Smell, wind and moving seats; only a few examples that give rise to a futuristic approach of perceiving films in a 4DX experience. Cinematic experience evolved slowly from a 2D and 3D multisensory adventure towards the fourth dimension by integrating not just two, but twenty – yes, you are reading this correctly - of your senses. And that just a stone’s throw away from Leiden.

Daily life media such as television, your phone, and radio mainly aim for the stimulation of the auditory and visual regions in the brain. Consider the waves of light from screens triggering our eyes and the incidence of radio waves stimulating our ears. Nevertheless, these are only two of the five traditional senses we have (seeing, hearing, touch, taste and smell). Not even speaking of our many other senses such as thermo- and equilibrioception (sense of temperature and balance respectively). Therefore, it is time for the introduction of a third traditional sensory organ to be activated while watching a film: our nose.

However, olfaction does not only take over cinemas, but also other fields such as Virtual Reality, and gaming. Moreover, its applications even reach to marketing, education and health. For this reason, it is of importance to understand more about this mysterious sense we possess. Due to the increasing integration of smell our brain has to cope with more signal input while watching a film than before. So what does the addition of smell do for the way your brain experiences a film?

Olfaction in a ‘noseshell’
Interestingly, as ancient as the sense of smell is, olfaction is quite a high-tech chemosensory phenomenon. The sense of smell is of great importance from an evolutionary point of view, for we need to be able to rapidly detect dangerous scents. This can be related to the fact that your olfactory sensory neurons, high up in the nose, have a direct connection to the brain. So you smell even before realizing that you are smelling something. This differs from other sensory neurons, such as the ones in your skin, as those signal information to the brain via the spinal cord.

This gained information is sent to the olfactory bulbs in the limbic system, to which the amygdala – involved in emotional processing – and hippocampus – related to memory – belong as well. These three structures have an interplay which provides an explanation of the association between olfaction, memory, and emotion. These factors, in turn, have influence on the way we perceive, pay attention and even the way we behave.

The crux of the matter here is that these brain regions can be triggered by smell in audio-visual media. But does our brain find this an annoying or enhancing experience?

A matter of timing and type
Imagine yourself enjoying Johnny English and then get in touch with a musty, sweaty odour spreading through the theatre. Does this seem pleasant to your olfactory bulbs? I bet the neurons in your Anterior Cingulate Cortex – a brain region involved in detecting errors – would fire in a scan right now.

Murray et al. performed experiments regarding when to introduce olfaction to a video, such that it enhances ones experience. Without video content, smells such as Fruity, Flowery and Chocolate were perceived as pleasant, others such as Foul, and Horse stable were regarded unpleasant. A Burnt smell could be pleasant or unpleasant – when seeing a campfire it could be enhancing your experience, but when showing a fresh cookie a burnt smell would be appreciated less.

A clear finding using olfaction-enhanced audio-visual stimuli was that we do not appreciate olfaction coming in before seeing the context on video. This may be explained by the fact that there could be a bidirectional interaction between different sensory information sources. For instance, the interaction between vision and smell: smelling popcorn without seeing it induces already an image of perhaps ‘corn or ‘something salty and not directly ‘popcorn. When seeing the popcorn and then smell is introduced, sensory input is combined and there is a good probability that you immediately smell ‘popcorn’. So vision already induces a smell – which we could consider as top-down influence – and smell induces a vague virtual image. How this mechanism of perceiving smell exactly occurs is not known. At least we know that first smelling and then seeing is annoying.

Smells like more: enhanced and decreased experiences
When olfaction was introduced at roughly the same time as when the context of the video was presented, participants had high ratings on sense of enjoyment, relevance and even the sense of reality. Perhaps due to the bidirectional interactions between olfaction and vision. We also seem to like the Flowery smell most as it was rated the highest enjoyment and relevance of all.

Strangely enough, Murrays research showed that we also tend to appreciate an unpleasant smell at some time: Foul. Participants reported unexpected high levels of Quality Of Experience when Foul was released after the video started. The scent may have emphasized the content of the video as it was congruent.

However, even pleasant odours – congruent and incongruent - could lead to a reduced experience. It may be explained by cross-modal competition. This indicates the suppression of audition and vision due to the presence of olfaction, compared with non-odour trials. So your brain experiences an attention problem. It does not know anymore what to attend to when there are many salient stimuli, which fMRI results confirmed in one participant. Of course this should be repeated in order to find out whether this is really the case.

So, enhancing or annoying?
A wide range of factors have influence on the perception of experiencing a 4D film. Pleasant and unpleasant smells both can increase, but also reduce your experience. The timing of introducing a scent, the type of odour and attention play a role. Whether olfaction-enhanced film watching is an annoying or enhancing experience? Follow your nose to Scheveningen and find out whether you are in good or bad odour with the smell of Johnny English!