The phenomenon you are referring to is now typically referred to as Dissociative Identity Disorder (DID), previously known as Multiple Personality Disorder. It's essential to understand that DID is a complex and controversial condition that is still not entirely understood by the scientific community. My knowledge is , and research on DID may have advanced since then.
In the context of DID, different personalities, also known as alters, may indeed manifest with distinct voices, speech patterns, and accents. However, this is not universally true for all individuals with DID. The degree of accent change, if present, can vary significantly between cases. Some people with DID might display minimal or no accent variation between alters, while others may have quite distinct accents for each alter.
The reason behind accent changes in DID is not well-established, but it's thought to be related to the brain's compartmentalization and the way different identities are formed and stored separately. As each alter has its own unique sense of self, mannerisms, and experiences, these factors might contribute to variations in speech patterns and accents.
It's crucial to approach DID with sensitivity and understanding, as it is a complex mental health condition that often arises from trauma. If you or someone you know is struggling with symptoms related to DID or any mental health issue, seeking professional help from a qualified mental health practitioner is essential. They can provide a proper evaluation, diagnosis, and appropriate treatment.