No abstract

The Somatic Signal Detection Task (SSDT) is a recent paradigm serving to examine perceptual processes likely relevant for somatoform disorders. We tested whether touch illusions are more easily induced in individuals suffering from somatoform disorders (SFD) and whether their perceptual threshold for tactile stimuli is lower compared to healthy controls. Thirty-three participants with SFD and 32 healthy controls reported whether they recognized near-threshold tactile stimuli at their fingertip, which were presented in half of the test trials. With a probability of 0.5, an auxiliary visual stimulus was additionally presented. Tactile detection thresholds, tactile sensitivity, response bias, and the rate of false-positive perceptions of the tactile stimulus were assessed. In both groups, the light stimulus led to an amelioration of tactile sensitivity as well as to a more liberal response style. The SFD group was characterized by a more liberal response bias in the first half of the light-absent condition compared to the healthy controls. Within the SFD group, the report of somatoform (especially pseudoneurological) symptoms correlated positively with illusory tactile perceptions in the SSDT. Tactile thresholds in the SSDT were measured reliably (r tt ϭ .86) and were significantly lower in the SFD group. The notion that general perceptual dispositions influence the formation of symptom perception may thus complement cognitive models of SFD.Keywords: Somatic Signal Detection Task, somatoform disorders, medically unexplained symptoms, tactile detection threshold, response bias Somatoform symptoms, also called "medically unexplained symptoms" (MUS), are a common phenomenon in primary health care settings (De Waal, Arnold, Eckhof, & van Hemert, 2004). Afflicted persons suffer from bodily complaints that cannot be explained sufficiently by medical conditions. Various models of somatoform disorders (SFD) have been developed, but the precise etiology of MUS and SFD is still unknown (Brown, 2004;Witthöft & Hiller, 2010). Most of the current models assume an interaction of cognitive and perceptual somatosensory processes that lead to behavioral, affective, and biological consequences. Cognitivebehavioral models emphasize factors like catastrophizing, bodyfocused attentional styles, and excessive illness behavior, for example, "doctor shopping," leading in combination to vicious circles that amplify symptom perception (Barsky, Wyshak, & Klerman, 1990;Rief, Hiller, & Margraf, 1998).According to a recently proposed filter model (Rief & Barsky, 2005), the perception of MUS is determined by factors that increase the likelihood of bodily signals (e.g., overarousal, sensitization), on the one hand, and factors that decrease activity of filter systems, on the other hand (e.g., selective attention, lack of distraction). The combination of these two factors could result in the perception of symptoms, which most individuals normally would not experience.Brown (2004) proposed an integrative, conceptual model of MUS focusing on cogniti...