1,720,967 research outputs found
Kin recognition and the perceived facial similarity of children
No full textWe 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 non-siblings. 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 = 0.96) 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
Spontaneous patterns in the perceived direction of motion in ambiguous motion quartets: Effect of perception or judgment?
No full textIn a motion quartet (MQ), perceived direction of rotation is bistable, sometimes clockwise (C) sometimes counterclockwise (c). We reported (Martello et al, 2004 Journal of Vision 4 in press, abstract) that observers exhibited spontaneous patterns across time in their responses. Our results could be explained as completion of two kinds of patterns: (i) sequences (eg CCCC > C), and (ii) alternations (eg CcCc > C). We report an experiment intended to determine whether the effect of past perceptions is present even when the observer does not overtly judge the direction of MQs. We collected psychometric functions P(C|angle) for sixteen subjects who viewed almost 2000 MQ trials each. The trials were organised in groups of four (tetrads) and the angles in the MQs for the first three trials in each tetrad were chosen so that we could control the perceived direction of motion on these trials. The observer did not respond to these trials but simply observed them. On the fourth trial of each tetrad, the subject saw an MQ whose direction he judged. We found that the alternating sequences CcC and cCc still led to a strong bias to completion but that the effect of the cumulative sequences ccc and CCC had vanishe
Sub-Optimal Allocation of Time in Sequential Movements
Full text linkThe 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
Planning sequences of arm-hand movements to maximise expected gain
No full textWe examined how subjects plan movement sequences in a 'foraging' task involving three disks that appeared simultaneously at a small number of possible locations on a touch-screen monitor. Subjects received monetary rewards for the disks they touched within 1.6 s. Disk colour signaled the value. The subjects could choose to attempt three disks in any order and could choose to attempt fewer than three disks. The dependent variable was the estimated probability of hitting each disk ( pA, pB, pC) as a function of sequence. It might be (0.9, 0.6, 0.5) for sequence ABC but (0.9, 0, 0.9) for sequence AC (no attempt to hit B). The sequence ABC offers the higher probability of hitting all three disks but, if A and C are made valuable enough, the sequence AC has higher expected gain. We tested whether subjects planned movement sequences that maximised expected gain. The experiment consisted of three sessions. In the first session, ten naive subjects were trained until their performance was stable. In the second session, we measured how accurately each subject could execute each of the 12 possible sequences of length 2 or 3 on three disks of equal value. In the last session, the values of the disks were altered by amounts that varied between blocks of trials. Subjects were told the values of the colour-coded disks before each block and were free to choose any sequence. On the basis of second-session performance we could predict the strategy each subject should adopt on each trial in order to maximise expected value for each assignment of values to disks. Subjects did change strategies in the expected direction but typically favoured strategies that maximised probability of hitting three disks over the maximum expected gain strateg
Past trials influence perception of ambiguous motion quartets through pattern completion
Full text linkThere are many celebrated examples of ambiguous perceptual configurations such as the Necker cube which abruptly and repeatedly ‘switch’ among possible perceptual states. When such ambiguous configurations are presented intermittently, observers tend to see the same perceptual state on successive trials. The outcome of each trial apparently serves to ‘prime’ the outcome of the following. We sought to determine how long the influence of a past trial persists using ambiguous motion quartets as stimuli.
We found large, significant effects of all four most recent trials, but the results were not consistent with any priming model. The results could be explained instead as perceptual completion of two kinds of temporal patterns, repeating and alternating. We conclude that the visual system does not passively remember perceptual state: it analyzes recent perceptual history and attempts to predict what will come next. These predictions can alter what is seen
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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