Table 2 Selected single action units from the Facial Action Coding System (FACS) [41];
From: Imitation and recognition of facial emotions in autism: a computer vision approach
| AU number | FACS name | Muscles |
|---|---|---|
| AU01 | Inner Brow Raiser | Frontalis, Pars Medialis |
| AU02 | Outer Brow Raiser | Frontalis, Pars Lateralis |
| AU04 | Brow Lowerer | Depressor Glabellae; Depressor Supercilli, Corrugator |
| AU05 | Upper Lid Raiser | Levator Palpebrae Superioris |
| AU06 | Cheek Raiser | Orbicularis Oculi, Pars Orbitalis |
| AU07 | Lid Tightener | Orbicularis Oculi, Pars Palebralis |
| AU09 | Nose Wrinkler | Levator Labii Superioris, Alaeque Nasi |
| AU10 | Upper Lip Raiser | Levator Labii Superioris, Caput Infraorbitalis |
| AU11* | Nasolabial Furrow Deepener | Zygomanic Minor |
| AU12 | Lip Corner Puller | Zygomatic Major |
| AU14** | Dimpler | Buccinator |
| AU15 | Lip Corner Depressor | Triangularis |
| AU16* | Lower Lip Depressor | Depressor Labii |
| AU17 | Chin Raiser | Mentalis |
| AU20 | Lip Stretcher | Risorius |
| AU22* | Lip Funneler | Orbicularis Oris |
| AU23 | Lip Tightener | Orbicularis Oris |
| AU24* | Lip Pressor | Orbicularis Oris |
| AU25 | Lips Part | Depressor Labii, or Relaxation of Mentalis or Orbicularis Oris |
| AU26 | Jaw Drop | Masetter; Temporal and Internal Pterygoid Relaxed |
| AU27* | Mouth Stretch | Pterygoids; Digastric |
| AU28** | Lip Suck | Orbicularis Oris |