Editing Visual processing (section)

==Top-down and bottom-up representations==

The visual system is organized hierarchically, with anatomical areas that have specialized functions in visual processing. Low-level visual processing is concerned with determining different types of contrast among images projected onto the retina whereas high-level visual processing refers to the cognitive processes that integrate information from a variety of sources into the visual information that is represented in one's mind. Object processing, including tasks such as [[cognitive neuroscience of visual object recognition|object recognition]] and location, is an example of higher-level visual processing. High-level visual processing depends on both top-down and bottom-up processes. Bottom-up processing refers to the visual system's ability to use the incoming visual information, flowing in a unidirectional path from the retina to higher cortical areas. Top-down processing refers to the use of prior knowledge and context to process visual information and change the information conveyed by neurons, altering the way they are tuned to a stimulus. All areas of the visual pathway except for the retina are able to be influenced by top-down processing.

There is a traditional view that visual processing follows a feedforward system where there is a one-way process by which light is sent from the retina to higher cortical areas, however, there is increasing evidence that visual pathways operate bidirectionally, with both feedforward and feedback mechanisms in place that transmit information to and from lower and higher cortical areas.<ref>{{Cite journal|last1=Gilbert|first1=Charles D.|last2=Li|first2=Wu|date=May 2013|title=Top-down influences on visual processing|journal=Nature Reviews Neuroscience|language=en|volume=14|issue=5|pages=350–363|doi=10.1038/nrn3476|pmid=23595013|pmc=3864796|issn=1471-0048}}</ref> Various studies have demonstrated this idea that visual processing relies on both feedforward and feedback systems (Jensen et al., 2015; Layher et al., 2014; Lee, 2002). Various studies that recorded from early visual neurons in [[macaque]] monkeys found evidence that early visual neurons are sensitive to features both within their receptive fields and the global context of a scene.<ref name=":0">{{Cite journal|last1=Allman|first1=J.|last2=Miezin|first2=F.|last3=McGuinness|first3=E.|date=1985|title=Stimulus specific responses from beyond the classical receptive field: neurophysiological mechanisms for local-global comparisons in visual neurons|journal=Annual Review of Neuroscience|volume=8|pages=407–430|doi=10.1146/annurev.ne.08.030185.002203|issn=0147-006X|pmid=3885829}}</ref> Two other monkey studies used [[electrophysiology]] to find different frequencies that are associated with feedforward and feedback processing in monkeys (Orban, 2008; Schenden & Ganis, 2005). Studies with monkeys have also shown that neurons in higher level visual areas are selective to certain stimuli. One study that used single unit recordings in macaque monkeys found that neurons in middle temporal visual area, also known as area MT or V5, were highly selective for both direction and speed (Maunsell & Van Essen, 1983).