RSE-box : an analysis and modelling package to study response times to multiple signals

This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC, grant number: BB/N010108/1).Responses to two redundant sensory signals are typically faster than responses to the individual component signals. This redundant signals effect (RSE) is extensively studied not only with an impressive variety of signals but also across different subject populations focusing on development, aging, and many clinical samples. Yet, a standardized methodology to analyse and interpret the RSE is not consistently employed. Moreover, an intriguing explanation of the effect, based on the so-called race model championed by Raab (1962), is typically not fully appreciated in its explanatory power. To facilitate RSE research, here, an analysis and modelling toolbox, called RSE-box, is introduced. It provides MATLAB functions that (1) perform basic analysis steps on response times (RTs), (2) investigate the RSE at the level of RT distributions, (3) fit the most recent race model by Otto and Mamassian (2012), and (4) simulate the RSE with synthetic data. The model functions are accompanied by parameter recovery simulations to test and validate the fitting procedures. An example of the simulation results is the demonstration that the analysis of group RT distributions can be biased. The RSE-box includes demonstration code and all functions are supported by help-documentation.Publisher PDFPeer reviewe

The Fate of Visible Features of Invisible Elements

To investigate the integration of features, we have developed a paradigm in which an element is rendered invisible by visual masking. Still, the features of the element are visible as part of other display elements presented at different locations and times (sequential metacontrast). In this sense, we can “transport” features non-retinotopically across space and time. The features of the invisible element integrate with features of other elements if and only if the elements belong to the same spatio-temporal group. The mechanisms of this kind of feature integration seem to be quite different from classical mechanisms proposed for feature binding. We propose that feature processing, binding, and integration occur concurrently during processes that group elements into wholes

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No selective integration required : a race model explains responses to audiovisual motion-in-depth

T.U.O. was supported by the Biotechnology and Biological Sciences Research Council (BBSRC, grant number: BB/N010108/1). S.F.A.C was partially funded by an Experimental Psychology Society Undergraduate Research Bursary.Looming motion is an ecologically salient signal that often signifies danger. In both audition and vision, humans show behavioral biases in response to perceiving looming motion, which is suggested to indicate an adaptation for survival. However, it is an open question whether such biases occur also in the combined processing of multisensory signals. Towards this aim, Cappe et al. (2009) found that responses to audiovisual signals were faster for congruent looming motion compared to receding motion or incongruent combinations. They considered this as evidence for selective integration of multisensory looming signals. To test this proposal, here, we successfully replicate the behavioral results by Cappe et al. (2009). We then show that the redundant signals effect (RSE - a speedup of multisensory compared to unisensory responses) is not distinct for congruent looming motion. Instead, as predicted by a simple probability summation rule, the RSE is primarily modulated by the looming bias in audition, which suggests that multisensory processing inherits a unisensory effect. Finally, we compare a large set of so-called race models that implement probability summation, but that allow for interference between auditory and visual processing. The best-fitting model, selected by the Akaike Information Criterion (AIC), virtually perfectly explained the RSE across conditions with interference parameters that were either constant or varied only with auditory motion. In the absence of effects jointly caused by auditory and visual motion, we conclude that selective integration is not required to explain the behavioral benefits that occur with audiovisual looming motion.Publisher PDFPeer reviewe

A comparative analysis of response times shows that multisensory benefits and interactions are not equivalent

This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC, grant number: BB/J01446X/1).Multisensory signals allow faster responses than the unisensory components. While this redundant signals effect (RSE) has been studied widely with diverse signals, no modelling approach explored the RSE systematically across studies. For a comparative analysis, here, we propose three steps: The first quantifies the RSE compared to a simple, parameter-free race model. The second quantifies processing interactions beyond the race mechanism: history effects and so-called violations of Miller’s bound. The third models the RSE on the level of response time distributions using a context-variant race model with two free parameters that account for the interactions. Mimicking the diversity of studies, we tested different audio-visual signals that target the interactions using a 2 × 2 design. We show that the simple race model provides overall a strong prediction of the RSE. Regarding interactions, we found that history effects do not depend on low-level feature repetition. Furthermore, violations of Miller’s bound seem linked to transient signal onsets. Critically, the latter dissociates from the RSE, demonstrating that multisensory interactions and multisensory benefits are not equivalent. Overall, we argue that our approach, as a blueprint, provides both a general framework and the precision needed to understand the RSE when studied across diverse signals and participant groups.Publisher PDFPeer reviewe

Grouping based feature attribution in metacontrast masking

The visibility of a target can be strongly suppressed by metacontrast masking. Still, some features of the target can be perceived within the mask. Usually, these rare cases of feature mis-localizations are assumed to reflect errors of the visual system. To the contrary, I will show that feature "mis-localizations" in metacontrast masking follow rules of motion grouping and, hence, should be viewed as part of a systematic feature attribution process

A (fascinating) litmus test for human retino-vs. non-retinotopic processing

In human vision, the optics of the eye map neighboring points of the environment onto neighboring photoreceptors in the retina. This retinotopic encoding principle is preserved in the early visual areas. Under normal viewing conditions, due to the motion of objects and to eye movements, the retinotopic representation of the environment undergoes fast and drastic shifts. Yet, perceptually our environment appears stable suggesting the existence of non-retinotopic representations in addition to the well-known retinotopic ones. Here, we present a simple psychophysical test to determine whether a given visual process is accomplished in retino-or non-retinotopic coordinates. As examples, we show that visual search and motion perception can occur within a non-retinotopic frame of reference. These findings suggest that more mechanisms than previously thought operate non-retinotopically. Whether this is true for a given visual process can easily be found out with our "litmus test.&quot

Plasmodium knowlesi Genome Sequences from Clinical Isolates Reveal Extensive Genomic Dimorphism.

Plasmodium knowlesi is a newly described zoonosis that causes malaria in the human population that can be severe and fatal. The study of P. knowlesi parasites from human clinical isolates is relatively new and, in order to obtain maximum information from patient sample collections, we explored the possibility of generating P. knowlesi genome sequences from archived clinical isolates. Our patient sample collection consisted of frozen whole blood samples that contained excessive human DNA contamination and, in that form, were not suitable for parasite genome sequencing. We developed a method to reduce the amount of human DNA in the thawed blood samples in preparation for high throughput parasite genome sequencing using Illumina HiSeq and MiSeq sequencing platforms. Seven of fifteen samples processed had sufficiently pure P. knowlesi DNA for whole genome sequencing. The reads were mapped to the P. knowlesi H strain reference genome and an average mapping of 90% was obtained. Genes with low coverage were removed leaving 4623 genes for subsequent analyses. Previously we identified a DNA sequence dimorphism on a small fragment of the P. knowlesi normocyte binding protein xa gene on chromosome 14. We used the genome data to assemble full-length Pknbpxa sequences and discovered that the dimorphism extended along the gene. An in-house algorithm was developed to detect SNP sites co-associating with the dimorphism. More than half of the P. knowlesi genome was dimorphic, involving genes on all chromosomes and suggesting that two distinct types of P. knowlesi infect the human population in Sarawak, Malaysian Borneo. We use P. knowlesi clinical samples to demonstrate that Plasmodium DNA from archived patient samples can produce high quality genome data. We show that analyses, of even small numbers of difficult clinical malaria isolates, can generate comprehensive genomic information that will improve our understanding of malaria parasite diversity and pathobiology

Perceptual learning of bisection stimuli under roving: Slow and largely specific

In perceptual learning, performance often improves within a short time if only one stimulus variant is presented, such as a line bisection stimulus with one outer-line-distance. However, performance stagnates if two bisection stimuli with two outerline-distances are presented randomly interleaved. Recently, S. G. Kuai, J. Y. Zhang, S. A. Klein, D. M. Levi, and C. Yu, (2005) proposed that learning under roving conditions is impossible in general. Contrary to this proposition, we show here that perceptual learning with bisection stimuli under roving is possible with extensive training of 18000 trials. Despite this extensive training, the improvement of performance is still largely specific. Furthermore, this improvement of performance cannot be explained by an accommodation to stimulus uncertainty caused by roving