Taste Perception in the Presence of Noise

Abstract

We investigated the role of background music in the evaluation of gustatory stimuli. It was assumed that loud background noise influences taste perception due to its attentional demanding nature. To test for this hypothesis, we generated high levels of attentional demand by exposing participants to 1) loud noise and 2) an auditory attention tasks. The taste stimuli we used were sugar solutions at different levels of sweetness. Previous research suggested that high attentional demands result in decreased perceived sweetness and a decreased ability to detect sugar. We tested the perceived sweetness and detectability of sugar in the presence of loud background noise, in the presence of an attention task or with both as well as in a baseline condition without noise or attention task. The current study did not find an effect of loud noise or attention task on the perceived sweetness or detectability of sugar.

Keywords: taste, perception, attention, detectability, sound, multisensory, background noise

Taste Perception in the Presence of Noise

We spend about 2 hours daily for food preparation and consumption, devoting noteworthy 12.5% of our waking time to eating (at least if you belong to the population of the Netherlands) (Warde, Cheng, Olsen, & Southerton, 2007). Even though we spend a remarkable amount of time doing it - what do we know about eating?

Scientific findings on food consumption have revealed that a variety of factors contribute on how we perceive what we eat (see Auvray & Spence, 2008; Carstens et al., 2002; Crisinel & Spence, 2010; M. Zampini & Spence, 2010). The perception of food is influenced by the complex interplay of the foods properties. Its visual appearance, the taste, the smell, the temperature and the haptic nature of food determines how it is perceived (Delwiche, 2004). The research on food perception often tries to specify the unique impact of each component; and the visual appearance of food has by far attracted the most attention. One example is that food items with a more intense color are also perceived as more flavored (e.g. (Norton & Johnson, 1987). Research on other components revealed that for example food crispness is seen as an indicator for high quality (M. Zampini & Spence, 2004). We also form an association between certain kinds of food and shapes or nonsense words (e.g. associating sparkling water with the word „Kiki‟) (Spence & Gallace, 2011). Further the effects of temperature (Delwiche, 2004), smell (Kuo, Pangborn, & Noble, 1993; Rozin, 1982), pain (Dessirier, O'Mahony, Iodi-Carstens, Yao, & Carstens, 2001) and sound have been shown to influence taste perception. In the present study we want to leave all other aspects aside and solely investigate the effect of sound on our food perception.

There is a diverse body of research on the effects of background music on the perception and taste of food. Some findings result from research on the potentially commercial usage of music. As an example customers bought more wine from a specific country when stereotypical music of that country was played (North, Hargreaves, & McKendrick, 1997; North, Hargreaves, & McKendrick, 1999). Research by Jacob in which she observed customers in a bar was also economically motivated. She found customers stayed in the bar longer and spent more money on drinks if typical drinking songs were played, compared to other background music (Jacob, 2006). Similar to her findings an increased speed for drinking was noted for fast tempo music compared to the same music played at a slower rate (Mcelrea & Standing, 1992).

Other research that did not address the influence of sound from a commercial perspective produced similarly interesting results. In an historical experiment Holt-Hansen found that two different brands of beer were associated with different pitches (Holthans.K, 1968). Congruently more recent research on implicit associations revealed that high pitches are attributed to both the names of sweet and sour food (e.g. honey juice, lemon) whereas low pitches are associated with names of bitter food items (e.g. coffee) (Crisinel & Spence, 2009; Crisinel & Spence, 2010).

In summary, research that investigated the role of sound in food perception showed that sound and music alters the perception, evaluation and intake of food in various ways. Studies mainly aimed to investigate the role of background music on food perception. However, there is relatively little research devoted to the underlying mechanisms of how background music influences food perception. One study that explicitly tested the effect of background noise was conducted by Woods et al. (Woods et al., 2011). We will describe Woods work in more detail, as our study based its research question mainly on their findings. In the first part of the study, participants were exposed to different level of noise while blindly consuming food cues (crisps, cheese, etc.) that were rated along gustatory properties. The noise was either played loud (75-85dB) or relatively subtle (45-55 dB). Both were compared to a baseline condition without noise. Ratings were obtained on how intense (sweet or salty) it was perceived and how much it was liked. Sweetness and saltiness are thought to be completely unrelated to background sound as their exclusively carry gustatory information. This is different for example for crispness, which is mainly perceived by means of the auditory channels (see M. Zampini & Spence, 2004).

It was found that the ratings for perceived sweetness and saltiness were significantly lower under loud noise. So participants perceived the same food to be less sweet or salty only due to the fact that they tasted it under loud noise. In order explain these findings, Woods et al. proposed four underling mechanisms. At first, the two different sensory inputs might interact in the sensory cortical area and produce a different perceptional result as opposed to independent or sequential processing. Secondly, the finding might be due to a contrast effect. A sensory input is evaluated and compared to all the other inputs currently processed. For example, a weak perceptual input is perceived as even weaker if it is compared to a very strong opponent. Contrast effect can act within a specific perceptual modality (e.g. two visual stimuli are compared to each other) but it also applies for different perceptual modalities (e.g. comparing auditory and taste stimuli). Following this, loud noise might reduce the perceived intensity of taste. As a third explanation the implicit associations between certain kinds of food and sounds was proposed. The last explanation is the most relevant to the current study. It states that attention might play a critical role in the perception of food properties. The level of attention devoted towards the taste stimulus might moderate the perceived intensity. It is assumed that attention (or conscious awareness) is limited in its capacity. If a gustatory stimulus is processed in an environment of loud noise the limited attention needs to be divided between two tasks. Through the lack of attention devoted to the tasting the stimuli is perceived as less intense resulting in decreased intensity ratings of sweetness and saltiness.

Woods et al. could not discriminate which of the four explanations accounted for their findings and suggested further research on each explanation. The aim of the current study is to investigate which role attention played in Woods findings. This should give further insight onto the effect of attention in food perception in general.

Two other studies that also investigate attention in taste perception are of interest and will be discussed here. The first research of interest was conducted by Marks and Wheelers on the effect of attention in the detectability of taste stimuli (Marks & Wheeler, 1998). However, there were some critical differences compared to the study by Woods et al. Marks and Wheelers argued that the effect of attention can be more sufficiently measured by the ability to detect a stimulus or not instead of the ratings on the foods intensity levels applied by Woods et al. Therefore, they introduced stimuli that varied on their difficulty to be detected and measured the obtained detection thresholds. So instead of real food cues (which are presumably always detectable) they used either acid or sucrose dissolved in water. Through this alternation it was possible to generate several concentration levels of the same stimulus and obtain different levels of difficulty for detection. A further difference was that Marks and Wheelers induced attention not by the absence or presence of noise. They rather instructed the participants to pay attention to only one of two stimuli and to ignore the other. In their study each round consisted of both sweet and sour stimuli and the participants were alternatingly instructed to which to attend. The results are in line with the findings by Woods et al. Participants detected lower concentrations when they attended to them and hence the mean thresholds for attended stimuli were lower.

A second study that supports the effect of attention on taste perception was conducted by Grabenhorst and Rolls (2008). Through an fMRI (functional Magnetic Resonance Imaging) study they shed light on which brain areas are associated with attention in taste perception. Participants tasted stimuli along two dimensions, either on the pleasantness of the taste or on the perceived intensity. Further attention towards one of the properties (pleasantness or intensity) was induced in a top-down manner during the entire experiment. That meant that participants focused their attention on the task due to the instructions given. Top-down attention can be differentiated from bottom-up attention in which the attentional focus derives from the salients of the stimuli (Sarter, Givens, & Bruno, 2001). The study found evidence that different brain areas are involved in the evaluation of taste pleasantness compared to taste intensity (Grabenhorst & Rolls, 2008).

In order to assess the role of attention during tasting, we require a better understanding of how attention operates in general. The theory of cognitive load by Sweller provides useful information (Sweller, van Merrienboer, & Paas, 1998)on attention in information processing. First of all cognitive load theory argues that the working memory is the only source of attention in humans, and that humans are only conscious of what is processed in the working memory. At the same time it is well known that the capacity of working memory is limited (up to seven ± two items according to Millers historical findings (Miller, 1956). The cognitive load theory thus states that if several stimuli are processed at once, attention on each task will be reduced. With respect to the demands in taste perception, this suggests that attention will be split if background music and tasting are present at the same time. The studies discussed above have shown that this results in a decreased perceived intensity of the taste stimulus.

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