Bernal S D_2010.pdf - University of Plymouth

2.1. OBJECT REC(JGNmON
The dorsal stream originates in the magnocellular layers of the retina and LGN, then projects
onto magno-dominated regions of VI and upwards into the tliiclc regions of secondary visual
cortex (V2). A high incidence of cells selective for direction of molion have been found in
lliesc regions, The subsequent exlrasiriaie areas involved are medial temporal (MT) cortex, and
medial superior temporal (MST) cortex, considered to be responsible for several motion analysis
processes. These in lum project onio the poslerior parietal (PP) cortex involved in higher level
funclions such as analyzing spatial relations and controlling eye movements. Overall the dorsal.
or where pathway, which spreads along the parietal cortex, is mainly concerned with space,
movement and action (Van Bssen and Gallant 1994).
On Ihe other hand, the ventral stream, or what pathway, is mostly concerned with object identi-
licalion and perception. It encompasses the blob-dominated (BD) and the intcrhlob-dominated
(ID) parallel streams, both of which receive input mainly from parvocellularand koniocellular
neurons in subcortical regions. The BD stream, which mediates color perception, originates in
ilie blob compartments of VI and feeds to the thin stripe regions of V2. The ID stream, respon­
sible for form perception, projects from inter-blob compartments of VI onto the inter-stripe
regions of V2. Both streams converge onto the extrastriate regions V4 and IT cortex, which are
associated with high-level funclions of pattern recognition (Van Essen and Gallant 1994).
The complex interactions which exist between these two parallel processing paihways are still
not well understood (Van Essen and Gallant 1994, Nassi and Callaway 2IX)9). To make things
Caption for Figure 2.1. a) Hierarchical siniciure of areas involved in visual professing in ihe macai|ue, TTie
diagram shows .12 different areas linked by 187 connection.s. ilie majoriiy of which are reciprocal paihways. [i highlights
[he complexity and imricaLe inierdependency iif regions in ihe visual system (F-elleman and Van Essen I9yi).
b| [•iineiional schematic representaiion of ihe Iwo hierarchical parallel visual pn)cessing sireams (veniralAiViiK and
dimM/where) in die macaque. Bo\es represent visual regions, while lines represent ihe main cimnection pathways
(usually bidirectional). Icons represent typical physiiilogical and functional properties allributed to each region. The
where path originates in the magnocellular layers of Ihe retina and UON (gray), then projects iiniii magno-dominated
regions i>f VI iind upwards into the thick regiiiii.s of V2 (reil). Cells in these regions typically show selectivity to
direction of motiim. The subsequent exu'aesiriaie areas involved are MT and PP (red), responsible for several molion
analysis processes. These in lum project onto the PI* cortex (orange) involved in higher level functions such as
analyzing spatial relations and controlling eye mnvemenis. The what path encompasses the blob-dominated (BD)
Iprcen) and the inierbiob-dominaleiJ (ID) (blue) parallel streams, both of which receive input mainly from parvocellular
(P) (pink) and konioceDular (K) (yelhwi neurons in subcortical regions. The BD stream, which mediates color
perception, originates in the blob compartments of V! and feeds lo the thin stripe regions of V2. The ID stream,
responsible for form perception, projects from inter-blob companments of VI onto intet-stripe region,s of V2, Both
streams converge onto the extraesiriate regions V4 and IT cortex which are associated with high-level funclions
o( pattern recognition [Van Es.sen and Gallant I'W). Pathways are partly based on anatomical information from
I'eMenuiii and Van Lssen (1991), represented in ligure a). Note colors in a) do not correspond with colors in b).
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