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The two-streams hypothesis is a widely accepted and influential model of the neural processing of vision. The hypothesis, given its most popular characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual systems. As visual information exits the occipital lobe, it follows two main pathways, or "streams". The ventral stream (also known as the "what pathway") travels to the temporal lobe and is involved with object identification and recognition. The dorsal stream (or, "where pathway") terminates in the parietal lobe and is involved with processing the object's spatial location relevant to the viewer.

HistoryEdit

Several researchers had proposed similar ideas previously. The authors themselves credit the inspiration of work on blindsight by Weiskrantz, and previous neuroscientific vision research. Schneider first proposed the existence of two visual systems for localisation and identification in 1969. Ingle described two independent visual systems in frogs in 1973. Ettlinger reviewed the existing neuropsychological evidence of a distinction in 1990. Moreover Trevarthen had offered an account of two separate mechanisms of vision in monkeys back in 1968.

In 1982 Ungerleider and Mishkin distinguished the dorsal and ventral streams, as processing spatial and visual features respectively, from their lesion studies of monkeys – proposing the original where vs what distinction. Though this framework was superseded by that of Milner & Goodale, it remains influential.

One hugely influential source of information that has informed the model has been experimental work exploring the extant abilities of visual agnosic patient DF. The first, and most influential report, came from Goodale and colleagues in 1991 and work is still being published on her two decades later. This has been the focus of some criticism of the model due to the perceived over-reliance on findings from a single case.

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