Functional relevance of the extrastriate body area for visual and haptic object recognition: a preregistered fMRI-guided TMS study.

The extrastriate body area (EBA) is a region in the lateral occipito-temporal cortex (LOTC), which is sensitive to perceived body parts. Neuroimaging studies suggested that EBA is related to body and tool processing, regardless of the sensory modalities. However, how essential this region is for visual tool processing and nonvisual object processing remains a matter of controversy. In this preregistered fMRI-guided repetitive transcranial magnetic stimulation (rTMS) study, we examined the causal involvement of EBA in multisensory body and tool recognition. Participants used either vision or haptics to identify 3 object categories: hands, teapots (tools), and cars (control objects). Continuous theta-burst stimulation (cTBS) was applied over left EBA, right EBA, or vertex (control site). Performance for visually perceived hands and teapots (relative to cars) was more strongly disrupted by cTBS over left EBA than over the vertex, whereas no such object-specific effect was observed in haptics. The simulation of the induced electric fields confirmed that the cTBS affected regions including EBA. These results indicate that the LOTC is functionally relevant for visual hand and tool processing, whereas the rTMS over EBA may differently affect object recognition between the 2 sensory modalities.

Tactile perception of pleasantness in relation to perceived softness.

The sense of touch allows us to infer objects' physical properties, while the same input also produces affective sensations. These affective sensations are important for interpersonal relationships and personal well-being, which raises the possibility that tactile preferences are adapted to the characteristics of the skin. Previous studies examined how physical properties such as surface roughness and temperature influence affective sensations; however, little is known about the effect of compliance (physical correlate of softness) on pleasantness. Thus, we investigated the psychophysical link between softness and pleasantness. Pieces of human skin-like rubber with different compliances were pressed against participants' fingers. Two groups of participants numerically estimated the perceived magnitude of either pleasantness or softness. The perceived magnitude of pleasantness and softness both increased monotonically as a function of increasing object compliance, levelling off at around the end of the stimulus range. However, inter-subject variability was greater for pleasantness than for perceived softness, whereas the slope of the linear function fit to the magnitude estimates was steeper for softness than for pleasantness. These results indicate that object compliance is a critical physical determinant for pleasantness, whereas the effect of compliance on pleasantness was more variable among individuals than the effect on softness was.

The Effect of Object Compliance on the Velvet Hand Illusion.

Movement of a grid of bars between the two hands creates the tactile illusion of a velvet-like material, namely, the velvet hand illusion (VHI). It was recently proposed that the VHI is caused by a masking effect; bar movement suppresses conscious perception of tactile inputs from the opposing hand. If this hypothesis sufficiently explains the VHI, the physical properties of the opposing hand should not affect the illusion. Another hypothesis suggests that the integration of inputs from the grid of bars and the hands plays a critical role in the VHI. To compare these two hypotheses, the VHI was elicited under two conditions; the grid of bars was between one hand and a soft texture or the grid of bars was between one hand and a hard texture. A hand was stimulated by moving bars while contacting the stationary texture held by the opposing hand. The grid of bars with the soft texture induced a stronger illusion and softer feeling than that with the hard texture. This result supports the integration hypothesis in which tactile inputs from both bars and textures attached to the opposing hand are integrated.

Cross-modal size-contrast illusion: Acoustic increases in intensity and bandwidth modulate haptic representation of object size.

Changes in the retinal size of stationary objects provide a cue to the observer's motion in the environment: Increases indicate the observer's forward motion, and decreases backward motion. In this study, a series of images each comprising a pair of pine-tree figures were translated into auditory modality using sensory substitution software. Resulting auditory stimuli were presented in an ascending sequence (i.e. increasing in intensity and bandwidth compatible with forward motion), descending sequence (i.e. decreasing in intensity and bandwidth compatible with backward motion), or in a scrambled order. During the presentation of stimuli, blindfolded participants estimated the lengths of wooden sticks by haptics. Results showed that those exposed to the stimuli compatible with forward motion underestimated the lengths of the sticks. This consistent underestimation may share some aspects with visual size-contrast effects such as the Ebbinghaus illusion. In contrast, participants in the other two conditions did not show such magnitude of error in size estimation; which is consistent with the "adaptive perceptual bias" towards acoustic increases in intensity and bandwidth. In sum, we report a novel cross-modal size-contrast illusion, which reveals that auditory motion cues compatible with listeners' forward motion modulate haptic representations of object size.

Brain networks require a network-conscious psychopathological approach.

In experimental psychology and neuroscience, technological advances and multisensory research have contributed to gradually dismiss a version of reductionism. Empirical results no longer support a brain model in which distinct "modules" perform discrete functions, but rather, a brain of partially overlapping networks. A similarly changed brain model is extending to psychopathology and clinical psychology, and partly accounts for the problems of reductionism.

Helmets improve estimations of depth and visual angle to safe targets.

Egocentric distance estimation has been shown to depend on wearing safety gear, which promotes compensatory behavior, and on target type, which regulates fight-or-flight responses. We hypothesized that the two factors interact, possibly in asymmetric fashion, and set out to uncover the limits of this interaction in a perceptual task where individuals wearing helmets or baseball caps estimated egocentric distance to non-threatening and threatening animals depicted on cards (i.e., safe and unsafe targets). We found that, compared to participants wearing caps, participants wearing helmets overshoot distance estimations and were able to distinguish not only between targets situated at two depth levels as participants wearing caps could, but also between safe targets situated at wide and narrow visual angles. Our findings help define the interaction between safety devices and target type, thereby contributing to the debate between advocates of prevention models and those who maintain that these are offset by compensatory strategies.

Visual loss alters multisensory face maps in humans.

Topographically organised responses to visual and tactile stimulation are aligned in the ventral intraparietal cortex. The critical biological importance of this region, which is thought to mediate visually guided defensive movements of the head and upper body, suggests that these maps might be hardwired from birth. Here, we investigated whether visual experience is necessary for the creation and positioning of these maps by assessing the representation of tactile stimulation in congenitally and totally blind participants, who had no visual experience, and late and totally blind participants. We used a single-subject approach to the analysis to focus on the potential individual differences in the functional neuroanatomy that might arise from different causes, durations and sensory experiences of visual impairment among participants. The overall results did not show any significant difference between congenitally and late blind participants; however, single-subject trends suggested that visual experience is not necessary to develop topographically organised maps in the intraparietal cortex, whilst losing vision disrupted topographic maps' integrity and organisation. These results discussed in terms of brain plasticity and sensitive periods.

Scanning movements during haptic search: similarity with fixations during visual search.

Finding relevant objects through vision, or visual search, is a crucial function that has received considerable attention in the literature. After decades of research, data suggest that visual fixations are more crucial to understanding how visual search works than are the attributes of stimuli. This idea receives further support from the field of haptic search.

Multisensory integration substantiates distributed and overlapping neural networks.

The hypothesis that highly overlapping networks underlie brain functions (neural reuse) is decisively supported by three decades of multisensory research. Multisensory areas process information from more than one sensory modality and therefore represent the best examples of neural reuse. Recent evidence of multisensory processing in primary visual cortices further indicates that neural reuse is a basic feature of the brain.

Sensory Substitution: The Spatial Updating of Auditory Scenes "Mimics" the Spatial Updating of Visual Scenes.

Visual-to-auditory sensory substitution is used to convey visual information through audition, and it was initially created to compensate for blindness; it consists of software converting the visual images captured by a video-camera into the equivalent auditory images, or "soundscapes". Here, it was used by blindfolded sighted participants to learn the spatial position of simple shapes depicted in images arranged on the floor. Very few studies have used sensory substitution to investigate spatial representation, while it has been widely used to investigate object recognition. Additionally, with sensory substitution we could study the performance of participants actively exploring the environment through audition, rather than passively localizing sound sources. Blindfolded participants egocentrically learnt the position of six images by using sensory substitution and then a judgment of relative direction task (JRD) was used to determine how this scene was represented. This task consists of imagining being in a given location, oriented in a given direction, and pointing towards the required image. Before performing the JRD task, participants explored a map that provided allocentric information about the scene. Although spatial exploration was egocentric, surprisingly we found that performance in the JRD task was better for allocentric perspectives. This suggests that the egocentric representation of the scene was updated. This result is in line with previous studies using visual and somatosensory scenes, thus supporting the notion that different sensory modalities produce equivalent spatial representation(s). Moreover, our results have practical implications to improve training methods with sensory substitution devices (SSD).

Transcranial random noise stimulation benefits arithmetic skills.

Although arithmetic skills are crucial cognitive abilities, numeric competence impairments affect a significant portion of the young population. These problems produce a high socio-economic cost by negatively affecting scholastic and work performance. The parietal cortex is the brain area that is classically associated with numeric processing, but it is still debated whether other cortical areas are involved, and only a few studies tried to directly assess the causal link between brain and this cognitive function by using transcranial random noise stimulation, tRNS. This non-invasive electric stimulation device has been shown to enhance activity in the underlying cortex. We tested three groups of participants with equivalent arithmetic skills - an arithmetic 'screening' was administered. One group was stimulated by tRNS on the frontal lobe, another on the parietal lobe, and a third group was assigned to the placebo condition. During the stimulation, participants performed a subtraction verification task. To investigate long-term effects of tRNS, the task was repeated seven days later without stimulation. Aside previously-tested (familiar) subtractions, in the second experimental session unfamiliar subtractions were also administered. We found that, compared to placebo, parietal and frontal stimulation significantly reduced reaction times immediately, and enhanced accuracy after seven days. This benefit encompassed both familiar and unfamiliar subtractions. These results suggest that modulation of frontal and parietal cortices may ameliorate basic arithmetic skills by benefitting working memory function. This could open new avenues for neuro-restorative applications of brain stimulation.

Two-Dimensional Rubber-Hand Illusion: The Dorian Gray Hand Illusion.

The rubber-hand illusion provides a window into body representation and consciousness. It has been found that body-ownership extended to numerous hand-like objects. Interestingly, the vast majority of these objects were three-dimensional. We adopted this paradigm by using hand drawings to investigate whether rubber-hand illusion could be extended to two-dimensional hand samples, and we measured skin conductance responses and behavioural variables. The fact that this illusion extended to two-dimensional stimuli reveals the dominant role of top-down information on visual perception for body representation and consciousness.

Neural Stimulation Has a Long-Term Effect on Foreign Vocabulary Acquisition.

Acquisition of a foreign language is a challenging task that is becoming increasingly more important in the world nowadays. There is evidence suggesting that the frontal and temporal cortices are involved in language processing and comprehension, but it is still unknown whether foreign language acquisition recruits additional cortical areas in a causal manner. For the first time, we used transcranial random noise stimulation on the frontal and parietal brain areas, in order to compare its effect on the acquisition of unknown foreign words and a sham, or placebo, condition was also included. This type of noninvasive neural stimulation enhances cortical activity by boosting the spontaneous activity of neurons. Foreign vocabulary acquisition was tested both immediately and seven days after the stimulation. We found that stimulation on the posterior parietal, but not the dorsolateral prefrontal cortex or sham stimulation, significantly improved the memory performance in the long term. These results suggest that the posterior parietal cortex is directly involved in acquisition of foreign vocabulary, thus extending the "linguistic network" to this area.

Multisensory perceptual learning and sensory substitution.

One of the most exciting recent findings in neuroscience has been the capacity for neural plasticity in adult humans and animals. Studies of perceptual learning have provided key insights into the mechanisms of neural plasticity and the changes in functional neuroanatomy that it affords. Key questions in this field of research concern how practice of a task leads to specific or general improvement. Although much of this work has been carried out with a focus on a single sensory modality, primarily visual, there is increasing interest in multisensory perceptual learning. Here we will examine how advances in perceptual learning research both inform and can be informed by the development and advancement of sensory substitution devices for blind persons. To allow 'sight' to occur in the absence of visual input through the eyes, visual information can be transformed by a sensory substitution device into a representation that can be processed as sound or touch, and thus give one the potential to 'see' through the ears or tongue. Investigations of auditory, visual and multisensory perceptual learning can have key benefits for the advancement of sensory substitution, and the study of sensory deprivation and sensory substitution likewise will further the understanding of perceptual learning in general and the reverse hierarchy theory in particular. It also has significant importance for the developing understanding of the brain in metamodal terms, where functional brain areas might be best defined by the computations they carry out rather than by their sensory-specific processing role.

Sensory deprivation: visual experience alters the mental number line.

Early studies on numeric cognition reported that numbers are spatially organised according to a left-to-right small-to-large 'number line'. We investigated whether this spatial-number organisation is dictated by visual experience. We tested congenitally and late blind, and blindfolded sighted participants in a random number generation task where in one block their heads were alternately turned left or right before uttering the number. We found that the 'random' number generation was biased according to the side where the head was turned to. Consistent with the standard number line, participants with visual experience generated smaller numbers for left turns, and larger numbers for right turns. In contrast, participants without any visual experience showed the opposite pattern of results. These results suggest a role for visual experience in the development of spatial and numerical representations, which is supported by cultural differences in number representation, and provide converging evidence for visually driven organisation of the parietal cortex.

The study of blindness and technology can reveal the mechanisms of three-dimensional navigation.

Jeffery et al. suggest that three-dimensional environments are not represented according to their volumetric properties, but in a quasi-planar fashion. Here we take into consideration the role of visual experience and the use of technology for spatial learning to better understand the nature of the preference of horizontal over vertical spatial representation.

Ambient visual information confers a context-specific, long-term benefit on memory for haptic scenes.

We investigated the effects of indirect, ambient visual information on haptic spatial memory. Using touch only, participants first learned an array of objects arranged in a scene and were subsequently tested on their recognition of that scene which was always hidden from view. During haptic scene exploration, participants could either see the surrounding room or were blindfolded. We found a benefit in haptic memory performance only when ambient visual information was available in the early stages of the task but not when participants were initially blindfolded. Specifically, when ambient visual information was available a benefit on performance was found in a subsequent block of trials during which the participant was blindfolded (Experiment 1), and persisted over a delay of one week (Experiment 2). However, we found that the benefit for ambient visual information did not transfer to a novel environment (Experiment 3). In Experiment 4 we further investigated the nature of the visual information that improved haptic memory and found that geometric information about a surrounding (virtual) room rather than isolated object landmarks, facilitated haptic scene memory. Our results suggest that vision improves haptic memory for scenes by providing an environment-centred, allocentric reference frame for representing object location through touch.

Congenital blindness improves semantic and episodic memory.

Previous studies reported that congenitally blind people possess superior verb-generation skills. Here we tested the impact of blindness on capacity and the fidelity of semantic memory by using a false memory paradigm. In the Deese-Roediger-McDermott paradigm, participants study lists of words that are all semantically related to a lure that is not presented. Subsequently, participants frequently recall the missing lure. We found that congenitally blind participants have enhanced memory performance for recalling the presented words and reduced false memories for the lure. The dissociation of memory capacity and fidelity provides further evidence for enhanced verbal ability in the blind, supported by their broader structural and functional brain reorganisation.

Visual experience facilitates allocentric spatial representation.

Representing the position of the objects independently from our own position is a fundamental cognitive ability. Here we investigated whether this ability depends on visual experience. Congenitally blind, late blind and blindfolded sighted participants haptically learnt a room-sized regularly shaped array of objects, and their spatial memory was tested to determine which spatial reference frame was used. Crucially, the use of an object-based reference frame requires representing the regular structure of the array. We found that blindfolded sighted and late blind participants, that is those with visual experience, showed a preferential use of the object-based or 'allocentric' reference frame. On the contrary, congenitally blind participants preferred a self-based, or egocentric, reference frame. This suggests that, due to its developmental effect on the multisensory brain areas involved in spatial cognition, visual experience is necessary to develop a preference for an object-based, allocentric reference frame.