The Thatcher illusion in humans and monkeys

Abstract

Primates possess the remarkable ability to differentiate faces of group members and to extract relevant information about the individual directly from the face. Recognition of conspecific faces is achieved by means of holistic processing, i.e. the processing of the face as an unparsed, perceptual whole, rather than as the collection of independent features (part-based processing). The most striking example of holistic processing is the Thatcher illusion. Local changes in facial features are hardly noticeable when the whole face is inverted (rotated 1808), but strikingly grotesque when the face is upright. This effect can be explained by a lack of processing capabilities for locally rotated facial features when the face is turned upside down. Recently, a Thatcher illusion was described in the macaque monkey analogous to that known from human investigations. Using a habituation paradigm combined with eye tracking, we address the critical follow-up questions raised in the aforementioned study to show the Thatcher illusion as a function of the observer's species (humans and macaques), the stimulus' species (humans and macaques) and the level of perceptual expertise (novice, expert).

What’s in a face (made of foods)? Comparing children’s and monkey’s perception of faces in face-like images of food

“…Studies employing looking time tasks among rhesus have reported positive evidence of the Thatcher effect in the same direction as human adults (Adachi et al, 2009;Dahl et al, 2010), but a recent study employing a matching-to-sample procedure found evidence for the Thatcher effect among chimpanzees but not rhesus monkeys (Weldon et al, 2013). In a series of follow up experiments in Weldon et al, rhesus monkeys appeared less sensitive to internal facial features and slight changes to these features (including inversion), instead of attending to external features of conspecific faces more readily than internal features.…”

“…Facial processing includes individual recognition, an essential socio-cognitive specialization among complex group-living species (see Parr, 2011a, for a review). Researchers have documented that some species also show the inversion effect when viewing conspecific and sometimes heterospecific faces and non-face images (e.g., Parr, 2011b;Parr, Dove, & Hopkins, 1998;Tomonaga, 1999;Tomonaga, Itakura, & Matsuzawa, 1993), including the special case of the Thatcher effect with conspecific faces (Adachi, Chou, & Hampton, 2009;Dahl, Logothetis, Bülthoff, & Wallraven, 2010, but see Parron &Fagot, 2008, andWeldon, Taubert, Smith, &Parr, 2013, for alternative findings among baboons and rhesus monkeys). Research also suggests that recognition of facial stimuli by chimpanzees involves similar psychological mechanisms and brain areas to those activated in humans (e.g., Parr, Hecht, Barks, Preuss, & Votaw, 2009;Parr, Winslow, Hopkins, & de Waal, 2000).…”

The evolution of face processing in primates

“…The Thatcher illusion occurs when the eyes and mouth are inverted in an upright face, creating a grotesque appearance that disappears when the face is inverted. Two studies using a viewing preference task reported evidence of the Thatcher illusion in rhesus monkeys [44,49], while one study failed to support the Thatcher illusion in baboons using a matching task [83]. The Thatcher illusion examines the importance of second-order configural cues, since inverting internal features also affects the spacing of these features.…”

The Thatcher illusion in squirrel monkeys (Saimiri sciureus)

“…Indeed, monkeys tended to look at the upright Thatcherized face longer than the inverted Thatcherized one; in other words, monkeys' perceived differences between upright normal faces and upright Thatcherized faces more readily than they did between inverted faces. Dahl et al (2010) also investigated the Thatcher illusion in macaque monkeys by using a habituation-dishabituation paradigm. In this study, both macaque monkey faces and human faces were used as face stimuli.…”

“…More recently, comparative cognitive studies of the Thatcher illusion in nonhuman primates have been conducted (Adachi et al 2009;Dahl et al 2010;Parron and Fagot 2008). Adachi et al (2009) investigated the Thatcher illusion in macaque monkeys by using a habituation-dishabituation paradigm.…”