Illusory Conjunctions Illusory conjunctions occur when features such as colour and shape are combined incorrectly. For example, when participants are shown a red A and blue X, they sometimes report seeing a blue A and red X. Other kinds of errors, such as a misreported letter (e.g., reporting T when no T was presented) or misreported colour (reporting green when no green was presented) occur rarely, indicating that illusory conjunctions are not the result of guessing (based on Robertson, 2003).