Abstract
Prolonged exposure to wide (thin) bodies causes a perceptual aftereffect such that subsequently viewed bodies appear thinner (wider) than they actually are. This phenomenon is known as visual adaptation. We used the adaptation paradigm to examine the gender selectivity of the neural mechanisms encoding body size and shape. Observers adjusted female and male test bodies to appear normal-sized both before and after adaptation to bodies digitally altered to appear heavier or lighter. In Experiment 1, observers adapted simultaneously to bodies of each gender distorted in opposite directions, e.g., thin females and wide males. The direction of resultant aftereffects was contingent on the gender of the test stimulus, such that in this example female test bodies appeared wider while male test bodies appeared thinner. This indicates at least some separation of the neural mechanisms processing body size and shape for the two genders. In Experiment 2, adaptation involved either wide females, thin females, wide males or thin males. Aftereffects were present in all conditions, but were stronger when test and adaptation genders were congruent, suggesting some overlap in the tuning of gender-selective neural mechanisms. Given that visual adaptation has been implicated in real-world examples of body size and shape misperception (e.g., in anorexia nervosa or obesity), these results may have implications for the development of body image therapies based on the adaptation model.
Highlights
While human perception is impressive in many respects, it is by no means infallible
These observations were confirmed by a 2way ANOVA1, where a significant interaction between adaptation direction and test gender reaffirmed the presence of contingent aftereffects F(1,25) = 12.045, p = 0.002, ηp2 = 0.325
Even if there had been a slight imbalance in the sizes and shapes of male and female stimuli, resulting in an asymmetric adaptation effect in the Male+/Female− compared to the Male−/Female+ adaptation condition, this should have resulted in equivalent Point of Subjective Normality (PSN) when male and female bodies were used as test stimuli
Summary
While human perception is impressive in many respects, it is by no means infallible. For example, many humans make consistent errors when estimating the size and shape of their own bodies – a phenomenon known as body size and shape misperception (BSSM; Challinor et al, 2017; Brooks et al, 2019b). It has been shown that some individuals who are obese or overweight may misperceive their body size as being normal (Truesdale and Stevens, 2008; Wetmore and Mokdad, 2012), while some individuals who are underweight, including those with the eating disorder anorexia nervosa, are prone to overestimate their body size (Probst et al, 1998; Cornelissen et al, 2017; Molbert et al, 2017) This example of regression to the mean for perceived body size has been referred to as “contraction bias” (Cornelissen et al, 2016). It is well known that prolonged exposure to a particular sensory stimulus (the “adaptor”) causes the perception of subsequently encountered “test” stimuli to be systematically biased. Often this aftereffect involves the test stimulus taking on perceived qualities that are, in a sense, opposite to the adaptor. Repeated viewing of thin bodies, such as those of models in the media may cause a fattening aftereffect, leading individuals to overestimate their size (Brooks et al, 2019b; Challinor et al, 2017)
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