"Long before it's in the papers"
January 27, 2015


Just four basic emotions, not six, study says

Feb. 4, 2014
Courtesy of the University of Glasgow
and World Science staff

Hu­mans have only four bas­ic emo­tions—not six, a new study based on fa­cial ex­pres­sions pro­poses.

A wide­spread be­lief, first pro­posed by the Amer­i­can psy­chol­o­gist Paul Ek­man, posits there are six bas­ic emo­tions: hap­pi­ness, sad­ness, fear, an­ger, sur­prise and dis­gust.

The new re­search, pub­lished in the jour­nal Cur­rent Bi­ol­o­gy by sci­en­tists at the Uni­vers­ity of Glas­gow in Scot­land, sug­gests fear and sur­prise are just one emo­tion, though per­haps with two var­iants, and similarly with an­ger and dis­gust.

The sci­en­tists stud­ied the range of dif­fer­ent mus­cles with­in the face – or Ac­tion Un­its as re­search­ers re­fer to them – in­volved in sig­nal­ing dif­fer­ent emo­tions, as well as the time frame over which each mus­cle was ac­ti­vat­ed. The find­ings drew on a un­ique “Gen­er­a­tive Face Gram­mar” plat­form de­vel­oped at the uni­vers­ity, in­clud­ing spe­cial tech­niques and soft­ware to syn­the­size fa­cial ex­pres­sions.

The in­ves­ti­ga­tors claim that while the fa­cial ex­pres­sion sig­nals of hap­pi­ness and sad­ness are clearly dis­tinct across time, fear and sur­prise share a com­mon sig­nal – the wide-o­pen eyes – early in the sig­nal­ing dy­nam­ics.

Sim­i­lar­ly, an­ger and dis­gust share the wrin­kled nose. These early sig­nals could rep­re­sent more bas­ic dan­ger sig­nals, the in­vesti­gators said; lat­er in the “sig­nal­ing dy­nam­ics,” all six ‘clas­sic’ fa­cial ex­pres­sions of emo­tion come out.

“Our re­sults are con­sist­ent with ev­o­lu­tion­ary pre­dic­tions, where sig­nals are de­signed by both bi­o­log­i­cal and so­cial ev­o­lu­tion­ary pres­sures to op­ti­mize their func­tion,” said lead re­searcher Rachael Jack.

“First, early dan­ger sig­nals con­fer the best ad­van­tages to oth­ers by en­a­bling the fastest es­cape. Sec­ond­ly, phys­i­o­logical ad­van­tages for the ex­press­er – the wrin­kled nose pre­vents in­spira­t­ion of po­ten­tially harm­ful par­t­i­cles, where­as widened eyes in­creases in­take of vis­u­al in­forma­t­ion use­ful for es­cape – are en­hanced when the face move­ments are made ear­ly.”

She added that “not all fa­cial mus­cles ap­pear sim­ul­ta­ne­ously dur­ing fa­cial ex­pres­sions, but rath­er de­vel­op over time.”

The Gen­er­a­tive Face Gram­mar uses cam­er­as to cap­ture a three-di­men­sion­ im­age of faces of in­di­vid­u­als trained to be able to ac­ti­vate all 42 in­di­vid­ual fa­cial mus­cles in­de­pend­ent­ly. From this a com­put­er can then gen­er­ate spe­cif­ic or ran­dom fa­cial ex­pres­sions on a 3D mod­el. By ask­ing vol­un­teers to watch the mod­el as it pulled var­i­ous ex­pres­sions and state which emo­tion was be­ing ex­pressed the re­search­ers meas­ured which spe­cif­ic “Ac­tion Un­its” ob­servers as­so­ci­ate with par­tic­u­lar emo­tions.

They found that the sig­nals for fear/sur­prise and an­ger/dis­gust were con­fused at the early stage of trans­mis­sion and only be­came clear­er lat­er when oth­er Ac­tion Un­its were ac­ti­vat­ed.

“We show that ‘bas­ic’ fa­cial ex­pres­sion sig­nals are per­cep­tu­ally seg­mented across time and fol­low an evolv­ing hi­er­ar­chy of sig­nals over time – from the bi­o­log­ic­ally-rooted bas­ic sig­nals to more com­plex so­cially-spe­cif­ic sig­nals,” Jack said. “Over time, and as hu­mans mi­grat­ed across the globe, so­cio­eco­log­ical di­vers­ity probably fur­ther spe­cialized once-com­mon fa­cial ex­pres­sions, al­ter­ing the num­ber, va­ri­e­ty and form of sig­nals across cul­tures.”

The re­search­ers plan to de­vel­op their study by look­ing at fa­cial ex­pres­sions of dif­fer­ent cul­tures, in­clud­ing East Asian popula­t­ions whom they have al­ready found in­ter­pret some of the six clas­si­cal emo­tions dif­fer­ently – plac­ing more em­pha­sis on eye sig­nals than mouth move­ments com­pared to West­ern­ers.

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Humans have only four basic emotions—not six, a new study based on facial expressions proposes. A widespread belief, first proposed by the American psychologist Paul Ekman, posits there are six basic emotions: happiness, sadness, fear, anger, surprise and disgust. The new research, published in the journal Current Biology by scientists at the University of Glasgow in Scotland, suggests fear and surprise are just one emotion, and so is anger and disgust. The scientists studied the range of different muscles within the face – or Action Units as researchers refer to them – involved in signaling different emotions, as well as the time frame over which each muscle was activated. The findings drew on a unique “Generative Face Grammar” platform developed at the university, including special techniques and software to synthesize facial expressions. The investigators claim that while the facial expression signals of happiness and sadness are clearly distinct across time, fear and surprise share a common signal – the wide-open eyes – early in the signaling dynamics. Similarly, anger and disgust share the wrinkled nose. It is these early signals that could represent more basic danger signals. Later in the signaling dynamics, facial expressions transmit signals that distinguish all six ‘classic’ facial expressions of emotion. “Our results are consistent with evolutionary predictions, where signals are designed by both biological and social evolutionary pressures to optimize their function,” said lead researcher Rachael Jack. “First, early danger signals confer the best advantages to others by enabling the fastest escape. Secondly, physiological advantages for the expresser – the wrinkled nose prevents inspiration of potentially harmful particles, whereas widened eyes increases intake of visual information useful for escape – are enhanced when the face movements are made early. “What our research shows is that not all facial muscles appear simultaneously during facial expressions, but rather develop over time supporting a hierarchical biologically-basic to socially-specific information over time.” The Generative Face Grammar uses cameras to capture a three-dimensional image of faces of individuals trained to be able to activate all 42 individual facial muscles independently. From this a computer can then generate specific or random facial expressions on a 3D model. By asking volunteers to watch the model as it pulled various expressions and state which emotion was being expressed the researchers measured which specific “Action Units” observers associate with particular emotions. They found that the signals for fear/surprise and anger/disgust were confused at the early stage of transmission and only became clearer later when other Action Units were activated. “We show that ‘basic’ facial expression signals are perceptually segmented across time and follow an evolving hierarchy of signals over time – from the biologically-rooted basic signals to more complex socially-specific signals,” Jack said. “Over time, and as humans migrated across the globe, socioecological diversity probably further specialized once-common facial expressions, altering the number, variety and form of signals across cultures.” The researchers plan to develop their study by looking at facial expressions of different cultures, including East Asian populations whom they have already found interpret some of the six classical emotions differently – placing more emphasis on eye signals than mouth movements compared to Westerners.