The representation of our body location is achieved by integrating sensorimotor inputs with information about our body size. Previous studies have shown that the metric representation of our hand, also called the body model, is distorted, namely overestimated in width and underestimated in length, although we are able to perform accurate fine movements. Considering the known dissociation between action-oriented and perception-oriented body representations, we asked whether the body model mainly serves body perception or whether it is also involved in movements. Twenty-one healthy adults were administered with the Localization Task (LT) which required the participants to localise the perceived position of their unseen hand by means of a stick held by their other hand, and the Proprioceptive Matching Task (PMT) which required the participants to match their perceived hand position with a visual target. LT and PMT maps were compared with the actual hand sizes. We found that the PMT map exhibited similar body model distortions, confirming that the body model is involved in motor programming. Furthermore, we observed that a partial adjustment of the distortions occurs in a motor condition.

Distorted representations of the body are observed in healthy individuals as well as in neurological and psychiatric disorders. Distortions of the body model have been attributed to the somatotopic cerebral representation. Recently, it has been demonstrated that visual biases also contribute to those distortions. To better understand the sources of such distortions, we compared the metric representations across five body parts affording different degrees of tactile sensitivity and visual accessibility. We evaluated their perceived dimensions using a Line Length Judgment task. We found that most body parts were underestimated in their dimensions. The estimation error relative to their length was predicted by their tactile acuity, supporting the influence of the cortical somatotopy on the body model. However, tactile acuity did not explain the distortions observed for the width. Visual accessibility in turn does appear to mediate body distortions, as we observed that the dimensions of the dorsal portion of the neck were the only ones accurately perceived. Coherent with the multisensory nature of body representations, we argue that the perceived dimensions of body parts are estimated by integrating visual and somatosensory information, each weighted differently, based on their availability for a given body part and a given spatial dimension.

Proprioception acquires a crucial role in estimating the configuration of our body segments in space when visual information is not available. Proprioceptive accuracy is assessed by asking participants to match the perceived position of an unseen body landmark through reaching movements. This task was also adopted to study the perceived hand structure by computing the relative distances between averaged proprioceptive judgments (hand Localization Task). However, the pattern of proprioceptive errors leading to the misperceived hand structure is unexplored. Here, we aimed to characterize this pattern across different hand landmarks, having different anatomo-physiological properties and cortical representations. Furthermore, we sought to describe the error consistency and its stability over time. To this purpose, we analyzed the proprioceptive errors of 43 healthy participants during the hand Localization Task. We found larger but more consistent errors for the fingertips compared to the knuckles, possibly due to poorer proprioceptive signal, compensated by other sources of spatial information. Furthermore, we found a shift (overlap effect) and a temporal drift of the hand perceived position towards the shoulder of origin, which was consistent within and between subjects. The overlap effect had a greater influence on lateral compared to medial landmarks, leading to the hand width overestimation. Our results are compatible with domain-general and body-specific spatial biases affecting the proprioceptive localization of the hand landmarks, thus the apparent hand structure misperception.

The MMSE (Mini-Mental State Examination), which is broadly used as a cognitive screening test for adults, has been successfully adapted and standardized for children of different nationalities. In the Italian clinical settings, the Mini-Mental State Pediatric Examination (MMSPE) is being more and more used as cognitive screening tool for children. However, the Italian norms for the MMSPE are available for the school age only. The current study was aimed at providing clinicians with the Italian normative data of the MMSPE for preschool age. Here, we therefore adapted the MMSE to the preschool age. The MMSPE for preschoolers assesses spatial and temporal orientation, verbal and visual memory, reading prerequisites, numerical knowledge, praxis, body representation, and executive functions through 16 items in a short period of time. It was administered to 305 Italian children aged 36 to 72 months. A Generalized Linear Model was fitted to explore predictors’ effects on the MMSPE total score. Raw scores were adjusted for critical variables (child’s age and parental mean education) and the 5th percentile cut-offs were obtained. With this study, we extended the Italian normative data of the MMSPE, formerly available for school age only, to preschool age population.