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1.  Grouping in object recognition: The role of a Gestalt law in letter identification 
Cognitive Neuropsychology  2009;26(1):36-49.
The Gestalt psychologists reported a set of laws describing how vision groups elements to recognize objects. The Gestalt laws “prescribe for us what we are to recognize ‘as one thing’” (Köhler, 1920). Were they right? Does object recognition involve grouping? Tests of the laws of grouping have been favourable, but mostly assessed only detection, not identification, of the compound object. The grouping of elements seen in the detection experiments with lattices and “snakes in the grass” is compelling, but falls far short of the vivid everyday experience of recognizing a familiar, meaningful, named thing, which mediates the ordinary identification of an object. Thus, after nearly a century, there is hardly any evidence that grouping plays a role in ordinary object recognition. To assess grouping in object recognition, we made letters out of grating patches and measured threshold contrast for identifying these letters in visual noise as a function of perturbation of grating orientation, phase, and offset. We define a new measure, “wiggle”, to characterize the degree to which these various perturbations violate the Gestalt law of good continuation. We find that efficiency for letter identification is inversely proportional to wiggle and is wholly determined by wiggle, independent of how the wiggle was produced. Thus the effects of three different kinds of shape perturbation on letter identifiability are predicted by a single measure of goodness of continuation. This shows that letter identification obeys the Gestalt law of good continuation and may be the first confirmation of the original Gestalt claim that object recognition involves grouping.
PMCID: PMC2679997  PMID: 19424881
Gestalt; Grouping; Contour integration; Good continuation; Letter identification; Object recognition; Features; Snake in the grass; Snake letters; Dot lattice
2.  The same binding in contour integration and crowding 
Journal of vision  2011;11(8):10.1167/11.8.10 10.
Binding of features helps object recognition in contour integration, but hinders it in crowding. In contour integration, aligned adjacent objects group together to form a path. In crowding, flanking objects make the target unidentifiable. But, to date, the two tasks have only been studied separately. May and Hess (2007) suggested that the same binding mediates both tasks. To test this idea, we ask observers to perform two different tasks with the same stimulus. We present oriented grating patches that form a “snake letter” in the periphery. Observers report either the identity of the whole letter (contour integration task) or the phase of one of the grating patches (crowding task). We manipulate the strength of binding between gratings by varying the alignment between them, i.e. the Gestalt goodness of continuation, measured as “wiggle”. We find that better alignment strengthens binding, which improves contour integration and worsens crowding. Observers show equal sensitivity to alignment in these two very different tasks, suggesting that the same binding mechanism underlies both phenomena. It has been claimed that grouping among flankers reduces their crowding of the target. Instead, we find that these published cases of weak crowding are due to weak binding resulting from target-flanker misalignment. We conclude that crowding is mediated solely by the grouping of flankers with the target and is independent of grouping among flankers.
PMCID: PMC3624759  PMID: 21757504
crowding; wiggle; grouping; binding; Gestalt; contour integration; good continuation; alignment; object recognition; snake letter
3.  A Century of Gestalt Psychology in Visual Perception I. Perceptual Grouping and Figure-Ground Organization 
Psychological bulletin  2012;138(6):1172-1217.
In 1912, Max Wertheimer published his paper on phi motion, widely recognized as the start of Gestalt psychology. Because of its continued relevance in modern psychology, this centennial anniversary is an excellent opportunity to take stock of what Gestalt psychology has offered and how it has changed since its inception. We first introduce the key findings and ideas in the Berlin school of Gestalt psychology, and then briefly sketch its development, rise, and fall. Next, we discuss its empirical and conceptual problems, and indicate how they are addressed in contemporary research on perceptual grouping and figure-ground organization. In particular, we review the principles of grouping, both classical (e.g., proximity, similarity, common fate, good continuation, closure, symmetry, parallelism) and new (e.g., synchrony, common region, element and uniform connectedness), and their role in contour integration and completion. We then review classic and new image-based principles of figure-ground organization, how it is influenced by past experience and attention, and how it relates to shape and depth perception. After an integrated review of the neural mechanisms involved in contour grouping, border-ownership, and figure-ground perception, we conclude by evaluating what modern vision science has offered compared to traditional Gestalt psychology, whether we can speak of a Gestalt revival, and where the remaining limitations and challenges lie. A better integration of this research tradition with the rest of vision science requires further progress regarding the conceptual and theoretical foundations of the Gestalt approach, which will be the focus of a second review paper.
PMCID: PMC3482144  PMID: 22845751
Gestalt; grouping principles; figure-ground organization; neural mechanisms; vision science
4.  Integrating Biological Motion: The Role of Grouping in the Perception of Point-Light Actions 
PLoS ONE  2011;6(10):e25867.
The human visual system is highly sensitive to biological motion and manages to organize even a highly reduced point-light stimulus into a vivid percept of human action. The current study investigated to what extent the origin of this saliency of point-light displays is related to its intrinsic Gestalt qualities. In particular, we studied whether biological motion perception is facilitated when the elements can be grouped according to good continuation and similarity as Gestalt principles of perceptual organization. We found that both grouping principles enhanced biological motion perception but their effects differed when stimuli were inverted. These results provide evidence that Gestalt principles of good continuity and similarity also apply to more complex and dynamic meaningful stimuli.
PMCID: PMC3185055  PMID: 21991376
5.  Bilateral Theta-Burst TMS to Influence Global Gestalt Perception 
PLoS ONE  2012;7(10):e47820.
While early and higher visual areas along the ventral visual pathway in the inferotemporal cortex are critical for the recognition of individual objects, the neural representation of human perception of complex global visual scenes remains under debate. Stroke patients with a selective deficit in the perception of a complex global Gestalt with intact recognition of individual objects – a deficit termed simultanagnosia – greatly helped to study this question. Interestingly, simultanagnosia typically results from bilateral lesions of the temporo-parietal junction (TPJ). The present study aimed to verify the relevance of this area for human global Gestalt perception. We applied continuous theta-burst TMS either unilaterally (left or right) or bilateral simultaneously over TPJ. Healthy subjects were presented with hierarchically organized visual stimuli that allowed parametrical degrading of the object at the global level. Identification of the global Gestalt was significantly modulated only for the bilateral TPJ stimulation condition. Our results strengthen the view that global Gestalt perception in the human brain involves TPJ and is co-dependent on both hemispheres.
PMCID: PMC3482242  PMID: 23110106
6.  Come Together, Right Now: Dynamic Overwriting of an Object’s History through Common Fate 
Journal of cognitive neuroscience  2014;26(8):1819-1828.
The objects around us constantly move and interact, and the perceptual system needs to monitor on-line these interactions and to update the object’s status accordingly. Gestalt grouping principles, such as proximity and common fate, play a fundamental role in how we perceive and group these objects. Here, we investigated situations in which the initial object representation as a separate item was updated by a subsequent Gestalt grouping cue (i.e., proximity or common fate). We used a version of the color change detection paradigm, in which the objects started to move separately, then met and stayed stationary, or moved separately, met, and then continued to move together. We monitored the object representations on-line using the contralateral delay activity (CDA; an ERP component indicative of the number of maintained objects), during their movement, and after the objects disappeared and became working memory representations. The results demonstrated that the objects’ representations (as indicated by the CDA amplitude) persisted as being separate, even after a Gestalt proximity cue (when the objects “met” and remained stationary on the same position). Only a strong common fate Gestalt cue (when the objects not just met but also moved together) was able to override the objects’ initial separate status, creating an integrated representation. These results challenge the view that Gestalt principles cause reflexive grouping. Instead, the object initial representation plays an important role that can override even powerful grouping cues.
PMCID: PMC4486205  PMID: 24564468
7.  A Century of Gestalt Psychology in Visual Perception II. Conceptual and Theoretical Foundations 
Psychological bulletin  2012;138(6):1218-1252.
Our first review paper on the occasion of the centennial anniversary of Gestalt psychology focused on perceptual grouping and figure-ground organization. It concluded that further progress requires a reconsideration of the conceptual and theoretical foundations of the Gestalt approach, which is provided here. In particular, we review contemporary formulations of holism within an information-processing framework, allowing for operational definitions (e.g., integral dimensions, emergent features, configural superiority, global precedence, primacy of holistic/configural properties) and a refined understanding of its psychological implications (e.g., at the level of attention, perception, and decision). We also review four lines of theoretical progress regarding the law of Prägnanz—the brain’s tendency of being attracted towards states corresponding to the simplest possible organization, given the available stimulation. The first considers the brain as a complex adaptive system and explains how self-organization solves the conundrum of trading between robustness and flexibility of perceptual states. The second specifies the economy principle in terms of optimization of neural resources, showing that elementary sensors working independently to minimize uncertainty can respond optimally at the system level. The third considers how Gestalt percepts (e.g., groups, objects) are optimal given the available stimulation, with optimality specified in Bayesian terms. Fourth, Structural Information Theory explains how a Gestaltist visual system that focuses on internal coding efficiency yields external veridicality as a side-effect. To answer the fundamental question of why things look as they do, a further synthesis of these complementary perspectives is required.
PMCID: PMC3728284  PMID: 22845750
Gestalt; holism; simplicity versus likelihood; dynamical systems; information theory
8.  Colony insularity through queen control on worker social motivation in ants. 
We investigated the relative contribution of the queen and workers to colony nestmate recognition cues and on colony insularity in the Carpenter ant Camponotus fellah. Workers were either individually isolated, preventing contact with both queen and workers (colonial deprived, CD), kept in queenless groups, allowing only worker-worker interactions (queen deprived, QD) or in queenright (QR) groups. Two weeks post-separation QD and QR workers were amicable towards each other but both rejected their CD nestmates, which suggests that the queen does not measurably influence the colony recognition cues. By contrast, aggression between QD and QR workers from the same original colony was apparent only after six months of separation. This clearly demonstrates the power of the Gestalt and indicates that the queen is not a dominant contributor to the nestmate recognition cues in this species. Aggression between nestmates was correlated with a greater hydrocarbon (HC) profile divergence for CD than for QD and QR workers, supporting the importance of worker-worker interactions in maintaining the colony Gestalt odour. While the queen does not significantly influence nestmate recognition cues, she does influence colony insularity since within 3 days QD (queenless for six months) workers from different colony origins merged to form a single queenless colony. By contrast, the corresponding QR colonies maintained their territoriality and did not merge. The originally divergent cuticular and postpharyngeal gland HC profiles became congruent following the merger. Therefore, while workers supply and blend the recognition signal, the queen affects worker-worker interaction by reducing social motivation and tolerance of alien conspecifics.
PMCID: PMC1691331  PMID: 12803913
9.  Defining the units of competition: Influences of perceptual organization on competitive interactions in human visual cortex 
Journal of cognitive neuroscience  2010;22(11):2417-2426.
Multiple stimuli that are present simultaneously in the visual field compete for neural representation. At the same time, however multiple stimuli in cluttered scenes also undergo perceptual organization according to certain rules originally defined by the Gestalt psychologists such as similarity or proximity, thereby segmenting scenes into candidate objects. How can these two seemingly orthogonal neural processes that occur early in the visual processing stream be reconciled? One possibility is that competition occurs among perceptual groups, rather than at the level of elements within a group. We probed this idea using fMRI by assessing competitive interactions across visual cortex in displays containing varying degrees of perceptual organization, or perceptual grouping (Grp). In strong Grp displays, elements were arranged such that either an illusory figure or a group of collinear elements were present, while in weak Grp displays the same elements were arranged randomly. Competitive interactions among stimuli were overcome throughout early visual cortex and V4, when elements were grouped regardless of Grp type. Our findings suggest that context-dependent grouping mechanisms and competitive interactions are linked to provide a bottom-up bias towards candidate objects in cluttered scenes.
PMCID: PMC2891594  PMID: 19925189
10.  Computed tomography-based diagnosis of diffuse compensatory enlargement of coronary arteries using scaling power laws 
Glagov's positive remodelling in the early stages of coronary atherosclerosis often results in plaque rupture and acute events. Because positive remodelling is generally diffused along the epicardial coronary arterial tree, it is difficult to diagnose non-invasively. Hence, the objective of the study is to assess the use of scaling power law for the diagnosis of positive remodelling of coronary arteries based on computed tomography (CT) images. Epicardial coronary arterial trees were reconstructed from CT scans of six Ossabaw pigs fed on a high-fat, high-cholesterol, atherogenic diet for eight months as well as the same number of body-weight-matched farm pigs fed on a lean chow (101.9±16.1 versus 91.5±13.1 kg). The high-fat diet Ossabaw pig model showed diffuse positive remodelling of epicardial coronary arteries. Good fit of measured coronary data to the length–volume scaling power law ( where Lc and Vc are crown length and volume) were found for both the high-fat and control groups (R2 = 0.95±0.04 and 0.99±0.01, respectively). The coefficient, KLV, decreased significantly in the high-fat diet group when compared with the control (14.6±2.6 versus 40.9±5.6). The flow–length scaling power law, however, was nearly unaffected by the positive remodelling. The length–volume and flow–length scaling power laws were preserved in epicardial coronary arterial trees after positive remodelling. KLV < 18 in the length–volume scaling relation is a good index of positive remodelling of coronary arteries. These findings provide a clinical rationale for simple, accurate and non-invasive diagnosis of positive remodelling of coronary arteries, using conventional CT scans.
PMCID: PMC3627114  PMID: 23365197
coronary compensatory enlargement; scaling power law; computed tomography
11.  Feasibility and Diagnostic Accuracy of Brief Health Literacy and Numeracy Screening Instruments in an Urban Emergency Department 
To evaluate the diagnostic accuracy of five health literacy screening instruments in emergency department (ED) patients: the Rapid Evaluation of Adult Literacy in Medicine-Revised (REALM-R), the Newest Vital Sign (NVS), Single Item Literacy Screens (SILS), health numeracy, and physician gestalt. A secondary objective was to evaluate the feasibility of these instruments as measured by administration time, time on task, and interruptions during test administration.
This was a prospective observational cross-sectional study of a convenience sampling of adult patients presenting during March 2011 and February 2012 to one urban university-affiliated ED. Subjects were consenting non-critically ill, English-speaking patients over the age of 18 years without aphasia, dementia, mental retardation, or inability to communicate. The diagnostic test characteristics of the REALM-R, NVS, SILS, health numeracy, and physician gestalt were quantitatively assessed by using the short Test of Functional Health Literacy in Adults (S-TOHFLA). A score of 22 or less was the criterion standard for limited health literacy (LHL).
Four hundred thirty-five participants were enrolled, with mean age of 45 years (SD ±15.7 years) and 18% had less than a high school education. As defined by an S-TOHFLA score of 22 or less, the prevalence of LHL was 23.9%. In contrast, the NVS, REALM-R, and physician gestalt identified 64.8%, 48.5%, and 35% of participants as LHL, respectively. A normal NVS screen was the most useful test to exclude LHL, with a negative likelihood ratio of 0.04 (95% CI = 0.01 to 0.17). When abnormal, none of the screening instruments, including physician gestalt, significantly increased the post-test probability of LHL. The NVS and REALM-R require 3 and 5 minutes less time to administer than the S-TOHFLA. Administration of the REALM-R is associated with less test interruptions.
One-quarter of these ED patients had marginal or inadequate health literacy. Among the brief screening instruments evaluated, a normal Newest Vital Sign result accurately reduced the probability of limited health literacy, although it will identify two-thirds of ED patients as high-risk for limited health literacy. None of the brief screening instruments significantly increases the probability of limited health literacy when abnormal.
PMCID: PMC4042843  PMID: 24673669
12.  Relations among early object recognition skills: Objects and letters 
Human visual object recognition is multifaceted, with several domains of expertise. Developmental relations between young children's letter recognition and their 3-dimensional object recognition abilities are implicated on several grounds but have received little research attention. Here, we ask how preschoolers’ success in recognizing letters relates to their ability to recognize 3-dimensional objects from sparse shape information alone. A relation is predicted because perception of the spatial relations is critical in both domains. Seventy-three 2 ½- to 4-year-old children completed a Letter Recognition task, measuring the ability to identify a named letter among 3 letters with similar shapes, and a “Shape Caricature Recognition” task, measuring recognition of familiar objects from sparse, abstract information about their part shapes and the spatial relations among those parts. Children also completed a control “Shape Bias” task, in which success depends on recognition of overall object shape but not of relational structure. Children's success in letter recognition was positively related to their shape caricature recognition scores, but not to their shape bias scores. The results suggest that letter recognition builds upon developing skills in attending to and representing the relational structure of object shape, and that these skills are common to both 2-dimensional and 3-dimensional object perception.
PMCID: PMC4426263  PMID: 25969673
shape caricatures; letter recognition; object recognition
13.  Learning to Identify Near-Acuity Letters, either with or without Flankers, Results in Improved Letter Size and Spacing Limits in Adults with Amblyopia 
PLoS ONE  2012;7(4):e35829.
Amblyopia is a developmental abnormality that results in deficits for a wide range of visual tasks, most notably, the reduced ability to see fine details, the loss in contrast sensitivity especially for small objects and the difficulty in seeing objects in clutter (crowding). The primary goal of this study was to evaluate whether crowding can be ameliorated in adults with amblyopia through perceptual learning using a flanked letter identification task that was designed to reduce crowding, and if so, whether the improvements transfer to untrained visual functions: visual acuity, contrast sensitivity and the size of visual span (the amount of information obtained in one fixation). To evaluate whether the improvements following this training task were specific to training with flankers, we also trained another group of adult observers with amblyopia using a single letter identification task that was designed to improve letter contrast sensitivity, not crowding. Following 10,000 trials of training, both groups of observers showed improvements in the respective training task. The improvements generalized to improved visual acuity, letter contrast sensitivity, size of the visual span, and reduced crowding. The magnitude of the improvement for each of these measurements was similar in the two training groups. Perceptual learning regimens aimed at reducing crowding or improving letter contrast sensitivity are both effective in improving visual acuity, contrast sensitivity for near-acuity objects and reducing the crowding effect, and could be useful as a clinical treatment for amblyopia.
PMCID: PMC3340394  PMID: 22558234
14.  Averaging facial expression over time 
Journal of vision  2009;9(11):1.1-113.
The visual system groups similar features, objects, and motion (e.g., Gestalt grouping). Recent work suggests that the computation underlying perceptual grouping may be one of summary statistical representation. Summary representation occurs for low-level features, such as size, motion, and position, and even for high level stimuli, including faces; for example, observers accurately perceive the average expression in a group of faces (J. Haberman & D. Whitney, 2007, 2009). The purpose of the present experiments was to characterize the time-course of this facial integration mechanism. In a series of three experiments, we measured observers’ abilities to recognize the average expression of a temporal sequence of distinct faces. Faces were presented in sets of 4, 12, or 20, at temporal frequencies ranging from 1.6 to 21.3 Hz. The results revealed that observers perceived the average expression in a temporal sequence of different faces as precisely as they perceived a single face presented repeatedly. The facial averaging was independent of temporal frequency or set size, but depended on the total duration of exposed faces, with a time constant of ~800 ms. These experiments provide evidence that the visual system is sensitive to the ensemble characteristics of complex objects presented over time.
PMCID: PMC2857387  PMID: 20053064
vision; perception; face; object recognition; temporal integration; texture; spatial vision
15.  Top-Down Control in Contour Grouping 
PLoS ONE  2013;8(1):e54085.
Human observers tend to group oriented line segments into full contours if they follow the Gestalt rule of 'good continuation'. It is commonly assumed that contour grouping emerges automatically in early visual cortex. In contrast, recent work in animal models suggests that contour grouping requires learning and thus involves top-down control from higher brain structures. Here we explore mechanisms of top-down control in perceptual grouping by investigating synchronicity within EEG oscillations. Human participants saw two micro-Gabor arrays in a random order, with the task to indicate whether the first (S1) or the second stimulus (S2) contained a contour of collinearly aligned elements. Contour compared to non-contour S1 produced a larger posterior post-stimulus beta power (15–21 Hz). Contour S2 was associated with a pre-stimulus decrease in posterior alpha power (11–12 Hz) and in fronto-posterior theta (4–5 Hz) phase couplings, but not with a post-stimulus increase in beta power. The results indicate that subjects used prior knowledge from S1 processing for S2 contour grouping. Expanding previous work on theta oscillations, we propose that long-range theta synchrony shapes neural responses to perceptual groupings regulating lateral inhibition in early visual cortex.
PMCID: PMC3542329  PMID: 23326575
16.  Evaluating Letter Recognition, Flicker Fusion, and the Talbot-Plateau Law using Microsecond-Duration Flashes 
PLoS ONE  2015;10(4):e0123458.
Four experiments examined the ability of respondents to identify letters that were displayed on an LED array with flashes lasting little more than a microsecond. The first experiment displayed each letter with a single, simultaneous flash of all the dots forming the letter and established the relation of flash intensity to the probability of letter identification. The second experiment displayed the letters with multiple flashes at different frequencies to determine the probability that the sequence of flashes would be perceived as fused. The third experiment displayed the letters at a frequency that was above the flicker-fusion frequency, varying flash intensity to establish the amount needed to elicit a given probability of letter identification. The fourth experiment displayed each letter twice, once at a frequency where no flicker was perceived and also with steady light emission. The intensity of each flash was fixed and the steady intensity was varied; respondents were asked to judge whether the fused-flicker display and the steady display appeared to be the same brightness. Steady intensity was about double the average flash intensity where the two conditions were perceived as being equal in brightness. This is at odds with Talbot-Plateau law, which predicts that these two values should be equal. The law was formulated relative to a flash lasting half of each period, so it is surprising that it comes this close to being correct where the flash occupies only a millionth of the total period.
PMCID: PMC4395448  PMID: 25875652
17.  On the Measurement of Movement Difficulty in the Standard Approach to Fitts' Law 
PLoS ONE  2011;6(10):e24389.
Fitts' law is an empirical rule of thumb which predicts the time it takes people, under time pressure, to reach with some pointer a target of width W located at a distance D. It has been traditionally assumed that the predictor of movement time must be some mathematical transform of the quotient of D/W, called the index of difficulty (ID) of the movement task. We ask about the scale of measurement involved in this independent variable. We show that because there is no such thing as a zero-difficulty movement, the IDs of the literature run on non-ratio scales of measurement. One notable consequence is that, contrary to a widespread belief, the value of the y-intercept of Fitts' law is uninterpretable. To improve the traditional Fitts paradigm, we suggest grounding difficulty on relative target tolerance W/D, which has a physical zero, unlike relative target distance D/W. If no one can explain what is meant by a zero-difficulty movement task, everyone can understand what is meant by a target layout whose relative tolerance W/D is zero, and hence whose relative intolerance 1–W/D is 1 or 100%. We use the data of Fitts' famous tapping experiment to illustrate these points. Beyond the scale of measurement issue, there is reason to doubt that task difficulty is the right object to try to measure in basic research on Fitts' law, target layout manipulations having never provided users of the traditional Fitts paradigm with satisfactory control over the variations of the speed and accuracy of movements. We advocate the trade-off paradigm, a recently proposed alternative, which is immune to this criticism.
PMCID: PMC3203862  PMID: 22053175
18.  Gestalt-binding of tropomyosin on actin during thin filament activation 
Journal of muscle research and cell motility  2013;34(0):10.1007/s10974-013-9342-0.
Our thesis is that thin filament function can only be fully understood and muscle regulation then elucidated if atomic structures of the thin filament are available to reveal the positions of tropomyosin on actin in all physiological states. After all, it is tropomyosin influenced by troponin that regulates myosin-crossbridge cycling on actin and therefore controls contraction in all muscles. In addition, we maintain that a complete appreciation of thin filament activation also requires that the mechanical properties of tropomyosin itself are recognized and then related to the effect of myosin-association on actin. Taking the Gestalt-binding of tropomyosin into account, coupled with our electron microscopy structures and computational chemistry, we propose a comprehensive mechanism for tropomyosin regulatory movement over the actin filament surface that explains the cooperative muscle activation process. In fact, well-known point mutations of critical amino acids on the actin-tropomyosin binding interface disrupt Gestalt-binding and are associated with a number of inherited myopathies. Moreover, dysregulation of tropomyosin may also be a factor that interferes with the gatekeeping operation of non-muscle tropomyosin in the controlling interactions of a wide variety of cellular actin-binding proteins. The clinical relevance of Gestalt-binding is discussed in articles by the Marston and the Gunning groups in this special journal issue devoted to the impact of tropomyosin on biological systems.
PMCID: PMC3773262  PMID: 23666668
Actin; muscle regulation; myosin; troponin; tropomyosin
19.  Systematic Breakdown of Amontons' Law of Friction for an Elastic Object Locally Obeying Amontons' Law 
Scientific Reports  2013;3:1586.
In many sliding systems consisting of solid object on a solid substrate under dry condition, the friction force does not depend on the apparent contact area and is proportional to the loading force. This behaviour is called Amontons' law and indicates that the friction coefficient, or the ratio of the friction force to the loading force, is constant. Here, however, using numerical and analytical methods, we show that Amontons' law breaks down systematically under certain conditions for an elastic object experiencing a friction force that locally obeys Amontons' law. The macroscopic static friction coefficient, which corresponds to the onset of bulk sliding of the object, decreases as pressure or system length increases. This decrease results from precursor slips before the onset of bulk sliding, and is consistent with the results of certain previous experiments. The mechanisms for these behaviours are clarified. These results will provide new insight into controlling friction.
PMCID: PMC3613807  PMID: 23545778
20.  Higher-contrast requirements for recognizing low-pass–filtered letters 
Journal of Vision  2013;13(1):13.
Kwon and Legge (2011) found that high levels of letter recognition accuracy are possible even when letters are severely low-pass filtered (0.9 cycles per letter). How is letter recognition possible with such severe reduction in the spatial resolution of stimulus letters? Clues may come from understanding the possible interaction between contrast and spatial resolution in letter recognition. Here, we asked what the effect is on the contrast threshold for detecting and recognizing letters as the spatial-frequency cutoff of letters is reduced (in cycles per letter). We measured contrast thresholds of seven normally sighted subjects for detecting and recognizing single letters of the English alphabet. The letters were low-pass filtered with several cutoff frequencies (0.9–3.5 cycles per letter, including unfiltered letters). We found that differences in contrast thresholds between detection and recognition increased substantially with decreasing cutoff frequency. We also incorporated the human contrast sensitivity function into an ideal observer model and found qualitatively good agreement between the pattern of performance for the model and our human subjects. Our findings show that the human visual system requires higher contrast for letter recognition when spatial resolution is severely limited. Good agreement between the model and human subjects shows that the greater contrast requirement for recognizing low-pass letters is due to a reduction in the information content of the letters rather than a change in human visual processing. The reduction in stimulus information may be due to increasing stimulus similarity associated with a reduction in spatial-frequency cutoff.
PMCID: PMC3586998  PMID: 23302216
letter recognition; spatial resolution; contrast; spatial-frequency bandwidth; peripheral vision; critical bandwidth; ideal observer; contrast sensitivity function; letter similarity
21.  Economic effect of a smoke‐free law in a tobacco‐growing community 
Tobacco Control  2007;16(1):66-68.
To determine whether Lexington, Kentucky's smoke‐free law affected employment and business closures in restaurants and bars. On 27 April 2004, Lexington‐Fayette County implemented a comprehensive ordinance prohibiting smoking in all public buildings, including bars and restaurants. Lexington is located in a major tobacco‐growing state that has the highest smoking rate in the US and was the first Kentucky community to become smoke‐free.
A fixed‐effects time series design to estimate the effect of the smoke‐free law on employment and ordinary least squares to estimate the effect on business openings and closings.
Subjects and settings
All restaurants and bars in Lexington‐Fayette County, Kentucky and the six contiguous counties.
Main outcome measures
ES‐202 employment data from the Kentucky Workforce Cabinet; Business opening/closings data from the Lexington‐Fayette County Health Department, Environmental Division.
A positive and significant relationship was observed between the smoke‐free legislation and restaurant employment, but no significant relationship was observed with bar employment. No relationship was observed between the law's implementation and employment in contiguous counties nor between the smoke‐free law and business openings or closures in alcohol‐serving and or non‐alcohol‐serving businesses.
No important economic harm stemmed from the smoke‐free legislation over the period studied, despite the fact that Lexington is located in a tobacco‐producing state with higher‐than‐average smoking rates.
PMCID: PMC2598448  PMID: 17297077
22.  Characterizing Flexible and Instrinsically Unstructured Biological Macromolecules by SAS using the Porod-Debye Law 
Biopolymers  2011;95(8):559-571.
Unstructured proteins, RNA or DNA components provide functionally important flexibility that is key to many macromolecular assemblies throughout cell biology. As objective, quantitative experimental measures of flexibility and disorder in solution are limited, small angle scattering (SAS), and in particular small angle X-ray scattering (SAXS), provides a critical technology to assess macromolecular flexibility as well as shape and assembly. Here, we consider the Porod-Debye law as a powerful tool for detecting biopolymer flexibility in SAS experiments. We show that the Porod-Debye region fundamentally describes the nature of the scattering intensity decay, which captures information needed for distinguishing between folded and flexible particles. Particularly for comparative SAS experiments, application of the law, as described here, can distinguish between discrete conformational changes and localized flexibility relevant to molecular recognition and interaction networks. This approach aids insightful analyses of fully and partly flexible macromolecules that is more robust and conclusive than traditional Kratky analyses. Furthermore, we demonstrate for prototypic SAXS data that the ability to calculate particle density by the Porod-Debye criteria, as shown here, provides an objective quality assurance parameter that may prove of general use for SAXS modeling and validation.
PMCID: PMC3103662  PMID: 21509745
23.  On a new law of bone remodeling based on damage elasticity: a thermodynamic approach 
Bone tissue is the main element of the human skeleton and is a dynamic tissue that is continuously renewed by bone-resorbing osteoclasts and bone-forming osteoblasts.
The bone is also capable of repairing itself and adapting its structure to changes in its load environment through the process of bone remodeling.
Therefore, this phenomenon has been gaining increasing interest in the last years and many laws have been developed in order to simulate this process.
In this paper, we develop a new law of bone remodeling in the context of damaged elastic by applying the thermodynamic approach in the case of small perturbations.
The model is solved numerically by a finite difference method in the one-dimensional bone structure of a n-unit elements model.
In addition, several numerical simulations are presented that confirm the accuracy and effectiveness of the model.
PMCID: PMC3564697  PMID: 23194460
Numerical simulation; Thermodynamic approach; Small perturbations hypothesis; Bone remodeling; Bone density; Damage; Fatigue; Osteocyte; Elasticity; N-unit elements
24.  A power law global error model for the identification of differentially expressed genes in microarray data 
BMC Bioinformatics  2004;5:203.
High-density oligonucleotide microarray technology enables the discovery of genes that are transcriptionally modulated in different biological samples due to physiology, disease or intervention. Methods for the identification of these so-called "differentially expressed genes" (DEG) would largely benefit from a deeper knowledge of the intrinsic measurement variability. Though it is clear that variance of repeated measures is highly dependent on the average expression level of a given gene, there is still a lack of consensus on how signal reproducibility is linked to signal intensity. The aim of this study was to empirically model the variance versus mean dependence in microarray data to improve the performance of existing methods for identifying DEG.
In the present work we used data generated by our lab as well as publicly available data sets to show that dispersion of repeated measures depends on location of the measures themselves following a power law. This enables us to construct a power law global error model (PLGEM) that is applicable to various Affymetrix GeneChip data sets. A new DEG identification method is therefore proposed, consisting of a statistic designed to make explicit use of model-derived measurement spread estimates and a resampling-based hypothesis testing algorithm.
The new method provides a control of the false positive rate, a good sensitivity vs. specificity trade-off and consistent results with varying number of replicates and even using single samples.
PMCID: PMC545082  PMID: 15606915
25.  Left atrial Frank–Starling law assessed by real‐time, three‐dimensional echocardiographic left atrial volume changes 
Heart  2007;93(11):1393-1397.
The Frank–Starling law describes the relation between left ventricular volume and function. However, only a few studies have described the relation between left atrial volume (LAV) and function.
To describe an LA Frank–Starling law by studying changes in LAV measured by real‐time, three‐dimensional echocardiography (RT3DE).
LAV was calculated by RT3DE in 70 patients at end‐systole (LAVmax), end‐diastole (LAVmin) and pre‐atrial contraction (LAVpre‐A). According to LAVmax, patients were classified into three groups: LAVmax <50 ml (group I), LAVmax 50–70 ml (group II) and LAVmax >70 ml (group III). Calculated indices of LA pump function were active atrial stroke volume (SV), defined as LAVpre‐A – LAVmin, and active atrial emptying fraction (EF), defined as active atrial SV/LAVpre‐A ×100%
Active atrial SV was significantly higher in group II than in group I (mean (SD) 19.0 (9.2) vs 8.2 (4.9) ml, p<0.0001), in group III it was non‐significantly lower than in group II (16.7 (12.5) vs 19.0 (9.2) ml). Active atrial SV correlated well with LAVpre‐A (r = 0.56, p<0.001), but decreased with larger LAVpre‐A. Active atrial EF tended to be higher in group II than in group I (43.1 (18.2) vs 33.2 (17.5), p<0.10), in group III it was significantly lower than in group II (26.2 (18.5) vs 43.1 (18.2), p<0.01).
A Frank–Starling mechanism in the left atrium could be described by RT3DE, shown by an increase in LA contractility in response to an increase in LA preload up to a point, beyond which LA contractility decreased.
PMCID: PMC2016907  PMID: 17502327
left atrial volume; left atrial function; Starling mechanism; real‐time; three‐dimensional echocardiography

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