Maria F. Dal Martello

Kin recognition and the perceived facial similarity of children.

We examine the connection between a hypothetical kin recognition signal available in visual perception and the perceived facial similarity of children. One group of observers rated the facial similarity of pairs of children portrayed in photographs. Half of the pairs were siblings but the observers were not told this. A second group classified the pairs as siblings or nonsiblings. An optimal Bayesian classifier, given the similarity ratings of the first group, was as accurate in judging siblings as the second group. Mean rated similarity was also an accurate linear predictor (R2 = .96) of the log-odds that the rated pair portrayed were, in fact, siblings. Surprisingly, mean rated similarity did not vary with the age difference or gender difference of the pairs, both of which were counterbalanced across the stimuli. We conclude that the perceived facial similarity of children is little more than a graded kin recognition signal and that this kin recognition signal is effectively an estimate of the probability that two children are close genetic relatives.

Talis Pater, Talis Filius: Perceived Resemblance and the Belief in Genetic Relatedness

People hardly ever realize that their belief in their high rate of success in detecting family resemblances is affected by their knowledge of the actual genetic link between individuals. In the three studies reported here, 100 men and 100 women were requested to estimate the facial resemblance of photographically portrayed child-adult pairs, while being given either truthful or deceitful information, or no information, about their relatedness. Believing that the members of a pair were parent and offspring was the main predictor of the perceived similarity between them. Men and women agreed in judging children as more similar to female than to male adults, except when the pair members were believed to be related; in this case, men judged the child as resembling the alleged parents equally. Common remarks on family resemblance thus appear to ensue less from a conscious desire to please or reassure the parents than from general hypothesis-testing biases in human reasoning, made perhaps more specific in men by a concern with the problem of uncertain paternity.

Sub-Optimal allocation of time in sequential movements

The allocation of limited resources such as time or energy is a core problem that organisms face when planning complex actions. Most previous research concerning planning of movement has focused on the planning of single, isolated movements. Here we investigated the allocation of time in a pointing task where human subjects attempted to touch two targets in a specified order to earn monetary rewards. Subjects were required to complete both movements within a limited time but could freely allocate the available time between the movements. The time constraint presents an allocation problem to the subjects: the more time spent on one movement, the less time is available for the other. In different conditions we assigned different rewards to the two tokens. How the subject allocated time between movements affected their expected gain on each trial. We also varied the angle between the first and second movements and the length of the second movement. Based on our results, we developed and tested a model of speed-accuracy tradeoff for sequential movements. Using this model we could predict the time allocation that would maximize the expected gain of each subject in each experimental condition. We compared human performance with predicted optimal performance. We found that all subjects allocated time sub-optimally, spending more time than they should on the first movement even when the reward of the second target was five times larger than the first. We conclude that the movement planning system fails to maximize expected reward in planning sequences of as few as two movements and discuss possible interpretations drawn from economic theory.

The effect of illustrative details on the recall of main points in simple fictional and factual passages

In a passage containing main points and illustrative details, do the details facilitate the memorization of the main points? Previous studies on this question suggest that the answer depends on the nature of the passage: For short simple stories, main points were remembered better as more details were added; for longer, more difficult, factual passages, instead, main points were better conveyed by summaries in which the details had been removed. The aim of the experiment reported here is to find out whether this difference is due to the fact/fiction variable. Six simple two‐paragraph passages were used, each passage existing in three versions (short, medium, long) in which the main points were illustrated by varying numbers of details. The results showed that for fictional and factual passages of this kind, the addition of details improves recall of main points. Some possible explanations of this finding, and of the earlier contrary finding, are suggested.