First, with the current knowledge in philosophy and neuroscience, I don’t think there’s a definite or unanimously-agreed answer to your question yet. So, the answer, which can only be deduced from current philosophical and neuroscientific knowledge, can only be an educated speculation.
Now, regarding your question, we have two ways to compare qualia of the same thing (such as visual qualia of the same house) in different persons or animals from two perspectives – the 1st person perspective and the 3rd person perspective.
The first way is to compare the qualia that occur in another person with the qualia that occur in you, by having experiences of both qualia by yourself and then comparing them. But, the only way to do this is for you to have an access to the qualia in the other person. Currently, this is not possible. Theoretically, it may be possible to access the qualia in the other person if there is a neural bridge that bridges the qualia-creating neural process (such as the visual-qualia-creating neural process – the final-step visual processing neural process??) in the other person to your consciousness neural process so that your consciousness can experience the qualia. The problems are, at present, we do not know exactly what and where the qualia-creating neural process for each kind of qualia (visual, auditory, olfactory, etc.) and the consciousness neural process are and we do not know how to make that neural bridge between them. So, practically, the possibility to compare qualia from the 1st person perspective seems to be very far off in the future.
What’s more, even if the bridge can be formed, there still is the problem of inevitable unidentical connections between the qualia-creating neural process and the two different consciousness neural processes because the two different consciousness neural processes, being separated, must be at different locations – rendering identical connections to the same qualia-creating neural process impossible. Consequently, the qualia may appear differently to the two consciousness neural processes in spite of being the same qualia. Thus, there is also this theoretical obstacle for the comparison of qualia from the 1st person perspective too.
Next, to compare qualia from the 3rd person perspective is to compare qualia in two or more persons from the perspective of the 3rd person who examines the qualia from the outside as an onlooker. Theoretically, this is possible if we know what qualia are physically (such as are some kind of signaling or information that are being sent out from the final sensory perception neural processes). We then examine and compare the physical parameters of the qualia in different persons. For example, if the visual qualia are the signaling of the final visual perception neural processes, we can compare parameters (e.g., the spatio-temproal parameters) of this signaling in different individuals to see if they are identical or not and can conclude from that physical comparison whether the qualia are identical or not.
The problems for this kind of comparison are, at present, we do not know exactly what qualia are physically or even whether they really are physical entities. However, currently, there are several neuroscientific theories positing what qualia are physically although none of them has been accepted widely as the correct one. For example, some theories assert that qualia are
- a geometry of integrated information (1)
- information cycled through a hierarchy of networks in a resonant state (2)
- the spatial pattern of neuron's dendritic electrical activity (3)
- a special kind of signaling pattern of neural processes (4)
Even if qualia are one of these physical entities, the problem of measuring and comparing these physical entities which involve the signaling of millions of neurons is certainly more than quite a daunting task and certainly not possible in the foreseeable future. Yet, despite this, if qualia really are physical entities, it must be possible to compare them from the 3rd person perspective, at least theoretically.
Balduzzi D, Tononi G. Qualia: The geometry of integrated information. Friston KJ, editor. PLoS Comput Biol. 2009 Aug; 5(8): e1000462. DOI: 10.1371/journal.pcbi.1000462.
Orpwood R. Information and the Origin of Qualia. Front Syst Neurosci. 2017Apr 21;11(Article 22):1-16. DOI: 10.3389/fnsys.2017.00022.
Sevush S. Single-neuron Theory of Consciousness. Journal of Theoretical Biology. 2005.
Ukachoke C. Theorem IV: A Quale is a Special Kind of Signaling Pattern In: The Basic Theory of the Mind. 1st ed. Bangkok, Thailand; Charansanitwong Printing Co. 2018.