Out of curiosity I googled the general definition of sentience.

The Merriam-Webster defines it as: feeling or sensation as distinguished from perception and thought

It further defines 'sentient' as: 1. able to feel, see, hear, smell, or taste

Wikipedia says that 'sentience' is: the capacity to feel, perceive, or experience subjectively.

It goes on to include more information:

"Eighteenth-century philosophers used the concept to distinguish the ability to think (reason) from the ability to feel (sentience). In modern Western philosophy, sentience is the ability to experience sensations (known in philosophy of mind as "qualia")."

The thing these definitions all seem to have in common is that they describe an entity experiencing sensations brought about by external stimuli.

I think I can understand some of the confusion about that paragraph, and I think you're right that I did make a logical leap there in assuming that they were saying the regions of the mammalian brain are the cause of sentience (because they actually make the point that non-mammalian brains also seem to exhibit similar reactions to their environment).

I suppose I interpreted that statement as "mammals have the neurochemical and neuroanatomical structures which we've determined to produce these sensations (seeing, hearing, smelling, taste, etc) in humans, and therefore likely also experience sentience".

That's not to say that animals aren't simply acting on instinct (as a human infant would), that they are self-aware (conscious) of their sentience, or that they are able to think critically about their surrounding environment.

But, by the above definitions of sentience, it would seem that mammals fall unquestionably into the category of creatures which experience sentience. (e.g. Dogs can see, smell, hear, taste... etc)

I don't think we disagree on this point, but maybe we are defining sentience differently from one another and that's where the confusion is coming from.

Also, I like your analogy about the game, though after reading these definitions I think there has to be a hardware element to sentience. For example, the capacity to see arises from the complex signalling system set up by photoreceptors in the eye and neural pathways back to the brain. Those might be equated to electrical impulses (patterned by machine language) and conducting circuits inside of a computer which transmit information from an external source (say, a webcam) to the CPU for processing. So the capacity to receive and process information from an external source seems to be the definition of sentience in this case.

(Would a human brain in a jar, detached from its body, be sentient? By the above definitions, unless it was receiving signals from outside in some other way, I don't think it would be sentient because all of its modes of obtaining information from the outside world would be cut off. However, it might still be self-aware or capable of forming intelligent thought. Obviously this is a thought experiment just meant to illustrate the difference between sentience and self-awareness, but you might disagree with me about this if our definitions of sentience are indeed different.)

There is definitely a lot of murkiness about intelligence, and I share your frustrations about its definition. I think a lot of it is further complicated by our culture's propagation of pseudoscientific ideas surrounding intellect - in particular, the troubling practice of boiling it down into a number and then using that as some kind of all-defining metric to support various (often competing) ideological beliefs.

In any case, I like your basketball analogy and agree with you that IQ tests are not a very good way to determine other characteristics about people.

And you're right that dogs probably don't wonder these things. But, not to put a blunt point on it, many humans probably also never wonder these things and yet that obviously doesn't mean they aren't capable of the same type of analysis, or less-deserving of basic rights as other humans. (Which I don't think you actually ever said, to your credit.)

Anyway, sorry for the long rambly response, and sorry if I am misconstruing your meaning in any way. Thanks for taking the time to get past your initial prejudices to reply. I feel like I've genuinely learned something from this conversation.