**1. Introduction**

Sensory organs independently process the corresponding external stimuli such as light, sound, pressure, taste, and smell. However, one sense rarely acts alone during the perception/cognition of a given event in daily life. Our experiences are dependent on the integration of the visual, auditory, somesthetic, gustatory, and olfactory systems. For example, during the act of smelling a strawberry, the sense of smell may vary according to the color of the strawberry (whether it is bright red or green-tinged), even if the physical odorant is the same (**Figure 1**). This example demonstrates that cognition is built upon cross-modality of function. The regions associated with cross-modality are spread throughout a wide area in brain [1]. For example, the integration of vision and touch is mainly associated with the right posterior fusiform gyrus and primary somatosensory cortices [2], whereas the integration of vision and audition is mainly associated with the right frontal lobe and right superior temporal gyrus [3].

The accuracy of each of the senses is different, and vision is often prioritized over other senses during integration. Several studies have demonstrated that visual input strongly influences hearing [4] touch [5], taste [6], and smell [7, 8] (**Figure 2**); however, the reverse, in which other senses influence vision, is a rare phenomenon, excluding the auditory-vision relationships such as the McGurk effect [9] or double flash illusion [10]. For the McGurk effect, on a video of audiovisual speech, if a lip movements show a "ba-ba" sound, whereas an auditory information

#### **Figure 1.**

*An example of the effect of color effect on smell recognition. The red strawberry on the left may seem to have a more pleasant odor than the green strawberry on the right.*

#### **Figure 2.**

*Diagram representing the effective relationship among the five senses. Vision is often prioritized over the other senses during integration.*

is that of "ga-ga", most people experiences an illusory sound "da-da". For the double flash illusion, if one dot flashes on the display when two beeps are sounded, most people reports experiencing two flashes. Thus, vision dominates the other senses in many cases. Although the mechanism of cross-modality has become increasingly clear in healthy persons [1–10], a function in disease states remains unclear.
