Contraction Bias Research Articles

Unifying network model links recency and central tendency biases in working memory

The central tendency bias, or contraction bias, is a phenomenon where the judgment of the magnitude of items held in working memory appears to be biased toward the average of past observations. It is assumed to be an optimal strategy by the brain and commonly thought of as an expression of the brain’s ability to learn the statistical structure of sensory input. On the other hand, recency biases such as serial dependence are also commonly observed and are thought to reflect the content of working memory. Recent results from an auditory delayed comparison task in rats suggest that both biases may be more related than previously thought: when the posterior parietal cortex (PPC) was silenced, both short-term and contraction biases were reduced. By proposing a model of the circuit that may be involved in generating the behavior, we show that a volatile working memory content susceptible to shifting to the past sensory experience – producing short-term sensory history biases – naturally leads to contraction bias. The errors, occurring at the level of individual trials, are sampled from the full distribution of the stimuli and are not due to a gradual shift of the memory toward the sensory distribution’s mean. Our results are consistent with a broad set of behavioral findings and provide predictions of performance across different stimulus distributions and timings, delay intervals, as well as neuronal dynamics in putative working memory areas. Finally, we validate our model by performing a set of human psychophysics experiments of an auditory parametric working memory task.

Unifying network model links recency and central tendency biases in working memory.

The central tendency bias, or contraction bias, is a phenomenon where the judgment of the magnitude of items held in working memory appears to be biased toward the average of past observations. It is assumed to be an optimal strategy by the brain and commonly thought of as an expression of the brain's ability to learn the statistical structure of sensory input. On the other hand, recency biases such as serial dependence are also commonly observed and are thought to reflect the content of working memory. Recent results from an auditory delayed comparison task in rats suggest that both biases may be more related than previously thought: when the posterior parietal cortex (PPC) was silenced, both short-term and contraction biases were reduced. By proposing a model of the circuit that may be involved in generating the behavior, we show that a volatile working memory content susceptible to shifting to the past sensory experience - producing short-term sensory history biases - naturally leads to contraction bias. The errors, occurring at the level of individual trials, are sampled from the full distribution of the stimuli and are not due to a gradual shift of the memory toward the sensory distribution's mean. Our results are consistent with a broad set of behavioral findings and provide predictions of performance across different stimulus distributions and timings, delay intervals, as well as neuronal dynamics in putative working memory areas. Finally, we validate our model by performing a set of human psychophysics experiments of an auditory parametric working memory task.

Acute effect of scapular mobilization with associated myofascial release on butterfly performance: Randomized clinical trial

IntroductionTo evaluate the acute effect of scapular mobilization with associated myofascial release compared to scapular mobilization without myofascial release on butterfly stroke sports performance. Design: Randomized clinical trial. MethodPilot study that non-probabilistically convenience sampling that selected butterfly swimmers who were simply randomized into three groups to receive the standard protocol (scapular mobilization with release of the subscapularis muscle by the lateral edge of the scapula and rib cage detachment) in intervention group (IG), sham group (SG) (scapular mobilization without subscapularis muscle release and without rib cage detachment) or no intervention in control group (CG). We evaluated the stroke frequency, length, and average speed of 30 swimmers using the 8.15 Kinovea® motion analysis system. ResultsThe findings showed that, compared to the CG and IG, the SG showed a significant reduction in mean velocity (p = 0.002; p = 0.02, respectively), stroke frequency (p = 0.002; p = 0.003, respectively), and stroke length (p = 0.01; p = 0.05, respectively). DiscussionThe results showed that manual therapy through scapular mobilization without associated myofascial release with detachment of the scapula from the rib cage worsened the swimming efficiency indicators even after 30 min of application of the technique. The limitations of the studies are related to the sample size, the risk of non-probabilistic contraction bias and the lack of blinding of the evaluators. Thus, the results of this study should be evaluated with caution.

Contraction bias in temporal estimation

When asked to compare the perceptual features of two serially presented objects, participants are often biased to over- or under-estimate the difference in magnitude between the stimuli. Overestimation occurs consistently when a) the two stimuli are relatively small in magnitude and the first stimulus is larger in magnitude than the second; or b) the two stimuli are relatively large in magnitude and the first stimulus is smaller in magnitude than the second; underestimation consistently occurs in the complementary cases. This systematic perceptual bias, known as the contraction bias, was demonstrated for a multitude of perceptual features and in various modalities. Here, we tested whether estimation of time-duration is affected by the contraction bias. In each trial of three experiments (n = 20 each), participants compared the duration of two visually presented stimuli. Findings revealed over- and under-estimation effects as predicted by the contraction bias. Here, we discuss this asymmetry and describe how these findings can be explained via a Bayesian inference framework.

Effects of contraction bias on the decision process in the macaque prefrontal cortex.

Our representation of magnitudes such as time, distance, and size is not always veridical because it is affected by multiple biases. From a Bayesian perspective, estimation errors are considered to be the result of an optimization mechanism for the behavior in a noisy environment by integrating previous experience with the incoming sensory information. One influence of the distribution of past stimuli on perceptual decisions is represented by the regression toward the mean, a type of contraction bias. Using a spatial discrimination task with 2 stimuli presented sequentially at different distances from the center, we show that this bias is also present in macaques when comparing the magnitude of 2 distances. We found that the contraction of the first stimulus magnitude toward the center of the distribution accounted for some of the changes in performance, even more so than the effect of difficulty related to the ratio between stimulus magnitudes. At the neural level in the dorsolateral prefrontal cortex, the coding of the decision after the presentation of the second stimulus reflected the effect of the contraction bias on the discriminability of the stimuli at the behavioral level.

On optimization of active contour methods in colonoscopy image segmentation

As colonoscopy is the standard screening approach for colorectal polyps, and the first step of the correct classification and the efficient automatic diagnostics is the accurate detection and segmentation of the existing polyps, it is worth researching systematically, how colonoscopy databases are responding to two of the most influential variational segmentation methods, the geodesic and Chan–Vese active contour methods. Due to the quality variation of the colonoscopy databases, pre-processing steps are made. Then, 14 various filtered images are evaluated as different inputs for the active contour methods using the Sørensen–Dice Similarity Coefficient as a performance measurement metric. The effects of the initial mask shape and its size together with the number of iterations, contraction bias and smoothness factor were studied. The number of necessary iterations depended on the image resolution. In general, the Chan-Vese method showed more efficiency to match the actual contour of the polyp than the geodesic one with an initial mask possibly located within the polyp area. Preprocessing such as reflection removal, background subtraction and mean or median filtering improve the Sørensen–Dice coefficient can improve by 0.3.

Dissecting the Roles of Supervised and Unsupervised Learning in Perceptual Discrimination Judgments.

Our ability to compare sensory stimuli is a fundamental cognitive function, which is known to be affected by two biases: choice bias, which reflects a preference for a given response, and contraction bias, which reflects a tendency to perceive stimuli as similar to previous ones. To test whether both reflect supervised processes, we designed feedback protocols aimed to modify them and tested them in human participants. Choice bias was readily modifiable. However, contraction bias was not. To compare these results to those predicted from an optimal supervised process, we studied a noise-matched optimal linear discriminator (Perceptron). In this model, both biases were substantially modified, indicating that the “resilience” of contraction bias to feedback does not maximize performance. These results suggest that perceptual discrimination is a hierarchical, two-stage process. In the first, stimulus statistics are learned and integrated with representations in an unsupervised process that is impenetrable to external feedback. In the second, a binary judgment, learned in a supervised way, is applied to the combined percept.SIGNIFICANCE STATEMENT The seemingly effortless process of inferring physical reality from the sensory input is highly influenced by previous knowledge, leading to perceptual biases. Two common ones are contraction bias (the tendency to perceive stimuli as similar to previous ones) and choice bias (the tendency to prefer a specific response). Combining human psychophysical experiments with computational modeling we show that they reflect two different learning processes. Contraction bias reflects unsupervised learning of stimuli statistics, whereas choice bias results from supervised or reinforcement learning. This dissociation reveals a hierarchical, two-stage process. The first, where stimuli statistics are learned and integrated with representations, is unsupervised. The second, where a binary judgment is applied to the combined percept, is learned in a supervised way.

Human biases in body measurement estimation

Body measurements, including weight and height, are key indicators of health. Being able to visually assess body measurements reliably is a step towards increased awareness of overweight and obesity and is thus important for public health. Nevertheless it is currently not well understood how accurately humans can assess weight and height from images, and when and how they fail. To bridge this gap, we start from 1,682 images of persons collected from the Web, each annotated with the true weight and height, and ask crowd workers to estimate the weight and height for each image. We conduct a faceted analysis taking into account characteristics of the images as well as the crowd workers assessing the images, revealing several novel findings: (1) Even after aggregation, the crowd’s accuracy is overall low. (2) We find strong evidence of contraction bias toward a reference value, such that the weight of light people and the height of short people are overestimated, whereas the weight of heavy people and the height of tall people are underestimated. (3) We estimate workers’ individual reference values using a Bayesian model, finding that reference values strongly correlate with workers’ own height and weight, indicating that workers are better at estimating people similar to themselves. (4) The weight of tall people is underestimated more than that of short people; yet, knowing the height decreases the weight error only mildly. (5) Accuracy is higher on images of females than of males, but female and male workers are no different in terms of accuracy. (6) Crowd workers improve over time if given feedback on previous guesses. Finally, we explore various bias correction models for improving the crowd’s accuracy, but find that this only leads to modest gains. Overall, this work provides important insights on biases in body measurement estimation as obesity-related conditions are on the rise.

Perceptual inference is impaired in individuals with ASD and intact in individuals who have lost the autism diagnosis

Beyond the symptoms which characterize their diagnoses, individuals with autism spectrum disorder (ASD) show enhanced performance in simple perceptual discrimination tasks. Often attributed to superior sensory sensitivities, enhanced performance may also reflect a weaker bias towards previously perceived stimuli. This study probes perceptual inference in a group of individuals who have lost the autism diagnosis (LAD); that is, they were diagnosed with ASD in early childhood but have no current ASD symptoms. Groups of LAD, current ASD, and typically developing (TD) participants completed an auditory discrimination task. Individuals with TD showed a bias towards previously perceived stimuli—a perceptual process called “contraction bias”; that is, their representation of a given tone was contracted towards the preceding trial stimulus in a manner that is Bayesian optimal. Similarly, individuals in the LAD group showed a contraction bias. In contrast, individuals with current ASD showed a weaker contraction bias, suggesting reduced perceptual inferencing. These findings suggest that changes that characterize LAD extend beyond the social and communicative symptoms of ASD, impacting perceptual domains. Measuring perceptual processing earlier in development in ASD will tap the causality between changes in perceptual and symptomatological domains. Further, the characterization of perceptual inference could reveal meaningful individual differences in complex high-level behaviors.

Overestimation and contraction biases of depth information stored in working memory depend on spatial configuration.

Depth perception is essential for effective interaction with the environment. Although the accuracy of depth perception has been studied extensively, it is unclear how accurate the depth information is stored in working memory. In this study, we investigated the accuracy and systematic biases of depth representation by a delayed estimation task. The memory array consisted of items presented at various stereoscopic depth positions, and the participants were instructed to estimate the depth position of one target item after a retention interval. We examined the effect of spatial configuration by comparing the memory performance in the whole-display condition where non-target memory items were present during retrieval with that in the single-display condition where non-target memory items were absent. In the single-display condition, we found an overestimation bias that the depth estimates were farther than the corresponding depth positions defined by disparity, and a contraction bias that the stored depth positions near the observer were overestimated and those far from the observer were underestimated. The magnitude of these biases increased with the number of to-be-stored items. However, in the whole-display condition, the overestimation bias was corrected and the contraction bias did not increase with the number of to-be-stored items. Our findings suggested that the number of to-be-stored items could affect the accuracy of depth working memory, and its effect depended crucially on whether the information of spatial configuration of memory display was available at the retrieval stage.

P.2.e.008 - Evaluation of inhaled loxapine treatment in psychiatric patients with acute agitation

Western populations have been getting progressively heavier and the prevalence of obesity in the general population has become a major public health problem. A potential contributory factor in the rise of obesity is the inability to accurately detect weight increase using visual cues. This is a problem not only for members of the public whose weight is increasing but also for healthcare professionals who need to detect weight gain in their patients. Three main visual biases effect body judgments: contraction bias, adaptation, and Weber’s law. Contraction bias (a result of how we estimate body size) leads to people overestimating the BMI of bodies thinner than the average and significantly underestimating the BMI of bodies heavier than the average. Adaptation (the effect of seeing heavier bodies in the general population) leads to a shift in what people regard as a normal and acceptable body size toward a heavier BMI. Weber’s law (which requires a detectable size change to be a fixed proportion of the body’s total size) means that size change in obese bodies becomes increasingly difficult to detect. The cumulative effect of these visual biases is to make it harder to detect both being obese and weight increase when obese.

Visual biases in judging body weight.

There has been a steady rise in obesity levels in Western countries, and a contributory factor is people's failure to recognize weight gain. Two important visual perceptual biases, contraction bias and Weber's law, that have hitherto been ignored in the obesity literature could contribute to this problem. Contraction bias predicts that the weight of obese bodies will be underestimated and the degree of underestimation will increase as body mass index (BMI) increases. Weber's law predicts that change in the body size will become progressively harder to detect as their BMI increases. In Experiment 1, 29 women participants estimated the weight of 120 women varying in their body mass. In Experiment 2, 28 women participants judged which body was the heavier in a 2-alternative forced choice paradigm. In Experiment 1, as predicted the participants showed a progressive underestimation of overweight and obese bodies, β1 =0.71, t=26.96, p<.0001. For Experiment 2, there was a significant effect of the BMI of the bodies being judged on the just noticeable difference needed to discriminate between them: F(1,196)=89.39, p<.0001 for 3D bodies and F(1,86.5)=44.57, p<.0001 for digital photographs. Normal visual perceptual biases influence our ability to determine body size: contraction bias and Weber's law mean that as bodies become overweight and obese, it is harder to judge their weight and detect any increase in size. These effects may therefore compromise people's ability to recognize weight gain and undertake compensatory weight control behaviours. Statement of contribution What is already known on this subject? It is common knowledge that obesity levels in the West are rapidly rising and that people fail to recognize weight gain. What has not been widely recognized before is that there are sound perceptual reasons for this failure. Here, we identify two such perceptual biases. What does this study add? Weber's law and contraction bias compromise people's ability to recognize weight gain. It becomes progressively harder to discriminate the size of bodies as their body mass index increases. This compromises the ability to recognize weight gain and undertake compensatory behaviours.

The influence of personal BMI on body size estimations and sensitivity to body size change in anorexia spectrum disorders

In this cross-sectional study, we investigated the influence of personal BMI on body size estimation in 42 women who have symptoms of anorexia (referred to henceforth as anorexia spectrum disorders, ANSD), and 100 healthy controls. Low BMI control participants over-estimate their size and high BMI controls under-estimate, a pattern which is predicted by a perceptual phenomenon called contraction bias. In addition, control participants’ sensitivity to size change declines as their BMI increases as predicted by Weber's law. The responses of women with ANSD are very different. Low BMI participants who have ANSD are extremely accurate at estimating body size and are very sensitive to changes in body size in this BMI range. However, as BMI rises in the ANSD participant group, there is a rapid increase in over-estimation concurrent with a rapid decline in sensitivity to size change. We discuss the results in the context of signal detection theory.

How Recent History Affects Perception: The Normative Approach and Its Heuristic Approximation

There is accumulating evidence that prior knowledge about expectations plays an important role in perception. The Bayesian framework is the standard computational approach to explain how prior knowledge about the distribution of expected stimuli is incorporated with noisy observations in order to improve performance. However, it is unclear what information about the prior distribution is acquired by the perceptual system over short periods of time and how this information is utilized in the process of perceptual decision making. Here we address this question using a simple two-tone discrimination task. We find that the “contraction bias”, in which small magnitudes are overestimated and large magnitudes are underestimated, dominates the pattern of responses of human participants. This contraction bias is consistent with the Bayesian hypothesis in which the true prior information is available to the decision-maker. However, a trial-by-trial analysis of the pattern of responses reveals that the contribution of most recent trials to performance is overweighted compared with the predictions of a standard Bayesian model. Moreover, we study participants' performance in a-typical distributions of stimuli and demonstrate substantial deviations from the ideal Bayesian detector, suggesting that the brain utilizes a heuristic approximation of the Bayesian inference. We propose a biologically plausible model, in which decision in the two-tone discrimination task is based on a comparison between the second tone and an exponentially-decaying average of the first tone and past tones. We show that this model accounts for both the contraction bias and the deviations from the ideal Bayesian detector hypothesis. These findings demonstrate the power of Bayesian-like heuristics in the brain, as well as their limitations in their failure to fully adapt to novel environments.

Bayesian Inference Underlies the Contraction Bias in Delayed Comparison Tasks

Delayed comparison tasks are widely used in the study of working memory and perception in psychology and neuroscience. It has long been known, however, that decisions in these tasks are biased. When the two stimuli in a delayed comparison trial are small in magnitude, subjects tend to report that the first stimulus is larger than the second stimulus. In contrast, subjects tend to report that the second stimulus is larger than the first when the stimuli are relatively large. Here we study the computational principles underlying this bias, also known as the contraction bias. We propose that the contraction bias results from a Bayesian computation in which a noisy representation of a magnitude is combined with a-priori information about the distribution of magnitudes to optimize performance. We test our hypothesis on choice behavior in a visual delayed comparison experiment by studying the effect of (i) changing the prior distribution and (ii) changing the uncertainty in the memorized stimulus. We show that choice behavior in both manipulations is consistent with the performance of an observer who uses a Bayesian inference in order to improve performance. Moreover, our results suggest that the contraction bias arises during memory retrieval/decision making and not during memory encoding. These results support the notion that the contraction bias illusion can be understood as resulting from optimality considerations.

Parent-of-origin differences of mutant HTT CAG repeat instability in Huntington’s disease

BackgroundHuntington’s disease (HD) is a progressive autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion in the HD gene (HTT). The CAG domain of mutant HTT is unstable upon intergenerational transmission, however, little is known about the underlying mechanisms. MethodsFrom the HD archives of the Leiden University Medical Centre DNA samples from all parent-offspring pairs involving 36 CAG repeats or more were selected. To minimize procedural variability, CAG repeat lengths in both mutant and normal HTT were reassessed using the same standardized protocol, which resulted in the identification of 337 parent-offspring transmissions. The effects of both parental (mutant and normal CAG repeat size, age and gender) and offspring (gender and season of conception) characteristics on CAG repeat instability were assessed. ResultsPaternal transmissions were often associated with CAG repeat expansion, whereas maternal transmissions mainly resulted in CAG repeat contraction (mean change: +1.76 vs. −0.07, p<0.001). Only in paternal transmissions larger mutant CAG repeat size was associated with a greater degree of CAG repeat expansion (β=0.73; p<0.001). Conversely, only in maternal transmissions larger CAG repeat size of the normal allele was associated with a greater degree of CAG repeat contraction (β=−0.07; p=0.029). Parental age, offspring gender and season of conception were not related to CAG repeat instability. ConclusionOur findings suggest a slight maternal contraction bias as opposed to a paternal expansion bias of the mutant HTT CAG repeat during intergenerational transmission, which only in the maternal line is associated with normal HTT CAG repeat size.

Pointing in Stereoscopic Space

Movements in virtual stereoscopic space tend to be difficult and slow. To shed some light on the origins of these difficulties, we studied open-loop pointing with targets presented in a mirror stereoscope. Whilst targets were placed in a virtual horizontal plane, movement end-points were located in an inclined plane. The inclination of this plane was a stable individual characteristic. Amplitude errors gave no evidence of a contraction bias. Open-loop movements had fairly straight trajectories, but closed-loop movements were strongly curved so that they ended in a horizontal plane rather than in an inclined one. Effects of closed-loop movements on subsequent open-loop movements (calibration effects) were only small. These findings reveal that movements in a virtual environment exhibit a number of characteristics also seen in real environments, but in addition they reflect specific visual illusions. Extensive calibration procedures are needed to overcome such errors for the reliance on closed-loop control of pointing to be relaxed.

Research Methods to Avoid Bias in Categorical Ratings of Brightness

This article presents evidence of potential contraction bias in the category rating task associated with the stimulus presentation sequence, response range and response range anchors, and a grouping bias associated with the number of stimuli and response categories. These biases tend to reduce the difference between ratings given to stimuli. It is demonstrated that such bias is sufficient to hide differences in brightness under lighting from lamps of different spectral power distribution but that precautions can be taken to successfully counter the bias. Research methods that can be employed to avoid bias in categorical ratings of brightness are summarized.

Counterbalancing Needed to Avoid Bias in Side-By-Side Brightness Matching Tasks

Spectral power distribution (SPD) is one of the variables that can be manipulated in lighting design. This article examines twenty previous studies which have investigated the effect of SPD on brightness using the side-by-side matching technique. Three sources of experimental bias are identified and are shown to be present in the majority of these studies, and hence must be considered to provide an unreliable estimate of the magnitude of the SPD effect on brightness. The first bias is associated with test participants' use of dimming control and two forms are apparent – a response contraction bias when the test is repeated at multiple reference illuminances and a conservative bias when the test is carried out at a single reference illuminance. The second bias is associated with the primary direction in which dimming must take place and the third bias is associated with the relative position of the stimuli within the apparatus.

Evidencefor response contraction bias in side-by-side matching tasks

A recent study of lamp spectrum effects at mesopic levels employed side-by-side matching to investigate brightness. The results revealed an unexpected effect, identified here as a response contraction bias, normally only expected when judging individual stimuli. Response contraction bias causes subjective responses to be biased toward the middle of a response range. Although the bias is small its effect on brightness matching can be significant if the test procedure does not employ appropriate counterbalancing.