"Acuity" refers to the sharpness or clarity of one's senses, particularly vision. It describes how well someone can see and perceive details. Full definition
Innis, S. M., Nelson, C. M., Rioux, M. F., and King, D. J. Development of visual acuity in relation to plasma and erythrocyte omega - 6 and omega - 3 fatty acids in healthy term gestation infants. (webmd.com)
Here's a bit of video included in «The Cove» that illustrates the level of mental acuity of dolphins: (dotearth.blogs.nytimes.com)
To have an unrestricted driver's license, the Department of Motor Vehicles requires visual acuity of at least 20/40 and a horizontal field of vision with both eyes open of at least 120 degrees. (sciencedaily.com)