A homunculus is a representation of a human. But the homunculus I am talking about is the scientific representation that illustrates some specific characteristics.
The sensory homunculus refers to the mapping of human body parts to the sensory cortex of the brain. Some body areas, the hands, feet and facial structures, map to a disproportionately large share of the brain, compared to their actual physical dimensions. Here is an illustration (source):
If we look at the current mobile health apps and devices, they are similarly skewed, but based on current technological limitations. The most basic ones rely on the innate sensory capabilities of the current generation of smart phones.
The motion sensor is often used to measure relative physical activity, common in many fitness-promoting apps.
The GPS capability measures where someone is geographically, sometimes where they are going and even how fast. This sensor is the basis of geomedicine apps that are just appearing. Examples include measuring where someone takes medication (e.g. where an asthma attack is triggered), when they visit restaurants (measuring eating periods and types of food e.g. if they visit fast food restaurants), when they are driving, etc.
The camera is also used to measure physical attributes such as the appearance of moles in monitoring for developing skin cancer, the ambient environment light, etc.
These default internal sensors in smartphones obviously limit the kind of information that can be obtained, so supplementary sensors that communicate with the smartphone are appearing. Often the input from these sensors is combined with data from the smartphone sensors. For example, a device that promotes medication compliance can record when medication is taken, combining it with geographic location from the smartphone. Similarly heart EKG and blood glucose measurements depend on secondary sensors as I have covered in recent posts. The range of health relevant sensors is still quite limited, although growing rapidly. The synergistic combination of data from different sensors will grow even faster.
Taking these examples above the current mobile health homunculus is currently very primitive, but clearly not for much longer.