Chimpanzee Use of Human and Conspecific Social Cues to Locate Hidden Food

Two studies are reported in which chimpanzees attempted to use social cues to locate hidden food in one of two possible hiding places. In the first study four chimpanzees were exposed to a local enhancement cue (the informant approached and looked to the location where food was hidden and then remained beside it) and a gaze/point cue (the informant gazed and manually pointed towards the location where the food was hidden). Each cue was given by both a human informant and a chimpanzee informant. In the second study 12 chimpanzees were exposed to a gaze direction cue in combination with a vocal cue (the human informant gazed to the hiding location and produced one of two different vocalizations: a ‘food-bark’ or a human word-form). The results were: (i) all subjects were quite skillful with the local enhancement cue, no matter who produced it; (ii) few subjects were skillful with the gaze/point cue, no matter who produced it (most of these being individuals who had been raised in infancy by humans); and (iii) most subjects were skillful when the human gazed and vocalized at the hiding place, with little difference between the two types of vocal cue. Findings are discussed in terms of chimpanzees’ apparent need for additional cues, over and above gaze direction cues, to indicate the presence of food.     

Chimpanzee gaze following in an object-choice task

Many primate species reliably track and follow the visual gaze of conspecifics and humans, even to locations above and behind the subject. However, it is not clear whether primates follow a human’s gaze to find hidden food under one of two containers in an object-choice task. In a series of experiments six adult female chimpanzees followed a human’s gaze (head and eye direction) to a distal location in space above and behind them, and checked back to the human’s face when they did not find anything interesting or unusual. This study also assessed whether these same subjects would also use the human’s gaze in an object-choice task with three types of occluders: barriers, tubes, and bowls. Barriers and tubes permitted the experimenter to see their contents (i.e., food) whereas bowls did not. Chimpanzees used the human’s gaze direction to choose the tube or barrier containing food but they did not use the human’s gaze to decide between bowls. Our findings allowed us to discard both simple orientation and understanding seeing-knowing in others as the explanations for gaze following in chimpanzees. However, they did not allow us to conclusively choose between orientation combined with foraging tendencies and understanding seeing in others. One interesting possibility raised by these results is that studies in which the human cannot see the reward at the time of subject choice may potentially be underestimating chimpanzees’ social knowledge. Received: 16 February 1998 / Accepted after revision: 5 July 1998     

Acoustic Distinctions in the Speech of Male Psychopaths

A key feature of psychopathy is the ability to deceive, manipulate, and con the unwary, while seeming to be perfectly sincere. Is this impression of sincerity achieved solely through body gestures and facial expression, or is there also something different about the voice quality of psychopaths? We analyzed the acoustic characteristics of speech in 20 male offenders (10 psychopaths and 10 nonpsychopaths), assessed with the Psychopathy Checklist—Revised (Hare, 1991). We used a computer program developed by Alpert, Merewether, Homel, Martz, and Lomask (1986) to measure variations in amplitude and prosody. Results indicated that psychopaths spoke more quietly than controls and did not differentiate, in voice emphasis, between neutral and affective words. These findings are consistent with the developing view that psychopaths are insensitive to the emotional connotations of language. In addition, their vocal characteristics may be part of a self-presentation mode designed to manipulate and control interpersonal interactions.     

The ethics of morphing

Here’s one piece of practical reasoning: “If I do this then a person will reap some benefits and suffer some costs. On balance, the benefits outweigh the costs. So I ought to do it.” Here’s another: “If I do this then one person will reap some benefits and another will suffer some costs. On balance, the benefits to the one person outweigh the costs to the other. So I ought to do it.” Many influential philosophers say that there is something dubious about the second piece of reasoning. They say that it makes sense to trade-off costs and benefits within lives, but not across lives. In this paper I make a case for the second piece of reasoning. My case turns on the existence of morphing sequences—sequences of possible states of affairs across which people transform smoothly into other people.

Score Metric Equivalence of the Psychopathy Checklist-Revised (PCL-R) across criminal offenders in North America and the United Kingdom: a critique of Cooke, Michie, Hart, and Clark (2005) and new analyses

David Cooke and colleagues have published a series of item response theory (IRT) studies investigating the equivalence of the Psychopathy Checklist-Revised (PCL-R) for European versus North American (NA) male criminal offenders. They have consistently concluded that PCL-R scores are not equivalent, with European offenders receiving scores up to five points lower than those in NA when matched according to the latent trait. In this article, the authors critique the Cooke et al. analyses and demonstrate how their anchor item selection method is responsible for their final conclusions concerning the apparent lack of equivalence. The authors provide a competing IRT analysis using an iterative purification strategy for anchor item selection and show how this more justifiable approach leads to very different conclusions regarding the equivalence of the PCL-R. More generally, it is argued that strong interpretations of IRT analyses in the presence of uncorroborated anchor items can be highly misleading when evaluating score metric equivalence.     

Risk‐taking and the adolescent brain: who is at risk?

Relative to other ages, adolescence is described as a period of increased impulsive and risk-taking behavior that can lead to fatal outcomes (suicide, substance abuse, HIV, accidents, etc.). This study was designed to examine neural correlates of risk-taking behavior in adolescents, relative to children and adults, in order to predict who may be at greatest risk. Activity in reward-related neural circuitry in anticipation of a large monetary reward was measured with functional magnetic resonance imaging, and anonymous self-report ratings of risky behavior, anticipation of risk and impulsivity were acquired in individuals between the ages of 7 and 29 years. There was a positive association between accumbens activity and the likelihood of engaging in risky behavior across development. This activity also varied as a function of individuals' ratings of anticipated positive or negative consequences of such behavior. Impulsivity ratings were not associated with accumbens activity, but rather with age. These findings suggest that during adolescence, some individuals may be especially prone to engage in risky behaviors due to developmental changes in concert with variability in a given individual's predisposition to engage in risky behavior, rather than to simple changes in impulsivity.