Table 2.
Description of facial action units (AU) used by human actors displaying different facial expressions to ponies (n = 20). Information taken from FACS with the corresponding facial muscles and example visual images for expressions of anger, joy, sadness and neutral [18].
| AU in FACS | Description | Facial Muscle | Visual Imaging |
|---|---|---|---|
| 1 | Inner Brow Raiser | Frontalis, pars medialis |
|
| 4 | Brow Lowerer | Depressor Glabellae, Depressor Supercilli, Currugator |
|
| 5 | Upper Lid Raiser | Levator palpebrae superioris |
|
| 6 | Cheek Raiser | Orbicularis oculi, pars orbitalis |
|
| 7 | Lid Tightener | Orbicularis oculi, pars palpebralis |
|
| 12 | Lip Corner Puller | Zygomatic Major |
|
| 15 | Lip Corner Depressor | Depressor anguli oris (Triangularis) |
|
| 23 | Lip Tightener | Orbicularis oris |
|