Human brain constantly combines multisensory information from our surrounding environment. Odors for instance are often perceived with visual cues; these sensations interact to form our own subjective experience. This integration process can have a profound impact on the resulting experience and can alter our subjective reality. Vision is dominant in our multisensory perception and can influence how we perceive information in our other senses, including olfaction. In new research, scientists from Liverpool John Moores University, the University of Liverpool and Cambridge University explored the effect that different odors have on human color perception by presenting olfactory stimuli while asking observers to adjust a color patch to be devoid of hue.
Ward et al. suggest that the presence of an odor can bias an observer’s decision of what their perceived version of a neutral gray is. Image credit: Kerstin Herrmann.
In our everyday life, we are simultaneously bombarded with information from different sensory modalities.
Our brain combines this information to better understand our surrounding environment; this integration process has been shown to influence our perception in different senses, for example.
Crossmodal correspondences are the tendency for a sensory attribute to be associated with a stimulus feature in a different sensory modality.
For instance, people have consistent correspondences between odors and a variety of different sensory modalities, including but not limited to the angularity of shapes, the smoothness of texture, pitch, colors, and musical dimensions.
These correspondences still occur outside of olfaction, including, but not limited to, sound-taste, temperature-color, and pitch-vertical position.
The nature and origin of these correspondences have diverse characterization in the literature with hedonics, semantics, and natural co-occurrence being frequently deducted.
In their new study, Liverpool John Moores University researcher Ryan Ward and colleagues tested for the existence and strength of odor-color associations in 24 adult women and men between 20 and 57 years of age.
The participants were seated in front of a screen in a room devoid of unwanted sensory stimuli for the duration of the experiments.
They wore no deodorants or perfumes, and none reported being color-blind or having an impaired sense of smell.
All ambient odors in the isolation room were purged with an air purifier for four minutes.
Then one of six odors (chosen at random from caramel, cherry, coffee, lemon, and peppermint, plus odorless water as a control) was broadcast into the room with an ultrasonic diffuser for five minutes.
“In a previous study, we had shown that the odor of caramel commonly constitutes a crossmodal association with dark brown and yellow, just like coffee with dark brown and red, cherry with pink, red, and purple, peppermint with green and blue, and lemon with yellow, green, and pink,” Dr. Ward said.
The participants were presented with a screen that showed them a square filled with a random color (from an infinite range) and were invited to manually adjust two sliders — one for yellow to blue, and another for green to red — to change its color to neutral gray.
After the final choice had been recorded, the procedure was repeated, until all odors had been presented five times.
The results showed that participants had a weak but significant tendency to adjust one or both of the sliders too far away from neutral gray.
For example, when presented with the odor of coffee, they wrongly perceived ‘gray’ to be more of a red-brown color than true neutral gray.
Likewise, when presented with the odor of caramel, they wrongly perceived a color enriched in blue as gray.
The presence of the smell thus distorted the participants’ color perception in a predictable manner.
An exception was when the odor of peppermint was presented: here, the participants’ choice of hue was different from the typical crossmodal association demonstrated for the other odors.
As expected, the participants’ selection likewise corresponded to true gray when presented with the neutral scent of water.
“These results show that the perception of grey tended towards their anticipated crossmodal correspondences for four out of five scents, namely lemon, caramel, cherry, and coffee,” Dr. Ward said.
“This ‘overcompensation’ suggests that the role of crossmodal associations in processing sensory input is strong enough to influence how we perceive information from different senses, here between odors and colors.”
The findings were published in the journal Frontiers in Psychology.
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Ryan J. Ward et al. 2023. Odors modulate color appearance. Front. Psychol 14; doi: 10.3389/fpsyg.2023.1175703
