Visual area V4
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Visual area V4 is an one of the visual areas in the extrastriate visual cortex of the macaque monkey. It is located anterior to visual area V2, and posterior to visual area PIT, and comprises four separate regions (left and right V4d, left and right V4v). It is unknown what the human homologue of V4 is, and this issue is currently the subject of much scrutiny.
V4 is the third cortical area in the ventral stream, receiving strong feedforward input from visual area V2, and sending strong connections to the posterior inferotemporal cortex (PIT). It also receives direct inputs from primary visual cortex (V1), especially for central space. In addition, it has weaker connections to visual area MT and visual area DP (the dorsal prelunate gyrus).
V4 is the first area in the ventral stream to show strong attentional modulation. Most studies indicate that selective attention can change firing rates in V4 by about 20%. A seminal paper by Moran and Desimone characterizing these effects was the first paper to find attention effects anywhere in the visual cortex.
Like V1, V4 is tuned for orientation, spatial frequency, and color. Unlike V1, it is tuned for object features of intermediate complexity, like simple geometric shapes, although no one has developed a full parametric description of the tuning space for V4. Visual area V4 is not tuned for complex objects such as faces, as areas in the inferotemporal cortex are.
The firing properties of V4 were first described by Semir Zeki in the late 1970s, who also named the area. Before that, V4 was known by its anatomical description, the prelunate gyrus. Originally, Zeki argued that the purpose of V4 was to process color information. Work in the early 1980s proved that V4 was as directly involved in form recognition as earlier cortical areas. This research supported the Two Streams hypothesis, first presented by Ungerleider and Mishkin in 1982.
Recent work has shown that V4 exhibits long-term plasticity, encodes stimulus salience, is gated by signals coming from the frontal eye fields, shows changes in the spatial profile of its receptive fields with attention, and encodes hazard functions.
References
- Moran and Desimone. Selective Attention Gates Visual Processing in the Extrastriate Cortex. Science 229(4715). 1985.--Sootymangabey 23:22, 10 Jun 2004 (UTC)