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BACKGROUND: During observation of the Necker cube perception becomes unstable and alternates repeatedly between a from-above-perspective ("fap") and a from-below-perspective ("fbp") interpretation. Both interpretations are physically equally plausible, however, observers usually show an a priori top-down bias in favor of the fap interpretation. Patients with Autism spectrum disorder are known to show an altered pattern of perception with a focus on sensory details. In the present study we tested whether this altered perceptual processing affects their reversal dynamics and reduces the perceptual bias during Necker cube observation. METHODS: 19 participants with Asperger syndrome and 16 healthy controls observed a Necker cube stimulus continuously for 5 minutes and indicated perceptual reversals by key press. We compared reversal rates (number of reversals per minute) and the distributions of dwell times for the two interpretations between observer groups. RESULTS: Asperger participants showed less perceptual reversal than controls. Six Asperger participants did not perceive any reversal at all, whereas all observers from the control group perceived at least five reversals within the five minutes observation time. Further, control participants showed the typical perceptual bias with significant longer median dwell times for the fap compared to the fbp interpretation. No such perceptual bias was found in the Asperger group. DISCUSSION: The perceptual system weights the incomplete and ambiguous sensory input with memorized concepts in order to construct stable and reliable percepts. In the case of the Necker cube stimulus, two perceptual interpretations are equally compatible with the sensory information and internal fluctuations may cause perceptual alternations between them-with a slightly larger probability value for the fap interpretation (perceptual bias). Smaller reversal rates in Asperger observers may result from the dominance of bottom-up sensory input over endogenous top-down factors. The latter may also explain the absence of a fap bias.

Ambiguous figures attract observers because perception alternates between different interpretations while the sensory information stays unchanged. Understanding the underlying processes is difficult because the precise time instant of this endogenous reversal event needs to be known but is difficult to measure. Presenting ambiguous figures discontinuously and using stimulus onset as estimation of the reversal event increased temporal resolution and provided a series of well-confirmed EEG signatures. In the current EEG study we used this 'onset paradigm' for the first time with Boring's old/young woman stimulus. We found an early occipital event-related potential (ERP) correlate of reversals between the perception of the old woman and the perception of the young woman that fits well with previous ERP findings. This component was not followed by the often-reported occipito-parietal Reversal Negativity at 260 ms, but instead by an occipito-temporal N170, that is typically reported with face stimuli. We interpret our results as follows: ambiguity conflicts take place during processing of stimulus elements in early visual areas roughly 130 ms after stimulus onset. The disambiguation of these elements and their assembly to object 'gestalts' result from an interplay between early visual and object-specific brain areas in a temporal window between 130 and 260 ms after stimulus onset. In the particular case of Boring's old/young woman the processes of element disambiguation and gestalt construction are already finished at 170 ms and, thus, 90 ms earlier than in the case of ambiguous geometric figures (eg Necker cube or Schroeder staircase) or of binocular rivalrous gratings.

INTRODUCTION: Few studies so far have directly compared the neural processing of visual sexual stimuli in men and women. Also, most of these studies only compared sexual with neutral stimuli, making it difficult to disentangle sexual stimulus processing from general emotional processing. AIM: The current study aimed to explore gender commonalities and differences in neural activity associated with the processing of visual sexual stimuli in a large sample of 50 men and 50 women. In order to disentangle effects of sexual processing from those of general emotional processing, we employed sexual, neutral, positive, and negative emotional pictures. METHODS: Subjects passively viewed sexual, neutral, positive, and negative emotional pictures during a functional magnetic resonance imaging (fMRI) session. Pictures were presented in 24 blocks of five pictures each. Every block was rated immediately after its presentation with respect to valence, arousal, and sexual arousal. MAIN OUTCOME MEASURES: Blood oxygen level dependent responses measured by fMRI and subjective ratings. RESULTS: fMRI analysis revealed a distributed network for the neural processing of sexual stimuli comprising the hypothalamus, the nucleus accumbens, as well as orbitofrontal, occipital, and parietal areas. This network could be identified (i) for both men and women, with men showing overall stronger activations than women and (ii) independent of general emotional arousal or valence effects. CONCLUSION: Our data speak in favor of a common neural network associated with the processing of visual sexual stimuli in men and women. Apart from the observed gender commonalities, overall stronger responses in men were observed that might indicate stronger sexual responsivity in men.

This functional magnetic resonance imaging study investigated long-term effects of cognitive behavior therapy (CBT) in individuals suffering from spider phobia. Ten female patients who had shown positive immediate CBT effects were invited to take part in a 6-month follow-up investigation. Here, the patients, along with eight non-phobic females, were presented with the same pictures depicting spiders, generally disgust-inducing, generally fear-inducing and neutral content, which they had viewed 6 months earlier. Patients' self-report and overt behavior indicated a positive long-term clinical improvement. Related hemodynamic changes included an increase in medial orbitofrontal cortex (OFC) activity. As the medial OFC is involved in emotion-related learning, especially in the representation of positive stimulus-outcome associations, we conclude that the medial OFC effect constitutes the neuronal basis of the lasting positive CBT outcome. Activity to disorder-irrelevant pictures decreased across the sessions in the lateral OFC and in the insula, which most likely reflects general habituation.

We investigated subjective and hemodynamic responses towards disgust-inducing, fear-inducing, and neutral pictures in a functional magnetic resonance imaging study. Within an interval of 1 week, 24 male subjects underwent the same block design twice in order to analyze possible response changes to the repeated picture presentation. The results showed that disgust-inducing and fear-inducing scenes provoked a similar activation pattern in comparison to neutral scenes. This included the thalamus, primary and secondary visual fields, the amygdala, the hippocampus, and various regions of the prefrontal cortex. During the retest, the affective ratings hardly changed. In contrast, most of the previously observed brain activations disappeared, with the exception of the temporo-occipital activation. An additional analysis, which compared the emotion-related activation patterns during the two presentations, showed that the responses to the fear-inducing pictures were more stable than the responses to the disgust-inducing ones.

fMRI studies have shown that the perception of facial disgust expressions specifically activates the insula. The present fMRI study investigated whether this structure is also involved in the processing of visual stimuli depicting non-mimic disgust elicitors compared to fear-inducing and neutral scenes. Twelve female subjects were scanned while viewing alternating blocks of 40 disgust-inducing, 40 fear-inducing and 40 affectively neutral pictures, shown for 1.5 s each. Afterwards, affective ratings were assessed. The disgust pictures, rated as highly repulsive, induced activation in the insula, the amygdala, the orbitofrontal and occipito-temporal cortex. Since during the fear condition the insula was also involved, our findings do not fit the idea of the insula as a specific disgust processor.

fMRI studies have shown that the perception of facial disgust expressions specifically activates the insula. The present fMRI study investigated whether this structure is also involved in the processing of visual stimuli depicting non-mimic disgust elicitors compared to fear-inducing and neutral scenes. Twelve female subjects were scanned while viewing alternating blocks of 40 disgust-inducing, 40 fear-inducing and 40 affectively neutral pictures, shown for 1.5 s each. Afterwards, affective ratings were assessed. The disgust pictures, rated as highly repulsive, induced activation in the insula, the amygdala, the orbitofrontal and occipito-temporal cortex. Since during the fear condition the insula was also involved, our findings do not fit the idea of the insula as a specific disgust processor.