Sensory Skills represent a character's senses and his ability to utilize them to gain information from his environment. Most player characters are limited to training the in skills associated with the senses they are most adept at using, Spot (for Vision) and Listen (for Hearing). Ranks in your character's sensory skills will affect his Awareness Score, which represents the ability to detect dangerous situations or inconsistencies in the environment.
While most player characters are limited to the Spot and Listen skills, skills related to the other senses can be used by other creatures, such as Scent or Touch. For example, dogs rely on their sense of smell heavily, and so are able to train in the Scent ability. Likewise, spiders can detect the faintest vibrations within their webs, and so are able to utilize the Touch skill.