# The characteristics of the implicit body model of the trunk

## TL;DR

This study shows that people's internal mental model of their trunk is distorted, perceiving it as squatter and wider than it actually is.

## Contribution

The study reveals specific directional biases in the perception of trunk landmarks, highlighting a distorted implicit body model.

## Key findings

- Participants perceived their trunk as squatter and wider at the waist and hips.
- A rightward bias was observed in the horizontal direction for most body landmarks.
- An inferior bias was found in the vertical direction at the thorax and waist.

## Abstract

Knowing where the body is in space requires reference to a stored model of the size and shape of body parts, termed the body model. This study sought to investigate the characteristics of the implicit body model of the trunk by assessing the position sense of midline and lateral body landmarks. Sixty-nine healthy participants localised midline and lateral body landmarks on their thorax, waist and hips, with perceived positions of these landmarks compared to actual positions. This study demonstrates evidence of a significant distortion of the implicit body model of the trunk, presenting as a squatter trunk, wider at the waist and hips. A significant difference was found between perceived and actual location in the horizontal (x) and vertical (y) directions for the majority of trunk landmarks. Evidence of a rightward bias was noted in the perception of six of the nine body landmarks in the horizontal (x) direction, including all midline levels. In the vertical (y) direction, a substantial inferior bias was evident at the thorax and waist. The implicit body model of the trunk is shown to be distorted, with the lumbar spine (waist-to-hip region) held to be shorter and wider than reality.