• No results found

Chapter VI: Mine, Thine, Ours

6.5 Embodied object ownership?

As outlined above numerous studies have examined owned objects as material aspects of the extended self. Yet the self is not just a psychological construct. It also has a physical counterpart:

the body. In this paragraph I will try to argue that the sensorimotor body processes and the spatial relationships with objects may contribute to the cognitive effects of object ownership.

First insight into the neurocognitive basis of the relationship between the core (corporeal) self and the extended (extracorporeal) self comes from the literature on somatoparaphrenia (Vallar and Ronchi, 2009). So far only a few studies have carefully investigated whether —and if so, to what degree—this disorder goes beyond body parts to encompass other possessions. In some patients, complex bidirectional interactions have been reported between the affected limb and possessed items that are frequently in contact with it. In a fascinating report, a patient described by Sandifer (1946, p. 123) falsely believed that her left hand belonged to the doctor, but then she recognized a ring on one of the fingers and said, ‘That’s my ring; you’ve got my ring, doctor.’ This example illustrates how non-corporeal elements of the extended self can influence corporeal elements of the core self. Even more interesting is that the opposite pattern has also bee n documented by Aglioti et al. (1996) in a patient who denied possession of her left hand. In one of the experiments, an examiner asked her to indicate whether she owned hand-related objects, including rings, watches, combs, brushes, scissors, and holy icons. When the objects were placed in her normal right hand, all of her judgments were accurate. On the contrary, when the same objects were placed in her repudiated left hand, she incorrectly denied possessing the ones that did in fact belong to her, while correctly rejecting ownership of the others. For example, when one of her rings was placed in her good right hand, she immediately recognized it as her own and recalled many autobiographical details about it (e.g., ‘I remember quite clearly that this ring was given to me by my late husband’). However, when the same ring was placed in her affected left hand a few minutes later, she maintained that, although it looked similar to the one she had seen earlier, it was not hers.

Thus, in this particular case, because the left hand was no longer treated as ‘‘mine’’, the associated objects were likewise disowned, at least when viewed and evaluated in the context of the now-denied body part. More generally, Aglioti et al. (1996) suggest that these results bolster James’s (1890) original proposal that there is a tight link between the body and the representation of closely related, personally significant possessions.

A further demonstration of the special relationship between body and “embodied ownership” comes from recent investigations aimed at examining whether object-directed actions modulate the ownership bias (Truong et al., 2016). The authors investigated whether the location of owned objects relative to the body would interact with recall performance for those objects. To

emphasize the dynamic spatial relationship between the participant’s body and the objects, participants were required to move and sort objects from a start position to a location close to or far from themselves. After the sorting task they examined participants’ recognition of the objects via a surprise memory test. Results revealed an enhanced object processing when the object was both self-related and self-moved toward the self. Specifically, self-owned objects moved to a location close to the body were subsequently remembered significantly better than self-owned objects moved to a far location, as well as other-owned objects moved to either location. Importantly, the modulatory effect was absent when the participant did not physically move the objects closer or farther from the body but instead watched them appear in either location as a result of a key press . These findings reveals therefore the contribution of physical actions to the sense of ownership: 1) moving self-owned objects closer to the body enhanced memory for those objects; 2) an active manual interaction seems to be necessary for memory benefits to emerge (Truong et al., 2016).

Similarly, Oakes and Onyper (2017) found a memory advantage for pictures and words categorized via a motion in the direction of the physical body. Interestingly, also movements toward one’s cell phone increased memorability of stimuli when compared to the same movement toward an unfamiliar phone (see also Salerno et al., 2012). This would appear to indicate that both a self-relevant frame of reference and a movement indicative of approach are required for the memory advantage to emerge. Taking all these findings together, it seems that acting on an object through bringing it toward the body may enable the body to “embody” the object.

In addition, ownership status of objects influences visuomotor processing. For instance, verbally acquired knowledge that a mug is owned by someone else directly modulates its affordances by eliminating the automatic potentiation of action towards a graspable object. When participants judged orientations on the handles of mugs assigned to either themselves or the experimenter, standard stimulus–response compatibility effects were abolished when they belonged to the experimenter. The finding that the object affordance compatibility effect emerged for a self-owned object only, but not experimenter-self-owned one, may suggest that there is a distinction between how self-owned and other-owned objects are represented in the visuomotor system (Experiment 2 in Constable et al., 2011).

The high-level concept of ownership has also been shown to affect physical movement towards objects when individuals act alone on with a partner. For example, Constable et al. (2011) focused on the influence of ownership in individuals’ daily lives by examining the movement trajectories of people moving mugs with different ownership statuses (i.e., the participant’s mug, the experimenter’s mug, and an un-owned mug). Ownership was established by having the participants to paint their mug to create their own design, and to take the mug home to use daily for

approximately two weeks before returning to complete the second half of the experiment. During testing participants were presented with one of the three mugs, and were asked to perform a simple natural lifting movement with the mug. Kinematic data such as movement trajectories and acceleration were measured. Participants lifted their own mug more forcefully (i.e., with a greater acceleration) and drew it closer to their own body, while they lifted the experimenter’s mug with greater care and moved it slightly more towards the experimenter. The authors discussed that this pattern of results is consistent with a general reticence to interact with other people’s objects and that it may reflect a reluctance to interact with other people’s possessions. They also speculated that the reduced acceleration exerted upon the experimenter’s mug may be an indication that the participant was attempting to develop and maintain a positive social relationship with the experimenter.

In a second investigation the same authors investigated whether object ownership status influenced motor behavior in joint action (Constable et al., 2016). Participants were instructed to pass mugs that differed in ownership status to a partner. It was shown that participants oriented handles less toward the partner when passing their own mugs than when passing mugs owned by the partner or by the experimenter. Because the objects were physically identical (aside from color), the difference in rotation is driven by top-down modulation of motor commands associated with ownership status, rather than bottom-up factors associated with the low-level perceptual properties of the mugs. Collectivity, these results indicates that individuals implement joint actions that assist less the partner if they intend to manipulate own objects (Constable et al. 2016).

6.6 In a nutshell…

In sum, the material summarized above indicates that during the past few decades, cognitive neuroscience and social science have been generating remarkably similar results regarding the representational domain of personal possessions. Simple act of deeming an object as one’s own bestows it with special status as the object in question becomes part of the extended (body) self.

Such feeling of object ownership would indeed appear to share some neural and cognitive mechanisms with the feeling of body ownership.

The sensorimotor system of the body self seems to have developed, both at collective and individual level, elegant solutions to the core problems of efficiently interacting within a social world. Object ownership can accordingly bias the perception of self-relevant objects as well as the execution of motor plans. That is, the perception of ownership influences the way in which an individual interacts in a given environment, suggesting an intricate relationship between action and perception. Given that PPS is a multisensory-motor representation of the space immediately surrounding the body, taking the body as spatial reference for encoding near objects, the ownership status of an object might shape PPS in social interactions.

Chapter VII: Our peri-personal property: Exploring the effect of