OBJECT RECOGNITION
Specialisation for function: vision for action=dorsal (ecological approach) is distinct from vision for recognition= ventral (constructivist approach). There appears to be 2 independent processing streams:
- Ventral: the ventral stream is primarily concerned with recognition and identification of visual input, whereas the dorsal stream provides information to guide visually guided behaviour such as pointing, grasping (Goodale & Milner, 1992).
- the ventral system is better at processing fine detail, whereas the dorsal system is better at processing motion – although differences are only relative, as the ventral system can still carry motion information.
- The ventral system appears to be knowledge-based using stored representations to recognise objects, whilst the dorsal system appears to have only short term storage available (Milner & Goodale, 1995).
- The dorsal system is faster
- We appear to be more conscious of ventral stream functioning than dorsal. For instance individuals may report awareness of ventral processing, while manifesting different dorsal processing (Ho, 1998).
- The ventral system aims to recognise and identify objects and is thus object-centred. The dorsal system is driving some action in relation to an object and thus uses a viewer-centred frame of reference (Goodale & Milner, 1992).
These characteristics support earlier research (Schneider, 1967, 69) which suggested that the ventral stream is concerned with the question “what is it?”, and the dorsal stream “where is it?” (Ungerleider & Mishkin, 1982). The functions and characteristics of the two streams thus seem to fit in nicely with the ecological and constructivist approaches, thus rather complementary of one another. There is evidence for a true distinction between the two systems: Goodale et al (1991): had a patient with impaired recognition, but with preserved visually guided action. Overall, the synchronisation of the two streams allows us maintain a phenomenological impression of a clear and sharp visual world all around us.
Marr’s theory of object recognition (1982)
Marr developed a computation theory, which saw object recognition as progressing through a number of stages until an internal representation of the