The Ash Twins Blog

In a review of “the new synthesis” in moral psychology, Haidt describes the following remarkable experiment:

We easily switch into “intuitive prosecutor” mode (24), using our reasoning capacities to challenge people’s excuses and to seek out—or fabricate—evidence against people we don’t like. Thalia Wheatley and I (12) recently created prosecutorial moral confabulations by giving hypnotizable subjects a  post-hypnotic suggestion that they would feel a flash of disgust whenever they read a previously neutral word (“take” for half the subjects; “often” for the others). We then embedded one of those two words in six short stories about moral violations (e.g., accepting bribes or eating one’s dead pet dog) and found that stories that included the disgust-enhanced word were condemned more harshly than those that had no such flash.

To test the limiting condition of this effect, we included one story with no wrongdoing, about Dan, a student council president, who organizes faculty-student discussions. The story included one of two versions of this sentence: “He [tries to take]/[often picks] topics that appeal to both professors and students in order to stimulate discussion.” We expected that subjects who felt a flash of disgust while reading this sentence would condemn Dan (intuitive primacy), search for a justification (post-hoc reasoning), fail to find one, and then be forced to override their hypnotically induced gut feeling using controlled processes. Most did. But to our surprise, one third of the subjects in the hypnotic disgust condition (and none in the other) said that Dan’s action was wrong to some degree, and a fewcame upwith the sort of post-hoc confabulations that Gazzaniga reported in some split-brain patients, such as “Dan is a popularity-seeking snob” or “It just seems like he’s up to something.” They invented reasons to make sense of their otherwise inexplicable feeling of disgust.

Humans have exceptionally large brains relative to their body size (about 2% of body mass). Perhaps surprisingly, some animals have brains which are even larger relative to body size. Take the mormyrid electric fish (better known as the elephant nose), whose brain takes up 3% of its body mass. The majority of this size increase is represented by a pornographically enlarged valvula, the medial lobe of the cerebellum (Fig. 1). In this species, the valvula takes on complex electrosensory and electromodulatory functions.

Fig.1 Sagittal section through the brain of a Mormyrid electric fish. Note the exceptionally large valvula dorsally. TH - thalamus, hyp - hypothalamus, Dm - dorsalis pars medialis, LC - caudal lobe, LP - posterior lateral line lobe, lfb - lateral forebrain bundle. Courtesy Prechtl et al. (1998).

In animals, muscles are electrically controlled: influxes and effluxes of electrically charged ions into myofiber cells drive the contraction and relaxation of muscles. Subsequently, animal motion generates electric fields. Due to the high conductance of water, these electrical fields can be sensed by marine life. Electrosensation allows fish to localize other animals in three dimensions, either for help in interception (in the case of sharks) or evasion (in the case of mormyrids). This sixth sense provides a high-speed complement to the slower-timescale chemosensation (i.e. smell).

In the case of mormyrids, not only can these animals sense electric fields in the nearby water, they can also induce electric fields around them. This ability aids navigation in turbid waters and can serve as a jamming signal to misdirect electrosensing carnivores. The valvula is believed to compute the fearsome biophysical differential equations necessary to perform this stealth operation.

Source: Striedter 2008 Principles of Brain Evolution