Can illusory deviant stimuli be used as attentional distractors to record vMMN in a passive three stimulus oddball paradigm?

A passive three stimulus oddball paradigm was used to investigate Visual Mismatch Negativity (vMMN) a component of the Event Related Potential (ERP) believed to represent a central pre-attentive change mechanism. Responses to a change in orientation were recorded to monochrome stimuli presented to subjects on a computer screen. One of the infrequent stimuli formed an illusory figure (Kanizsa Square) aimed to capture spatial attention in the absence of an active task. Nineteen electrodes (10-20 system) were used to record the electroencephalogram in fourteen subjects (ten females) mean age 34.5 years. ERPs to all stimuli consisted of a positive negative positive complex recorded maximally over lateral occipital areas. The negative component was greater for deviant and illusory deviant compared to standard stimuli in a time window of 170-190 ms. A P3a component over frontal/central electrodes to the illusory deviant but not to the deviant stimulus suggests the illusory figure was able to capture attention and orientate subjects to the recording. Subtraction waveforms revealed visual discrimination responses at occipital electrodes, which may represent vMMN. In a control study with 13 subjects (11 females; mean age 29.23 years), using an embedded active attention task, we confirmed the existence of an earlier (150-170 ms) and attenuated vMMN. Recordings from an intracranial case study confirmed separation of N1 and discrimination components to posterior and anterior occipital areas, respectively. We conclude that although the illusory figure captured spatial attention in its own right it did not draw sufficient attentional resources from the standard-deviant comparison as revealed when using a concurrent active task.