Treatment effect on biases in size estimation in spider phobia

- We found a clear size estimation bias in spider phobic participants towards a living spider.
- We found that effective exposure treatment conducted in virtual reality to reduce the bias in size estimation.
- Post treatment size bias in spider phobic participants was comparable to the size bias displayed by healthy participants.

BackgroundThe current study investigates biases in size estimations made by spider-phobic and healthy participants before and after treatment.MethodForty-one spider-phobic and 20 healthy participants received virtual reality (VR) exposure treatment and were then asked to rate the size of a real spider immediately before and, on average, 15 days after the treatment. During the VR exposure treatment skin conductance response was assessed.ResultsPrior to the treatment, both groups tended to overestimate the size of the spider, but this size estimation bias was significantly larger in the phobic group than in the control group. The VR exposure treatment reduced this bias, which was reflected in a significantly smaller size rating post treatment. However, the size estimation bias was unrelated to the skin conductance response.ConclusionOur results confirm the hypothesis that size estimation by spider-phobic patients is biased. This bias is not stable over time and can be decreased with adequate treatment.