Non-Cartesian Substance Dualism

Perhaps he feels there is nothing to track the enduring self if it's extensionless?

Really the argument would only seem to hold weight in regards to periods of unconsciousness, yet the very fact of our dreams and our ability to be awakened by sensory stimulus (sometimes of our own internal organs) negates this issue IMO.

It would make logical sense that the enduring self extends itself to encompass the form with which it identifies. A field is an extension, after all. An extensionless point has no existence, no definition, no nature.

Even in periods of unconsciousness, we are still perceiving through a brain, so the self must be extended to affected by the brain and body. Even more relevant is that even when we are unconscious, there are still biological processes happening, which are maintained by the unconscious layer of mind.

Perhaps. He seems to be saying in that quote that if the self can't be externally perceived, then for all we know it's rapidly being replaced moment to moment. Why only external perception counts would then perhaps be explained as you go on to suggest: that during periods of unconsciousness like (supposedly) sleep, internal perception ceases.

Except that we know that internal perception doesn't cease ~ it's just different. The fact that we can have dreams that we don't even recall, only for memories of said dreams being triggered later by something in the waking world is evidence of this.

For me, the argument's a non-starter even allowing for periods of unconsciousness. Why would we entertain the bizarre possibility that our selves might replace themselves from moment to moment in the first place, whether conscious or unconscious? Even if we did entertain it as a possibility, why would we then take it seriously enough to consider it the basis of an argument against substance dualism? It makes no sense to me.

I don't think it's logical in any case ~ there's no evidence for it, and it's one of the poorer arguments against Substance Dualism.

[Laird]

Except that we know that internal perception doesn't cease ~ it's just different. The fact that we can have dreams that we don't even recall, only for memories of said dreams being triggered later by something in the waking world is evidence of this.

Just to be clear, do you allow for the temporary cessation of internal perception during general anaesthesia?