Lara Audrey Coelho

In the Somatic Rubber Hand Illusion (SRHI), synchronous brushing of a participant’s hidden hand and a dummy hand induces proprioceptive drift, a shift in perceived position of the hand towards the dummy hand, along with the sensation of brushing one’s own hand. While sighted individuals experience proprioceptive drift since childhood, blind adults are immune. Here, we tested Severely Visually Impaired (SVI, n = 13) children and sighted controls (n = 44) with the SRHI. Surprisingly, both groups subjectively reported illusory self-touch. We posit that children with severe visual impairment tentatively infer a common cause when experiencing synchronous stroking of both a dummy hand and their own hand – just like sighted children do. However, unlike sighted children, their perceived hand position is not updated accordingly. Contrary to our hypothesis, we found that only in the SVI group proprioceptive precision predicts drift values, as well as illusory self-touch, with higher precision leading to larger drifts and a stronger illusion. We suggest that higher proprioceptive competence is required for SVI children to develop sighted-like responses to the illusion and overcome difficulty in re-mapping body position onto external space based on multisensory stimulation.

There is contradictory evidence on the effect that visual experience has on haptic abilities. Indeed, some studies have documented that a lack of vision (blindness) results in decreased haptic perception, whereas other studies report an enhanced haptic ability in blind individuals. To examine the role of vision in haptic spatial processing, we recruited early blind, late blind, and sighted participants. Each participant completed a haptic task in which they explored a two-piece LEGO model for eight seconds before searching for the same pieces in a bowl of distractors. Our results showed that blind individuals made more errors than sighted participants. Furthermore, early blind participants performed worse than both late blind and sighted participants, who performed similarly. These findings highlight the importance that vision plays in the development of accurate haptic spatial perception. Additionally, we investigated whether the commonly reported male advantage in haptic tasks depends on visual experience. Our results showed better performance by males in all groups when compared to females. This result suggests that sex differences in haptic spatial processing are a fundamental characteristic of human sensory function, independent of visual experience. Highlights No study has investigated if the previously identified male advantage in haptic spatial processing is mediated by visual experience. Blind participants made more errors than sighted participants; early blind performed the worst. The findings suggest vision is crucial for the development of accurate haptic spatial perception. There was a consistent male advantage in haptic performance across all visual experience groups. Sex differences in haptic spatial ability appear to be independent of visual expertise. Plain language summary Some researchers have suggested that being blind reduces abilities in their other senses, while others believe that a lack of vision can improve them. To further understand which is true, we investigated whether the haptic system—the combination of touch and proprioception (awareness of where the body is in space)—is affected by blindness. To do this, we tested people who were blind from birth (early blind), people who became blind later in life (late blind), and people who can see (sighted) on a simple haptic task. In the task, participants felt a small LEGO model with their hands for eight seconds. Then, they had to find the same LEGO pieces in a bowl filled with other, distractor pieces—using only haptics. We found that blind participants made more mistakes than sighted participants. Those who were blind from birth had the most difficulty. People who became blind later in life performed similarly to sighted individuals. This suggests that vision plays an important role in developing accurate haptic perception. As previous work has shown that males outperform females on haptic tasks, we also investigated whether those differences depended on vision. We found that males performed better than females in all groups, regardless of whether they were blind or sighted. This suggests that sex differences in haptic ability may be a basic feature of how our senses work and not just related to vision.

Despite constantly performing actions with their hands, healthy individuals display distorted hand representations. These distortions have been found in a body representation called ‘the body model’, which plays a fundamental role in position sense. There is a growing number of studies showing that changes in this representation may optimize performance in certain skills (e.g., magicians, baseball players). This has led to the hypothesis that the distortions may facilitate our actions. One highly trained group of individuals that rely on an accurate position sense about the fingers, are piano players. However, musicians have yet to be studied in the body model task. Therefore, we recruited a group of expert piano players (average practice time 12.85 h/week, average years playing 16.22 ± 3.6) and an age- and sex-matched control group. We hypothesized that piano players would have more accurate hand representation, as precise finger location knowledge is essential for skilled piano performance. Our results showed that piano players were significantly more accurate at estimating hand width compared to the controls; in fact, their estimates of this measure were not different than their physical size. This supports our hypothesis and suggests that the need for more accurate localization of the fingertips when playing may result in a more accurate estimate of hand width in the body model task. There was, however, no difference between the groups for finger length, as both piano and control groups significantly underestimated this measure. This result may reflect the typical position of the hands while playing piano, as the fingers are kept curved to aid proper technique. Taken together, our results support the hypothesis that distortions may in fact facilitate our actions.

The present study assessed the structural and functional representation of the upper limb in a large cohort (N = 84) of typically developing children aged 6 to 10. The first task aimed at obtaining a structural measure of the representation of the arm, specifically the two segments that compose it: the forearm and the hand. Participants were asked to localize three landmarks (elbow, wrist, and tip of the middle finger) while blindfolded and upon tactile stimulation of the three landmarks. The second task required a functional estimation of the represented length of the arm. Participants judged whether their arm fully outstretched would be long enough to touch an object presented at seven different distances without being allowed to perform the movement. The two tasks revealed opposite patterns of (mis‐)representation. At the structural level, the hand length was underestimated, while the forearm representation matched the actual size. This resulted in an underestimation of total arm length in the structural task. At the functional level, total arm length was overestimated across all age groups. Moreover, there was no relationship between estimates on the structural and functional tasks. These results support the coexistence of multiple, independent body representations in children.

It has long been assumed that an accurate representation of the size and shape of one’s body is necessary to successfully interact with the environment. Previous research has shown accurate representations when healthy participants make overt judgments (i.e. explicit) about the size of their bodies. However, when body size is judged implicitly, studies have shown systematic distortions. One suggestion for these differences, is that explicit and implicit representations are informed by different sensory modalities. Explicit representations rely on vision whereas implicit representations are informed by haptics. We designed an experiment to investigate if explicit representations that are informed by haptics are more like implicit representation featuring systematic distortions. We asked female participants to estimate the size of their fingers and hands in three different tasks: an explicit-haptic, an implicit, and an explicit-vision task. The results showed that all three representations were distorted and furthermore, the distortions for each representation were different from one another. These results suggest that inaccurate finger and hand length are a stereotypical feature of body representation that is present in both visual and haptic domains. We discuss the results in relation to theories of body representation.

We rely on accurate body representations to successfully interact with the environment. As adults, we rely on many years of experience with a body that has stayed relatively the same size. Children, however, go through periods of rapid growth and whether or not their body representation matches this physical growth is unknown. To address this question, we examined the developmental trajectory of the body model of the hand. The body model is the representation of our bodies that underlies position sense. We recruited a group of children (8–16 years) and a control group of young adults (18–26 years) and asked them to complete the body model task. In this task, participants estimated the location of ten different landmarks (the tips and metacarpophalangeal joints of each of their five fingers). The position (XY location) of each estimate was tracked using an Optotrak camera. From the XY locations we derived hand width and finger length. Not surprisingly, children’s physical hand width and finger length were smaller than adults but remarkably, the body model, was similar for both groups. This result indicates that children overestimate hand size and suggests that the body model is ahead of physical growth. This result contradicts the notion that body representation lags physical growth during puberty, accounting for the clumsy motor behaviour characteristic of teens. We discuss the results in relation to the different taxonomies of body representation and how an enlarged representation of the hand during childhood may influence action.

Executive function (EF) is a term that defines a group of cognitive abilities fundamental to goal-directed behaviour. EF is a strong predictor of both academic and life success. Therefore, it is important to develop EFs in the early years of life. We created a curriculum of games (BBF) for preschool children that focused on improving EFs. The purpose of the study was to assess the curriculum's impact. We asked the parents of 86 children to respond to three surveys. The majority (72) of these children participated in the BBF curriculum, while 14 were in a control group. These surveys were given twice; pre- and post-curriculum implementation. We found significant improvements in various behaviours measured by the three questionnaires in the BBF group that did not occur in the control group. This suggests that the BBF curriculum can be implemented as a programme to improve cognitive abilities in children.

Executive functions (EF) are a grouping of cognitive abilities essential for daily life. Previous research has shown that physical activity (PA) may in fact preserve EF in older adults, but the link between sedentary behavior (SB) and cognitive ability has been less explored. The purpose of this study was to examine the relationship between SB and cognition (executive function and memory) in older adults. Seventy five older adults (74.6 ± 9 years) self-reported their sedentary time (ST) and PA, as well as EF ability (paper-based measure of EF). Participants also completed several performance-based measures of EF and a memory task. Older adults who were less sedentary had superior EF and memory (e.g., Stroop time was significantly faster in less sedentary adults (34.7 s ± 1.9) compared to more sedentary adults (39.6 s ± 1.8), p = .02). Regression analysis showed that total ST was associated with several measures of EF after adjusting for age, and physical activity (e.g., Stroop time β = .005 (.002, .009). Less cognitively demanding SB (TV viewing and napping) was associated with worse performance on most EF and in the memory task. Performing a hobby was also associated with lower levels of EF and memory. For example, the building times for the Lego task were positively related to napping (r² = .34), watching TV (r² = .27), and performing a hobby (r² = .46). Associations of ST with cognitive abilities were more pronounced in older adults who engaged in less PA. These results suggest that SB may play an important role in cognitive abilities of older adults. Longitudinal studies using performance-based assessments of EF are needed. Lara Coelho and Kayla Hauck contributed equally to the manuscript.