Olfactory discrimination: when vision matters?

Many previous studies have attempted to investigate the effect of visual cues on olfactory perception in humans. The majority of this research has only looked at the modulatory effect of color, which has typically been explained in terms of multisensory perceptual interactions. However, such crossmodal effects may equally well relate to interactions taking place at a higher level of information processing as well. In fact, it is well-known that semantic knowledge can have a substantial effect on people's olfactory perception. In the present study, we therefore investigated the influence of visual cues, consisting of color patches and/or shapes, on people's olfactory discrimination performance. Participants had to make speeded odor discrimination responses (lemon vs. strawberry) while viewing a red or yellow color patch, an outline drawing of a strawberry or lemon, or a combination of these color and shape cues. Even though participants were instructed to ignore the visual stimuli, our results demonstrate that the accuracy of their odor discrimination responses was influenced by visual distractors. This result shows that both color and shape information are taken into account during speeded olfactory discrimination, even when such information is completely task irrelevant, hinting at the automaticity of such higher level visual-olfactory crossmodal interactions.