People who present with minor damage to the small intestine may have seronegative findings so many patients with coeliac disease often are missed. In patients with villous atrophy, anti-endomysial (EMA) antibodies of the immunoglobulin A (IgA) type can detect coeliac disease with a sensitivity and specificity of 90% and 99%, respectively. Serology for anti-transglutaminase antibodies (anti-tTG) was initially reported to have a higher sensitivity (99%) and specificity (>90%). However, it is now thought to have similar characteristics to anti-endomysial antibodies. Both anti-transglutaminase and anti-endomysial antibodies have high sensitivity to diagnose people with classic symptoms and complete villous atrophy, but they are only found in 30–89% of the cases with partial villous atrophy and in less than 50% of the people who have minor mucosal lesions (duodenal lymphocytosis) with normal villi.Tissue transglutaminase modifies gluten peptides into a form that may stimulate the immune system more effectively. These peptides are modified by tTG in two ways, deamidation or transamidation. Modern anti-tTG assays rely on a human recombinant protein as an antigen. tTG testing should be done first as it is an easier test to perform. An equivocal result on tTG testing should be followed by anti-endomysial antibodies.Guidelines recommend that a total serum IgA level is checked in parallel, as people with coeliac with IgA deficiency may be unable to produce the antibodies on which these tests depend ("false negative"). In those people, IgG antibodies against transglutaminase (IgG-tTG) may be diagnostic.If all these antibodies are negative, then anti-DGP antibodies (antibodies against deamidated gliadin peptides) should be determined.
The "afterimage on empty shape" effect is related to a class of effects referred to as contrast effects.In this effect, an empty (white) shape is presented on a colored background for several seconds. When the background color disappears (becomes white), an illusionary color similar to the original background is perceived within the shape. The mechanism of the effect is still unclear, and may be produced by one or two of the following mechanisms:

During the presentation of the empty shape on a colored background, the colored background induces an illusory complementary color ("induced color") inside the empty shape. After the disappearance of the colored background an afterimage of the "induced color" might appear inside the "empty shape". Thus, the expected color of the shape will be complementary to the "induced color", and therefore similar to the color of the original background. After the disappearance of the colored background, an afterimage of the background is induced. This induced color has a complementary color to that of the original background. It is possible that this background afterimage induces simultaneous contrast on the "empty shape". Simultaneous contrast is a psychophysical phenomenon of the change in the appearance of a color (or an achromatic stimulus) caused by the presence of a surrounding average color (or luminance).