shadows has only examined the informativeness of shadows cast upon flat background surfaces. In outdoor environments, however, background surfaces often possess significant curvature (large rocks, trees, hills, etc.), and this background curvature distorts the shape of cast shadows. The purpose of this study was to determine the extent to which observers can "discount" the distorting effects of curved background surfaces. In our experiments, observers viewed deforming or static shadows of naturally shaped objects, which were cast upon flat and curved background surfaces. The results showed that the discrimination of 3-D object shape from cast shadows was generally invariant over the distortions produced by hemispherical background surfaces. The observers often had difficulty, however, in identifying the shadows cast onto saddle-shaped background surfaces. The variations in curvature which occur in different directions on saddle-shaped background surfaces cause shadow distortions that lead to difficulties in object recognition and discrimination.

The effect of aging on contour integration

Perception of global patterns requires the integration of local orientation information across space. The present study examined whether this integration ability declines in older age. We measured contrast thresholds for discriminating the global orientation of a "C" shaped contour against a blank background in younger and older subjects. Performance of younger subjects improved when the elements composing the "C" were aligned along the contour path, as opposed to being orthogonal to it or of mixed orientations. However, older subjects' performance was not affected by the orientation of the local elements. This indicates an age-related decline in contour integration.

Learning to perceive differences in solid shape through vision and touch

A single experiment was designed to investigate perceptual learning and the discrimination of 3-D object shape. Ninety-six observers were presented with naturally shaped solid objects either visually, haptically, or across the modalities of vision and touch. The observers' task was to judge whether the two sequentially presented objects on any given trial possessed the same or different 3-D shapes. The results of the experiment revealed that significant perceptual learning occurred in all modality conditions, both unimodal and cross-modal. The amount of the observers' perceptual learning, as indexed by increases in hit rate and d', was similar for all of the modality conditions. The observers' hit rates were highest for the unimodal conditions and lowest in the cross-modal conditions. Lengthening the inter-stimulus interval from 3 to 15 s led to increases in hit rates and decreases in response bias. The results also revealed the existence of an asymmetry between two otherwise equivalent cross-modal conditions: in particular, the observers' perceptual sensitivity was higher for the vision-haptic condition and lower for the haptic-vision condition. In general, the results indicate that effective cross-modal shape comparisons can be made between the modalities of vision and active touch, but that complete information transfer does not occur.

The influence of reduced visual acuity on age-related decline in spatial working memory: an investigation

To investigate the relationship between visual acuity and cognitive function with aging, we compared low-vision and normally-sighted young and elderly individuals on a spatial working memory (WM) task. The task required subjects to memorise target locations on different matrices after perceiving them visually or haptically. The haptic modality was included as a control to look at the effect of aging on memory without the confounding effect of visual deficit. Overall, age and visual status did not interact to affect WM accuracy, suggesting that age does not exaggerate the effects of visual deprivation. Young participants performed better than the elderly only when the task required more operational processes (i.e., integration of information). Sighted participants outperformed the visually impaired regardless of testing modality suggesting that the effect of the visual deficit is not confined to only the most peripheral levels of information processing. These findings suggest that vision, being the primary sensory modality, tends to shape the general supramodal mechanisms of memory.