Temporal characteristics of visibility in chimpanzees (Pan troglodytes) and humans (Homo sapiens) assessed by a visual-masking paradigm

We used the visual-masking paradigm to compare temporal characteristics of chimpanzee vision with those of humans. Two types of masking experiments were conducted. One type involved masking by noise, in which the visibility of the geometric pattern target was tested with a spatially overlapping noise as the mask stimulus. The other type involved paracontrast and metacontrast masking, in which the mask stimuli flanked but did not spatially overlap the target stimuli. Temporal characteristics regarding the visibility of target stimuli, displayed as functions of temporal asynchrony between target and mask stimuli, differed with the mask type in chimpanzees as in humans. Peak deterioration in visibility occurred at the point of minimum temporal asynchrony both in forward and backward masking by noise, but was not at 0 ms temporal asynchrony when the target and mask stimuli did not spatially overlap. These results suggest that chimpanzees and humans share the underlying mechanisms in two kinds of temporal inhibition caused by spatially overlapping and non-overlapping mask stimuli.     

Enhanced recognition of emotional stimuli in the chimpanzee (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

Humans often have a better memory of emotional events than neutral events. From the comparative-cognitive perspective, we explored the enhancement of recognition memory by emotion in chimpanzees (Pan troglodytes) using a serial probe recognition task. In this task, we sequentially presented a list of pictures to subjects and then tested their recognition of specific pictures from within the list. We selected pictures of aggressive chimpanzees as emotional stimuli and less tensed, relaxed chimpanzees as neutral stimuli. In Experiment 1, we gave four-item lists to two young chimpanzees; one showed significantly greater recognition of pictures depicting aggressive chimpanzees than neutral ones. In Experiment 2, this chimpanzee was further tested using a recognition task with eight-item lists. The subject again showed better recognition of emotional stimuli than neutral. Furthermore, the presence of an emotional stimulus in the list also facilitated recognition of the neutral item immediately following it. Overall, although only one of the two chimpanzees showed enhanced recognition memory by emotional stimuli, this is the first demonstration of such a response in the chimpanzee. The findings are discussed in comparison with those of human studies.     

Development of cultural strategies of attention in North American and Japanese children

Recent studies suggest that North American adults exhibit a focused strategy of attention that emphasizes focal information about objects, whereas Japanese adults exhibit a divided strategy of attention that emphasizes contextual information about objects. The current study investigated whether 4- and 5-, 6- to 8-, and 9- to 13-year-old North American and Japanese children exhibit these divergent attention strategies. Two experiments suggest that those older than 6 years of age exhibit measurable cultural differences in attention, whereas 4- to 6-year-olds do not. We suggest that sociocognitive development and socialization experiences that occur around 5 to 7 years of age may foster the development of cultural strategies of attention.     

Human ostensive signals do not enhance gaze following in chimpanzees,but do enhance object-oriented attention

The previous studies have shown that human infants and domestic dogs follow the gaze of a human agent only when the agent has addressed them ostensively—e.g., by making eye contact, or calling their name. This evidence is interpreted as showing that they expect ostensive signals to precede referential information. The present study tested chimpanzees, one of the closest relatives to humans, in a series of eye-tracking experiments using an experimental design adapted from these previous studies. In the ostension conditions, a human actor made eye contact, called the participant’s name, and then looked at one of two objects. In the control conditions, a salient cue, which differed in each experiment (a colorful object, the actor’s nodding, or an eating action), attracted participants’ attention to the actor’s face, and then the actor looked at the object. Overall, chimpanzees followed the actor’s gaze to the cued object in both ostension and control conditions, and the ostensive signals did not enhance gaze following more than the control attention-getters. However, the ostensive signals enhanced subsequent attention to both target and distractor objects (but not to the actor’s face) more strongly than the control attention-getters—especially in the chimpanzees who had a close relationship with human caregivers. We interpret this as showing that chimpanzees have a simple form of communicative expectations on the basis of ostensive signals, but unlike human infants and dogs, they do not subsequently use the experimenter’s gaze to infer the intended referent. These results may reflect a limitation of non-domesticated species for interpreting humans’ ostensive signals in inter-species communication.     

Changes in somatosensory evoked potentials and Hoffmann reflexes during fast isometric contraction of foot plantarflexor in humans

In the present study, the extent to which the early component of somatosensory evoked potentials (SEPs) and the Hoffmann (H-) reflex induced by stimulation of the posterior tibial nerve are altered during the ascending and descending phases of fast plantarflexion was investigated. SEPSs and H-reflex of the soleus following tibial nerve stimulation were examined during fast plantarfiexion when performed by nine normal subjects. The analyses focused on differences in amplitude modulation of the P30-P40 component of SEP and the H-reflex between the ascending and descending phases of full-wave rectified and averaged soleus electromyographic (EMG) activity. The H-reflex amplitude was significantly increased and decreased during the ascending and descending phases more than under resting control conditions, respectively. The reduction of SEP amplitude was 49% for the ascending phase and 83% for the descending phases with respect to the resting situation. Modulation of SEP during the ascending and descending phases was robustly retained even during ischemic nerve blockade of large diameter afferent fibers. These findings suggest that the transmission of afferent inputs from muscle spindles to motoneurons and to the somatosensory cortex during fast isometric contraction of the plantar flexor is regulated in a time-dependent fashion by descending commands.     

The "ripple effect": cultural differences in perceptions of the consequences of events

Previous research has demonstrated that people from East Asian cultural backgrounds make broader, more complex causal attributions than do people from Western cultural backgrounds. In the current research, the authors hypothesized that East Asians also would be aware of a broader, more complex distribution of consequences of events. Four studies assessed cultural differences in perceptions of the consequences of (a) a shot in a game of pool, (b) an area being converted into a national park, (c) a chief executive officer firing employees, and (d) a car accident. Across all four studies, compared to participants from Western cultural backgrounds, participants from East Asian cultural backgrounds were more aware of the indirect, distal consequences of events. This pattern occurred on a variety of measures, including spontaneously generated consequences, estimations of an event's impact on subsequent events, perceived responsibility, and predicted affective reactions. Implications for our understanding of cross-cultural psychology and social perception are discussed.     

Are Japanese groups more competitive than Japanese individuals? A cross‐cultural validation of the interindividual–intergroup discontinuity effect

The interindividual–intergroup discontinuity effect is the tendency for relationships between groups to be more competitive than the relationships between individuals. It has been observed robustly in studies conducted in the United States, which is a society characterized as “individualistic.” In this study, it was explored whether the effect was replicable in a “collectivistic” society such as Japan. From the traditional view in cross‐cultural psychology, which emphasizes the collectivistic nature of East Asian peoples, it was expected that the discontinuity effect would be greater in Japan than in the United States. On the other hand, based on recent empirical findings suggesting that North Americans are no less group‐oriented than East Asians, it was expected that the discontinuity effect would be no greater in Japan than in the United States. One hundred and sixty Japanese university students played a 10‐trial repeated prisoner's dilemma game: 26 sessions of interindividual and 18 sessions of intergroup. Following exactly the procedure of prior experiments in the US, individuals and groups were allowed face‐to‐face communication with their opponents before making their decisions, and participants in the intergroup condition were further allowed to converse freely with their in‐group members. Results replicated previous findings in the United States; groups made more competitive choices than did individuals. In addition, neither the magnitude of the discontinuity effect, nor the frequency of competitive choices made by the groups, were larger in Japan than they were in the majority of prior studies conducted in the United States. These findings suggest cross‐cultural robustness of the interindividual–intergroup discontinuity effect. Also, interestingly, they contradict the simple distinction between individualism and collectivism. Implications for studies of culture and group processes are discussed.     

Is chimpanzee (Pan troglodytes) spatial attention reflexively triggered by gaze cue?

Humans show a reflexive shift in spatial attention triggered by gaze cues. Chimpanzees (Pan troglodytes) have an excellent ability to follow another's gaze, but they exhibit a limited capacity to engage in triadic interactions based on joint attention, suggesting the possibility of contributions of the different mechanisms underlying joint attention between humans and chimpanzees. The present study thus examined how the chimpanzee's visual spatial attention is triggered by gaze cues. Two chimpanzees showed no clear signs of attention shift triggered by various kinds of nonfacial and facial stimuli with averted gaze under the letter-discrimination tasks but showed significant cueing effects when the head-turning cue was presented in a quasi-dynamic manner. These cueing effects were, however, affected by the predictability of the gaze cue: Highly predictive gaze cues caused stronger cueing effects than less predictive cues. Thus, these results suggest that the shift in spatial attention caused by gaze cues does occur in chimpanzees, but, in contrast to humans, vulnerability against the cue predictability suggests that the voluntary mechanism contributes more dominantly than the reflexive mechanism to this attention shift.