I'm sure in principle the rule is the same for all mediums, but in practice our sensory systems are not unbiased and its far easier to hold up two pieces of art

I'm sure in principle the rule is the same for all mediums, but in practice our sensory systems are not unbiased and its far easier to hold up two pieces of art side by side than it is to listen to two different songs in two different ears.I think it may be as simple as visual similarity is just more obvious and easier to point out.