Is this blood? An ERP study on the visual identification of red fluids in patients with blood phobia

Blood can be easily recognized in situations involving injury. However, very little is known about the ability of humans to identify blood without such context information. We investigated the blood detection capacity and associated electrocortical correlates (event-related potentials) in 20 women with blood phobia and 20 non-phobic females. The participants viewed images depicting droplets of pig blood, and water with pink or red food coloring. They were asked to decide, whether the pictures showed real blood or not. Blood provoked enhanced P100 amplitudes (90-140 ms) in blood phobics. Late positivity (P300: 340-500 ms) as well as classification accuracy did not differ between the groups. However, blood elicited a general P300 enhancement (relative to red and pink fluids) possibly reflecting elevated visual attention to blood as a general characteristic in humans. The P100 augmentation in blood phobics very likely reflects enhanced early selective attention. Patients with BII phobia showed prioritized visual processing of blood without having to rely on contextual information.