"Looked-but-failed-to-see" errors are a common cause of accidents, but it has never been determined whether obstructive elements within an automobile (e.g., window posts or the interior rearview mirror) have actually been an obstacle to vision. This work describes a technique that can easily be used to determine the available visual field of drivers at the wheel and illustrates its potential in a number of applications.The technique involves calibrating a minicamera for use as a device for perimetry and then mounting it on spectacles so that it lies between the eyes of the subject who wears them. With the spectacle-mounted camera worn by a driver, snapshots were taken when the automobile was parked and the driver looked in different directions, and video sequences were recorded during natural driving in an urban area and on a winding mountain road.All of the automobiles studied place obstacles to vision for any given direction of gaze, although the resultant scotomata have different sizes and are placed in different regions of the visual field for each combination of car and driver. These regions encroach into central vision as drivers turn their head and eyes as required by the characteristics of the road or the urban area during natural driving, in some cases resulting in very poor visibility regardless of the good vision of the driver and the certification of the automobile.Our technique is useful for determining what parts of a given scene are visible to a given driver on a given automobile and, hence, it is useful not only as a tool for accident investigation and in visual ergonomics, but also as an aid for the design of automobiles and road environments.