Recent studies have revealed that human position sense relies on a massively distorted representation of hand size and shape. By comparing the judged location of landmarks on an occluded hand, Longo and Haggard (2010) constructed implicit perceptual maps of represented hand structure, showing large underestimation of finger length and overestimation of hand width. Here, we investigated the contribution of two potential sources of distortions to such effects: perceptual distortions reflecting spatial warping of the representation of bodily tissue itself, perhaps reflecting distortions of somatotopic cortical maps, and conceptual distortions reflecting mistaken beliefs about the locations of different landmarks within the body. In Experiment 1 we compared distorted hand maps to a task in which participants explicitly judged the location of their knuckles in a hand silhouette. The results revealed the conceptual distortions are responsible for at least part of the underestimation of finger length, but cannot explain overestimation of hand width. Experiment 2 compared distortions of the participant’s own hand based on position sense with a prosthetic hand based on visual memory. Underestimation of finger length was found for both hands, providing further evidence that it reflects a conceptual distortion. In contrast, overestimation of hand width was specific to representation of the participant’s own hand, confirming it reflects a perceptual distortion. Together, these results suggest that distorted body representations do not reflect a single underlying cause. Rather, both perceptual and conceptual distortions contribute to the overall configuration of the hand representation.

SummaryEye gaze is a key channel of non-verbal communication in humans [1, 2, 3]. Eye contact with others is present from birth [4], and eye gaze processing is crucial for social learning and adult-infant communication [5, 6, 7]. However, little is known about the effect of selectively different experience of eye contact and gaze communication on early social and communicative development. To directly address this question, we assessed 14 sighted infants of blind parents (SIBPs) longitudinally at 6–10 and 12–16 months. Face scanning [8] and gaze following [7, 9] were assessed using eye tracking. In addition, naturalistic observations were made when the infants were interacting with their blind parent and with an unfamiliar sighted adult. Established measures of emergent autistic-like behaviors [10] and standardized tests of cognitive, motor, and linguistic development [11] were also collected. These data were then compared with those obtained from a group of infants of sighted parents. Despite showing typical social skills development overall, infants of blind parents allocated less attention to adult eye movements and gaze direction, an effect that increased between 6–10 and 12–16 months of age. The results suggest that infants adjust their use of adults’ eye gaze depending on gaze communication experience from early in life. The results highlight that human functional brain development shows selective experience-dependent plasticity adaptive to the individual’s specific social environment.

Recent research has shown that proprioception relies on distorted representations of body size and shape. By asking participants to localise multiple landmarks on their occluded hand, perceptual maps of hand size and shape can be constructed and compared to actual hand structure. These maps are different from the actual size and shape of the occluded hand, revealing underestimation of finger length and overestimation of hand width. Here we tested whether the same distorted body model underlies proprioceptive imagery (i.e. imagining the hand at a specific location, and in a different posture than it actually is). In Experiment 1, participants placed their left hand under an occluding board (real condition) or imagined their left hand under the board (imagined condition). Highly similar distortions were found in both conditions. Furthermore, results across the two conditions were strongly correlated. In Experiment 2, participants completed the real condition and two imagined conditions. In the imagined-fist condition, participants held their left hand in a fist, in their lap, while in the imagined-flat condition, participants held their left hand flat, with palm down, in their lap. In both imagined conditions, participants were asked to imagine their left hand lying flat, with palm down, under the occluding board. A similar pattern of distortions was found in all three conditions. These results suggest that both proprioception and proprioceptive imagery reply on a common stored model of the body's metric properties.The Body and Proprioceptive Imagery 3

A fundamental question in functional brain development is how the brain acquires specialised processing optimised for its individual environment. The current study is the first to demonstrate that distinct experience of eye gaze communication, due to the visual impairment of a parent, affects the specificity of brain responses to dynamic gaze shifts in infants. Event-related potentials (ERPs) from 6 to 10 months old sighted infants with blind parents (SIBP group) and control infants with sighted parents (CTRL group) were recorded while they observed a face with gaze shifting Toward or Away from them. Unlike the CTRL group, ERPs of the SIBP group did not differentiate between the two directions of gaze shift. Thus, selective brain responses to perceived gaze shifts in infants may depend on their eye gaze communication experience with the primary caregiver. This finding highlights the critical role of early communicative experience in the emerging functional specialisation of the human brain.

A fundamental question about the development of communication behavior in early life is how infants acquire adaptive communication behavior that is well-suited to their individual social environment, and how the experience of parent-child communication affects this development. The current study investigated how infants develop communication skills when their parents are visually impaired and cannot see their infants’ eye gaze. We analyzed 6-min video recordings of naturalistic interaction between 14 sighted infants of blind parents (SIBP) with (a) their blind parent, and (b) a sighted experimenter. Data coded from these interactions were compared with those from 28 age-matched sighted infants of sighted parents (controls). Each infant completed two visits, at 6–10 months and 12–16 months of age. Within each interaction sample, we coded the function (initiation or response) and form (face gaze, vocalization, or action) of each infant communication behavior. When interacting with their parents, SIBP made relatively more communicative responses than initiations, and used more face gaze and fewer actions to communicate, than did controls. When interacting with a sighted experimenter, by contrast, SIBP made slightly (but significantly) more communicative initiations than controls, but otherwise used similar forms of communication. The differential communication behavior by infants of blind versus sighted parents was already apparent by 6–10 months of age, and was specific to communication with the parent. These results highlight the flexibility in the early development of human communication behavior, which enables infants to optimize their communicative bids and methods to their unique social environment.