Fear of spiders makes you believe creepy crawlies are bigger What is your biggest fear? His team recruited 57 participants with a spider phobia who were asked to undergo five encounters with live tarantulas in uncovered glass tanks and then provide size estimates. The more afraid they rated in anxiety scores the bigger they described the hairy beasts, which spanned between one and six inches. Prof Vasey said: "When it comes to phobias, it is all about avoidance as a primary means of keeping oneself safe. As long as you avoid, you cannot discover you are wrong. And you are stuck. So to the extent that perceiving spiders as bigger than they really are fosters fear and avoidance, it then potentially is part of this cycle that feeds the phobia that leads to its persistence. We are trying to understand why phobias persist so we can better target treatments to change those reasons they persist. The volunteers, who were studied over a period of eight weeks, began their encounters 12 feet from the tank and were asked to approach the spider. Once they were standing next to it, they had to guide the spider around by touching it with an 8-inch probe, and then with a shorter one. Throughout their ordeal they reported how afraid they were feeling on a scale of 0-100 according to an index of subjective units of distress. Afterwards they completed additional self-report measures of their specific fear of spiders, any panic symptoms they experienced and thoughts about fear reduction and future spider encounters. Finally, they estimated the size of the spiders - while no longer being able to see them - by drawing a single line on an index card indicating the length between the tips of its front and back legs. Prof Vasey said: "It would appear fear is driving or altering the perception of the feared object, in this case a spider. We already knew fear and anxiety alter thoughts about the feared thing. For example, the feared outcome is interpreted as being more likely than it really is. But this study shows even perception is altered by fear. In this case, the feared spider is seen as being bigger. And that may serve as a maintaining factor for the fear. The approach tasks with the spiders are a classic example of exposure therapy, a common treatment for people with phobias. Although this therapy is known to be effective, scientists still do not fully understand why it works. And for some, the effects do not last - but it is difficult to predict who will have a relapse of fear, said Prof Vasey. He and colleagues are studying these biased perceptions as well as attitudes with hopes that the new knowledge will enhance treatment for people with various phobias. The work suggests that fear not only alters one's perception of the feared thing, but also can influence a person's automatic attitude toward an object. Those who have developed an automatic negative attitude toward a feared object might have a harder time overcoming their fear. Although individuals with arachnophobia are unlikely to seek treatment, the use of spiders in this research was a convenient way to study the complex effects of fear on visual perception and how those effects might cause fear to persist, Prof Vasey noted. He added: "Ultimately, we are interested in identifying predictors of relapse so we can better measure when a person is done with treatment."