I think the idea that souls are the "seat of intellect" has gone out of favor as more and more is learned about the brain. The prevailing idea is now that it represents the consciousness of the being; it is that entity which uses the intellectual power of its brain to solve the white and red light problem. Proponents of this view would argue that there is such an entity when a human is taking the test, but with the chicken there is nothing "inside", just a network of conditioned responses predicated on anticipation of reward. The test as designed is not equipped to demonstrate the existence of that variable, however.
The problem for this back-peddling view is that there is now clear evidence that not just the problem solving intellect but every aspect of the "mind" from emotions and personality traits to sense of personal identity and conscious experience is a neurological by-product. People with specific brain lesions can actually be instructed to engage in highly specific physical interactions with objects in front of them that they perform perfectly (likely inserting envelopes into a slot randomly rotating on a 360 degree axis) despite not having any conscious experience of seeing the slot. IOW, consciousness is not needed to control actions but is more of a by-product experiencing our brain execute processes. The importance of conscious processing for most of what people think, feel, and do is highly over-rated. It is more of an observer than a director of the brains operations.
If we believe words are somehow things, we belong in a nuthouse. If we regards language as a means to fantasy-enjoyment, we'd do better with drugs. Language is a wholly-inadequate tool that has taken us over and hugely slowed human progress, and the best we can do is try hard to clarify and improve it: to do anything else is self-indulgence.