When speaking about sensory inputs, it makes sense to say that different species (even different individuals) have different ranges, so one can percieve something and other can't.

With computation it is known that sufficiently strong programming languages are in some sense equal. For example, you could speak about relative advantages of Basic, C/C++, Java, Lisp, Pascal, Python, etc., but in each of these languages you can write a simulator of the remaining ones. This means that if an algorithm can be implemented in one of these languages, it can be implemented in all of them -- in worst case, it would be implemented as a simulation of another language running its native implementation.

There are some technical details, though. Simulating another program is slower and requires more memory than the original program. So it could be argued that on a given hardware you could do a program in language X which uses all the memory and all available time, so it does not necessarily follow that you can do the same program in language Y. But on this level of abstraction we ignore hardware limits. We assume that the computer is fast enough and has enough memory for whatever purpose. (More precisely, we assume that in available time a computer can do any finite number of computation steps; but it cannot do an infinite number of steps. The memory is also unlimited, but in a finite time you can only manage to use a finite amount of memory.)

So on this level of abstraction we only care about whether something can or cannot be implemented by a computer. We ignore time and space (i.e. speed and memory) constraints. Some problems can be solved by algorithms, others can not. (Then, there are other interesting levels of abstraction which care about time and space complexity of algorithms.)

Are all programming languages equal in the above sense? No. For example, although programmers generally want to avoid infinite loops in their programs, if you remove a potential for infinite loops from the programming language (e.g. in Pascal you forbid "while" and "repeat" commands, and a possibility to call functions recursively), you lose ability to simulate programming languages which have this potential, and you lose ability to solve some problems. On the other hand, some universal programming languages seem extremely simple -- a famous example is a Turing machine. This is very useful, because it is easier to do mathematical proofs about a simple language. For example if you invent a new programming language X, all you have to do to prove its universality, is to write a Turing machine simulator, which is usually very simple.

Now back to the original discussion... Eliezer suggests that brain functionality should be likened to computation, not to sensory input. A human brain is computationally universal, because (given enough time, pen and paper) we can simulate a computer program, so all brains should be equal when optimally used (differing only in speed and use of resources). In another comment he adds that ability to compute isn't the same as ability to understand. Therefore (my conclusion) what one human can understand, another human can at least correctly calculate without understanding, given a correct algorithm.