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Successful aging depends upon maintaining executive functions, which enable flexible response coordination. Although flexible responses are required for both hands and feet, as in driving, few studies have examined executive functions and brain activity in older adults, in terms of foot responses. In this study, younger (mean age = 20.8) and older participants (mean age = 68.7) performed a newly developed bimanual/bipedal response-position selection compatibility task while we measured their brain activity using functional near-infrared spectroscopy. Participants had to press either a left or right button using either their left or right foot (or hand), as directed by a two-dimensional cue signal. They executed either a straight or diagonal press response that mimicked stepping on the accelerator or brake pedal in a car. Foot responses produced more errors, longer reaction times, and greater brain activation than hand responses. Greater brain activation in the left dorsolateral prefrontal cortex (BA 46) was observed in incongruent (i.e., diagonal) than in congruent (straight) trials for foot responses, but not for hand responses, suggesting that participants had difficulty executing a diagonal foot response (as braking in a car), but not a diagonal hand response. Older participants exhibited greater brain activation across the PFC than younger participants, indicating that older adults activate additional brain circuits to compensate for declining executive functions. We discuss potential relationships between declining executive functions of older adults and the frequent automobile accidents (i.e., missteps) in which they are involved.

Inhibitory deficits are one of the predominant causes of cognitive aging. This study examined age-related changes in response inhibition. In this study, young and older participants performed a bimanual/bipedal response inhibition task while we measured their brain activity via functional near-infrared spectroscopy. Participants performed most trials bimanually (bipedally). However, they had to occasionally cancel both responses [Stop/Stop (SS) trials] or the response of one hand/foot while responding with the other [Go/Stop (GS) trials]. The participants produced more errors in the selective (GS) than in the nonselective canceling trials (SS), and in by-foot response more than in by-hand response trials, irrespective of their age. However, older participants made more errors in the selective cancelation (GS) trials and by-foot responses than young participants did. Older participants showed more frontal brain activity than young participants. The GS trials triggered more activity in the frontal brain areas than the SS trials irrespective of age at many channels, while older participants recruited more brain activation in the GS trials than in the SS trials compared to young participants. Overall, older participants exhibited higher activity in the right, middle, and inferior frontal gyrus than did young participants when performing selective and nonselective inhibition response. These results suggest that neural activation of the core inhibition network declines with age and that compensational recruitment of additional networks is used to yield an expanded inhibition circuit.

Food tastes better and people eat more when eating with others compared to eating alone. Although previous research has shown that watching television facilitates eating, the influencing factors regarding video content are unclear. We compared videos of a person speaking with those of only objects (food and a cell phone) in Experiment 1, and videos of groups of four people talking in Experiment 2. Half of these videos presented human voices (including the objects-only video), while the other half had no audio. Results showed participants rated the popcorn as tasting better and consumed more when eating alone while listening to someone talking, irrespective of whether the person was present or absent in the video in Experiment 1. A similar result was found in Experiment 2, irrespective of the increased number of people talking in the video. In Experiment 3, we assessed to what extent human voices contributed to an increase in food intake and the perceived taste of food by substituting sine-wave speech (SWS) for human voices used in Experiment 1 and found that the perceived taste of food and food intake were not facilitated when participants watched videos with SWS. The present study indicates that the human voice plays a crucial role in the perceived taste of food and consumption amount when people eat alone while watching television. Suggestions to improve food enjoyment when dining alone are discussed.

Food tastes better and people eat more of it when eaten with company than alone. Although several explanations have been proposed for this social facilitation of eating, they share the basic assumption that this phenomenon is achieved by the existence of co-eating others. Here, we demonstrate a similar "social" facilitation of eating in the absence of other individuals. Elderly participants tasted a piece of popcorn alone while in front of a mirror (which reflects the participant themselves eating popcorn) or in front of a wall-reflecting monitor, and were found to eat more popcorn and rate it better tasting in the self-reflecting condition than in the monitor condition. Similar results were found for younger adults. The results suggest that the social facilitation of eating does not necessarily require the presence of another individual. Furthermore, we observed a similar "social" facilitation of eating even when participants ate a piece of popcorn in front of a static picture of themselves eating, suggesting that static visual information of "someone" eating food is sufficient to produce the "social" facilitation of eating.

Humans can efficiently detect a face among non-face objects, but few studies of this ability have been conducted in animals. Here, in Japanese macaques and humans, we examined visual searching for a face and explored what factors contribute to efficient facial information processing. Subjects were asked to search for an odd target among the different numbers of distracters. Faces of the subjects' own species, the backs of the head of the subjects' own species, faces of the subjects' closely related species or race, and faces of species that are clearly different from the subjects' own species were used as the target. Both the macaques and humans detected a face of their own species more efficiently than a face from a clearly different species. Similar efficient detections were confirmed for the faces of the subjects' closely related species or race. These results suggest that conspecific faces and faces that share morphological similarity with conspecific faces can be detected efficiently among non-face objects by both humans and Japanese macaques. In another experiment, facial recognition efficiency was observed when the subjects searched for own-species faces that had lower-spatial-frequency components compared to faces with higher-spatial-frequency components. It seems reasonable that the ability to search efficiently for faces by using holistic face processing is derived from fundamental social cognition abilities that are broadly shared among species.

Visual search asymmetry has been used as an important tool for exploring cognitive mechanisms in humans. Here, we examined visual search asymmetry in two macaques toward two types of stimulus: the orientation of line stimuli and face-like stimuli. In the experiment, the monkeys were required to detect an odd target among numerous uniform distracters. The monkeys detected a tilted-lines target among horizontal- or vertical-lined distracters significantly faster than a horizontal- or vertical-lined target among tilted-lined distracters, regardless of the display size. However, unlike the situation in which inverted-face stimuli were introduced as distracters, this effect was diminished if upright-face stimuli were used as distracters. Additionally, monkeys detected an upright-face target among inverted-face distracters significantly faster than an inverted-face target among upright-face distracters, regardless of the display size. These results demonstrate that macaques can search a target efficiently to detect both tilted lines among non-tilted lines and upright faces among inverted faces. This clarifies that there are several types of visual search asymmetry in macaques.

Like humans, Old World monkeys are known to use configural face processing to distinguish among individuals. The ability to recognize an individual through the perception of subtle differences in the configuration of facial features plays an important role in social cognition. To test this ability in New World monkeys, this study examined whether squirrel monkeys experience the Thatcher illusion, a measure of face processing ability in which changes in facial features are difficult to detect in an inverted face. In the experiment, the monkeys were required to distinguish between a target face and each of the three kinds of distracter faces whose features were altered to be different from those of the target. For each of the pairs of target and distracter faces, four rotation-based combinations of upright and inverted face presentations were used. The results revealed that when both faces were inverted and the eyes of the distracter face were altered by rotating them at an angle of 180° from those of the target face, the monkeys' discrimination learning was obstructed to a greater extent than it was under the other conditions. Thus, these results suggest that the squirrel monkey does experience the Thatcher illusion. Furthermore, it seems reasonable to assume that squirrel monkeys can utilize information about facial configurations in individual recognition and that this facial configuration information could be useful in their social communications.

In three experiments, we explored the perception of neon-color spreading in squirrel monkeys and compared it with that of humans. In Experiment 1, human observers were tested to confirm the effect of stimulus aspects that were controlled in a series of experiments on the neon-color effect. The strength of the neon-color effect was modulated by the width, spacing, and luminance ratio of crosshatched lines that induced neon-color spreading. In Experiment 2A, one squirrel monkey was taught to discriminate a circle from three other shapes induced by the neon-color effect under the same stimulus conditions as in Experiment 1. The dependent measure was the percentage of correct responses. In Experiment 2B, two monkeys were trained to discriminate a target stimulus from three nontarget stimuli that were neon-color effect versions of the target stimulus. The dependent measure was the error rate that monkeys committed in their task of discrimination. The results in Experiments 2A and 2B were comparable with the results in Experiment 1, which suggests that squirrel monkeys perceive neon-color spreading.

Face representation, which is believed to be processed in the temporal visual pathway, has been extensively investigated in humans and monkeys through neuroimaging and electroneurophysiology. Lesion studies in monkeys indicate that simple facial features are processed in the caudal regions, and that the combined and integrated features of the face are stored in the perirhinal cortex (PRC). However, this hypothesis still lacks experimental evidence in normal human subjects; therefore, we conducted 2 functional magnetic resonance imaging experiments to investigate whether the function of the PRC differs from that of conventional face-related areas during face recognition tests. In experiment 1, normal subjects learned 6 facial identity–figure associations before scanning, and their brain activity was measured during recognition testing of correct and incorrect face–figure pairs in 3 different angles. The degree of activation in the PRC differed among the facial angles, and activation in response to frontal views was greater than that to other views. In experiment 2, where face angle, but not identity, was paired with an abstract figure, activation was significantly greater in response to the frontal view than that to other views. In contrast, the degree of activation in conventional face-related areas, i.e., the fusiform gyrus, did not differ among viewing angles in both experiments. The results indicate that the function of face representation in the PRC differs from that in the conventional face-related areas, and that a frontal view of the face plays a role in the activation of face representation stored in the PRC.

To investigate the neural representations of faces in primates, particularly in relation to their personal familiarity or unfamiliarity, neuronal activities were chronically recorded from the ventral portion of the anterior inferior temporal cortex (AITv) of macaque monkeys during the performance of a facial identification task using either personally familiar or unfamiliar faces as stimuli. By calculating the correlation coefficients between neuronal responses to the faces for all possible pairs of faces given in the task and then using the coefficients as neuronal population-based similarity measures between the faces in pairs, we analyzed the similarity/dissimilarity relationship between the faces, which were potentially represented by the activities of a population of the face-responsive neurons recorded in the area AITv. The results showed that, for personally familiar faces, different identities were represented by different patterns of activities of the population of AITv neurons irrespective of the view (e.g., front, 90° left, etc.), while different views were not represented independently of their facial identities, which was consistent with our previous report. In the case of personally unfamiliar faces, the faces possessing different identities but presented in the same frontal view were represented as similar, which contrasts with the results for personally familiar faces. These results, taken together, outline the neuronal representations of personally familiar and unfamiliar faces in the AITv neuronal population.

To investigate the neural basis of the associative aspects of facial identification, we recorded neuronal activity from the ventral, anterior inferior temporal cortex (AITv) of macaque monkeys during the performance of an asymmetrical paired-association (APA) task that required associative pairing between an abstract pattern and five different facial views of a single person. In the APA task, after one element of a pair (either an abstract pattern or a face) was presented as a sample cue, the reward-seeking monkey correctly identified the other element of the pair among various repeatedly presented test stimuli (faces or patterns) that were temporally separated by interstimulus delays. The results revealed that a substantial number of AITv neurons responded both to faces and abstract patterns, and the majority of these neurons responded selectively to a particular associative pair. It was demonstrated that in addition to the view-invariant identity of faces used in the APA task, the population of AITv neurons was also able to represent the associative pairing between faces and abstract patterns, which was acquired by training in the APA task. It also appeared that the effect of associative pairing was not so strong that the abstract pattern could be treated in a manner similar to a series of faces belonging to a unique identity. Together, these findings indicate that the AITv plays a crucial role in both facial identification and semantic associations with facial identities.