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This is a summary and explanation of:
Carvalho et al. (2016). "Smooth operator": Music modulates the perceived creaminess, sweetness, and bitterness of chocolate. Appetite 108, 383-390.
In this experiment, participants tasted and rated chocolate while listening to two distinct soundtracks, coined "creamy" or "rough". What they didn't know was the chocolates they ate during both experiments were the same. The idea here is that the participant's perception of the chocolate will change according to the type of music they listened to.
What ideas and facts lead to this hypothesis?
Sound has a profound effect on our perception of food. Soundtracks have been used to modulate basic taste attributes such as sweetness or bitterness. As well, the more pleasant a person perceives a sound, the more they will perceive an odour to be pleasant (sensation transference). Since flavour combines taste and odour, sound may also affect overall eating experience.
The look of food also has an effect on the experience of it. Round shapes tend to be associated with creaminess and sweetness, and angular shapes tend to be associated with a food being bitter.
The bouba-kiki effect was considered, which states that people associated round/smooth visual or auditory cues with "bouba"-like words, and sharp/rough stimuli with "kiki"-like words. They found a flute's simpler sound wave was rated smoother than the complex sound of a violin.
Components of the experiment:
Participants were told they will be tasting chocolate while listening to music. The experiment lasted about 10 minutes. They were not given any details about the chocolate they ate.
1. Taste stimuli
While listening to the "creamy" soundtrack, they ate 4 chocolates in total. Two were 71% dark chocolate (one smooth dome chocolate, and one angular shaped chocolate), and two were 80% dark chocolate in the shame two shapes. While listening to the "rough" soundtrack, they ate the exact same line of 4 chocolates. The chocolate contained cocoa mass, sugar, cocoa butter, and natural vanilla flavor).
2. Auditory stimuli
Two soundtracks were prepared, one corresponded to smoothness/creaminess, and the other to roughness.
The creamy soundtrack consisted of a loop-ascending scale of consonant-long flute notes, mixed with large hall reverberation.
The rough soundtrack consisted of a loop-ascending scale of three blended dissonant-dry pizzicato short violin lines.
The reasoning for the choice in soundtrack is that soft/smooth sounds correlated with long-constant legato notes. Hard rough sounds were associated with long-constant-legato notes. In a study by Eitan and Rothschild (2010) higher louder pitches/notes were rated as rougher/harder. Violin was rated rougher and drier compared to the flute.
Participants rated chocolates creamier when listening to the "creamy" soundtrack. Chocolate type (71% or 80%) did not have a significant effect on the participants. Chocolates also tasted sweeter when listening to the creamy soundtrack, which might be due to a positive correlation with creaminess and sweetness in the minds of the participants. Sweetness could be used as a proxy for creaminess, just as bitterness can be used as a proxy for alcohol level as seen by Stafford et al. (2012). As well, notes for creaminess are the same used to represent sweetness. Therefore, the creamy soundtrack could enhance the effect on texture while also giving the perception of the chocolate's sweetness. Participants also rated chocolates as tasting more bitter when listening to the "rough" soundtrack.
Overall, participants liked the creamy soundtrack more, but no significant difference was found in terms of participants enjoyment of the chocolates when comparing the two soundtrack ratings. That is, participants liking for the soundtrack didn't affect overall enjoyment of the chocolates. This part is key, since those in the industry can use music to alter the perceptual effect of food without altering its hedonic experience (whether they like it or not). The shape of the chocolate didn't seem to affect the participant's rating of creamy or roughness.
Limitations & further questions:
The author notes some limitations in the experiment. It's difficult to know if there is only one or several mechanisms underlying these sound-chocolate associations. It could be argued that the results reflect some form of sensation transference effect, rather than true crossmodal correspondence (which is using multiple sensory input such as auditory and taste and how they overlap with one another to affect the outcome)
There is also the possibility of cross modal attention, which is essentially multi tasking our sensory system. Doing so may cause delays, such as delay in visual cues if listening to the phone while driving. These participants were in a sense, multi tasking by actively listening while actively tasting. Does directing your attention to one sensory modality happen at the expense of others? Does an individual listen to the music, which affects their mood, then taste the chocolate? Or are they actively taking in the music while tasting, or tuning out the music while they focus on tasting? Some interesting questions to better understand the mechanisms behind this sound-taste correlation.