*2.6. Smell*

A tactile interaction created in 3D can be communicated through the touch of a brush and an olfactory stimulus that matches the space in the work, allowing the visually impaired to experience works of art through several senses [47]. Although many people have considered the effects of adding scent to art and museum exhibits, the addition of this normally unstimulated sense will not necessarily enhance the multisensory experience of those who are exposed to it [48]. Nina Levent and Alvaro Pascual-Leone in their book "The Multi-Sense Museum" [49] emphasized the use of forms such as smell, sound, and touch, providing visual and other impaired customers with a more immersive experience and a variety of sensory engagement. Although the use of congruen<sup>t</sup> scents has been shown to enhance people's self-reported willingness to return to a museum [50], the appropriate distribution of scent in/through a space faces significant challenges [49]. More than any other sensory modality, olfaction contributes a positive (appetitive) or negative (aversive) valence to an environment. Certain odors reproducibly induce emotional states [51]. Odor-evoked memories carry more emotional and evocative recollections than memories triggered by any other cue [52].

Dobbelstein et al. [53] introduced a mobile scent operated device that connects to a 3.5 mm audio jack and contains only one scent. Scent actuators that trigger mobile notifications by touch screen input or incoming text message. The scent was less reliable than the traditional vibrations or sound, but it was also perceived as less disruptive and more pleasant. Individual scents can add anticipation and emotion to the moment of being notified and entail a very personal meaning. For this reason, scent should not replace other output modalities, but rather complement them to convey additional meaning (e.g., amplifying notifications). Scent can also be used to express a unique identity.

For Sound Perfume [54], a personal sound and perfume are emitted during interpersonal face-to-face interactions, whereas for light perfume [55], the idea was to stimulate two users with the same visual and olfactory output to strengthen their empathic connection.

Additionally, picture books are also considered beneficial to children because they provide a rich experience [56,57]. Some picture books offer multisensory experiences to enrich learning and gratitude. For example, the Dorling Kindersley publishing house (https: //www.dk.com/uk/ accessed on 30 November 2020) has introduced a variety of books that children can touch, feel, scratch, and smell. These books have tactile textures in the pictures and contain a variety of smells [56–58]. The MIT Media Lab has developed an interactive pop-up book that combines material experimentation, artistic design, and engineering [59]. To improve the expression of movement, a study introduced continuous acoustic interaction to augmented pop-up books to provide a different experience of storytelling. The mental image of a blind person is a product of touch, taste, smell, and sound.

Edirisinghe et al. [60] introduced a picture book with multisensory interactions for children with visual impairments and it was found to provide an exciting and novel experience. It emits a specific odor through the olfactory device, which uses a commercially available Scentee (https://scentee.com/ accessed on 30 November 2020) device to respond to sounds. Children with visual impairments can smell and imagine broken objects. The

olfactory device is contained inside the page, and the fragrance is emitted from a small hole in the center of the panel [60].

At the Cooper Hewitt Smithsonian Museum, chemist and artist Sissel Tolaas designed a touch-activated map with fragrant paint. After analyzing the scent molecules of different elements from within Central Park, Tolaas reproduced them as closely as possible, using a "microencapsulation" process, containing them inside tiny capsules. She then mixed them with a latex-based binder, creating a special paint that was applied to the wall of the Cooper Hewitt, which can be activated by touch. When visitors go to the wall that has been painted with the special paint, just by touching the wall they are able to break the capsules open and release the scent: a scientifically advanced scratch-and-sniff sticker [61]. Using powdered scents, incense, and spices, Ezgi Ucar stamped fragrances on different photos that form part of a painting. She took inspiration from scratch-and-sniff stickers and used the same method, allowing visitors to scratch and sniff some of the photographed parts of the painting. The human sense of smell has been called the "poet of sensory systems", because it is deeply connected to structures in our brain that relate to our emotions, memories, and awareness of the environment, which can be exploited to enhance user experiences.

Given the ability of smell to influence human experiences, multimodal interfaces are increasingly integrating olfactory signals to create emotionally engaging experiences [62]. Sense of Agency [63] can be defined as "the sense that I am the one who is causing or generating an action". The sense of agency is of utmost importance when a person is controlling an external device, because it influences their affect toward the technology and thus their commitment to the task and its performance. Research into human–computer interactions has recently studied agency with visual, auditory, haptic, and olfactory interfaces [64]. Jacobs et al. [65] showed that humans can define an arbitrary location in space as a coordinate location on an odor grid.
