Faces capture the visuospatial attention of chimpanzees (Pan troglodytes): evidence from a cueing experiment

[Background]Faces, as socially relevant stimuli, readily capture human visuospatial attention. Although faces also play important roles in the social lives of chimpanzees, the closest living species to humans, the way in which faces are attentionally processed remains unclear from a comparative-cognitive perspective. In the present study, three young chimpanzees (Pan troglodytes) were tested with a simple manual response task in which various kinds of photographs, including faces as non-informative cues, were followed by a target. [Results]When the target appeared at the location that had been occupied by the face immediately before target onset, response times were significantly faster than when the target appeared at the opposite location that had been by the other object. Such an advantage was not observed when a photograph of a banana was paired with the other object. Furthermore, this attentional capture was also observed when upright human faces were presented, indicating that this effect is not limited to own-species faces. On the contrary, when the participants were tested with inverted chimpanzee faces, this effect was rather weakened, suggesting the specificity to upright faces. [Conclusion]Chimpanzee's visuospatial attention was easily captured by the face stimuli. This effect was face specific and stronger for upright faces than inverted. These results are consistent with those from typically developing humans

Pacman in the sky with shadows: the effect of cast shadows on the perceptual completion of occluded figures by chimpanzees and humans

<p>Abstract</p> <p>Background</p> <p>Humans readily perceive whole shapes as intact when some portions of these shapes are occluded by another object. This type of amodal completion has also been widely reported among nonhuman animals and is related to pictorial depth perception. However, the effect of a cast shadow, a critical pictorial-depth cue for amodal completion has been investigated only rarely from the comparative-cognitive perspective. In the present study, we examined this effect in chimpanzees and humans.</p> <p>Results</p> <p>Chimpanzees were slower in responding to a Pacman target with an occluding square than to the control condition, suggesting that participants perceptually completed the whole circle. When a cast shadow was added to the square, amodal completion occurred in both species. On the other hand, however, critical differences between the species emerged when the cast shadow was added to the Pacman figure, implying that Pacman was in the sky casting a shadow on the square. The cast shadow prevented, to a significant extent, compulsory amodal completion in humans, but had no effect on chimpanzees.</p> <p>Conclusion</p> <p>These results suggest that cast shadows played a critical role in enabling humans to infer the spatial relationship between Pacman and the square. For chimpanzees, however, a cast shadow may be perceived as another "object". A limited role for cast shadows in the perception of pictorial depth has also been reported with respect to human cognitive development. Further studies on nonhuman primates using a comparative-developmental perspective will clarify the evolutionary origin of the role of cast shadows in visual perception.</p

Visual Search for Human Gaze Direction by a Chimpanzee (Pan troglodytes)

Background: Humans detect faces with direct gazes among those with averted gazes more efficiently than they detect faces with averted gazes among those with direct gazes. We examined whether this ‘‘stare-in-the-crowd’ ’ effect occurs in chimpanzees (Pan troglodytes), whose eye morphology differs from that of humans (i.e., low-contrast eyes, dark sclera). Methodology/Principal Findings: An adult female chimpanzee was trained to search for an odd-item target (front view of a human face) among distractors that differed from the target only with respect to the direction of the eye gaze. During visualsearch testing, she performed more efficiently when the target was a direct-gaze face than when it was an averted-gaze face. This direct-gaze superiority was maintained when the faces were inverted and when parts of the face were scrambled. Subsequent tests revealed that gaze perception in the chimpanzee was controlled by the contrast between iris and sclera, as in humans, but that the chimpanzee attended only to the position of the iris in the eye, irrespective of head direction. Conclusion/Significance: These results suggest that the chimpanzee can discriminate among human gaze directions and are more sensitive to direct gazes. However, limitations in the perception of human gaze by the chimpanzee are suggeste

Eye preferences in capuchin monkeys (Sapajus apella)

This study explored whether capuchin monkey eye preferences differ systematically in response to stimuli of positive and negative valence. The &lsquo;valence hypothesis&rsquo; proposes that the right hemisphere is more dominant for negative emotional processing and the left hemisphere is more dominant for positive emotional processing. Visual information from each eye is thought to be transferred faster to and primarily processed by the contralateral cerebral hemisphere. Therefore, it was predicted capuchin monkeys would show greater left eye use for looking at negative stimuli and greater right eye use for looking at positive stimuli. Eleven captive capuchin monkeys were presented with four images of different emotional valence (an egg and capuchin monkey raised eyebrow face were categorised as positive, and a harpy eagle face and capuchin monkey threat face were categorised as negative) and social relevance (consisting of capuchin monkey faces or not), and eye preferences for viewing the stimuli through a monocular viewing hole were recorded. While strong preferences for using either the left or right eye were found for most individuals, there was no consensus at the population level. Furthermore, the direction of looking, number of looks and duration of looks did not differ significantly with the emotional valence of the stimuli. These results are inconsistent with the main hypotheses about the relationship between eye preferences and processing of emotional stimuli. However, the monkeys did show significantly more arousal behaviours (vocalisation, door-touching, self-scratching and hand-rubbing) when viewing the negatively valenced stimuli than the positively valenced stimuli, indicating that the stimuli were emotionally salient. These findings do not provide evidence for a relationship between eye preferences and functional hemispheric specialisations, as often proposed in humans. Additional comparative studies are required to better understand the phylogeny of lateral biases, particularly in relation to emotional valence

Longevity and mortality of captive chimpanzees in Japan from 1921 to 2018

日本の飼育チンパンジーの平均寿命を算出. 京都大学プレスリリース. 2019-10-08.Utilizing the Great Ape Information Network (GAIN), an open-access nationwide database containing the detailed life history information of all apes who have lived or currently reside in Japan, we present a robust chimpanzee life table by single year of age and sex including 821 individuals spanning nearly a century, current through March 11, 2019. While the demographic composition and status of captive chimpanzees in Japan has been previously reported, longevity and mortality statistics have not. We show that female and male survivorship do not differ significantly, and that a live-born chimpanzee in Japan can expect to live 28.3 years (females 26.3, males 30.3). Life expectancy increases to 34.6 years (females 33.4, males 35.7) for individuals who reach one year of age, and to 40.4 years (females 39.2, males 41.5) for those who survive to adulthood. The oldest chimpanzee in Japan, a wild-born male, lived an estimated 68 years. One in six infants are stillborn, and nearly 80% of all infants born alive survive beyond their first birthday. Finally, we report that a seasonal death pattern exists and chimpanzees in Japan are more likely to decease in the winter months (Dec–Feb) than in any other season

Exploring attentional bias towards threatening faces in chimpanzees using the dot probe task

Primates have evolved to rapidly detect and respond to danger in their environment. However, the mechanisms involved in attending to threatening stimuli are not fully understood. The dot-probe task is one of the most widely used experimental paradigms to investigate these mechanisms in humans. However, to date, few studies have been conducted in non-human primates. The aim of this study was to investigate whether the dot-probe task can measure attentional biases towards threatening faces in chimpanzees. Eight adult chimpanzees participated in a series of touch screen dot-probe tasks. We predicted faster response times towards chimpanzee threatening faces relative to neutral faces and faster response times towards faces of high threat intensity (scream) than low threat intensity (bared teeth). Contrary to prediction, response times for chimpanzee threatening faces relative to neutral faces did not differ. In addition, we found no difference in response times for faces of high and low threat intensity. In conclusion, we found no evidence that the touch screen dot-probe task can measure attentional biases specifically towards threatening faces in our chimpanzees. Methodological limitations of using the task to measure emotional attention in human and non-human primates, including stimulus threat intensity, emotional state, stimulus presentation duration and manual responding are discussed

Slowly walking down to the more food: Relative quantity discrimination in African spurred tortoises (Centrochelys sulcata)

Quantity discrimination, is thought to be highly adaptive as it allows an organism to select greater amounts of food or larger social groups. In contrast to mammals, the processes underlying this ability are not as well understood in reptiles. This study examined the effects of ratio and number size on relative quantity discrimination in African spurred tortoises (Centrochelys sulcata). To assess these effects, tortoises were presented with trays containing favored food pieces in all possible number combinations between 1 and 7. The tortoises had to approach the tray they perceived as having the larger quantity. If correct, they received one piece of food as reinforcement. The results revealed that relative quantity discrimination was influenced by the ratio between the numbers of pieces, with performance improving as the ratio between the numbers increased. This finding suggests that the approximate number system or analogue magnitude estimation may control their behavior. However, as the number size increased, their performance declined, also suggesting that the approximate number system alone could not explain the present result

Gap Effect for Manual Responses in Chimpanzees (Pan troglodytes): Temporal Aspects of Attentional Disengagement, Cognitive aging, and the Test for Attentional Bias Toward Infant Faces

This study examined factors influencing the gap effect, a phenomenon where the saccadic latency is faster when the fixation point disappears than when it overlaps with the target. The gap effect has been used in basic attentional research, as well as in developmental, neurophysiological, and comparative research. This effect is found not only in oculomotor tasks but also in manual response tasks in humans. In this study, we conducted a gap-overlap task using manual spatially orienting responses in chimpanzees and examined several factors that influence this effect. The results confirmed the gap effect for manual orienting responses in chimpanzees. Response times for gap trials showed a floor effect at around the gap with 200 ms and more. The duration of the fixation point did not affect the gap effect, although it did affect the chimpanzees’ response times. The presence or absence of auditory stimuli at the fixation point offset did not affect the gap effect. We also analyzed the data from two geriatric individuals (51 years old) who participated in this study and confirmed the usefulness of this effect for studying comparative cognitive-aging studies. In a second task we examined attentional bias for infant faces, an effect which has been reported in humans. However, while a gap effect was observed overall, there was no significant difference in the gap effect among stimulus types