Ambiguous images produce a curious phenomenon: when people see the image change from one perception to another in a bistable image (like the duck/rabbit image), or when they see the visual illusion, they laugh. (I realized this phenomenon from watching Al Seckel’s Ted Talk, Visual illusions that show us how we (mis)think, posted April, 2007. I recommend watching it, and listen to the audience, especially during the first third or so of the presentation while you do.) Now why should they laugh? And what does it tell us about humor? About mirth? Most interestingly (to us) is how this phenomenon could help us find a physiological index of mirth. I am wont to think that laughter is an expression of a subjective feeling of mirth. You might have noticed that this thinking implies that laughter is stimulated by the subjective feeling of mirth, that is, first mirth then laughter. (It could be the other way around, as the James-Lange theory of emotion would have it, that the behavior—laughter—precedes the emotion--mirth.) Although a bit speculative, perhaps mirth is generated by neurons in the ventral striatal reward area in response to a rewarding cognition and sends its message to the supplemental motor area to generate laughter. We would like to find evidence to support this causal chain, at least insofar as subjective feeling preceding motor response.
A question then is what generates mirth? Is there something in common between jokes and bistable images? The hypothesis we plan to test is that the common “cognition” is comprehension. With both “getting” jokes and “resolving” ambiguous images is “I get it,” I see it,” or “I understand it.” Comprehension is the rewarding cognition” that mediates mirth and laughter, or so we will test.
The purpose of the exploration into the physiology of mirth is that something besides jokes is needed to determine if stroke survivors can experience mirth—feelings of joy. While it is clear that some stroke survivors experience mirth—they laugh at jokes, it is not clear if other stroke survivors do experience mirth. One difference between stroke survivors who laugh and those who do not laugh at jokes is the location and extent of the brain lesion caused by the stroke. Jokes are a problem for some stroke survivors because jokes require intact language but various aspects of language are compromised for some stroke survivors. Not only could the damage from the stroke have affected language processing, it could be also that a stroke damaged the ventral striatal “reward area” thereby eliminating mirth experiences (I suspect). And too, if we can find a way to elicit mirth from language compromised patients, can it be used therapeutically? We need other avenues to mirth.
Methodologically, we will collect some neurophysiological measures. We are going to place sensors on the face to detect activity in the zygomaticus muscle, which runs from the corner of the mouth to the tip of the ear lobe, to detect even the faintest tendency to smile. We will connect another sensor on the forehead just between the eyes to detect activity in the corrugator muscle, which will register a tendency to frown. In addition to these electromyographic (EMG) responses, we will connect a third set of sensors to the volar phalanges of the index and middle fingers of the non-dominant hand to detect electrodermal activity (EDA, also known as GSR). EDA activity will suggest an emotional response. If the emotional response is related to mirth, then we expect EDA to be correlated with activity in the zygomaticus but not correlated with activity in the corrugator. Perhaps I should say correlated more strongly with activity in the zygomaticus than in the corrugator because a frown will be associated with a subjective emotional response generated by unjokes, as one grad student called them—too but hopefully a much weaker one. However, mirth will have to be detected neurophysiologically and these measures compared between different (potential) sources of mirth.