Washington DC [US], October 6 : Our five senses constantly flood us with environmental information. One way our brain makes sense of this plethora of information is by combining information from two or more senses, such as odours and the smoothness of textures, pitch, colour, and musical dimensions. This sensory integration also allows us to identify greater temperatures with warmer colours, lower sound pitches with lower elevations, and colours with the flavour of specific foods - for example, the flavour of oranges with the colour of the same name.
Now, a study in Frontiers in Psychology has shown experimentally that such unconscious 'crossmodal' associations with our sense of smell can affect our perception of colors.
"Here we show that the presence of different odors influences how humans perceive color," said lead author Dr Ryan Ward, a senior lecturer at Liverpool John Moores University in Liverpool, UK.
Sensory-deprived room
Ward and colleagues tested for the existence and strength of odor-colour 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 colour-blind or having an impaired sense of smell.
All ambient odours in the isolation room were purged with an air purifier for four minutes. Then one of six odours (chosen at random from caramel, cherry, coffee, lemon, and peppermint, plus odourless 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 odour 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," explained Ward.
Participants were presented with a screen that showed them a square filled with random colour (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 colour to neutral grey. After the final choice had been recorded, the procedure was repeated, until all odours had been presented five times.
Overcompensating for unconscious associations
The results showed that participants had a weak but significant tendency to adjust one or both of the sliders too far away from neutral grey. For example, when presented with the odour of coffee, they wrongly perceived 'grey' to be more of a red-brown colour than true neutral grey. Likewise, when presented with the odour of caramel, they wrongly perceived a colour enriched in blue as grey. The presence of the smell thus distorted the participants' colour perception in a predictable manner.
An exception was when the odour of peppermint was presented: here, the participants' choice of hue was different from the typical crossmodal association demonstrated for the other odours. As expected, the participants' selection likewise corresponded to true grey 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," said Ward.
"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 odours and colours."
Questions remain
The researchers emphasize the need to investigate how far-reaching such crossmodal associations between odours and colours are.
"We need to know the degree to which odours influence colour perception. For example, is the effect shown here still present for less commonly encountered odours, or even for odours encountered for the first time?" said Ward.
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