Ik Soo Lim | Bangor University (original) (raw)

Papers by Ik Soo Lim

Physical Review E

Trusting in others and reciprocating that trust with trustworthy actions are crucial to successfu... more Trusting in others and reciprocating that trust with trustworthy actions are crucial to successful and prosperous societies. The trust game has been widely used to quantitatively study trust and trustworthiness, involving a sequential exchange between an investor and a trustee. Deterministic evolutionary game theory predicts no trust and no trustworthiness, whereas the behavioral experiments with the one-shot anonymous trust game show that people substantially trust and respond trustworthily. To explain these discrepancies, previous works often turn to additional mechanisms, which are borrowed from other games such as the prisoner's dilemma. Although these mechanisms lead to the evolution of trust and trustworthiness to an extent, the optimal or the most common strategy often involves no trustworthiness. In this paper, we study the impact of asymmetric demographic parameters (e.g., different population sizes) on game dynamics of the trust game. We show that, in a weak-mutation limit, stochastic evolutionary dynamics with the asymmetric parameters can lead to the evolution of high trust and high trustworthiness without any additional mechanisms in well-mixed finite populations. Even full trust and near full trustworthiness can be the most common strategies. These results are qualitatively different from those of the previous works. Our results thereby demonstrate rich evolutionary dynamics of the asymmetric trust game.

Physical Review E

Evolutionary game theory has been widely used to study the evolution of cooperation in social dil... more Evolutionary game theory has been widely used to study the evolution of cooperation in social dilemmas where imitation-led strategy updates are typically assumed. However, results of recent behavioral experiments are not compatible with the predictions based on the imitation dynamics, casting doubts on the assumption of the imitation-led updates and calling for alternative mechanisms of strategy updates. An aspiration-led update is often considered as an alternative to the imitationled one. While details of update rules can have significant impacts on the evolutionary outcomes and many variations in imitation-led updates are thus studied, however, few variations exist in aspirationled updates. We introduce an aspiration-led update mechanism ("Satisfied-Defect, Unsatisfied-Cooperate") that is psychologically intuitive and can yield a behavior richer than the conventional aspiration-led update does in Prisoner's Dilemma games. Using analytical and numerical methods, we study and link the stochastic dynamics of it in well-mixed finite populations and the deterministic dynamics of infinite populations.

Computer Graphics Forum

ABSTRACT We present a visualization tool aimed specifically at the development and optimization o... more ABSTRACT We present a visualization tool aimed specifically at the development and optimization of photon map denoising methods. Our tool allows the rapid testing of hypotheses and algorithms through the use of parallel coordinates, domain-specific scripting, colour mapping and point plots. Interaction is carried out by brushing, adjusting parameters and focus-plus-context and yields interactive visual feedback and debugging information. We demonstrate the use of the tool to explore high-dimensional photon map data, facilitating the discovery of novel parameter spaces which can be used to dissociate complex caustic illumination. We then show how these new parametrizations may be used to improve upon pre-existing noise removal methods in the context of the photon relaxation framework.

Animal Behaviour, 2015

The risk-sensitive foraging theory formulated in terms of the (daily) energy budget rule has been... more The risk-sensitive foraging theory formulated in terms of the (daily) energy budget rule has been influential in behavioural ecology as well as other disciplines. Predicting risk aversion on positive budgets and risk proneness on negative budgets, however, the budget rule has recently been challenged both empirically and theoretically. In this paper, we critically review these challenges as well as the original derivation of the budget rule and propose a 'gradual' budget rule, which is normatively derived from a gradual nature of risk sensitivity and encompasses the conventional budget rule as a special case. The gradual budget rule shows that the conventional budget rule holds when the expected reserve is close enough to a threshold for overnight survival, selection pressure being significant. The gradual view also reveals that the conventional budget rule does not need to hold when the expected reserve is not close enough to the threshold, selection pressure being insignificant. The proposed gradual budget rule better fits the empirical findings including those that used to challenge the conventional budget rule.

We grve a neural net approach to correcting the image distortions produced by camera configuratio... more We grve a neural net approach to correcting the image distortions produced by camera configurations, to produce a geometrically 'ideal' image. The network learns by comparison of actual and desired versions of response to standard inputs, and then produces corrected versions of arbitrary images. The correction system once learned is rapid, and easy to configure into a chip for the particular camera. Correcting a new camera requires only an automated Iearning process, not an engineering analysis of the sources of error.

IEEE Geoscience and Remote Sensing Letters, 2015

Hyperspectral image visualization reduces color bands to three, but prevailing linear methods fai... more Hyperspectral image visualization reduces color bands to three, but prevailing linear methods fail to address data characteristics, and nonlinear embeddings are computationally demanding. Qualitative evaluation of embedding is also lacking. We propose faithful stochastic proximity embedding (FSPE), which is a scalable and nonlinear dimensionality reduction method. FSPE considers the nonlinear characteristics of spectral signatures, yet it avoids the costly computation of geodesic distances that are often required by other nonlinear methods. Furthermore, we employ a pixelwise metric that measures the quality of hyperspectral image visualization at each pixel. FSPE outperforms the state-of-art methods by at least 12% on average and up to 25% in the qualitative measure. An implementation on graphics processing units is two orders of magnitude faster than the baseline. Our method opens the path to high-fidelity and real-time analysis of hyperspectral images.

Studies in health technology and informatics, 2008

Recent years have seen a significant increase in the use of Interventional Radiology (IR) as an a... more Recent years have seen a significant increase in the use of Interventional Radiology (IR) as an alternative to open surgery. A large number of IR procedures commences with needle puncture of a vessel to insert guidewires and catheters: these clinical skills are acquired by all radiologists during training on patients, associated with some discomfort and occasionally, complications. While some visual skills can be acquired using models such as the ones used in surgery, these have limitations for IR which relies heavily on a sense of touch. Both patients and trainees would benefit from a virtual environment (VE) conveying touch sensation to realistically mimic procedures. The authors are developing a high fidelity VE providing a validated alternative to the traditional apprenticeship model used for teaching the core skills. The current version of the CRaIVE simulator combines home made software, haptic devices and commercial equipments.

Proceedings of ICNN'95 - International Conference on Neural Networks, 1995

Simple mechanisms of synaptic plasticity are examined to enable a chaotic neuml unit to learn set... more Simple mechanisms of synaptic plasticity are examined to enable a chaotic neuml unit to learn sets of prescribed stable outputs, in spite of the unit's dynamics having various behavioral regimes lake those observed experimentally in neurons.

2009 IEEE International Conference on Acoustics, Speech and Signal Processing, 2009

Proceedings of the 2000 ACM symposium on Applied computing - SAC '00, 2000

Proceedings of the 2000 ACM symposium on Applied computing - SAC '00, 2000

Presentation of audio or video files for browsing is dif-ficult due to their serial and transitor... more Presentation of audio or video files for browsing is dif-ficult due to their serial and transitory nature whereas texts or photos may be simply placed in the user's visual field. This paper describes a simple technique for brows-ing and selecting among temporal signals such as audio ...

Deformable Avatars, 2001

We approach the problem of example-based motion synthesis by transforming motion data into a vect... more We approach the problem of example-based motion synthesis by transforming motion data into a vector space representation. This allows many techniques successful for stationary object synthesis applicable to that of motion. Especially, by separating generation of motion into a time-consuming preprocess and a fast process, it lets on-the-fly motion synthesis able to use a rich set of examplar motions and handle motion attributes invariant for each individual, both of which are difficult to be addressed by previous approaches based on interpolation. * This work is supported in part by PAVR under the EU Training and Mobility of Researchers program. † Thanks to Norman Badler for helpful discussions.

Eurographics, 1999

This paper addresses the issue of allowing a user more control over the outcomes of interactive e... more This paper addresses the issue of allowing a user more control over the outcomes of interactive evolution for computer animation, a variation on genetic algorithms. By using a point-for-point representation for genotype, the control both in selection and variation process is possible while the genotype represented by procedural rules in previous works allows it only in the selection. We experimentally validate these points on generating different walk styles out of a prototype walk motion and also discuss about interactive evolution to be used as a general approach to setting parameters for computer graphics.

Journal of Visual Communication in Medicine, 2007

The medical domain provides excellent opportunities for communication and teaching of healthcare ... more The medical domain provides excellent opportunities for communication and teaching of healthcare issues using computer graphics, visualization techniques, and virtual environments. Possible applications include anatomical educational tools; patient education; diagnostic aids; virtual autopsies; planning and guidance aids; skills training; and computer augmented reality. Both clinicians and patients can benefit from the appropriate use of tools that make use of these technologies. This paper provides an overview of the state-of-the-art technologies in this exciting field, including detailed examples from our research. The term cybermedicine is discussed and issues for effective cybermedicine are highlighted.

A forager in a patchy environment faces two types of uncertainty: ambiguity regarding the quality... more A forager in a patchy environment faces two types of uncertainty: ambiguity regarding the quality of the current patch and risk associated with the background opportunities. We argue that the order in which the forager deals with these uncertainties has an impact on the decision whether to stay at the current patch. The order effect is formalised with a context-dependent quantum probabilistic framework. Using Heisenberg's uncertainty principle, we demonstrate the two types of uncertainty cannot be simultaneously minimised, hence putting a formal limit on rationality in decision making. We show the applicability of the contextual decision function with agent-based modelling. The simulations reveal order-dependence. Given that foraging is a universal pattern that goes beyond animal behaviour, the findings help understand similar phenomena in other fields.

Computer Vision Theory and Applications, 2008

In many applications it is necessary to segment the foreground of an image from the background. H... more In many applications it is necessary to segment the foreground of an image from the background. However images from microscope slides illuminated using transmitted light have uneven background light levels. The non-uniform illumination makes segmentation difficult. We propose to fit a set of parabolas in order to segment the image into background and foreground. Parabolas are fitted separately on horizontal and vertical stripes of the grey level intensity image. A pixel is labelled as background or foreground based on the two corresponding parabolas. The proposed method outperforms the following four standard segmentation techniques, (1) thresholding determined manually or by fitting a mixture of Gaussians, (2) clustering in the RGB space, (3) fitting a two-argument quadratic function on the whole image and (4) using the morphological closure method.

2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007

We present a context-preserving visualisation method for segmented volumetric medical images. A s... more We present a context-preserving visualisation method for segmented volumetric medical images. A segmented volumetric image contains a number of anatomical objects which are important features to be visualised. Our context-preserving rendering utilises the curvature at the surfaces of the segmentation objects to modulate the opacity contribution during rendering. This results in the areas of high curvature, typically the most important features, being opaque and visible while everything else being transparent.

Physical Review E

Trusting in others and reciprocating that trust with trustworthy actions are crucial to successfu... more Trusting in others and reciprocating that trust with trustworthy actions are crucial to successful and prosperous societies. The trust game has been widely used to quantitatively study trust and trustworthiness, involving a sequential exchange between an investor and a trustee. Deterministic evolutionary game theory predicts no trust and no trustworthiness, whereas the behavioral experiments with the one-shot anonymous trust game show that people substantially trust and respond trustworthily. To explain these discrepancies, previous works often turn to additional mechanisms, which are borrowed from other games such as the prisoner's dilemma. Although these mechanisms lead to the evolution of trust and trustworthiness to an extent, the optimal or the most common strategy often involves no trustworthiness. In this paper, we study the impact of asymmetric demographic parameters (e.g., different population sizes) on game dynamics of the trust game. We show that, in a weak-mutation limit, stochastic evolutionary dynamics with the asymmetric parameters can lead to the evolution of high trust and high trustworthiness without any additional mechanisms in well-mixed finite populations. Even full trust and near full trustworthiness can be the most common strategies. These results are qualitatively different from those of the previous works. Our results thereby demonstrate rich evolutionary dynamics of the asymmetric trust game.

Physical Review E

Evolutionary game theory has been widely used to study the evolution of cooperation in social dil... more Evolutionary game theory has been widely used to study the evolution of cooperation in social dilemmas where imitation-led strategy updates are typically assumed. However, results of recent behavioral experiments are not compatible with the predictions based on the imitation dynamics, casting doubts on the assumption of the imitation-led updates and calling for alternative mechanisms of strategy updates. An aspiration-led update is often considered as an alternative to the imitationled one. While details of update rules can have significant impacts on the evolutionary outcomes and many variations in imitation-led updates are thus studied, however, few variations exist in aspirationled updates. We introduce an aspiration-led update mechanism ("Satisfied-Defect, Unsatisfied-Cooperate") that is psychologically intuitive and can yield a behavior richer than the conventional aspiration-led update does in Prisoner's Dilemma games. Using analytical and numerical methods, we study and link the stochastic dynamics of it in well-mixed finite populations and the deterministic dynamics of infinite populations.

Computer Graphics Forum

ABSTRACT We present a visualization tool aimed specifically at the development and optimization o... more ABSTRACT We present a visualization tool aimed specifically at the development and optimization of photon map denoising methods. Our tool allows the rapid testing of hypotheses and algorithms through the use of parallel coordinates, domain-specific scripting, colour mapping and point plots. Interaction is carried out by brushing, adjusting parameters and focus-plus-context and yields interactive visual feedback and debugging information. We demonstrate the use of the tool to explore high-dimensional photon map data, facilitating the discovery of novel parameter spaces which can be used to dissociate complex caustic illumination. We then show how these new parametrizations may be used to improve upon pre-existing noise removal methods in the context of the photon relaxation framework.

Animal Behaviour, 2015

The risk-sensitive foraging theory formulated in terms of the (daily) energy budget rule has been... more The risk-sensitive foraging theory formulated in terms of the (daily) energy budget rule has been influential in behavioural ecology as well as other disciplines. Predicting risk aversion on positive budgets and risk proneness on negative budgets, however, the budget rule has recently been challenged both empirically and theoretically. In this paper, we critically review these challenges as well as the original derivation of the budget rule and propose a 'gradual' budget rule, which is normatively derived from a gradual nature of risk sensitivity and encompasses the conventional budget rule as a special case. The gradual budget rule shows that the conventional budget rule holds when the expected reserve is close enough to a threshold for overnight survival, selection pressure being significant. The gradual view also reveals that the conventional budget rule does not need to hold when the expected reserve is not close enough to the threshold, selection pressure being insignificant. The proposed gradual budget rule better fits the empirical findings including those that used to challenge the conventional budget rule.

We grve a neural net approach to correcting the image distortions produced by camera configuratio... more We grve a neural net approach to correcting the image distortions produced by camera configurations, to produce a geometrically 'ideal' image. The network learns by comparison of actual and desired versions of response to standard inputs, and then produces corrected versions of arbitrary images. The correction system once learned is rapid, and easy to configure into a chip for the particular camera. Correcting a new camera requires only an automated Iearning process, not an engineering analysis of the sources of error.

IEEE Geoscience and Remote Sensing Letters, 2015

Hyperspectral image visualization reduces color bands to three, but prevailing linear methods fai... more Hyperspectral image visualization reduces color bands to three, but prevailing linear methods fail to address data characteristics, and nonlinear embeddings are computationally demanding. Qualitative evaluation of embedding is also lacking. We propose faithful stochastic proximity embedding (FSPE), which is a scalable and nonlinear dimensionality reduction method. FSPE considers the nonlinear characteristics of spectral signatures, yet it avoids the costly computation of geodesic distances that are often required by other nonlinear methods. Furthermore, we employ a pixelwise metric that measures the quality of hyperspectral image visualization at each pixel. FSPE outperforms the state-of-art methods by at least 12% on average and up to 25% in the qualitative measure. An implementation on graphics processing units is two orders of magnitude faster than the baseline. Our method opens the path to high-fidelity and real-time analysis of hyperspectral images.

Studies in health technology and informatics, 2008

Recent years have seen a significant increase in the use of Interventional Radiology (IR) as an a... more Recent years have seen a significant increase in the use of Interventional Radiology (IR) as an alternative to open surgery. A large number of IR procedures commences with needle puncture of a vessel to insert guidewires and catheters: these clinical skills are acquired by all radiologists during training on patients, associated with some discomfort and occasionally, complications. While some visual skills can be acquired using models such as the ones used in surgery, these have limitations for IR which relies heavily on a sense of touch. Both patients and trainees would benefit from a virtual environment (VE) conveying touch sensation to realistically mimic procedures. The authors are developing a high fidelity VE providing a validated alternative to the traditional apprenticeship model used for teaching the core skills. The current version of the CRaIVE simulator combines home made software, haptic devices and commercial equipments.

Proceedings of ICNN'95 - International Conference on Neural Networks, 1995

Simple mechanisms of synaptic plasticity are examined to enable a chaotic neuml unit to learn set... more Simple mechanisms of synaptic plasticity are examined to enable a chaotic neuml unit to learn sets of prescribed stable outputs, in spite of the unit's dynamics having various behavioral regimes lake those observed experimentally in neurons.

2009 IEEE International Conference on Acoustics, Speech and Signal Processing, 2009

Proceedings of the 2000 ACM symposium on Applied computing - SAC '00, 2000

Proceedings of the 2000 ACM symposium on Applied computing - SAC '00, 2000

Presentation of audio or video files for browsing is dif-ficult due to their serial and transitor... more Presentation of audio or video files for browsing is dif-ficult due to their serial and transitory nature whereas texts or photos may be simply placed in the user's visual field. This paper describes a simple technique for brows-ing and selecting among temporal signals such as audio ...

Deformable Avatars, 2001

We approach the problem of example-based motion synthesis by transforming motion data into a vect... more We approach the problem of example-based motion synthesis by transforming motion data into a vector space representation. This allows many techniques successful for stationary object synthesis applicable to that of motion. Especially, by separating generation of motion into a time-consuming preprocess and a fast process, it lets on-the-fly motion synthesis able to use a rich set of examplar motions and handle motion attributes invariant for each individual, both of which are difficult to be addressed by previous approaches based on interpolation. * This work is supported in part by PAVR under the EU Training and Mobility of Researchers program. † Thanks to Norman Badler for helpful discussions.

Eurographics, 1999

This paper addresses the issue of allowing a user more control over the outcomes of interactive e... more This paper addresses the issue of allowing a user more control over the outcomes of interactive evolution for computer animation, a variation on genetic algorithms. By using a point-for-point representation for genotype, the control both in selection and variation process is possible while the genotype represented by procedural rules in previous works allows it only in the selection. We experimentally validate these points on generating different walk styles out of a prototype walk motion and also discuss about interactive evolution to be used as a general approach to setting parameters for computer graphics.

Journal of Visual Communication in Medicine, 2007

The medical domain provides excellent opportunities for communication and teaching of healthcare ... more The medical domain provides excellent opportunities for communication and teaching of healthcare issues using computer graphics, visualization techniques, and virtual environments. Possible applications include anatomical educational tools; patient education; diagnostic aids; virtual autopsies; planning and guidance aids; skills training; and computer augmented reality. Both clinicians and patients can benefit from the appropriate use of tools that make use of these technologies. This paper provides an overview of the state-of-the-art technologies in this exciting field, including detailed examples from our research. The term cybermedicine is discussed and issues for effective cybermedicine are highlighted.

A forager in a patchy environment faces two types of uncertainty: ambiguity regarding the quality... more A forager in a patchy environment faces two types of uncertainty: ambiguity regarding the quality of the current patch and risk associated with the background opportunities. We argue that the order in which the forager deals with these uncertainties has an impact on the decision whether to stay at the current patch. The order effect is formalised with a context-dependent quantum probabilistic framework. Using Heisenberg's uncertainty principle, we demonstrate the two types of uncertainty cannot be simultaneously minimised, hence putting a formal limit on rationality in decision making. We show the applicability of the contextual decision function with agent-based modelling. The simulations reveal order-dependence. Given that foraging is a universal pattern that goes beyond animal behaviour, the findings help understand similar phenomena in other fields.

Computer Vision Theory and Applications, 2008

In many applications it is necessary to segment the foreground of an image from the background. H... more In many applications it is necessary to segment the foreground of an image from the background. However images from microscope slides illuminated using transmitted light have uneven background light levels. The non-uniform illumination makes segmentation difficult. We propose to fit a set of parabolas in order to segment the image into background and foreground. Parabolas are fitted separately on horizontal and vertical stripes of the grey level intensity image. A pixel is labelled as background or foreground based on the two corresponding parabolas. The proposed method outperforms the following four standard segmentation techniques, (1) thresholding determined manually or by fitting a mixture of Gaussians, (2) clustering in the RGB space, (3) fitting a two-argument quadratic function on the whole image and (4) using the morphological closure method.

2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007

We present a context-preserving visualisation method for segmented volumetric medical images. A s... more We present a context-preserving visualisation method for segmented volumetric medical images. A segmented volumetric image contains a number of anatomical objects which are important features to be visualised. Our context-preserving rendering utilises the curvature at the surfaces of the segmentation objects to modulate the opacity contribution during rendering. This results in the areas of high curvature, typically the most important features, being opaque and visible while everything else being transparent.