Visual event related potentials modulated by contextually relevant and irrelevant olfactory primes

Visual evoked potentials were recorded from 16 scalp locations on 10 young subjects during presentation of a series of high-quality photographs on a c omputer screen. The photographs consisted of equal numbers of pictures of f ruit (citrus and non-citrus fruits), flowers (roses and other flowers) and objects (e.g. buildings, vehicles, animals etc.). Every picture was differe nt in order to avoid repetition effects. The pictures were presented under four odour conditions: no odour, rose odour, jasmine odour and citrus odour . in order to keep the subjects alert they were asked to make categorizing decisions for the visual stimuli (e.g. flower or fruit). No decision was re quired concerning the relationship between the visual stimulus and the odou r. As expected, the N400 peak was more negative when the picture stimulus d id not match the odour. It is hypothesized that the N400 peak can be used a s a measure of relatedness of a sensory stimulus to a previous or on-going prime, irrespective of the made of the stimuli.