Representing human hands haptically or visually from first-person versus third-person perspectives

Vision- and touch-dependent brain correlates of body-related mental processing

In humans, the nature of sensory input influences body-related mental processing. For instance, behavioral differences (e.g., response time) can be found between mental spatial transformations (e.g., mental rotation) of viewed and touched body parts. It can thus be hypothesized that distinct brain activation patterns are associated with such sensory-dependent body-related mental processing. However, direct evidence that the neural correlates of body-related mental processing can be modulated by the nature of the sensory stimuli is still missing. We thus analyzed event-related functional magnetic resonance imaging (fMRI) data from thirty-one healthy participants performing mental rotation of visually- (images) and haptically-presented (plastic) hands. We also dissociated the neural activity related to rotation or task-related performance using models that either regressed out or included the variance associated with response time. Haptically-mediated mental rotation recruited mostly the sensorimotor brain network. Visually-mediated mental rotation led to parieto-occipital activations. In addition, faster mental rotation was associated with sensorimotor activity, while slower mental rotation was associated with parieto-occipital activations. The fMRI results indicated that changing the type of sensory inputs modulates the neural correlates of body-related mental processing. These findings suggest that distinct sensorimotor brain dynamics can be exploited to execute similar tasks depending on the available sensory input. The present study can contribute to a better evaluation of body-related mental processing in experimental and clinical settings.

Altered perspective-dependent brain activation while viewing hands and associated imitation difficulties in individuals with autism spectrum disorder

Background

Individuals with autism spectrum disorder (ASD) appear to have a unique awareness of their own body, which may be associated with difficulties of gestural interaction. In typically developing (TD) individuals, the perception of body parts is processed in various brain regions. For instance, activation of the lateral occipito-temporal cortex (LOTC) is known to depend on perspective (i.e., first- or third-person perspective) and identity (i.e., own vs. another person's body). In the present study, we examined how perspective and identity affect brain activation in individuals with ASD, and how perspective- and identity-dependent brain activation is associated with gestural imitation abilities.

Methods

Eighteen young adults with ASD and 18 TD individuals participated in an fMRI study in which the participants observed their own or another person's hands from the first- and third-person perspectives. We examined whether the brain activation associated with perspective and identity was altered in individuals with ASD. Furthermore, we identified the brain regions the activity of which correlated with gestural imitation difficulties in individuals with ASD.

Results

In the TD group, the left LOTC was more strongly activated by viewing a hand from the third-person perspective compared with the first-person perspective. This perspective effect in the left LOTC was significantly attenuated in the ASD group. We also observed significant group differences in the perspective effect in the medial prefrontal cortex (mPFC). Correlation analysis revealed that the perspective effect in the inferior parietal lobule (IPL) and cerebellum was associated with the gestural imitation ability in individuals with ASD.

Conclusions

Our study suggests that atypical visual self-body recognition in individuals with ASD is associated with an altered perspective effect in the LOTC and mPFC, which are thought to be involved in the physical and core selves, respectively. Furthermore, the gestural imitation difficulty in individuals with ASD might be associated with the altered activation in the IPL and cerebellum, but not in the LOTC. These findings shed light on common and divergent neural mechanisms underlying atypical visual self-body awareness and gestural interaction in ASD.

The neural correlates of biomechanical constraints in hand laterality judgment task performed from other person's perspective: A near-infrared spectroscopy study

Previous studies, mainly using a first-person perspective (1PP), have shown that the judgments of the hand laterality judgment (HLJ) task are dependent on biomechanical constraints (BC). Specifically, differing reaction times (RT) for hand pictures rotated medially or laterally around the mid sagittal plane are attributed to the BC effect on motor imagery. In contrast, we investigated whether the HLJ task is also subject to BC when performed from a third-person perspective (3PP) as well as 1PP using near-infrared spectroscopy (NIRS) to measure the brain activity of prefrontal cortex (PFC) in right-handed participants assigned to 1PP or 3PP groups. The 1PP group judged whether a presented hand was their own left or right hand, and the 3PP group whether it was the other’s left or right hand. Using their HLJ task error rates, the 1PP and 3PP groups were subdivided into an Error Group (EG) and No Error Group (NEG). For the 1PP group, both EG and NEG showed a significant Hand Laterality × Orientation interaction for RT, indicating the BC effect on motor imagery. For the 3PP group, however, neither EG nor NEG showed the interaction, even though EG showed a significantly longer RT than NEG. These results suggest that the 3PP EG appropriately followed the 3PP task instruction, while the NEG might have taken 1PP. However, the 3PP EG NIRS profile of left PFC showed a significant Hand Laterality × Orientation interaction, while the 1PP EG did not. More noteworthy is that the left PFC activation of EG showed an interaction between the 1PP and 3PP groups when the left hand was presented. Furthermore, in the NEG, the PFC activation was not influenced by the BC in either the 1PP or 3PP condition. These results indicate that BC interferes with the HLJ task performed from the 1PP and 3PP.

Interpersonal touch suppresses visual processing of aversive stimuli

Social contact is essential for survival in human society. A previous study demonstrated that interpersonal contact alleviates pain-related distress by suppressing the activity of its underlying neural network. One explanation for this is that attention is shifted from the cause of distress to interpersonal contact. To test this hypothesis, we conducted a functional MRI (fMRI) study wherein eight pairs of close female friends rated the aversiveness of aversive and non-aversive visual stimuli under two conditions: joining hands either with a rubber model (rubber-hand condition) or with a close friend (human-hand condition). Subsequently, participants rated the overall comfortableness of each condition. The rating result after fMRI indicated that participants experienced greater comfortableness during the human-hand compared to the rubber-hand condition, whereas aversiveness ratings during fMRI were comparable across conditions. The fMRI results showed that the two conditions commonly produced aversive-related activation in both sides of the visual cortex (including V1, V2, and V5). An interaction between aversiveness and hand type showed rubber-hand-specific activation for (aversive > non-aversive) in other visual areas (including V1, V2, V3, and V4v). The effect of interpersonal contact on the processing of aversive stimuli was negatively correlated with the increment of attentional focus to aversiveness measured by a pain-catastrophizing scale. These results suggest that interpersonal touch suppresses the processing of aversive visual stimuli in the occipital cortex. This effect covaried with aversiveness-insensitivity, such that aversive-insensitive individuals might require a lesser degree of attentional capture to aversive-stimulus processing. As joining hands did not influence the subjective ratings of aversiveness, interpersonal touch may operate by redirecting excessive attention away from aversive characteristics of the stimuli.

Mental rotation of tactile stimuli: using directional haptic cues in mobile devices

Haptic interfaces have the potential to enrich users' interactions with mobile devices and convey information without burdening the user's visual or auditory attention. Haptic stimuli with directional content, for example, navigational cues, may be difficult to use in handheld applications; the user's hand, where the cues are delivered, may not be aligned with the world, where the cues are to be interpreted. In such a case, the user would be required to mentally transform the stimuli between different reference frames. We examine the mental rotation of directional haptic stimuli in three experiments, investigating: 1) users' intuitive interpretation of rotated stimuli, 2) mental rotation of haptic stimuli about a single axis, and 3) rotation about multiple axes and the effects of specific hand poses and joint rotations. We conclude that directional haptic stimuli are suitable for use in mobile applications, although users do not naturally interpret rotated stimuli in any one universal way. We find evidence of cognitive processes involving the rotation of analog, spatial representations and discuss how our results fit into the larger body of mental rotation research. For small angles (e.g., less than 40 degree), these mental rotations come at little cost, but rotations with larger misalignment angles impact user performance. When considering the design of a handheld haptic device, our results indicate that hand pose must be carefully considered, as certain poses increase the difficulty of stimulus interpretation. Generally, all tested joint rotations impact task difficulty, but finger flexion and wrist rotation interact to greatly increase the cost of stimulus interpretation; such hand poses should be avoided when designing a haptic interface.