Adaptive scaling of reward in episodic memory: a replication study

Reward is thought to enhance episodic memory formation via dopaminergic consolidation. Bunzeck, Dayan, Dolan, and Duzel [(2010). A common mechanism for adaptive scaling of reward and novelty. Human Brain Mapping, 31, 1380–1394] provided functional magnetic resonance imaging (fMRI) and behavioural evidence that reward and episodic memory systems are sensitive to the contextual value of a reward—whether it is relatively higher or lower—as opposed to absolute value or prediction error. We carried out a direct replication of their behavioural study and did not replicate their finding that memory performance associated with reward follows this pattern of adaptive scaling. An effect of reward outcome was in the opposite direction to that in the original study, with lower reward outcomes leading to better memory than higher outcomes. There was a marginal effect of reward context, suggesting that expected value affected memory performance. We discuss the robustness of the reward memory relationship to variations in reward context, and whether other reward-related factors have a more reliable influence on episodic memory.     

Investigating emotional contagion in dogs (<Emphasis Type="Italic">Canis familiaris</Emphasis>) to emotional sounds of humans and conspecifics

Emotional contagion, a basic component of empathy defined as emotional state-matching between individuals, has previously been shown in dogs even upon solely hearing negative emotional sounds of humans or conspecifics. The current investigation further sheds light on this phenomenon by directly contrasting emotional sounds of both species (humans and dogs) as well as opposed valences (positive and negative) to gain insights into intra- and interspecies empathy as well as differences between positively and negatively valenced sounds. Different types of sounds were played back to measure the influence of three dimensions on the dogs’ behavioural response. We found that dogs behaved differently after hearing non-emotional sounds of their environment compared to emotional sounds of humans and conspecifics (“Emotionality” dimension), but the subjects responded similarly to human and conspecific sounds (“Species” dimension). However, dogs expressed more freezing behaviour after conspecific sounds, independent of the valence. Comparing positively with negatively valenced sounds of both species (“Valence” dimension), we found that, independent of the species from which the sound originated, dogs expressed more behavioural indicators for arousal and negatively valenced states after hearing negative emotional sounds. This response pattern indicates emotional state-matching or emotional contagion for negative sounds of humans and conspecifics. It furthermore indicates that dogs recognized the different valences of the emotional sounds, which is a promising finding for future studies on empathy for positive emotional states in dogs.     

Do capuchin monkeys use weight to select hammer tools?

The extent to which tool-using animals take into account the properties of the tool is little explored. The use of percussors to crack open encapsulated fruit is a complex form of tool use, the choice of an adequate tool being a critical aspect in success. Several properties (e.g., material, resistance, friability, shape and weight) affect the suitability of an object to open a hard-shelled nut, with weight being amongst the most important factors. In general, heavier tools require fewer strikes to crack open a nut.     

Inferential reasoning by exclusion in pigeons, dogs, and humans

The ability to reason by exclusion (which is defined as the selection of the correct alternative by logically excluding other potential alternatives; Call in Anim Cogn 9:393–403 2006) is well established in humans. Several studies have found it to be present in some nonhuman species as well, whereas it seems to be somewhat limited or even absent in others. As inconsistent methodology might have contributed to the revealed inter-species differences, we examined reasoning by exclusion in pigeons (n = 6), dogs (n = 6), students (n = 6), and children (n = 8) under almost equal experimental conditions. After being trained in a computer-controlled two-choice procedure to discriminate between four positive (S+) and four negative (S−) photographs, the subjects were tested with displays consisting of one S− and one of four novel stimuli (S′). One pigeon, half of the dogs and almost all humans preferred S′ over S−, thereby choosing either by novelty, or by avoiding S− without acquiring any knowledge about S′, or by inferring positive class membership of S′ by excluding S−. To decide among these strategies the subjects that showed a preference for S′ were then tested with displays consisting of one of the S′ and one of four novel stimuli (S′′). Although the pigeon preferentially chose the S′′ and by novelty, dogs and humans maintained their preference for S′, thereby showing evidence of reasoning by exclusion. Taken together, the results of the present study suggest that none of the pigeons, but half of the dogs and almost all humans inferred positive class membership of S′ by logically excluding S−. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Responding in configural discrimination problems depends on density of reinforcement in time

Previous research has shown that conditioned responding in differential skin conductance conditioning increased for reinforced stimuli (CSs+) but remained constant for nonreinforced stimuli (CSs-) due to decreasing reinforcement density. The present two experiments (Experiment 1: Negative patterning; Experiment 2: Positive patterning) were designed to disentangle a possible confound of reinforcement density with stimulus frequency. In order to achieve this, we varied the intertrial interval (18 s, 24 s, or 48 s) and held constant the numbers of CSs+ and of CSs- in each of both discrimination problems. With increasing intertrial intervals, we found higher responding both to CSs+ and to CSs- as well as increased response differentiation. We discuss these results with respect to two mechanisms offered by Wagner's SOP model and conclude that the observed effects are due to variations in density of reinforcement in time.     

Paraverbal indicators of deception: a meta‐analytic synthesis

This meta‐analysis provides a quantitative synthesis of paraverbal indicators of deception as a function of different moderator variables. Of nine different speech behaviours analysed only two were reliably associated with deception in the weighted, and four in the analysis unweighted by sample size. Pitch, response latency and speech errors were positively, message duration negatively related to deception. As most effect sizes were found to be heterogeneous, analyses of moderator variables revealed that many of the observed relationships varied as a function of content, preparation, motivation, sanctioning of the lie, experimental design and operationalization. Of different theoretical approaches reviewed, a working memory model of lie production may best account for the findings. Because of the small effect sizes, and the heterogeneity in findings, practitioners must be cautioned to use such indicators in assessing the truthfulness of reports but nonetheless practical implications for different types of situations are outlined. Copyright © 2006 John Wiley & Sons, Ltd.     

Gaze following in the red-footed tortoise (Geochelone carbonaria)

Gaze following refers to the ability of an animal to orient its gaze direction to that of another organism. Such a behavior may be adaptive as it alerts the observer to important objects in the environment such as food or predators. This behavior has been shown in mammals and birds, but the evolutionary history and the distribution of this behavior throughout the animal kingdom remain unclear. Here, we show that a reptile, the red-footed tortoise (Geochelone carbonaria), is able to follow the gaze of a conspecific in a lookup task. Controls revealed that neither the mere presence of a conspecific nor the presentation of a light stimulus (without a demonstrator present) controlled the tortoises’ behavior. The findings indicate that the ability to follow gaze may be found in mammals, birds and reptiles and could have evolved before the amniotic line diverged, or may result from a general ability to learn.