From Molecule to Metaphor (2006), chapter 7

As a part of his general introduction to non-neurological psychology, Jerome Feldman cites a 1979 study that indirectly sheds some new light on Tim Rohrer's fMRI findings.

Ambiguity and Primed Priming
In the 1979 priming experiment by Tanenhaus et al., subjects were asked to decide whether a given string (e.g., season) was an English word. They did this in one of two conditions.

In one condition, the subjects were primed with a completely unrelated sentence, e.g., she was afraid to talk. In the other condition, they were also primed with an unrelated sentence; but in this case, the sentence contained an ambiguous word, e.g., she was afraid to fall.

These sentences were constructed so that there was only one possible way to read the ambiguous word. For instance, in the example above, the word fall can only be read as the verb, not the noun. Any activation in the concept of falling would be a secondary effect and would not contribute to the understanding of the sentence.

However, the researchers consistently found that the indirectly related primes would nudge the subjects into faster and more accurate decisions, just as if they were responding to unproblematically related words (e.g., cat--kitten).

It thus seems that the seasonal meaning of fall is, to some extent, activated by the sentence she was afraid to fall. This is not plausibly explained as a metaphorical process, especially since a number of the ambiguous words were clearly not related, e.g. I put it in the box as a prime for fight.

Relation or Disambiguation?
Now look again at Rohrer's findings: He had his subjects read sentences that contained metaphorical uses of words such as grasp or fist, and he found that such words, on average, lead to increase in activity in same the brain regions that are associated with the actual hands and arms.

He took this as a confirmation of the conceptual mapping hypothesis. Since hand metaphors activate the hand concept, literal meaning must be involved in metaphorical understanding. His findings are indeed consistent with this hypothesis.

However, as the experiment by Tanenhaus et al. shows, the brain activity could just as well be a byproduct of a disambiguation process. We can take grasp the theory and grasp the cup to apply two distinct meanings of the word grasp. Both meanings would then presumably be activated during reading, just like the verb and noun meanings of box are both activated during the reading of I put it in the box.

Rohrer's results are then equally also consistent with another theory that does not assume a productive and active link between the two meanings of grasp. Instead, it assumes a link from the sound grasp to two meanings, but only one is picked on the basis of the context.