Visual transients reveal the veridical position of a moving object

The position of a moving object is often mislocalised in the direction of movement. At the input stage of visual processing, the position of a moving object should still be represented veridically, whereas it should become closer to the mislocalised position at a later processing stage responsible for positional judgment. Here, we show that visual transients expose the veridical position of a moving object represented in early visual areas. For example, when a ring is flashed on a moving bar, the part of the bar within the ring is perceived at the veridical position, whereas the part outside the ring is perceived to be ahead of the ring as in the flash-lag effect. Our observations suggest that a filling-in process is triggered at the edges of the flash. This indicates that, in early cortical areas, moving objects are still represented at their veridical positions, and the perceived location is determined by the higher visual areas.     

Selection-for-action in visual search

Grasping an object rather than pointing to it enhances processing of its orientation but not its color. Apparently, visual discrimination is selectively enhanced for a behaviorally relevant feature. In two experiments we investigated the limitations and targets of this bias. Specifically, in Experiment 1 we were interested to find out whether the effect is capacity demanding, therefore we manipulated the set-size of the display. The results indicated a clear cognitive processing capacity requirement, i.e. the magnitude of the effect decreased for a larger set size. Consequently, in Experiment 2, we investigated if the enhancement effect occurs only at the level of behaviorally relevant feature or at a level common to different features. Therefore we manipulated the discriminability of the behaviorally neutral feature (color). Again, results showed that this manipulation influenced the action enhancement of the behaviorally relevant feature. Particularly, the effect of the color manipulation on the action enhancement suggests that the action effect is more likely to bias the competition between different visual features rather than to enhance the processing of the relevant feature. We offer a theoretical account that integrates the action-intention effect within the biased competition model of visual selective attention.     

The influence of chromatic and achromatic variability on chromatic induction and perceived colour

Judgments of the colour of a surface are influenced by the colour of the surrounding. To determine whether only the average colour of the surrounding matters, or also the chromatic variability, judgments in colourful scenes are often compared with ones in which a target is surrounded by a plain background that provides the same average physical illumination of the retina as the colourful scene. The variability sometimes makes a difference (eg Shevell and Wei, 1998 Vision Research 38 1561-1566), and sometimes it does not (eg Brenner and Cornelissen, 1998 Vision Research 38 1789-1793). Is this because of the nonlinearity in cone responses? We designed scenes that stimulated the cones in an equivalent manner, both on average and in terms of variability, and yet differed markedly in chromatic variability. The more colourful surroundings had considerably less influence on subjects' colour judgments. We conclude that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and deduce that chromatic induction takes place after contrast gain control.     

The Eyelink Toolbox: Eye tracking with MATLAB and the Psychophysics Toolbox

The Eyelink Toolbox software supports the measurement of eye movements. The toolbox provides an interface between a high-level interpreted language (MATLAB), a visual display programming toolbox (Psychophysics Toolbox), and a video-based eyetracker (Eyelink). The Eyelink Toolbox enables experimenters to measure eye movements while simultaneously executing the stimulus presentation routines provided by the Psychophysics Toolbox. Example programs are included with the toolbox distribution. Information on the Eyelink Toolbox can be found at http://psychtoolbox.org/.     

Using Two-Level Factor Analysis to Test for Cluster Bias in Ordinal Data

The test for cluster bias is a test of measurement invariance across clusters in 2-level data. This article examines the true positive rates (empirical power) and false positive rates of the test for cluster bias using the likelihood ratio test (LRT) and the Wald test with ordinal data. A simulation study indicates that the scaled version of the LRT that accounts for nonnormality of the data gives untrustworthy results, whereas the unscaled LRT and the Wald test have acceptable false positive rates and perform well in terms of empirical power rate if the amount of cluster bias is large. The test for cluster bias is illustrated with data from research on teacher-student relations.     

Expertise-related differences in conceptual and ontological knowledge in the legal domain

Little research has been conducted on expertise-related differences in conceptual and ontological knowledge in law, even though this type of knowledge is prerequisite for correctly interpreting and reasoning about legal cases, and differences in conceptual and ontological knowledge structures between students and between students and teachers, might lead to miscommunication. This study investigated the extent and organisation of conceptual and ontological knowledge of novices, advanced students, and experts in law, using a card-sorting task and a concept-elaboration task. The results showed that novices used more everyday examples and were less accurate in their elaborations of concepts than advanced students and experts, on top of that, the organisation of their knowledge did not overlap within their group (i.e., no “shared” ontology). Experts gave more judicial examples based on the lawbook and were more accurate in their elaborations than advanced students, and their knowledge was strongly overlapping within their group (i.e., strong ontology). Incorrect conceptual knowledge seems to impede the correct understanding of cases and the correct application of precise and formal rules in law.     

Mental Causation and Searle’s Impossible Conception of Unconscious Intentionality

In my article I evaluate Searle’s account of mental causation, in particular his account of the causal efficacy of unconscious intentional states. I argue that top-down causation and overdetermination are unsolved problems in Searle’s philosophy of mind, despite his assurances to the contrary. I also argue that there are conflicting claims involved in his account of mental causation and his account of the unconscious. As a result, it becomes impossible to understand how unconscious intentional states can be causally efficacious. My conclusion will be that if Searle’s conception of unconscious intentionality is to play a genuine role in the causal explanation of human action, it needs to be rethought.     

Cognitive abilities of street children: Low-SES Bolivian boys with and without experience of living in the street

Objectives: This study compared results on cognitive tests measuring nonverbal visualization and reasoning, executive functions, and creativity between 36 boys with experience of living in the street and 31 housed yet socioeconomically equivalent boys, in Bolivia.

Results: The street children scored significantly higher on the creativity measure, which is discussed in relation to contextual relevance. No significant differences were found on the other cognitive tests. Time elapsed after living in the street and drug use were strongly associated with cognition, while age was not. Both groups scored below average compared to Western norms. The results are discussed in terms of the cultural relevance of the tests and the impact of socioeconomic status, stress, and stimulation on cognition.