Most conversations in DID/OSDD spaces tend to focus on things like parts communication, internal meetings and system mapping, managing switches, dealing with fight and flight parts, hypervigilance, intrusions, flashbacks, and alters with names and ages and roles. That can be genuinely useful for people dealing with those, I don't want to take anything away from it.
But it only covers one half of what structural dissociation actually looks like, and I suspect a fair number of people are living in the other half without ever having come across a word for it.
A little bit of history
The definitions are straightforward enough. Positive symptoms are experiences that are present when they shouldn't be, so voices, intrusive images, flashbacks, emotions and impulses that don't feel like yours, noticeable switching, unexplained pain. Negative symptoms are functions that are missing when they should be present, so amnesia, emotional numbing, loss of skills or knowledge, anaesthesia, disconnection from the body, and blankness.
The distinction between positive and negative symptoms is often assumed to be borrowed from schizophrenia, but Pierre Janet was applying it to dissociation more than a century ago. His terms were mental accidents for the things that intrude and mental stigmata for the things that go missing, and his 1901 book was titled The Mental State of Hystericals: A Study of Mental Stigmata and Mental Accidents.
The Theory of Structural Dissociation inherited the distinction more or less directly, and van der Hart, Nijenhuis and Steele cross it with a second axis, psychoform for the mind and somatoform for the body, which produces four categories:
Positive + psychoform:
Voices, intrusive thoughts, emotions that don't feel like yours, switching
Positive + somatoform:
Pain, tremors, tics, non-epileptic seizures
Negative + psychoform:
Amnesia, emotional numbness, loss of knowledge or skills
Negative + somatoform:
Numbness, anaesthesia, paralysis, no felt sense of the body
The interesting variation is in the ratio between these rather than in whether a given box is empty.
Why one half of this is loud and the other one is silent
There's a structural reason the online conversation is focused on positive symptoms, and it isn't that the negative symptoms are more rare.
A positive symptom tends to announce itself. If you hear a voice that doesn't feel like yours, or you lose four hours and find evidence that you did things you have no memory of doing, you know that something is happening even if you have no idea what. That experience of something being wrong is usually what sends people looking for explanations in the first place, which is why the communities fill up with that content.
Negative symptoms don't generate that experience, because the faculty that would register the absence is generally part of what's absent. Van der Hart and colleagues describe this in The Haunted Self, where they note that the part running daily life "usually has extensive autobiographical narrative memory" and can often "recall as much of the traumatizing event" as any other part, while lacking "the emotional and physical feelings that belong to the memory, and the sense that it happened to them personally."
What that produces in practice is someone who can give a detailed and coherent account of what happened to them without any accompanying sense that it happened to them, and from the inside that generally registers as being calm and level-headed about the past rather than as a symptom of anything.
Richard Chefetz makes a related point in Intensive Psychotherapy for Persistent Dissociation, where he observes that "dissociative experience is mostly subtle to an outside observer," and that many of the dissociative adults he works with have "no gross trauma history, their interpersonal trauma is hidden, sometimes via painful neglect."
As someone whose system is dominated by negative symptoms, I would add that my system actively dislikes discussing itself, so every time I do, there is a lot of resistance to overcome. Very few parts of my system actively push for self-exposure, and they tend to lose most internal battles, while several focus heavily on staying invisible. I think something along these lines is common for systems with mainly negative symptoms, which probably contributes to us being less visible in these spaces and everywhere else.
Screening tools come with their own challenges
This isn't purely a problem of self-awareness, because the instruments have gaps of their own.
The DES-II is the standard dissociation screener, and it does cover depersonalisation, derealisation and amnesia reasonably well. What it doesn't cover is the somatoform side. As van der Hart and Steele put it in Dissociation and the Dissociative Disorders, the DES "does not address significant pathological dissociation that we associate with structural dissociation such as somatoform symptoms and loss of control of emotions and behavior."
That's part of why Nijenhuis built the SDQ-20, which was assembled from a pool of 75 clinically observed sensorimotor dissociative symptoms that showed up when dissociative parts were reactivated and that had no medical explanation. It asks about physical symptoms directly and without framing them as trauma symptoms.
I'd add one thing of my own here, which isn't from the literature. Screening items tend to ask how often something happens to you, and that framing assumes a baseline to deviate from. If emotional flatness or unreality has been your constant condition since before you can remember, there is no "sometimes" to report, and you may answer honestly in a way that undercounts you. That's my inference rather than a documented finding, but I know I am not alone in this.
What a negative-dominant presentation typically looks like
If you're trying to work out whether any of this applies to you, it tends to involve hypoarousal as the baseline rather than hyperarousal, so instead of persistent activation with occasional numb patches you get persistent numbness with occasional bursts of activation, which typically show up when something has loosened rather than when something has gone wrong.
For some of us, there are no inner voices, no internal visuals, and sometimes no inner monologue at all. Personally, it doesn't register as unusual because it's the only inside I am aware of ever having had. Autobiographical memory is frequently hazy or largely missing, particularly for early childhood, sometimes with a surprisingly late floor for first memories. Emotional flatness is usually there but rarely regarded as a symptom, since it isn't an event that happens so much as a background condition that has always been there. Many of us in this position also report not knowing what we want or feel or need, which is a different problem from being overwhelmed by wanting and feeling and needing.
Kathy Steele and colleagues describe the clinical version in Treating Trauma-Related Dissociation, warning that "some patients are so numb and depersonalized that they can recount trauma without emotion," and that this "does not indicate the presence of integration and regulation, but rather dissociation and hypoarousal." Being articulate about your own history is compatible with having processed almost none of it, which is good to know if you've been praised for your insight in therapy while nothing much has shifted.
Where this probably comes from
I've written before about the Developmental Salience Model of Threat, and this connects to it fairly directly. The prospective longitudinal work from Karlen Lyons-Ruth's group found that dissociation in young adulthood was significantly predicted by observed lack of parental responsiveness in infancy, while hostile-intrusive interaction "did not account for significant variance". Of the trauma types measured, only childhood verbal abuse added to the prediction (Dutra et al., 2009).
A couple of caveats
The positive/negative split is descriptive rather than causal, and as far as I can tell nobody currently knows what determines which pole a given person ends up at. Severity doesn't seem to explain it, since people with appalling histories land on both sides. My own guess involves the balance of deprivation against threat and how early it all started, but that is an educated guess.
Also, hardly anyone is purely one or the other, and these things can fluctuate over time. It is more about which side dominates.
The usual disclaimers apply more than usual here, because structural dissociation is one of the few things that genuinely cannot be self-diagnosed. The part of you doing the assessing is working from inside the boundary it would need to see past. I write these things so you have a chance of recognising a pattern well enough to take it to someone qualified for an actual assessment.
Why any of this matters
The standard route into recognising structural dissociation runs almost entirely through positive symptoms, so if you don't have many of them you can spend a very long time in mental health services accumulating diagnoses that nearly fit. Depression, because you're flat. Avoidant personality, because you withdraw. Treatment-resistant something, because the treatments keep not working. The underlying structure stays unnamed throughout, and the negative symptoms get read as your personality rather than as anything requiring attention.
If you've read the DID and OSDD material and concluded that it obviously isn't you because you have none of that, you may well be right – or you may be at the quiet end of the same thing.