Delboeuf Illusion

Here, we studied whether domestic dogs perceive the Delboeuf illusion. In human and non-human primates, this illusion creates a misperception of item size as a function of its surrounding context. To examine this effect in dogs, we adapted the spontaneous preference paradigm recently used with chimpanzees. The Delboeuf illusion is an optical illusion of relative size perception. It was named for the Belgian Philosopher, Mathematician, Experimental Psychologist, Hypnotist and Psychophysicist, Joseph Remi Leopold Delboeuf, who created it sometime in 1887 – 1888. In the best-known version of the.

DESIGN AND METHODSWithin-subjects experimental design. Experiment 1 tested the effect of rim width on perceived food portion size. Experiment 2 tested the effect of rim coloring on perceived food portion size. In both experiments, participants observed a series of photographic images of paired, side-by-side plates varying in designs and amounts of food. From each pair, participants were asked to select the plate that contained more food.

Multi-level logistic regression examined the effects of rim width and coloring on perceived food portion size. RESULTSExperiment 1: Participants overestimated the diameter of food portions by 5% and the visual area of food portions by 10% on plates with wider rims compared to plates with very thin rims ( P. INTRODUCTIONSmall changes in the food environment can alter perceptions of food size, influence food choices, and reduce how much food people serve themselves and consume. These environmental changes include, but are not limited to alterations in portion size (-), container size (-), food variety (, ), and visual cues about the amount consumed. As a result, it may be possible to develop environmental interventions that bypass conscious, cognitive self-control and, instead, “passively” or “mindlessly” produce consistent reductions in energy intake and weight loss over time.Plate size is one environmental factor that researchers have focused on because it may be an easy factor to manipulate.

In the last three decades, the size of the average dinner plate increased more than a third (36%). Observational data suggest that the increase in the average size of plates used at meals is concurrent with the rise in obesity rates in the United States. Pixel people game.

Research using mathematical modeling indicates that a small increase in dishware size can lead to a substantial increase in energy intake, particularly if food is energy dense. Experimental studies show that larger plates make a given portion size look smaller. However, smaller plates did not reduce food intake at meals in laboratory studies. It is possible that reducing total plate size may be insufficient to reduce intake because substantially smaller plates may make people more aware of smaller portion sizes, which might subsequently result in caloric compensation.

However, not all same-sized plates are equal. It may be necessary to pay more attention to plate design characteristics, such as plate color and rim design.Plate designs that make use of visual illusions, such as the Delboeuf illusion, may independently affect perceived portion size and subsequent food intake. The Delboeuf illusion demonstrates that a circle appears larger when surrounded by a slightly larger circle, but smaller when surrounded by a much larger circle. The proximity and the color contrast of the concentric circles affect the illusion (-). Research suggests that when the space between concentric circles is small (right image of ), the circles appear to be one whole object. Therefore, people are more likely to emphasize the similarities between the two circles and perceive the inner circle as looking larger than it actually is. Conversely, when the space between concentric circles is large (left image of ), the circles are perceived as two different objects.

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Therefore, people will emphasize the differences between the two circles , leading the inner circle to be perceived as smaller than it actually is. In the case of food on a plate, a portion of food may be perceived as larger on a small plate, but smaller on a large plate due to the space between the food and the edge of the plate. Increasing color contrast between the circles has also been shown to enhance the differences between concentric circles. Manipulating rim coloring may highlight the edge of the outer circle and color contrast leads people to perceive the size of the inner circle as larger than it actually is (, ) and perceive a larger food portion size when the color of the plate is different from the color of the food. The Delboeuf IllusionRecent research by Van Ittersum and Wansink illustrates that the Delboeuf illusion influences serving behavior as the diameter of dishware increases and when there is a color contrast between food and dishware.

Big bowls (larger diameter) lead people to serve more food and small bowls (smaller diameter) lead people to serve less food. People also serve themselves more food when food and plates had similar coloring (low-contrast).

Conversely, people serve themselves less food when food and plates were different colors (high-contrast).The current study extends previous research on how the Delboeuf illusion applies to food on a plate. Because the rim of a round plate can be conceptualized as an outer circle surrounding food, we hypothesized that the Delboeuf illusion would apply to plate rims surrounding food on a plate. We describe two experiments in which we manipulated images of plate rim designs and food portions on plates. Our goal was to determine the effect of rim width and color on the perception of portion size. To do this, we quantified perceived food portion size for each rim design used in the study. Experiment 1 examines the effect of rim width on perceived food portion size.

Experiment 2 examines the effect of rim coloring on perceived food portion size. Prior work suggests that the Delboeuf illusion is strongest when the outer circle is only slightly larger and/or the color is more greatly contrasted with the inner circle (-).

Therefore, in Experiment 1 we hypothesized wider rims (and thus the closer the inner edge of the rim surrounds the food) would cause food to appear larger on the same sized plate (Hypothesis 1). In Experiment 2 we hypothesized colored rims (highlighting the rim to create contrast) would cause food to appear larger than uncolored rims (Hypothesis 2). Results could help inform a superior plate design to influence perceived portion size.

ParticipantsWe recruited adult participants (age 18 years or older) via Amazon’s Mechanical Turk (AMT), an online labor market that allows researchers to run experiments in similar formats to computer simulations. AMT has proven to be a reliable tool to conduct behavioral experiments quickly, with valid data.

Workers in AMT tend to be more representative of the US population as a whole and exhibit behaviors and biases more similar than participants recruited from traditional university subject pools. On AMT, we posted a task that required participants to complete an experiment in exchange for $0.50. The task was only visible to participants who were in the United States and were considered to be good workers, defined as having greater than 95% of their past AMT surveys approved as acceptable for data-use by other surveyors. Research DesignBoth experiments used a within-subject experimental design. In each experiment, participants observed multiple side-by-side photographic images of two plates of identical size (total diameter 600 pixels).

In both experiments we included test stimuli with seven food portion sizes (images were sized to 170, 175, 180, 185, 190, 195, 200 pixels in diameter) on plates with varying rim characteristics in a random order to quantify perceived food size for each rim design used in the study. Every rim characteristic and food size combination was then compared to a standard stimulus (i.e. A referent plate), defined as an image with a 185 pixel-food portion size on a plate and a rim width-to-plate radius ratio of 1/3 with no rim coloring. Varying food portion sizes in addition to plate design characteristics is instrumental to quantifying the effects of rim size and coloring on perceived portion using a psychophysical response curve (described below). The test stimuli showing varying food portion sizes and rim characteristics were presented randomly to the left or right of the standard stimulus and the trials were displayed in random order. From each pair, participants were asked to select the plate that contained more food. Food type (macaroni and cheese or fruit salad) was the same in both images within each trial but varied from trial-to-trial and subject-to-subject.

Examples of pictures used as stimuliA) Standard stimulus (i.e. Food size of 185 pixels on a plate with a 1/3 rim width-to-plate radius proportion) is on right; Rimless plate with same food size is on left and B) Standard stimulus is on left; same rim size with smaller food size is on rightExperiment 1 consisted of 42 trials (7 depicted food portion sizes × 6 rim widths; no rim, and 1/8, 1/4, 1/3, 3/8, and 1/2 rim width-to-plate radius proportions). Rim widths were chosen by methodically increasing the rim width-to-plate radius proportion of a plate with no rim until the rim width-to-plate radius proportion was half the size of the plate, and no longer judged realistic in a real world setting.Experiment 2 consisted of 28 trials (7 depicted food portion sizes × 4 rim colors; plain uncolored rim, solid blue colored rim, colored blue line marking the inner border of rim, and colored blue lines around inner and outer borders of rim). All plates (standard and test stimuli) had a standard rim of a 1/3 rim width-to-plate radius proportion. Because research shows that increasing color contrast between the circles enhances the differences between concentric circles , leading people to perceive the size of the inner circle as smaller than it actually is (, ), we chose a dark rim color to create contrast against the white plate, highlighting the inner rim surrounding the food image. We also wanted the plate to look as realistic as possible and chose blue because it is one of the most popular plate colors in dishware catalogues. Rim coloring designs (highlighting the rim width as single line on the inner border; highlighting the rim around the inner and outer border of the rim; and coloring the entire rim) were chosen to provide visual cues and highlight the multiple concentric circles on a plate with a rim (Refer to images of plates in ).

Psychophysical Model of Food Portion SizeTo examine how adults estimate food portion size based on plate rim design, we used a psychophysical research approach that is frequently used to describe the relationship between subjective perceptions of objective differences. We created psychophysical response curves based on a participant’s ability to correctly identify a larger food portion size when comparing images of plates with different food portion sizes and/or rim characteristics with a standard food portion size and design.

Each point on the curve represents the probability of choosing a depicted food size compared to the standard stimulus for each rim design. The point of equivalence, or where each curve crosses 50% probability, marks the point where participants cannot distinguish the difference in food portion size between the test and standard stimulus, even when they truly exist; where there is an equal 50% chance that participants pick the standard stimulus versus the test stimulus. Comparing points of equivalence allows one to estimate the magnitudes of over- or under-estimating in perceived food portion sizes across the different rim characteristics by examining the horizontal shift of the response curve. Statistical AnalysisMulti-level logistic regression examined the main effect of rim characteristic on the probability of choosing a depicted food size compared to the standard stimulus across rim characteristics, adjusting for the fixed effects of depicted test stimulus food size, food type, the rim characteristics by food size interaction, and a random effect for within person variation. We include the rim characteristics × food size interaction term in the primary analysis model, to obtain an unbiased estimate of the main effect of rim characteristics, as recommended in the statistical literature (-). The interaction between rim characteristic and depicted food portion size tested whether the probability of picking the test stimulus (i.e. Rim characteristic) differed by the depicted food size.

When interaction terms were significant, post-hoc analyses explored how food size differed by plate design. In all the analysis models, food portion sizes and rim characteristics were centered on their standard stimulus values. Descriptive statistics were used to calculate the magnitude of the relative difference in choosing the test stimulus using odds ratios with 95% confidence intervals, and the points of equivalence for each rim characteristic across food sizes, with the reference point being the standard stimulus. The Wald χ 2 test statistic tested the null hypothesis that there is no significant difference between rim characteristics. All tests were two-sided and conducted at the 0.05 level of significance. Data were analyzed with version 9.2 of the SAS statistical software package (SAS, Cary, NC). Resultsillustrates the probability of choosing a depicted food size compared to the standard stimulus for each rim width-to-plate radius proportion.

Presents a summary of the multi-level logistic model examining the effect of rim width on perceived food portion size. Depicted food portion size was significant in the model ( P. Β (SE)P valueOdds Ratios(95% Confidence Interval)Point ofEquivalence a(% Exaggeration)Small Food Size bMedium Food Size cLarge Food Size dIntercept0.46 (0.01).Denotes statistical significanceThe odds ratios indicate that when comparing the same food size, people were 1.5 times as likely to pick the widest rim plate as having more food compared to the standard plate.

Conversely, people were 0.6 times as likely to pick the plate with no rim as having more food. The point of equivalence values estimate the differences in perceived food portion sizes between plates with different rim widths and indicated that there is a 5.2% difference in perceived diameter of the food image when food is viewed on a plate with a very wide rim (1/2 rim width-to-plate radius proportion) compared to a plate with a very narrow rim (1/8 rim width-to-plate radius proportion).

Resultsillustrates the probability of choosing a depicted food size compared to the standard stimulus for each rim coloring. Presents a summary of the multi-level logistic model examining the effect of rim coloring on perceived food portion size. Depicted food portion size was significant in the model ( P. Β (SE)P valueOdds Ratios(95% Confidence Interval)Point ofEquivalence a(% Exaggeration)Small Food Size bMedium Food Size cLarge Food Size dIntercept0.52 (0.02).Denotes statistical significanceThe odds ratios indicate that with small food sizes, people were 2.3 times as likely to pick the rims with solid blue coloring as having more food compared to a plate with no rim coloring. However, with larger food sizes, people were only 0.6 times as likely to pick rims with solid blue coloring as having more food compared to a plate with no rim coloring. The point of equivalence indicated there is a 1.5-1.6% overestimation in diameter of food portion size when food is viewed on a plate with rim coloring compared to a plate without rim coloring. DISCUSSIONWe examined whether a plate’s rim design, namely rim width and rim coloring affect perceived food portion size.

Confirming that the Delboeuf illusion applies to plate rims surrounding food on a plate, these experiments found that wider and colored rims each exaggerate perceptions of the amount of food on a plate, making images of food look larger. Food type had no effect on the illusion, suggesting that the illusion persists regardless of the type of food depicted on the plate. The effect of rim width is greater with larger food portion sizes consistent with our expectations from the Delboeuf illusion. However, the effect of rim coloring is greater with smaller food portion sizes. The color contrast illusion was inverted when food sizes were larger, resulting in rim coloring making food appear smaller on a plate.The psychophysical response curve illustrated not only that wider rims and rim coloring exaggerate perceived food portion size, but illustrate how much more food is perceived on the plate. In Experiment 1, the point of equivalence illustrated that food on plates with wider rims looks approximately 5% larger in diameter than food on plates with a very thin rim.

This difference in diameter is equivalent to a two dimensional area of 10% which would represent an even greater exaggeration in terms of three-dimensional food volume. In Experiment 2, food on plates with colored rims looks approximately 1.1% larger in diameter, equivalent to an exaggeration of 3% larger in area compared to food on plates with no rim coloring. This research was supported, in part, by Award Numbers R01HL096015 and U01HL103629 from the National Heart, Lung, and Blood Institute and the Children’s Health Research Institute at Stanford University. McClain was supported by Public Health Service Training Grant 5 T32 HL 007034 from the National Heart, Lung, and Blood Institute.

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Heart, Lung, And Blood Institute, the National Institutes of Health, or Stanford University.