Event-related potentials when identifying or color-naming threatening schematic stimuli in spider phobic and non-phobic individuals

Iris-Tatjana Kolassa 0 1 Frauke Musial 1 Stephan Kolassa 1 Wolfgang HR Miltner 1 0 Clinical Psychology & Neuropsychology, University of Konstanz , P.O. Box 5560, D25, 78457 Konstanz , Germany 1 Biological and Clinical Psychology, Friedrich Schiller University Jena , Germany Background: Previous studies revealed increased parietal late positive potentials (LPPs) in response to spider pictures in spider phobic individuals. This study searched for basic features of fear-relevant stimuli by investigating whether schematic spider images are sufficient to evoke differential behavioral as well as differential early and late ERP responses in spider phobic, social phobic (as a clinical control group), and non-phobic control participants. Methods: Behavioral and electrophysiological correlates of the processing of schematic spider and flower images were investigated while participants performed a color (emotional Stroop) and an object identification task. Stimuli were schematic pictures of spiders and flowers matched with respect to constituting visual elements. Results: Consistent with previous studies using photographic spider pictures, spider phobic persons showed enhanced LPPs when identifying schematic spiders compared to schematic flowers. In addition, spider phobic individuals showed generally faster responses than the control groups. This effect was interpreted as evidence for an increased general behavioral hypervigilance in this anxiety disorder group. Furthermore, both phobic groups showed enhanced P100 amplitudes compared to controls, which was interpreted as evidence for an increased (cortical) hypervigilance for incoming stimuli in phobic patients in general. Finally, all groups showed faster identification of and larger N170 amplitudes in response to schematic spider than flower pictures. This may reflect either a general advantage for fear-relevant compared to neutral stimuli, or might be due to a higher level of expertise in processing schematic spiders as compared to the more artificially looking flower stimuli. Conclusion: Results suggest that schematic spiders are sufficient to prompt differential responses in spider-fearful and spider-non-fearful persons in late ERP components. Early ERP components, on the other hand, seem to be modified by anxiety status per se, which is consistent with recent theories on general hypervigilance in the anxiety disorder spectrum. - Background Spiders are genuinely feared stimuli for individuals with spider phobia, but they are also considered fear-relevant (ancestral) stimuli for humans in general, and it has been hypothesized that such stimuli are detected and processed preferentially to other stimuli [1-4]. In support of this hypothesis, hman, Flykt, and Esteves [5] reported faster detection of fear-relevant stimuli among neutral stimuli than vice versa in a visual search task (however, see [6] for a critical comment on the study). Furthermore, phobic persons detected feared stimuli even faster than fear-relevant stimuli they did not fear [5]. Thus, it has been suggested that phobic individuals are characterized by an attentional bias towards their feared object, i.e., phobics' attention is drawn involuntarily and automatically to the feared object, and they process it with high selectivity and priority ([7-9], for an overview see [9]). However, in a visual search paradigm Miltner et al. [6] observed no threat advantage in spider phobic and control persons for spiders when participants' task was to search for a spider target stimulus among a crowd of neutral stimuli displayed in a 4 4 grid pattern search array. Instead, they found delayed responses in spider phobic individuals to a neutral target (mushroom) in a crowd of neutral objects (flowers) in the presence of a spider distractor. In the same series of studies, by measuring eye movements they observed that phobic individuals first moved their eyes toward the spider distractor before focusing on the neutral target, delaying phobics' target detection times. These findings might suggest that an attentional bias is present in phobic persons only if the feared stimulus is not the focus of attention (cf. also [10]). One paradigm that allows the investigation of the processing of threatening stimuli when the threatening information itself is not task-relevant is the emotional Stroop paradigm. The emotional Stroop paradigm is a modified version of the original Stroop task [11] and is commonly used to assess attentional biases in anxiety disorders or high trait anxiety (for an overview see [9]). In this paradigm, the difference in color-naming latencies between emotionally relevant and emotionally neutral words or pictures is measured. The phenomenon that anxious persons show prolonged response latencies when color-naming feared stimuli has been called emotional Stroop interference (see [9]). Numerous studies have reported emotional interference in animal phobic individuals ([1217]; but see [18]). The emotional Stroop paradigm can be regarded as an implicit task, i.e. the emotional content of the stimulus is not the focus of attention, as compared to an explicit task in which subjects explicitly identify the emotional content of the stimulus. It has been shown that task conditions affect brain activation to emotional stimuli [10,19-21], and thus implicit and explicit tasks should Although spiders are commonly regarded as fear-relevant stimuli, it remains largely unclear which perceptual properties make a spider fear-relevant. It has been postulated that specific feature detectors with high sensitivity to elementary threat features exist, "programmed" either genetically or by conditioning (cf. [1,22]). These detectors screen incoming information for specific threat cues (e.g. high intensity or biologically prepared stimulus characteristics). As soon as a specific threat feature has been detected, the arousal system is activated still preattentively, and the stimulus is selected for preferential treatment by succeeding stages of stimulus elaboration [1]. However, as hman et al. ([5], p. 475) remark, "such elementary threat features [. . .] still remain to be specified". This study searched for basic features of fear-relevant stimuli by investigating whether schematic spider pictures are sufficient to evoke differential responses in spider phobic and spider-non-phobic individuals, in order to provide first insights regarding the question which properties constitute the fear-relevance of a spider. The advantages of schematic stimuli are obvious: schematic stimuli reduce the depicted object to its essential features and are therefore simple and unequivocal. Schematic stimuli show less variance: in the case of spider stimuli there is no confoundation with spider species, hairiness, size, or camera angle. Finally, it is easier to design a control stimulus matched with respect to color, size, and spatial frequency: if one shifts the angles of the legs of a schematic spider ima (...truncated)