My Psychology of Language class was having their third “Critical Issues Discussion” the other day – this one was entitled “Is language uniquely human?” Early in the term I gave them a basic guide, a number of things to look up to get them started; read specific chapters in Pinker’s The Language Instinct and Carroll’s The Psychology of Language, read up on communication abilities by dolphins, parrots, apes, and other species. One specific mention I made was to discuss mirror self-recognition and what “success” in the task might mean about the conceptual abilities of the organism. I hoped, as I wrote the little how-to guide to jumpstart them early in the term, that they would find the discussion interesting.
The students did really well, and they alerted me to one part of the primary source that I thought was interesting. For the visible white mark on the elephant’s head, titanium dioxide was used, which is alleged to be odorless. For the sham mark, zinc sulfide was used, and here’s what the author’s had to say about that:
The zinc sulfide, which is used to make the sham-mark paint luminescent, may have a slight odor, but we would expect that if the zinc sulfide odor in the sham-mark paint was detectable and differentiated from the mark by the elephants, they would have been attracted to the sham-mark rather than the visual mark. However, as our data show, no such attraction was evident. Therefore, we conclude that the odor and tactile components of the mark and the sham-mark are either equal or negligible and that any differential touching of the mark should be due to its visual component.
The later negative outcomes in all three subjects seem to confirm the absence of tactile and odor clues of the marks.
What struck me about this is how the researchers stacked the deck against themselves; the elephant’s trunk is apparently a marvel for smelling (for examples, see here and here). So, the presence of the mirror (it wasn’t novel anymore; days of testing had been conducted) and in particular the mark on the forehead was of great importance, enough to swamp whatever odor came from the sham mark.
Other correlates (in humans) are the way vision trumps proprioception in the rubber hand illusion (just look around this blog for that) and that perennial classic classroom demonstration, the McGurk Effect.