Bodily awareness and novel multisensory features

According to the decomposition thesis, perceptual experiences resolve without remainder into their different modality-specific components. Contrary to this view, I argue that certain cases of multisensory integration give rise to experiences representing features of a novel type. Through the coordinated use of bodily awareness—understood here as encompassing both proprioception and kinaesthesis—and the exteroceptive sensory modalities, one becomes perceptually responsive to spatial features whose instances couldn’t be represented by any of the contributing modalities functioning in isolation. I develop an argument for this conclusion focusing on two cases: 3D shape perception in haptic touch and experiencing an object’s egocentric location in crossmodally accessible, environmental space

Altered visual feedback from an embodied avatar unconsciously influences movement amplitude and muscle activity

Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs. However, whether altered visual feedback during limb movement can induce substantial unconscious motor and muscular adjustments is not known. To address this question, we covertly manipulated virtual body movements in immersive virtual reality. Participants were instructed to flex their elbow to 90° while tensing an elastic band, as their virtual arm reproduced the same, a reduced (75°), or an amplified (105°) movement. We recorded muscle activity using electromyography, and assessed body ownership, agency and proprioception of the arm. Our results not only show that participants compensated for the avatar’s manipulated arm movement while being completely unaware of it, but also that it is possible to induce unconscious motor adaptations requiring significant changes in muscular activity. Altered visual feedback through body ownership illusions can influence motor performance in a process that bypasses awareness

Unstable Sense of Agency under Consistent Force Feedback

The present study undertakes an ecological approach to haptic interfaces grounded in the sense of agency that accompanies human action. The study had two aims. The first aim was to investigate the effect of two top-down cues (perceived initiation of action and presence of action options) on sense of agency in haptic interfaces. The second aim was to investigate the consistency of the sense of agency and answer the question whether consistent force feedback (bottom-up cue) is sufficient to grant stable experience of agency. The results of the study suggest that while high number of action options can be associated with stronger agency, low numbers of action options are unlikely to produce such effect, and that the cue of task completion might be critical for the sense of agency. The study also showed that sense of agency was relatively inconsistent, with the main source of uncertainty being computer-attributed agency. The discussion addresses issues of joint human-computer agency and the contribution of multiple sources of information to agency experience

Where Are Your Fingers?

How do we know how our fingers are oriented in space? Contributions to limb and finger perception include afferent sensory signals from the muscles, joints, skin, as well as vision and other senses, and top-down assumptions about the bodys dimensions. A growing body of literature has examined the perception of finger and hand position and dimensions in a bid to understand how the limbs are represented in the brain. However, no studies have examined perception of the orientation of the fingers. A comprehensive model of highly articulated body parts must include perception of their orientation as well as their position. This dissertation seeks to fill an existing gap in the literature by exploring contributions to finger orientation perception, using a novel line-matching task. In Chapter 3 I provide evidence that vestibular disruption using galvanic vestibular stimulation (GVS) leads to an inward rotation of perceived finger orientation, and provide some evidence that finger orientation perception may not be accurate at baseline. In Chapter 4 I show that left- and right-handers may have differ- ent strategies for finger orientation perception, and provide evidence for an outward rotational bias that increases as the hands are placed further laterally from the body midline. In Chapter 5, I show that the way the probe line is initially displayed has a significant impact on performance, specifically on asymmetries of responses for the two hands and the compression of responses across the test range. I further show that the outward bias observed in Chapter 4 might be due to order of hand placement and differences in muscle strain across conditions. In Chapters 6 and 7, I show no difference in orientation perception for the ring and index fingers, but find an overall inward rotation of orientation estimates for palm-down hand postures, compared to palm-up postures. My research clearly shows that perceived finger orientation, as measured in my line-matching paradigm, is highly context-dependent. I discuss this in the greater context of the limb perception literature and outline some of the questions which much still be addressed in order to arrive at a comprehensive model of hand and finger perception

Heterosexual, gay, and lesbian people’s reactivity to virtual caresses on their embodied avatars’ taboo zones

Embodying an artificial agent through immersive virtual reality (IVR) may lead to feeling vicariously somatosensory stimuli on one’s body which are in fact never delivered. To explore whether vicarious touch in IVR reflects the basic individual and social features of real-life interpersonal interactions we tested heterosexual men/women and gay men/lesbian women reacting subjectively and physiologically to the observation of a gender-matched virtual body being touched on intimate taboo zones (like genitalia) by male and female avatars. All participants rated as most erogenous caresses on their embodied avatar taboo zones. Crucially, heterosexual men/women and gay men/lesbian women rated as most erogenous taboo touches delivered by their opposite and same gender avatar, respectively. Skin conductance was maximal when taboo touches were delivered by female avatars. Our study shows that IVR may trigger realistic experiences and ultimately allow the direct exploration of sensitive societal and individual issues that can otherwise be explored only through imagination

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Rubber Hands Feel Touch, but Not in Blind Individuals

Psychology and neuroscience have a long-standing tradition of studying blind individuals to investigate how visual experience shapes perception of the external world. Here, we study how blind people experience their own body by exposing them to a multisensory body illusion: the somatic rubber hand illusion. In this illusion, healthy blindfolded participants experience that they are touching their own right hand with their left index finger, when in fact they are touching a rubber hand with their left index finger while the experimenter touches their right hand in a synchronized manner (Ehrsson et al. 2005). We compared the strength of this illusion in a group of blind individuals (n = 10), all of whom had experienced severe visual impairment or complete blindness from birth, and a group of age-matched blindfolded sighted participants (n = 12). The illusion was quantified subjectively using questionnaires and behaviorally by asking participants to point to the felt location of the right hand. The results showed that the sighted participants experienced a strong illusion, whereas the blind participants experienced no illusion at all, a difference that was evident in both tests employed. A further experiment testing the participants' basic ability to localize the right hand in space without vision (proprioception) revealed no difference between the two groups. Taken together, these results suggest that blind individuals with impaired visual development have a more veridical percept of self-touch and a less flexible and dynamic representation of their own body in space compared to sighted individuals. We speculate that the multisensory brain systems that re-map somatosensory signals onto external reference frames are less developed in blind individuals and therefore do not allow efficient fusion of tactile and proprioceptive signals from the two upper limbs into a single illusory experience of self-touch as in sighted individuals