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The face inversion effect in non-human primates revisited - an investigation in chimpanzees (Pan troglodytes).

Dahl CD, Rasch MJ, Tomonaga M, Adachi I - Sci Rep (2013)

Bottom Line: With inversion the perceptual processing of the spatial relationship among facial parts is disrupted.Although these results are not inconsistent with findings from humans they have some controversy in their methodology.Their performances were deteriorated by inversion.

View Article: PubMed Central - PubMed

Affiliation: Primate Research Institute, Kyoto University, Section of Language and Intelligence, Inuyama, Aichi, Japan. dahl@pri.kyoto-u.ac.jp

ABSTRACT
Faces presented upside-down are harder to recognize than presented right-side up, an effect known as the face inversion effect. With inversion the perceptual processing of the spatial relationship among facial parts is disrupted. Previous literature indicates a face inversion effect in chimpanzees toward familiar and conspecific faces. Although these results are not inconsistent with findings from humans they have some controversy in their methodology. Here, we employed a delayed matching-to-sample task to test captive chimpanzees on discriminating chimpanzee and human faces. Their performances were deteriorated by inversion. More importantly, the discrimination deterioration was systematically different between the two age groups of chimpanzee participants, i.e. young chimpanzees showed a stronger inversion effect for chimpanzee than for human faces, while old chimpanzees showed a stronger inversion effect for human than for chimpanzee faces. We conclude that the face inversion effect in chimpanzees is modulated by the level of expertise of face processing.

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Related in: MedlinePlus

Face discrimination task and modulation by inversion.(a), Procedure. In each trial, a face picture of an individual (cue) was presented on the display, followed by an inter trial interval and a presentation of two face pictures (match, distractor). All faces were either upright or inverted. Chimpanzees indicated their choice by touching either the match or distractor picture (the pictures in this panel were taken by I.A.). (b), Proportion of correct responses. Performance scores (correct trials/number of trials) were average across age groups (YC, OC), stimulus classes (chimpanzee, human faces) and manipulation (upright, inverted). (c), (d), Deterioration of discrimination performances by inversion. c, Performance scores of upright faces were subtracted from the performance scores of inverted faces to determine the relative deterioration due to inversion for each participant and stimulus class. (e), Face Inversion Species Index (FI species index). The ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined are shown. Values below .5 indicate greater deterioration for chimpanzee faces, while values above .5 indicate greater deterioration for human faces.
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f1: Face discrimination task and modulation by inversion.(a), Procedure. In each trial, a face picture of an individual (cue) was presented on the display, followed by an inter trial interval and a presentation of two face pictures (match, distractor). All faces were either upright or inverted. Chimpanzees indicated their choice by touching either the match or distractor picture (the pictures in this panel were taken by I.A.). (b), Proportion of correct responses. Performance scores (correct trials/number of trials) were average across age groups (YC, OC), stimulus classes (chimpanzee, human faces) and manipulation (upright, inverted). (c), (d), Deterioration of discrimination performances by inversion. c, Performance scores of upright faces were subtracted from the performance scores of inverted faces to determine the relative deterioration due to inversion for each participant and stimulus class. (e), Face Inversion Species Index (FI species index). The ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined are shown. Values below .5 indicate greater deterioration for chimpanzee faces, while values above .5 indicate greater deterioration for human faces.

Mentions: We tested the discrimination performances (percent correct responses) of young and old chimpanzee participants for upright and inverted faces of chimpanzees and humans (Figure 1a). A cue stimulus (e.g. face image 1 of individual 1) was centrally presented for 750 ms, followed by an inter-stimulus interval (ISI) of 500 ms and the match-distractor stimulus pair, with the stimulus for the match being a different image than the cue stimulus to avoid picture-matching strategies (e.g. face image 2 of individual 1 and a face image of individual 2). The participants were required to indicate which of the two pictures of the match-distractor pair displayed the same individual as the cue picture by touching it. Critical for our hypothesis is to replicate the modulation of correct responses for the two types of faces between age groups as shown in our previous study46, reflecting the specific tuning to one or the other face class: We therefore ran a mixed model ANOVA (with stimulus class and age group as fixed factors and participants as random factor nested in age group) and found a significant interaction between the factors age group and stimulus class (F(1,11) = 7.79, p < .05, mean square = .047) (Figure 1b, solid colors). There were no significant main effects for the factors age group (p = .96) and stimulus class (p = .51). Jarque-Bera tests affirmed normally distributed samples in both age groups and stimulus classes (all p > 0.23). Further we predict that this modulation in upright faces between age groups is not evident in inverted faces. We ran the same type of analysis on inverted faces and found no significant interaction between the factors age group and stimulus class (F(1,11) = 0.58, p = .49, mean square = .007) (Figure 1b, light red and light blue). There were no significant main effects for the factors age group (p = .58) and stimulus class (p = .54). In the next step we tested if inversion causes a significant change in the response latencies: We ran a mixed model ANOVA (with stimulus class, age group and stimulus manipulation (upright vs. inverted) as fixed factors and participants as random factor nested in age group) and found a significant interaction between the factors age group, stimulus class and stimulus manipulation (F(1,23) = 73.7, p < .001, mean square = .046) (Figure 1b,c). In addition, the factor stimulus manipulation showed a main effect (F(1,23) = 38.57, p < .01, mean square = .13; mean upright = .75, mean inverted = .60). To account for our hypothesis that YC show an increased FIE in chimpanzee as opposed to human faces and OC show an increased FIE in human as opposed to chimpanzee faces, we collapsed the response latencies for chimpanzee faces of YC and those for human face of OC and compared between stimulus manipulation (upright vs. inverted). A two-sample t-test showed a significant effect with a greater discrimination performance for upright than inverted faces (t(10) = 2.01, p < .05, standard deviation = .21; mean upright = .81, mean inverted = .58) (illustrated in Figure 1c,d). Using an iterative randomization procedure (see Methods) to account for the low sample size, we confirmed that a random effect can be excluded (CI 95%). In contrast, a comparison between discrimination performances for human faces of YC and those for chimpanzee faces of OC, compared between stimulus manipulations, did not show a significant deterioration due to inversion (t(10) = 0.59, p = .57, standard deviation = .17; mean upright = .68, mean inverted = .63) (illustrated in Figure 1c,d). Accordingly, an iterative randomization procedure confirmed that a random effect occurred with 60% likelihood. Further, based on the deterioration caused by inversion (performance scores upright – inverted faces) for each participant and stimulus class (see values in Figure 1c), we calculated a Face Inversion Species Index (FI species index, Figure 1e) by the ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined (Det_Human/(Det_Human + Det_Chimpanzee)) (Figure 1e). Values below .5 indicate stronger deterioration for chimpanzee as opposed to human faces; values above .5 indicate stronger deterioration for human as opposed to chimpanzee faces.


The face inversion effect in non-human primates revisited - an investigation in chimpanzees (Pan troglodytes).

Dahl CD, Rasch MJ, Tomonaga M, Adachi I - Sci Rep (2013)

Face discrimination task and modulation by inversion.(a), Procedure. In each trial, a face picture of an individual (cue) was presented on the display, followed by an inter trial interval and a presentation of two face pictures (match, distractor). All faces were either upright or inverted. Chimpanzees indicated their choice by touching either the match or distractor picture (the pictures in this panel were taken by I.A.). (b), Proportion of correct responses. Performance scores (correct trials/number of trials) were average across age groups (YC, OC), stimulus classes (chimpanzee, human faces) and manipulation (upright, inverted). (c), (d), Deterioration of discrimination performances by inversion. c, Performance scores of upright faces were subtracted from the performance scores of inverted faces to determine the relative deterioration due to inversion for each participant and stimulus class. (e), Face Inversion Species Index (FI species index). The ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined are shown. Values below .5 indicate greater deterioration for chimpanzee faces, while values above .5 indicate greater deterioration for human faces.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3753590&req=5

f1: Face discrimination task and modulation by inversion.(a), Procedure. In each trial, a face picture of an individual (cue) was presented on the display, followed by an inter trial interval and a presentation of two face pictures (match, distractor). All faces were either upright or inverted. Chimpanzees indicated their choice by touching either the match or distractor picture (the pictures in this panel were taken by I.A.). (b), Proportion of correct responses. Performance scores (correct trials/number of trials) were average across age groups (YC, OC), stimulus classes (chimpanzee, human faces) and manipulation (upright, inverted). (c), (d), Deterioration of discrimination performances by inversion. c, Performance scores of upright faces were subtracted from the performance scores of inverted faces to determine the relative deterioration due to inversion for each participant and stimulus class. (e), Face Inversion Species Index (FI species index). The ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined are shown. Values below .5 indicate greater deterioration for chimpanzee faces, while values above .5 indicate greater deterioration for human faces.
Mentions: We tested the discrimination performances (percent correct responses) of young and old chimpanzee participants for upright and inverted faces of chimpanzees and humans (Figure 1a). A cue stimulus (e.g. face image 1 of individual 1) was centrally presented for 750 ms, followed by an inter-stimulus interval (ISI) of 500 ms and the match-distractor stimulus pair, with the stimulus for the match being a different image than the cue stimulus to avoid picture-matching strategies (e.g. face image 2 of individual 1 and a face image of individual 2). The participants were required to indicate which of the two pictures of the match-distractor pair displayed the same individual as the cue picture by touching it. Critical for our hypothesis is to replicate the modulation of correct responses for the two types of faces between age groups as shown in our previous study46, reflecting the specific tuning to one or the other face class: We therefore ran a mixed model ANOVA (with stimulus class and age group as fixed factors and participants as random factor nested in age group) and found a significant interaction between the factors age group and stimulus class (F(1,11) = 7.79, p < .05, mean square = .047) (Figure 1b, solid colors). There were no significant main effects for the factors age group (p = .96) and stimulus class (p = .51). Jarque-Bera tests affirmed normally distributed samples in both age groups and stimulus classes (all p > 0.23). Further we predict that this modulation in upright faces between age groups is not evident in inverted faces. We ran the same type of analysis on inverted faces and found no significant interaction between the factors age group and stimulus class (F(1,11) = 0.58, p = .49, mean square = .007) (Figure 1b, light red and light blue). There were no significant main effects for the factors age group (p = .58) and stimulus class (p = .54). In the next step we tested if inversion causes a significant change in the response latencies: We ran a mixed model ANOVA (with stimulus class, age group and stimulus manipulation (upright vs. inverted) as fixed factors and participants as random factor nested in age group) and found a significant interaction between the factors age group, stimulus class and stimulus manipulation (F(1,23) = 73.7, p < .001, mean square = .046) (Figure 1b,c). In addition, the factor stimulus manipulation showed a main effect (F(1,23) = 38.57, p < .01, mean square = .13; mean upright = .75, mean inverted = .60). To account for our hypothesis that YC show an increased FIE in chimpanzee as opposed to human faces and OC show an increased FIE in human as opposed to chimpanzee faces, we collapsed the response latencies for chimpanzee faces of YC and those for human face of OC and compared between stimulus manipulation (upright vs. inverted). A two-sample t-test showed a significant effect with a greater discrimination performance for upright than inverted faces (t(10) = 2.01, p < .05, standard deviation = .21; mean upright = .81, mean inverted = .58) (illustrated in Figure 1c,d). Using an iterative randomization procedure (see Methods) to account for the low sample size, we confirmed that a random effect can be excluded (CI 95%). In contrast, a comparison between discrimination performances for human faces of YC and those for chimpanzee faces of OC, compared between stimulus manipulations, did not show a significant deterioration due to inversion (t(10) = 0.59, p = .57, standard deviation = .17; mean upright = .68, mean inverted = .63) (illustrated in Figure 1c,d). Accordingly, an iterative randomization procedure confirmed that a random effect occurred with 60% likelihood. Further, based on the deterioration caused by inversion (performance scores upright – inverted faces) for each participant and stimulus class (see values in Figure 1c), we calculated a Face Inversion Species Index (FI species index, Figure 1e) by the ratio of deterioration for human faces as opposed to the deterioration for human and chimpanzee faces combined (Det_Human/(Det_Human + Det_Chimpanzee)) (Figure 1e). Values below .5 indicate stronger deterioration for chimpanzee as opposed to human faces; values above .5 indicate stronger deterioration for human as opposed to chimpanzee faces.

Bottom Line: With inversion the perceptual processing of the spatial relationship among facial parts is disrupted.Although these results are not inconsistent with findings from humans they have some controversy in their methodology.Their performances were deteriorated by inversion.

View Article: PubMed Central - PubMed

Affiliation: Primate Research Institute, Kyoto University, Section of Language and Intelligence, Inuyama, Aichi, Japan. dahl@pri.kyoto-u.ac.jp

ABSTRACT
Faces presented upside-down are harder to recognize than presented right-side up, an effect known as the face inversion effect. With inversion the perceptual processing of the spatial relationship among facial parts is disrupted. Previous literature indicates a face inversion effect in chimpanzees toward familiar and conspecific faces. Although these results are not inconsistent with findings from humans they have some controversy in their methodology. Here, we employed a delayed matching-to-sample task to test captive chimpanzees on discriminating chimpanzee and human faces. Their performances were deteriorated by inversion. More importantly, the discrimination deterioration was systematically different between the two age groups of chimpanzee participants, i.e. young chimpanzees showed a stronger inversion effect for chimpanzee than for human faces, while old chimpanzees showed a stronger inversion effect for human than for chimpanzee faces. We conclude that the face inversion effect in chimpanzees is modulated by the level of expertise of face processing.

Show MeSH
Related in: MedlinePlus