Seeing ear to eye

Humans' sense of smell is far less powerful than sight, yet new findings suggest olfaction has a surprisingly significant influence on vision. Image: Flickr/linkurl:tuexperto_com3;http://www.flickr.com/photos/21626156@N02/2509246163/ The findings, published online today (July 1) in Current Biology, show that what you smell can alter your visual perception. Previous studies have linked vision with the senses of hearing and touch, "but it's kind of more surprising that olfaction -- smells -- cou

Jef Akst

| 2 min read

Humans' sense of smell is far less powerful than sight, yet new findings suggest olfaction has a surprisingly significant influence on vision.

Image: Flickr/linkurl:tuexperto_com3;http://www.flickr.com/photos/21626156@N02/2509246163/

The findings, published online today (July 1) in Current Biology, show that what you smell can alter your visual perception. Previous studies have linked vision with the senses of hearing and touch, "but it's kind of more surprising that olfaction -- smells -- could influence vision," said cognitive neuroscientist linkurl:Joel Pearson;http://www.psy.unsw.edu.au/profiles/jpearson.html of the University of New South Wales in Australia. "Smell is considered one of the older senses; it's still quite prehistoric." Because "vision is by far the dominant sense," Pearson said, one might not expect smells to have much of an effect on sight. Humans integrate information from all sensory modalities to form an image of the world, but give different "weights" to each modality "based on the reliability of that information," explained psychologist and study author linkurl:Wen Zhou;http://sourcedb.cas.cn/sourcedb_psych_cas/en/epsychexpert/200909/t20090929_2529813.html of the Chinese Academy of Sciences. "It seems quite likely that olfaction is going to be given a smaller weight than vision." To determine what influence smells do have on visual processing, Zhou and her colleagues presented subjects with two different visual images (a rose or two Sharpie markers), one to each eye -- a test known as binocular rivalry. Because the brain cannot simultaneously process the conflicting stimuli, the subject sees an alternation of the two images. The team then paired the images with a specific smell (either rose-like or marker-like), and found that people saw the image that corresponded with the smell for longer than if presented the conflicting smell. This result suggested that their brains had integrated the two types of sensory input -- sight and scent. The researchers further showed that the integration of these stimuli occurred automatically. They presented subjects with one of the two images to one eye, but initially prevented them from being able to consciously see that image by also presenting flashing lights to their other eye. But when the images were accompanied by a corresponding smell, the subjects were able to see that image sooner. Because subjects could not even see the rose or the markers before smelling the fragrance, this process seems to occur without conscious awareness. "It tells us about how the brain's wired up," Pearson said -- "how information coming in from completely different senses can interact to give us a more complete picture of the world." Of course, "this is only a behavioral study," Zhou said. "It would be really nice to probe the neural mechanism underlying the integration between olfaction and vision." Interestingly, the two systems are located at the far sides of the brain -- visual processing mainly in the back of the brain in the visual cortex, and olfaction near the front of the brain in the olfactory bulb. "Where exactly in the brain [the integration occurs] is not totally clear yet," she said. "It [will be] really interesting to look at where in the brain the information from these two sensory modalities comes together." W. Zhou, et al., "Olfaction modulates visual perception in binocular rivalry," Current Biology, 20:1-3, 2010. Correction (posted July 1): This article has been updated from its original version to clarify that presenting smells allowed subjects to see the corresponding objects sooner, not more often. The Scientist regrets the error.
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