The University of Sussex, UK, is recruiting participants aged 18 or over to complete an online questionnaire relating to the visual symptoms associated with visual snow syndrome and hallucinogen persisting perception disorder (HPPD). To participate you should experience the visual symptoms associated with visual snow syndrome and/or HPPD. The questionnaire will take approximately one to two hours to complete, depending on the number of questions you answer and the detail of your responses. It will include answering some questions about what visual symptoms you experience alongside on-screen illustrations of those visual symptoms. You will also be asked about how your visual symptoms impact your life. Other questions include those which ask about some aspects of your medical history. The questionnaire must be completed either on a laptop computer, a desktop computer or an iPad. To complete the questionnaire, please visit: https://universityofsussex.eu.qualtrics.com/jfe/form/SV_blrsONUZAQ19BGZ Some extras: - You can complete the questionnaire in more than one sitting so long as you have cookies enabled and return to the same browser on the same computer. Your progress is automatically saved when you continue to a new page within the questionnaire. Your partial responses are saved for one week. - We are carrying out ongoing research on visual snow syndrome and hallucinogen persisting perception disorder at the University of Sussex. This is the first of a series of questionnaires which will be released over the coming months. It’s really important for our research that we receive a high number of responses, and so I would encourage you to complete this questionnaire if you are able to!