Encoding contact size using static and dynamic electrotactile finger stimulation: natural decoding vs. trained cues.

Electrotactile stimulation through matrix electrodes is a promising technology to restore high-resolution tactile feedback in extended reality applications. One of the fundamental tactile effects that should be simulated is the change in the size of the contact between the finger and a virtual object. The present study investigated how participants perceive the increase of stimulation area when stimulating the index finger using static or dynamic (moving) stimuli produced by activating 1 to 6 electrode pads. To assess the ability to interpret the stimulation from the natural cues (natural decoding), without any prior training, the participants were instructed to draw the size of the stimulated area and identify the size difference when comparing two consecutive stimulations. To investigate if other "non-natural" cues can improve the size estimation, the participants were asked to enumerate the number of active pads following a training protocol. The results demonstrated that participants could perceive the change in size without prior training (e.g., the estimated area correlated with the stimulated area, p < 0.001; ≥ two-pad difference recognized with > 80% success rate). However, natural decoding was also challenging, as the response area changed gradually and sometimes in complex patterns when increasing the number of active pads (e.g., four extra pads needed for the statistically significant difference). Nevertheless, by training the participants to utilize additional cues the limitations of natural perception could be compensated. After the training, the mismatch in the activated and estimated number of pads was less than one pad regardless of the stimulus size. Finally, introducing the movement of the stimulus substantially improved discrimination (e.g., 100% median success rate to recognize ≥ one-pad difference). The present study, therefore, provides insights into stimulation size perception, and practical guidelines on how to modulate pad activation to change the perceived size in static and dynamic scenarios.

Biases in the spectral amplitude distribution of a natural scene modulate horizontal size perception.

Introduction: Visual perception is a complex process that involves the analysis of different spatial and temporal features of the visual environment. One critical aspect of this process is adaptation, which allows the visual system to adjust its sensitivity to specific features based on the context of the environment. Numerous theories highlight the significance of the visual scene and its spectral properties in perceptual and adaptation mechanisms. For example, size perception is known to be influenced by the spatial frequency content of the visual scene. Nonetheless, several inquiries still exist, including how specific spectral properties of the scene play a role in size perception and adaptation mechanisms. Methods: In this study, we explore aftereffects on size perception following adaptation to a natural scene with a biased spectral amplitude distribution. Twenty participants had to manually estimate the horizontal size of a projected rectangle after adaptation to three visually biased conditions: vertical-biased, non-biased, and horizontal-biased. Size adaptation aftereffects were quantified by comparing the perceptual responses from the non-biased condition with the vertical- and horizontal-biased conditions. Results: We found size perception shifts which were contingent upon the specific orientation and spatial frequency distribution inherent in the amplitude spectra of the adaptation stimuli. Particularly, adaptation to vertical-biased produced a horizontal enlargement, while adaptation to horizontal-biased generated a decrease in the horizontal size perception of the rectangle. On average, size perception was modulated by 5-6%. Discussion: These findings provide supporting evidence for the hypothesis that the neural mechanisms responsible for processing spatial frequency channels are involved in the encoding and perception of size information. The implications for neural mechanisms underlying spatial frequency and size information encoding are discussed.

Body image and behavioural and emotional difficulties in German children and adolescents.

BACKGROUND: Behavioural and emotional difficulties might play an important role in the development of body image disturbances, which represent serious risk factors for eating disorders or depression. The present study provides a detailed overview on body image disturbances and several behavioural and emotional difficulties (differences between gender, age, and weight status) and their inter-relations in German children and adolescents. METHODS: Data on body image disturbances, assessed through a Figure Rating Scale, and on behavioural and emotional difficulties, assessed through Goodman's Strengths and Difficulties Questionnaire (SDQ), were available for 5255 observations of 1982 German children and adolescents aged 8 to 18 years from the LIFE Child study, based in Leipzig, Germany. Associations were investigated using multiple logistic regression. Each association was checked for interaction with gender, age, and weight status. RESULTS: Boys reported more behavioural difficulties than girls, while girls reported more emotional difficulties. Gender, age and weight status were related to behavioural and emotional difficulties as well as body image disturbances. Individuals with fewer difficulties were more satisfied with their own body. Children and adolescents who desired to be larger showed more prosocial behaviour problems, conduct and emotional problems and more signs of hyperactivity. Those, who desired to be thinner showed more problems in all SDQ-subscales. A more accurate body size perception was associated with fewer behavioural and emotional difficulties. Children and adolescents who overestimated their body size showed more prosocial behaviour and emotional problems. Underestimation one's body size was associated with more signs of hyperactivity. CONCLUSION: The current findings highlight the importance of raising the awareness about the association between behavioural and emotional difficulties and body image disturbances in children and adolescents to prevent negative outcomes.

Impact of a Web-Based Nutrition Intervention on Eating Behaviors and Body Size Preoccupations among Adolescents.

We aimed to evaluate the impact of a web-based school nutrition intervention on eating behavior traits, body weight concern, body size perception and body size dissatisfaction in adolescents. Ten classes of secondary students in Canada (13.6 ± 0.8 years) were randomized into an intervention (n = 162 students) or control group (n = 75 students). Adolescents in the intervention, conducted between 2011 and 2013, participated in an online nutrition challenge to increase their consumption of vegetables, fruits and dairy products using a web-based platform over six weeks. Measurements were taken at baseline (PRE) and post-intervention (POST). No significant negative changes were observed between the intervention and control groups for eating behavior traits, body weight concern, body size perception and dissatisfaction. However, results suggest a trend for a positive effect of the intervention on susceptibility to hunger in boys (group × time interaction, p = 0.10). Specifically, boys experienced a reduction in their susceptibility to hunger in response to the intervention (PRE: 6.1 ± 3.8, POST: 4.8 ± 3.7, p = 0.009). An intervention aimed at improving the eating habits of adolescents did not negatively influence body size preoccupations. In response to the intervention, boys tended to show a lower susceptibility to hunger, which might help them to prevent overeating and adopt healthy eating habits.

A Randomised Control Trial Investigating the Efficacy of the MapMe Intervention on Parental Ability to Correctly Categorise Overweight in Their Child and the Impact on Child BMI Z-Score Change at 1 Year.

Research suggests parental ability to recognise when their child has overweight is limited. It is hypothesised that recognition of child overweight/obesity is fundamental to its prevention, acting as a potential barrier to parental action to improve their child's health-related behaviours and/or help seeking. The purpose of this study was to investigate the efficacy of an intervention (MapMe) to improve parental ability to correctly categorise their child as having overweight one-month post-intervention, and reduce child body mass index (BMI) z-score 12 months post-intervention. MapMe consists of body image scales of known child BMI and information on the consequences of childhood overweight, associated health-related behaviours and sources of support. We conducted a three-arm (paper-based MapMe, web-based MapMe and control) randomised control trial in fifteen English local authority areas with parents/guardians of 4-5- and 10-11-year-old children. Parental categorisation of child weight status was assessed using the question 'How would you describe your child's weight at the moment?' Response options were: underweight, healthy weight, overweight, and very overweight. Child weight status and BMI z-scores were calculated using objectively measured height and weight data and UK90 clinical thresholds. There was no difference in the percentage of parents correctly categorising their child as having overweight/very overweight (n = 264: 41% control, 48% web-based, and 43% paper-based, p = 0.646). BMI z-scores were significantly reduced for the intervention group at 12 months post-intervention compared to controls (n = 338, mean difference in BMI z-score change -0.11 (95% CI -0.202 to -0.020, p = 0.017). MapMe was associated with a decrease in BMI z-score 12 months post-intervention, although there was no direct evidence of improved parental ability to correctly categorise child overweight status. Further work is needed to replicate these findings in a larger sample of children, investigate mechanisms of action, and determine the use of MapMe as a public health initiative.

Percepção da redução do tamanho após rinoplastia de aumento não cirúrgica: Análise retrospectiva de 116 casos / Perception of size reduction after non-surgical augmentation rhinoplasty: Retrospective analysis of 116 cases

Introdução: Tradicionalmente, o rebaixamento do dorso é o único método de correção da giba. Raras séries apontam a elevação do radix como possível solução. O que explica essa maciça predominância do procedimento redutor? Ineficácia dos métodos de aumento de radix e ponta? Percepção de nariz grande com os procedimentos de aumento? Nossos objetivos são descobrir se a percepção de redução ocorre na rinoplastia não cirúrgica (RNC), feita exclusivamente com adição de volume, e se a percepção de redução é importante na RNC. Método: Análise retrospectiva de 116 pacientes consecutivos submetidos a RNC. As imagens dos pacientes foram analisadas por 12 observadores independentes que avaliaram as mudanças percebidas no tamanho do nariz e a qualidade da correção, dando notas de 1 a 10 para os dois quesitos. Quanto ao tamanho, 1 representava muito menor que antes, 5 mesmo tamanho (neutralidade) e 10 muito maior que antes. A qualidade da correção foi classificada de 1 a 10. Resultados: 92 casos (79%) foram percebidos como redução do tamanho, enquanto 20 casos (17%) foram percebidos como aumento. Houve percepção de redução na média das pontuações de tamanho (4,71). A média da qualidade da correção foi de 8,28 na escala de 1 a 10. Ademais, nossos resultados sugerem que pode haver correlação indireta entre a percepção do tamanho e a qualidade da correção. Conclusão: O aumento proporcionado pela RNC pode causar percepção de redução do tamanho do nariz, e o grau da redução percebida pode estar diretamente relacionado ao grau de qualidade percebida da correção.

Introduction: Traditionally, lowering the dorsum is the only method of hump correction. Rare series point to raising the radix as a possible solution. What explains this massive predominance of the reduction procedure? Ineffectiveness of radix and tip augmentation methods? Big nose perception with augmentation procedures? Our objectives are to determine if the perception of reduction occurs in non-surgical rhinoplasty (NSR), performed exclusively with volume addition, and if the perception of reduction is important in NSR. Method: Retrospective analysis of 116 consecutive patients undergoing NSR. The patients' images were analyzed by 12 independent observers who evaluated the perceived changes in the nose's size and the correction's quality, giving scores from 1 to 10 for both questions. As for size, 1 represented much smaller than before, 5 same size (neutrality), and 10 much larger than before. The quality of correction was graded from 1 to 10. Results: 92 cases (79%) were considered size reduction, while 20 cases (17%) were considered enlargement. There was a perception of a reduction in the average size scores (4.71). The mean correction quality was 8.28 on a scale of 1 to 10. Furthermore, our results suggest that there may be an indirect correlation between perceived size and correction quality. Conclusion: The increase provided by the NSR can cause a perception of a reduction in the size of the nose, and the degree of perceived reduction can be directly related to the degree of perceived quality of the correction.

Effects of cortical distance on the Ebbinghaus and Delboeuf illusions.

The Ebbinghaus and Delboeuf illusions affect the perceived size of a target circle depending on the size and proximity of circular inducers or a ring. Converging evidence suggests that these illusions are driven by interactions between contours mediated by their cortical distance in primary visual cortex. We tested the effect of cortical distance on these illusions using two methods: First, we manipulated retinal distance between target and inducers in a two-interval forced choice design, finding that targets appeared larger with a closer surround. Next, we predicted that targets presented peripherally should appear larger due to cortical magnification. Hence, we tested the illusion strength when positioning the stimuli at various eccentricities, with results supporting this hypothesis. We calculated estimated cortical distances between illusion elements in each experiment and used these estimates to compare the relationship between cortical distance and illusion strength across our experiments. In a final experiment, we modified the Delboeuf illusion to test whether the influence of the inducers/annuli in this illusion is influenced by an inhibitory surround. We found evidence that an additional outer ring makes targets appear smaller compared to a single-ring condition, suggesting that near and distal contours have antagonistic effects on perceived target size.

Misreporting of height and weight by primary school children in Japan: a cross-sectional study on individual and environmental determinants.

BACKGROUND: Appropriate body constitution during childhood is important for future health. However, it has been suggested that thinness is increasing among adolescent girls and boys in Japan. Since misreporting of height/weight may be a possible reflection of the child's ideal body image, we investigated the magnitude and direction of height/weight misreporting and its determinants among Japanese young adolescents. METHODS: A total of 1019 children in public primary schools were included in the analysis. Both measured and self-reported values of height/weight were obtained. Misreporting of height/weight was calculated by subtracting the measured value from the self-reported value. The association between misreporting and several variables such as the BMI z-score of individuals and body constitution of surrounding children was explored by multivariate linear mixed models. RESULTS: As BMI z-score increased, 'overreporting' of height by boys and 'underreporting' of height by girls became larger (p = 0.06 in boys, p = 0.02 in girls). Both boys and girls with a larger body size tended to underreport their weight (p < 0.01 in boys, p < 0.01 in girls). Boys who belonged to a school with a larger average BMI z-score were more likely to overreport their weight. This tendency was not observed for girls. CONCLUSIONS: Self-reported height/weight was generally accurate in Japanese primary school children. However, even primary school children misreported their height/weight intentionally like adults, possibly due to social pressure to lose weight or that not to stand out. Thus, health education about appropriate body constitution should be provided from the beginning of adolescence, particularly for girls.

The Role of Tableware Size in Healthy Eating-Effects on Downstream Food Intake.

Recent studies show that visual exposure to different portion sizes can lead to portion alterations in subsequent meals, suggesting that manipulations of tableware sizes may also modify portion size perception and downstream eating behaviour. The present study aims to address this novel question by testing 61 male participants (20-40 years; 19.7-41.5 kg·m-2) over three breakfast sessions in a controlled laboratory. In each session, the participant was served a pre-determined breakfast portion in either medium (control; CT), small (SC), or large (LC) jars. Participants were asked to rate post-meal satiety, and then recorded food intake for the rest of the day using Food Records. Our results indicated significant changes in post-meal satiety following the SC or LC condition, compared to CT (SC: 55.3 ± 10.8, LC: 31.0 ± 8.4, CT: 42.1 ± 9.6, F(2, 108) = 25.22, p < 0.001). SC led to a reduction in post-breakfast energy intake (F(2, 108) = 61.28, p < 0.001), but was counteracted by a substantial increase in downstream intake at the following meal (F(2, 108) = 47.79, p < 0.001), resulting in an overall increase in total daily energy intake (F(2, 108) = 11.45, p < 0.001). This study provides the first evidence that small tableware may not be a long-term solution for addressing overeating and related health issues (e.g., obesity), reinforcing the importance of considering downstream intake in eating-related intervention.

Object Image Size Is a Fundamental Coding Dimension in Human Vision: New Insights and Model.

In previous psychophysical work we found that luminance contrast is integrated over retinal area subject to contrast gain control. If different mechanisms perform this operation for a range of superimposed retinal regions of different sizes, this could provide the basis for size-coding. To test this idea we included two novel features in a standard adaptation paradigm to discount more pedestrian accounts of repulsive size-aftereffects. First, we used spatially jittering luminance-contrast adaptors to avoid simple contour displacement aftereffects. Second, we decoupled adaptor and target spatial frequency to avoid the well-known spatial frequency shift aftereffect. Empirical results indicated strong evidence of a bidirectional size adaptation aftereffect. We show that the textbook population model is inappropriate for our results, and develop our existing model of contrast perception to include multiple size mechanisms with divisive surround-suppression from the largest mechanism. For a given stimulus patch, this delivers a blurred step-function of responses across the population, with contrast and size encoded by the height and lateral position of the step. Unlike for textbook population coding schemes, our human results (N = 4 male, N = 4 female) displayed two asymmetries: (i) size aftereffects were greatest for targets smaller than the adaptor, and (ii) on that side of the function, results did not return to baseline, even when targets were 25% of adaptor diameter. Our results and emergent model properties provide evidence for a novel dimension of visual coding (size) and a novel strategy for that coding, consistent with previous results on contrast detection and discrimination for various stimulus sizes.

Comparison of body size perception of young women in Korea and the United States.

Body size perception among young women in Asian and Western countries is believed to be quite different, however, there are no confirming studies. We analyzed the data from young women aged between 20 and 40 who participated in the National Health and Nutrition Examination Survey (2001-2018) of the United States (US) and Korea. US young women had higher rates of being overweight and obesity than Korean young women, and there was no significant change over 20 years. In both countries, the percentage of properly estimating one's own weight exceeded 70 percent and remained relatively steady. The percentage of overestimating one's own weight was only about 10 percent in Korea in 2001, but increased to 20 percent. In the case of the US, the percentage was about 15 percent in 2001-2002, but has since continued to decline. The percentage of underestimating one's own body weight was about 18 percent in Korea in 2001, but decreased to about 8 percent. In the case of the US, the percentage was very low at about 10 percent in 2001-2002, but gradually increased to about 18 percent in 2017-2018. In conclusion, young women in the US tend to underestimate their body size, and those in Korea tend to overestimate it.

Reliabilities of the Two-Point Discrimination Test and the Two-Point Estimation Test for Use in the Lumbar Spine Area in Healthy Young Adults.

Two-point discrimination (TPD) testing and two-point estimation (TPE) methods are often used to determine tactile acuity, but their reliability is uncertain. Our aim in this study was to assess the reliability of TPD and TPE measurements in the same lumbar spine region of healthy young adults. Participants were 37 young adults (16 females and 21 males; age range: 20-27 years - M age = 21.65, SD = 1.9), who received two tests (TPD and TPE) to determine their tactile acuity. The tests were performed in the lumbar spine area, at the level of the L3 segment, bilaterally, with a 10-minute interval between the measurements. The first test session assessed the reliability of measurements performed by two examiners (inter-rater reliability); and, after 7 days, another examiner repeated the measurements (intra-rater reliability). The reliability of both tests was evaluated using intra-class correlation coefficients (ICC), and results revealed high intra-rater, and inter-rater repeatability for immediate administration of TPD and TPE tests (i.e, after 10 minutes) and moderate repeatability when they were performed at a 7-day interval. Thus, we confirmed high reliability of TPD and TPE assessments of tactile acuity repeated at a short time interval and moderate reliability after 7 days. There was slightly higher reliability for the TPE method.

Preschoolers BMI: Associations with Patterns of Caregivers' Feeding Practices Using Structural Equation Models.

Background: Childhood obesity is a major health concern. Caregivers' feeding practices are modifiable targets of obesity prevention. The study tested two hypotheses: (1) autonomy-promoting feeding practices are associated with lower BMI; and (2) diet mediates the association. We also explored examined whether feeding practices and BMI z-score (BMIz) associations are moderated by child sex, caregiver race, education, family poverty level, and food insecurity. Methods: Cross-sectional study of 437 preschoolers (44.4% girls, 38.2% Black/Other, mean age 48.1 months) and caregivers (90.2% female) from 50 child care centers. Feeding Practices were measured by Comprehensive Feeding Practices Questionnaire, child-size perception by preschooler silhouettes, temperament by the Behavior Rating Inventory of Executive Function, child diet by Young Children Food and Drink Questionnaire, and BMIz by measured weight and height. Latent profile analysis delineated feeding practice patterns. Structure equation modeling assessed the patterns in relationship to BMIz. Mediation and multiple-group analyses were used to assess mechanisms of feeding practice patterns and BMIz association. Results: From the three feeding practice patterns, Controlling, Balancing, and Regulating, Regulating was associated with lower child BMIz (b = -0.09) compared to Controlling. Higher difficult temperament (b = 0.09), higher caregiver BMIz (b = 0.26), and caregiver desire for thinner (b = 0.23) were associated with BMIz (p < 0.05). Evaluations of moderators and mediators were not significant. Conclusions: Comprehensive feeding practices support family factors related to child BMIz. Longitudinal research is needed to examine temporal associations between feeding practices and BMIz, with attention to autonomy-supporting practices, promotion of young children's self-regulation, and caregivers' perceptions of child temperament and size. Trial Registration: NCT03111264.

The relationship of body image and weight: A cross-sectional observational study of a Dutch female sample.

Body image concerns may play a role in weight changing behaviour. The objective of this study was to assess body image in different weight groups. Participants reported satisfaction with (AE) and investment in (AO) appearance, and the discrepancy between current and ideal body size (BS). These scores were compared between weight groups based on body-mass index (BMI) using analysis of variance. One-sample t-tests and Cohen's d effect sizes examined the magnitude of differences within each weight group relative to neutral midpoints of the scales; cluster analysis identified body image profiles. A total of 27 896 women were included in this study. AE scores were highest for people with underweight and normal weight, AO scores were highest for the underweight group and lowest in class III obesity, and BS scores were largest in the obese groups (all p < .001) Cluster analysis identified eight body image profiles. In people with obesity, the most prevalent profiles included a preference for a smaller body and low satisfaction with appearance, but differed in investment in appearance (low vs. high). Most people with underweight were allocated to profiles showing high investment in their appearance, preference of a larger body, but differences in satisfaction with appearance (neutral vs. high). While people with a higher BMI have on average more body image concerns, different body image profiles exist in all weight groups. Future research should examine whether and which individuals in terms of body image profile may benefit more from weight interventions.

Familiar size affects perception differently in virtual reality and the real world.

The promise of virtual reality (VR) as a tool for perceptual and cognitive research rests on the assumption that perception in virtual environments generalizes to the real world. Here, we conducted two experiments to compare size and distance perception between VR and physical reality (Maltz et al. 2021 J. Vis. 21, 1-18). In experiment 1, we used VR to present dice and Rubik's cubes at their typical sizes or reversed sizes at distances that maintained a constant visual angle. After viewing the stimuli binocularly (to provide vergence and disparity information) or monocularly, participants manually estimated perceived size and distance. Unlike physical reality, where participants relied less on familiar size and more on presented size during binocular versus monocular viewing, in VR participants relied heavily on familiar size regardless of the availability of binocular cues. In experiment 2, we demonstrated that the effects in VR generalized to other stimuli and to a higher quality VR headset. These results suggest that the use of binocular cues and familiar size differs substantially between virtual and physical reality. A deeper understanding of perceptual differences is necessary before assuming that research outcomes from VR will generalize to the real world. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Can a Common Magnitude System Theory Explain the Brain Representation of Space, Time, and Number?

Space, time, and number are important parts of our experiences and they are crucial for maintaining our behaviors in daily life. Comprehending the spatial and numerical features of our environment and perceiving and constructing the temporal framework are critical for healthy cognitive functioning and also survival. Although the problem of how these three perceptual processes work was initially studied separately, the emergence of behavioral interactions between these perceptions led to the idea that they could be run by a "common system". Besides the behavioral interactions for space, time, and number perception, the lesion and neuroimaging studies investigating the neural basis of these perceptions suggest the existence of a common size perception system represented in a fronto-parietal network formed around the intraparietal sulcus. However, on the other side of the coin, there are different views proposed based on findings that contradict this common magnitude system theory. The purpose of this review is to evaluate suggested ideas together and to examine whether the representation of space, time, and number perception in the brain can be explained by a common magnitude system theory.

A post hoc comparison between inpatients with obesity and healthy-weight subjects in the size estimation accuracy of shoulders, waist, and hips widths and circumferences.

PURPOSE: This post hoc study aimed to assess the hypothesis that subjects with obesity could underestimate their body size. METHODS: Data from a previous study with different aims were used to compare 22 female inpatients with obesity with 21 healthy-weight women in the size estimation accuracy of their shoulders, waist, and hips circumferences and widths. The body estimation task with an individualized metric methodology was used to collect data. Frequentist and Bayesian analyses were performed. RESULTS: Samples differed significantly in the accuracy measures of shoulders width and hips as well as waist circumferences: inpatients with obesity underestimated them, while healthy-weight subjects estimated shoulders width accurately but overestimated their hips and waist circumferences. Multiple regression showed that the between-group difference in the accuracy measure of shoulders width was explained by the individuals' education level, while the difference in the accuracy measure of waist circumference resulted to be independent of both age and education level. CONCLUSION: This post hoc study supports the hypothesis that female patients with obesity might underestimate their body size. If these results will be confirmed in future studies, interventions specifically designed to equalize estimations to match the real measures of body size may play a key role in weight-reduction programs for people with obesity. LEVEL OF EVIDENCE: Level III, evidence obtained from cohort or case-control analytic studies.

Body image and health-related behaviors among fitspirit participants.

BACKGROUND: Body image variables such as body size perception (BSP) and body size dissatisfaction (BSD) can influence health-related behaviors. However, few studies have investigated these body image variables in adolescent girls participating in a physical activity intervention. Therefore, the study objectives were to examine the 1) associations between health-related behaviors (physical activity, screen-time, eating habits and sleep duration) and BSP and BSD among girls participating in FitSpirit, a physical activity intervention for girls; and 2) influence of weight control practices on the association between health-related behaviors and BSP and BSD. METHODS: This cross-sectional study assessed a sample of 545 adolescent girls (mean age: 15.0±1.5 years) from 240 schools. Body mass index, health-related behaviors, perceived actual body size and desired body size variables were self-reported and collected via an online questionnaire at the end of the FitSpirit intervention. A negative BSP score [perceived actual body size - calculated BMI z-score] indicates an underestimation of body size. A positive BSD score [perceived actual body size - desired body size] indicates a desire to reduce body size. A multiple linear regression analysis examined the effects of age, zBMI and health behaviors on BSP and BSD. A second multiple linear regression analysis examined the independent associations between BSP and BSD by weight control practice. The linear relationships between BSP and BSD were evaluated with Pearson's correlations. RESULTS: Underestimation and dissatisfaction of body size are more prevalent in participants living with overweight/obesity. Screen-time and sleep duration were independently associated with BSP score (Beta=0.02; P<0.05 and Beta=-0.07; P<0.05, respectively), whereas only screen-time was associated with the BSD score (Beta=0.07; P<0.001). Physical activity was independently associated with the BSP score only in participants trying to control (maintain) their weight (Beta=-0.18; P<0.05). CONCLUSIONS: Body size overestimation and dissatisfaction are associated with health-related behaviors, specifically with more screen-time and less optimal sleeping habits. Physical activity level does not appear to be associated with body image in girls engaged in a physical activity intervention and who want to lose or gain weight. Health promotion interventions could include screen-time and sleep components as they may influence body image.

Familiarity with an Object's Size Influences the Perceived Size of Its Image.

It is known that judgments about objects' distances are influenced by familiar size: a soccer ball looks farther away than a tennis ball if their images are equally large on the retina. We here investigate whether familiar size also influences judgments about the size of images of objects that are presented side-by-side on a computer screen. Sixty-three participants indicated which of two images appeared larger on the screen in a 2-alternative forced-choice discrimination task. The objects were either two different types of balls, two different types of coins, or a ball and a grey disk. We found that the type of ball biased the comparison between their image sizes: the size of the image of the soccer ball was over-estimated by about 5% (assimilation). The bias in the comparison between the two balls was equal to the sum of the biases in the comparisons with the grey disk. The bias for the coins was smaller and in the opposite direction (contrast). The average precision of the size comparison was 3.5%, irrespective of the type of object. We conclude that knowing a depicted object's real size can influence the perceived size of its image, but the perceived size is not always attracted towards the familiar size.