The use of bouts and frequencies in the evaluation of hand preferences for a coordinated bimanual task in chimpanzees (Pan troglodytes): an empirical study comparing two different indices of laterality

Hand preferences for a coordinated bimanual task were assessed in 109 chimpanzees (Pan troglodytes). Hand preference was evaluated for 4 test sessions using bouts and frequencies of hand use to compare the sensitivity of each level of analysis in evaluating individual variation in handedness. Overall, significant population-level right-handedness was found using several different measures of hand use. Handedness indices based on bouts and frequencies were highly and significantly correlated. Moreover, hand preferences were consistent across tests despite efforts to situationally bias preference during each test. Taken together, these data do not support the view that bouts are a better level of analysis for evaluating hand preference. The results further suggest that hand preferences for coordinated bimanual actions are not influenced by situational factors and may reflect an inherent specialization of the left hemisphere for motor skill.     

Now you see me,now you don't: evidence that chimpanzees understand the role of the eyes in attention

Chimpanzees appear to understand something about the attentional states of others; in the present experiment, we investigated whether they understand that the attentional state of a human is based on eye gaze. In all, 116 adult chimpanzees were offered food by an experimenter who engaged in one of the four experimental manipulations: eyes closed, eyes open, hand over eyes, and hand over mouth. The communicative behavior of the chimpanzees was observed. More visible behaviors were produced when the experimenter's eyes were visible than when the experimenter's eyes were not visible. More vocalizations were produced when the experimenter's eyes were closed than when they were open, but there were no differences in other attention getting behaviors. There was no effect of age or rearing history. The results suggest that chimpanzees use the presence of the eyes as a cue that their visual gestures will be effective.     

Using ROC curves to test models of recognition memory: The relationship between presentation duration and slope

Many theories of memory predict that the slope of the z-transformed receiver-operating characteristic (ROC) curve should decrease with increases in the memory strength of old items. While several prior studies have failed to demonstrate this effect, the results of two experiments demonstrate that increasing presentation duration can reduce the slope of the z-transformed ROC curve. These results raise questions about the generality of prior results and of dual-process theories designed to accommodate those results. We close by emphasizing that determining the experimental circumstances that affect whether or not the slope of the z-transformed ROC curve decreases will provide important constraints on theories of recognition memory.     

When do gestures communicate? A meta-analysis

Do the gestures that speakers produce while talking significantly benefit listeners' comprehension of the message? This question has been the topic of many research studies over the previous 35 years, and there has been little consensus. The present meta-analysis examined the effect sizes from 63 samples in which listeners' understanding of a message was compared when speech was presented alone with when speech was presented with gestures. It was found that across samples, gestures do provide a significant, moderate benefit to communication. Furthermore, the magnitude of this effect is moderated by 3 factors. First, effects of gesture differ as a function of gesture topic, such that gestures that depict motor actions are more communicative than those that depict abstract topics. Second, effects of gesture on communication are larger when the gestures are not completely redundant with the accompanying speech; effects are smaller when there is more overlap between the information conveyed in the 2 modalities. Third, the size of the effect of gesture is dependent on the age of the listeners, such that children benefit more from gestures than do adults. Remaining questions for future research are highlighted.     

Action Attenuates the Effect of Visibility on Gesture Rates

Much evidence suggests that semantic characteristics of a message (e.g., the extent to which the message evokes thoughts of spatial or motor properties) and social characteristics of a speaking situation (e.g., whether there is a listener who can see the speaker) both influence how much speakers gesture. However, the Gesture as Simulated Action (GSA) framework (Hostetter & Alibali, 2008 ) predicts that these effects should not be independent but should interact such that the effect of visibility is lessened when a message evokes strong thoughts of action. This study tested this claim by comparing the gesture rates produced by speakers as they described 24 nouns that vary in how strongly they evoke thoughts of action. Further, half of the words were described with visibility between speaker and listener blocked. The results demonstrated a significant interaction as predicted by the GSA framework.     

Grip morphology and hand use in chimpanzees (Pan troglodytes): evidence of a left hemisphere specialization in motor skill

Three experiments on grip morphology and hand use were conducted in a sample of chimpanzees. In Experiment 1, grip morphology when grasping food items was recorded, and it was found that subjects who adopted a precision grip were more right-handed than chimpanzees using other grips. In Experiment 2, the effect of food type on grasping was assessed. Smaller food items elicited significantly more precision grips for the right hand. In Experiment 3, error rates in grasping foods were compared between the left and right hands. Significantly more errors were made for the left compared with the right hand. The cumulative results indicate that chimpanzees show a left-hemisphere asymmetry in motor skill that is associated with the use of precision grips.     

Differential use of vocal and gestural communication by chimpanzees (Pan troglodytes) in response to the attentional status of a human (Homo sapiens)

This study examined the communicative behavior of 49 captive chimpanzees (Pan troglodytes), particularly their use of vocalizations, manual gestures, and other auditory- or tactile-based behaviors as a means of gaining an inattentive audience's attention. A human (Homo sapiens) experimenter held a banana while oriented either toward or away from the chimpanzee. The chimpanzees' behavior was recorded for 60 s. Chimpanzees emitted vocalizations faster and were more likely to produce vocalizations as their 1st communicative behavior when a human was oriented away from them. Chimpanzees used manual gestures more frequently and faster when the human was oriented toward them. These results replicate the findings of earlier studies on chimpanzee gestural communication and provide new information about the intentional and functional use of their vocalizations.