Perhaps those people perceive their back to be straight when it has been curved for years. Their sense of normal is warped and they dont have the feedback syste

Perhaps those people perceive their back to be straight when it has been curved for years. Their sense of normal is warped and they dont have the feedback system to correct it without first adjusting their proprioception of where they are in relation to their body (and how parts of their body are in relation to each other).