![]() Linked mastoids (TP9 and TP10) served as reference electrodes. The initial sampling rate was 1000 Hz, but data were down-sampled off-line to 250 Hz. The impedance of each electrode was kept below 10 kOhm. The remaining electrodes were interspaced equally between these 21 sites. The experiment was performed using Presentation® software (Version 17.1, Neurobehavioral Systems, Inc., Berkeley, CA, EEGĮEG was recorded from 64 EEG electrodes with 21 electrodes localized according to the 10–20 system on participants’ heads. Each Oddball task consisted of 500 stimuli and lasted about 10 minutes. Each stimulus was displayed for 500 ms at the center of a monitor screen, separated by an inter-stimulus interval of 1000 to 2000 ms. Stimuli occupied a visual angle of 4.6 degrees. The three types of stimuli comprising the Oddball paradigm included triangles as frequent stimuli, appearing in 80% of trials while circles and squares served as rare stimuli, each appearing in 10% of trials. On average, participants earned 24 Euros for the whole study. Participants received 6 Euros per hour for participation. Mean age of participants was 23.1 years (range 18–44 years). Our sample consisted of 60 participants (30 female, 30 male) with 20 low suggestible, 20 middle suggestible and 20 high suggestible participants. A total number of 0 to 3 successful tasks indicates low suggestibility, 4 to 7 moderate suggestibility and 8 to 12 tasks high suggestibility 11. ![]() At the end of the test, participants rated whether and how well they responded on each of these 12 tasks. ![]() arm immobilization), ideomotor items (e.g. This test consists of 12 suggestions including challenge items (e.g. The assessment of suggestibility of participants was organized in groups of about 8 participants using the Harvard Group Scale of Hypnotic Susceptibility 9. The study was approved by the ethics committee of the Faculty of Social and Behavioral Sciences of the Friedrich Schiller University of Jena and followed the ethics declaration of Helsinki. All participants signed informed consent statements. Participants with neurological, psychological, cardiovascular, or visual diseases were excluded from the experiment. We recruited healthy participants at the University of Jena. Furthermore, it was shown repeatedly that the less probable the rare stimuli, the larger the magnitude of the P3b response 6. Many previous studies have shown that rare to-be-counted stimuli are associated with a large late component of the event-related brain potential called P3b 6, 7. Participants were requested to count one of the rare stimuli and leave the other stimuli unattended. Using a three stimulus Oddball paradigm 6, one frequent and two rare stimuli were presented in random order on the monitor. The translated text of the suggestion is provided as supplementary online material. In our study, we show that the suggestion of a virtual perceptual blockade can significantly block one’s visual perception and the cognitive performance associated with correct and unimpaired perception.Īfter the induction of hypnosis, we suggested to participants that they would see a virtual wooden board in front of their eyes blocking their view of a monitor in front of them, although being required to keep the eyes open. When susceptible participants are suggested to see grey instead of colored stimuli or vice versa while hypnotized, they see what they are suggested, mirrored by corresponding changes in visual areas of the brain 1. Another impressive example is the impact of suggestions on color vision. Pain can be significantly reduced by suggestions of analgesia while participants are hypnotized 5. To date, the most impressive and best-examined example for the power of suggestion is its effect on pain. It is an astonishing power of the human mind that a suggestion during hypnosis can have a deep impact on behavior and perception 1, 2, 3, 4. This illustrates the impact of suggestions and the power of mind. We conclude that the suggestion of the blockade affects later stages of visual perception, leaving early processes intact. In contrast, earlier brain responses (N1, P2) that reflect basic processing of the visual stimuli were not affected by the suggested blockade. Smaller P3b amplitudes were significantly associated with deficient counting performance, and this effect was largest in participants who reported the blockade as real. At the same time, the P3b amplitude of the event-related brain potential was about 37% reduced. In the hypnosis condition, counting performance was about 20% worse than in the control condition. ![]() Participants counted rare visual stimuli presented on a screen, once during a hypnosis condition where they were suggested that their vision of the screen is blocked by a virtual wooden board in front of their eyes and once during a control condition without suggestion. The present study investigated the effects of suggestion on the processing of visual stimuli. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |