Reference Frames

A means of assigning a set of directions to a spatial representation of an object, a scene, or the body. Consist of several types:

1. Viewer-Based: Uses a part of the viewer's body as the landmark, to which spatial locations of other body parts or external stimuli are referenced. Crucial for the implementation of motor behavior towards stimuli in near space (e.g., reflexive orienting). For example, a rapidly approaching baseball must be located with respect to the viewer's body, if the viewer is to be able to effectively avoid it.
2. Object-Based: Describes the spatial relations among various components of an object. Important for object identification. For example, a tilted figure requires that an object-based set of directions be applied to that object, independent of other objects, or the environment in general, in order for its intrinsic spatial relations (e.g, top, bottom, sides, etc.) to be recognized, and thus in order for the object itself to be recognized.
3. Scene-based: Describes the spatial relations among components of a scene (usually a number of objects, but may include the viewer as well). For example, letters on a stop sign may be considered as components of the scene (the sign). Regardless of the position of the sign in relation to the viewer, when the sign is divided into left and right sides, the 'S' and 'T' are on the left of the scene, and the 'O' and 'P' are on the right of the scene.
4. Gravitational: Describes the dimensions of up and down using the pull of the Earth's gravity as a spatial landmark. The gravitational reference is maintained by the vestibular and somatosensory systems of the brain, which allow the organism to maintain balance and posture, and to locomote effectively.

References:

1. Arguin, M., & Bub, D. (1993). Evidence for an independent stimulus-centred spatial reference frame from a case of visual hemineglect. Cortex, 29, 349-367.
2. Kolb, B., & Whishaw, I. (1990). Fundamentals of human neuropsychology. Freeman: New York.
3. Rock, I. (1973). Orientation and form. Academic Press: New York.