EASY-TO-UNDERSTAND SUMMARY: PERIPERSONAL SPACE:
HOW WE PERCEIVE THE SPACE AROUND US IN THE AFTERMATH OF TRAUMA
What is peripersonal space, and how could our sense of it be impacted by trauma?
“Peripersonal space” (PPS) is the space surrounding our bodies - the distance within our reach, or the reach of others. Awareness of our PPS allows us to interact with our environment (e.g., turning a door knob, picking up a drinking glass), and to protect our body (e.g., avoiding sharp table corners, ducking to avoid a baseball). The perception of our own PPS involves the combination of many senses (e.g., sight, sound, touch). For example, when picking up a glass, our bodies send us information from a number of sources – the sight of the glass on the table, the feeling of the angle in our elbow while reaching for it, the pressure on our fingertips when we grasp the glass, to name just a few. The combination of all these senses helps us pick up the glass successfully.
Beyond picking up objects, awareness of our PPS also helps us locate ourselves in our surroundings, and to locate other people/things that are nearby, all of which helps us interact with the world around us. Knowing this, one can imagine that PPS would play an important role when interacting socially with others – an activity that tends to be challenging for people who have experienced interpersonal trauma (i.e., trauma at the hands of other people).
A simple example of how awareness of PPS can affect social interaction is how it can help us physically approach others in a socially acceptable way – without standing too closely or bumping into them and being able to locate their extended hand for a handshake. With this in mind, we wondered how trauma might affect PPS.
How do classic PTSD and dissociative PTSD impact someone's sense of peripersonal space?
Rabellino D, Frewen PA, McKinnon MC, & Lanius RA. (2020). Peripersonal Space and Bodily Self-Consciousness: Implications for Psychological Trauma-Related Disorders, Frontiers in Neuroscience, 14, doi: 10.3389/fnins.2020.586605
For this paper, we wanted to begin investigating how PTSD might affect someone’s sense of PPS. In particular, we wanted to learn more about how the dissociative subtype of PTSD might impact this sense, because we know that dissociation often creates a feeling of disconnection between the body and its surroundings. For this reason, we decided to review previous research on trauma-related disorders and its connection to PPS, and a few of these findings are summarized here.
One interesting finding is that our sense of PPS can be flexible, meaning it can change over time as a result of our experiences. For example, studies have shown that repeated use of tools (e.g., the hammer in the hand of a master carpenter) can change the brain, so that the tool is sensed as if it were an extension of the arm rather than a separate tool – i.e., the master carpenter feels almost as if the hammer has become part of their body. Other studies have shown that the sense of our PPS is dynamic, meaning that it can change as a result of our current activity. For example, our PPS seems to be smaller while we are standing still, but it expands when we are walking.
Thinking more specifically about trauma, we know that traumatic experiences can change how we think about ourselves in a number of ways – e.g., intellectually (“I'm bad” or “I'm stupid”), bodily (“I’m ugly”), and socially (“I’m unlikeable”) – all leading to changes in how we interact with the environment. Often, these issues lead to a sense of needing/wanting to hide from the world in an attempt to feel safer. Knowing this, we believe that people with classic PTSD probably have larger PPSs than people without PTSD - i.e., they would be aware of a larger area around their bodies in an attempt to notice any potential danger.
There is, in fact, some evidence for this from another research group's study involving war veterans who tended to prefer having more distance between themselves and others. In a different study with individuals with PTSD, a larger distance between themselves and other people was preferred if the people were approaching them from behind.
For individuals with the dissociative subtype of PTSD, however, PPS size is likely to be a bit different. This type of PTSD interferes with a person having a stable sense of their body and surroundings, which likely interferes with their ability to create a stable “safety zone” around their body. For this reason, we believe that someone with the dissociative subtype of PTSD would likely have a PPS that changes depending on their state of mind (e.g., dissociated or more present). When dissociated, however, we believe their PPS would typically be smaller due to their decreased awareness. Interestingly, we saw some evidence for this variability in PPS size in one of our studies involving the “rubber hand illusion” (see our section entitled Sensory Processing: The Rubber Hand Illusion).
Overall, as a result of our review, we hypothesized (i.e., assumed or concluded) that, typically, PPS will be larger in individuals with the classic type of PTSD, and smaller in individuals with the dissociative subtype of PTSD - especially for individuals who are very disconnected from their bodies. These differences likely stem from trauma-related changes in brain areas responsible for self-awareness and the processing of our senses.
This summarizes only a few of the details we reviewed – please see the full paper for more details. Further research will be necessary to fully understand the impact of trauma on PPS, and then how to try to correct this impact. We know that positive changes can be made in the brain with certain therapies, so we’re hopeful this can be as well!
