Adventures with gelatinous ellipses--constraints on models of human motion analysis

An ellipse rotating rigidly about its center may appear to rotate rigidly or to deform nonrigidly so that it appears gelatinous. We use this ambiguous stimulus to study how motion information is propagated across space. We find that features that are quite far from the contour of the ellipse may have a strong influence on the percept of the ellipse, provided they move in a way consistent with the motion of the ellipse. We show that the percept cannot be accounted for by computational models that pool constraints over a local area only, or by models that propagate information along contours, or by models that indiscriminately propagate information across space. However, the percept can be accounted for by a class of models that assume smoothness in a layered representation.     

Generalization gradients and stimulus control in delayed matching-to-sample

Neurological patients were subjects in delayed visual matching-to-sample. The sample and choice stimuli were ellipses of varying size. By measuring the difference in size between the sample on a given trial and the ellipse the subject chose on that trial, gradients of differences between samples and choice stimuli could be plotted. These difference gradients broadened with increasing delays. Sharp gradients were controlled by the samples. Flat gradients were controlled by features of the choice display, independently of the samples. Intermediate gradients reflected combined control by the samples and by the choice displays.     

Zipf's Law in transcribed speech

Summary Based on large samples of written text. Zipf:s Law holds that the logarithms of frequencies of words, and the number of different words at those frequencies, have an inverse linear relationship. This study tested this law on an oral sample by analysis of a transcribed interview which had been conducted for an unrelated study. A second purpose was to test whether the law holds differently for open- vs closed-class words. The words in the interview were tabulated by frequencies and numbers of words at each frequency, and separated by syntactic class. As Zipf found for written samples, the law provides a reasonable summary of the data for the less frequently used words but predicts fewer different words among the most frequently used words than were actually found. Linear regressions performed for each syntactic class revealed that the regression equation for open-class words provided the best fit to Zipf's law. The sample of closed-class words, containing a much smaller proportion of low frequency words, revealed a poor fit to Zipf's law.The author wishes to thank Diane Beyerchen, Wendy Calla, Edward Kulick, and Clinton B' Walker for their cooperation and suggestions.     

On tests for correlated proportions in the presence of incomplete data

This paper proposes test statistics based on the likelihood ratio principle for testing equality of proportions in correlated data with additional incomplete samples. Powers of these tests are compared through Monte Carlo simulation with those of tests proposed recently by Ekbohm (based on an unbiased estimator) and Campbell (based on a Pearson-Chi-squared type statistic). Even though tests based on the maximum likelihood principle are theoretically expected to be superior to others, at least asymptotically, results from our simulations show that the gain in power could only be slight.     

Exact procedures for the analysis of multidimensional contingency tables

The log-linear model for contingency tables expresses the logarithm of a cell frequency as an additive function of main effects, interactions, etc., in a way formally identical with an analysis of variance model. Exact statistical tests are developed to test hypotheses that specific effects or sets of effects are zero, yielding procedures for exploring relationships among qualitative variables which are suitable for small samples. The tests are analogous to Fisher's exact test for a 2 × 2 contingency table. Given a hypothesis, the exact probability of the obtained table is determined, conditional on fixed marginals or other functions of the cell frequencies. The sum of the probabilities of the obtained table and of all less probable ones is the exact probability to be considered in testing the null hypothesis. Procedures for obtaining exact probabilities are explained in detail, with examples given.     

Critical bands and mixed-frequency scaling: sequential dependencies, equal-loudness contours, and power function exponents

Stimuli of random intensities and various but predictable frequencies were presented for repeated magnitude estimations on the same scale (mixed-frequency scaling). The frequencies for a particular judgment session were selected so that they lay either inside each other's critical bands or outside them. Contrastive dependencies of current magnitude estimation responses on previous stimuli of a different frequency were significantly affected by whether the two frequencies were inside or outside each other's critical bands, while assimilative dependencies were not. This reinforces the idea that such dependencies are sensory in nature and arise from a different mechanism than do the assimilative dependencies. Mixed-frequency scaling of loudness also gives rise to cross-frequency matching functions from which equal-loudness contours can be calculated. These contours calculated from the present judgments are similar to those produced from other methods, even when they are extrapolated to untested intensities. Power function exponents for loudness scaled in this way are larger for lower frequencies, as has been found in previous studies, and are consistent with the flattening of the calculated equal-loudness contours for low frequencies as intensity increases.     

Perceptual alternations in stereokinesis

When a flat ellipse is slowly rotated in the frontoparallel plane, two different 3-D percepts can be obtained: (i) a rigid circular disc tilting back and forth in 3-D space, and (ii) an elongated egg, slanted into 3-D space, whose end parts seem to be located at different distances from the observer and describe a circular trajectory with respect to the frontal plane. Under prolonged observation, the two 3-D percepts alternate in time, separated by brief intervals in which either the rotation of a rigid flat ellipse in the frontal plane or an amoeba-like distortion of a 2-D shape can be perceived. An experiment is reported in which the sequence of perceptual alternations was investigated. Results show that the 3-D disc is mostly preceded by impressions of elastic amoeba-like deformations, whereas the 3-D egg is mostly preceded by the percept of a rotating flat ellipse. Direct transitions from egg to disc are not as frequent as transitions from disc to egg. Results are discussed in relation to Braunstein and Andersen's hypothesis that phenomena of this sort might result from the stimulation of automatic mechanisms for perceiving size change (changing-size neutral channels).     

The relationship between Fisher's exact test and Pearson's chi-square test: A bayesian perspective

It is demonstrated in this paper that two major tests for 2 × 2 talbes are highly related from a Bayesian perspective. Although it is well-known that Fisher's exact and Pearson's chi-square tests are asymptotically equivalent, the present analysis shows that a formal similarity also exists in small samples. The key assumption that leads to the resemblance is the presence of a continuous parameter measuring association. In particular, it is shown that Pearson's probability can be obtained by integrating a two-moment approximation to the posterior distribution of the log-odds ratio. Furthermore, Pearson's chi-square test gave an excellent approximation to the actual Bayes probability in all 2×2 tables examined, except for those with extremely disproportionate marginal frequencies.     

Internet-based questionnaire assessment: appropriate use in clinical contexts

Use of internet-mediated questionnaire assessment is growing in behavioural telehealth provision. Literature on web-based psychological testing indicates that--while tests used online should be validated for online use--such measures can be reliable and valid. However, use of normative data (especially data from paper-and-pencil samples) presents problems. Studies have shown score distributions may differ across testing media, even when comparisons are made between equivalent samples. Data from 3 different projects illustrate such (substantive) differences, and the errors that would result from using established norms to interpret internet-mediated assessments. Given representativeness issues with "internet norms", it is recommended that if online tests are used for clinical purposes, this should currently be done in a manner that does not rely on normative data.     

Feedback enhances the positive effects and reduces the negative effects of multiple-choice testing

Multiple-choice tests are used frequently in higher education without much consideration of the impact this form of assessment has on learning. Multiple-choice testing enhances retention of the material tested (the testing effect); however, unlike other tests, multiple-choice can also be detrimental because it exposes students to misinformation in the form of lures. The selection of lures can lead students to acquire false knowledge (Roediger & Marsh, 2005). The present research investigated whether feedback could be used to boost the positive effects and reduce the negative effects of multiple-choice testing. Subjects studied passages and then received a multiple-choice test with immediate feedback, delayed feedback, or no feedback. In comparison with the no-feedback condition, both immediate and delayed feedback increased the proportion of correct responses and reduced the proportion of intrusions (i.e., lure responses from the initial multiple-choice test) on a delayed cued recall test. Educators should provide feedback when using multiple-choice tests.     

Purely chromatic perception of motion in depth: two eyes as sensitive as one

Motion hyperacuity (phase) thresholds were measured for both lateral and stereoscopic oscillatory motion in both luminance and equiluminant red/green gratings of 2 cycles per degree. Thresholds for lateral chromatic motion did not exhibit the inhibitory fall-off at low temporal frequencies that was found for luminance motion. Phase thresholds for purely chromatic motion were substantially higher than those for luminance gratings, in proportion to the ratio of cone signal modulation, but they could be predicted from the corresponding contrast sensitivities for both types of stimulus. Stereomovement thresholds in luminance gratings showed the stereomovement suppression effect relative to monocular motion sensitivity previously reported for line stimuli, but purely chromatic gratings did not. Together with the lack of an inhibitory fall-off, these results imply that chromatic and luminance motion are processed by different neural pathways, and that the chrominance pathway is capable of supporting a strong percept of stereoscopic motion from purely chromatic gratings.     

Why is test-restudy practice beneficial for memory? An evaluation of the mediator shift hypothesis

Although the memorial benefits of testing are well established empirically, the mechanisms underlying this benefit are not well understood. The authors evaluated the mediator shift hypothesis, which states that test-restudy practice is beneficial for memory because retrieval failures during practice allow individuals to evaluate the effectiveness of mediators and to shift from less effective to more effective mediators. Across a series of experiments, participants used a keyword encoding strategy to learn word pairs with test-restudy practice or restudy only. Robust testing effects were obtained in all experiments, and results supported predictions of the mediator shift hypothesis. First, a greater proportion of keyword shifts occurred during test-restudy practice versus restudy practice. Second, a greater proportion of keyword shifts occurred after retrieval failure trials versus retrieval success trials during test-restudy practice. Third, a greater proportion of keywords were recalled on a final keyword recall test after test-restudy versus restudy practice.     

When and for whom do frequencies facilitate performance? On the role of numerical literacy

The thesis that the mind is better prepared to process frequencies—as compared to other numerical formats—continues to be debated. A recent aspect of this issue is the role of numeracy (numerical literacy; one's ability to understand and work with numerical information) and specifically the argument that individual differences in numeracy interact with numerical formats. This interaction, either that frequencies improve performance only for those of low numeracy or that frequencies work only for those of high numeracy, would suggest that better performance using frequencies could be due to (nonevolutionary) numeracy effects. The three present studies revisited prior work with cumulative probability, Bayesian reasoning, and scenario risk assessments to study the effects of numeracy on frequency facilitation. Results from these experiments consistently failed to replicate previous findings of interactions; however, a more consistent finding emerged of a straightforward frequency effect. The lack of interactions and observations of frequency main effects lend support to the evolutionary explanation of the frequency effect. In addition, some possible statistical processes are proposed to explain the observation of interactions in past studies.     

Testing the age related differentiation hypothesis through the Wechsler’s scales

According to the age differentiation hypothesis (ADH), g becomes increasingly invested in specific abilities with age: with increasing age, g should account for a decreasing proportion of the variance in any particular cognitive test. However, there is no conclusive evidence concerning this important topic. Data from the Italian, Spanish, and American standardisation samples of the WPPSI and the WISC-R were analysed in the present study for testing the ADH. No changes in the proportion of variance associated with g in the 4–16 age range were found. This pattern does not change depending on the country. Therefore, the ADH is rejected: g seems to be very stable across age, and, thus, it seems to be an equally important component of intelligence test performance from early childhood to late adolescence.     

Estimation tests as a means of quantifying linguistic expectancy

Objective word counts of English and Dutch were used to carry out binary choice tests concerning frequencies of occurrence of word-initial consonant clusters. Subjects were native speakers of English or Dutch. Results indicate that subjective estimations are logarithmically related to objective data and that there is an improvement in frequency judgments with increased overall second language proficiency.Frequency estimation tests are envisaged as a means for testing second language proficiency. The degree of difficulty in estimating frequencies of clusters seems to be language specific.     

The effects of errors on children's performance on a circle-ellipse discrimination

Children first learned by means of a teaching program to discriminate a circle from relatively flat ellipses. Children in the control group then proceeded into a program which gradually reduced the difference between the circle and the ellipses. They advanced to a finer discrimination when they made a correct choice, and reversed to an easier discrimination after making errors ("backup" procedure). The children made relatively few errors until they approached the region of their difference threshold (empirically determined under the conditions described). When they could no longer discriminate the forms, they learned other bases for responding that could be classified as specifiable error patterns. Children in the experimental group, having learned the preliminary circle-ellipse discrimination, were started at the upper end of the ellipse series, where it was impossible for them to discriminate the forms. The backup procedure returned them to an easier discrimination after they made errors. They made many errors and reversed down through the ellipse series. Eventually, most of the children reached a point in the ellipse series where they abandoned their systematic errors and began to make correct first choices; then they advanced upward through the program. All of the children advanced to ellipse sizes that were much larger than the ellipse size at the point of their furthest descent.     

Accounting for auto-dependency in binary dyadic time series data: A comparison of model- and permutation-based approaches for testing pairwise associations

Many theories have been put forward on how people become synchronized or co-regulate each other in daily interactions. These theories are often tested by observing a dyad and coding the presence of multiple target behaviours in small time intervals. The sequencing and co-occurrence of the partners’ behaviours across time are then quantified by means of association measures (e.g., kappa coefficient, Jaccard similarity index, proportion of agreement). We demonstrate that the association values obtained are not easy to interpret, because they depend on the marginal frequencies and the amount of auto-dependency in the data. Moreover, often no inferential framework is available to test the significance of the association. Even if a significance test exists (e.g., kappa coefficient) auto-dependencies are not taken into account, which, as we will show, can seriously inflate the Type I error rate. We compare the effectiveness of a model- and a permutation-based framework for significance testing. Results of two simulation studies show that within both frameworks test variants exist that successfully account for auto-dependency, as the Type I error rate is under control, while power is good.     

Use of binaural cues for sound localization in two species of Phyllostomidae: the Greater spear-nosed bat (Phyllostomus hastatus) and the Short-tailed fruit bat (Carollia perspicillata)

Unlike humans, not all mammals use both of the binaural cues for sound localization. Whether an animal uses these cues can be determined by testing its ability to localize pure tones; specifically, low frequencies are localized using time-difference cues, and high frequencies are localized using intensity-difference cues. We determined the ability to use binaural cues in 2 New World bats, Phyllostomus hastatus, large omnivores, and Carollia perspicillata, small frugivores, by testing their tone-localization ability using a conditioned avoidance procedure. Both species easily localized high-frequency tones, indicating that they could use the interaural intensity-difference cue. However, neither species was able to use the phase-difference cue to localize either low-frequency pure tones or amplitude-modulated tones (which provided an envelope for additional time analysis). We now know of 3 bat species that cannot use binaural time cues and 2 that can. Further exploration of localization in bats may provide insight into the neural analysis of time cues in species that do not hear low frequencies.     

The luminance conditions of Fuchs's transparency in two-dimensional patterns

Fuchs's transparency occurs when the contour of a transparent surface encloses the contour of another surface located on an underlying homogeneous background. The luminance conditions of Fuchs's transparency have not yet been determined. Six experiments were designed to study this problem with achromatic two-dimensional patterns. An ellipse enclosing a coplanar square was briefly presented. It simulated the cast of an elliptical spotlight or shadow on the square. The duration of the ellipse, the luminance of the square before the ellipse appeared, and the luminance of two squares outside the ellipse did not substantially affect the probability of perceiving the ellipse as transparent. However, this probability varied largely with the single values of the stimulus luminance differences and with the order relations of the stimulus luminances. It is concluded that this local and global luminance information conditioned the occurrence of Fuchs's transparency in two-dimensional patterns.