higher visual cortices Flashcards
blob regions in V1 project to
thin stripe region in V2
inter blob region in V1 projects to
inter-stripe region in V2
4B of V1 projects to
thick stipe region in V2
V4 receives input from which areas in V2?
thin stripe and inter-stripe
V5 receives input from which regions in V2?
thick stripe
where does V5 (MT) project to?
V4 and V1
where does V2 project to?
V1, V4, V5
where does V4 project to?
V1, V2, V5
input to V2 from earlier processing stages
V1 projects to layer 4
layer 4 projects to layer 2/3
V2 output to subsequent processing stages
from layer 2/3
V2 feedback to earlier processing stages
layer 2/3 to layer 5 to V1
layer 2/3 to layer 6 to V1
what pathway is the motion pathway part of?
the dorsal (parietal) pathway
what main two areas does the motion pathway include?
MT: middle temporal (v5)
MST: medial superior temporal
what makes the signal in the MT fast?
strong myelination
what cells give the main input for the motion pathway?
magnocellular
temporal preferred frequency and spatial acuity of motion pathway
low spatial acuity
high preferred temporal frequency
what does the motion pathway receive indirect input from?
layer 2/3 in V1 via thick stripes in V2
receptive fields in magnocellular pathway
much larger than V1
can also detect colour (some parvo input)
direction selective
what is perceived motion in drifting grids and plaids
composite of the two gratings
what do drifting grating and plaids allow?
allows us to provide direction information that is distinct from the orientation and direction of either component
what percentage of V5 cells are selective for composite stimulus
~20%
generate perceived motion
using dot clouds to study motion
Here no motion but can convey information, particularly in motion
* Population of cells in V5 that like»_space; or «_space;motion alternately active
corresponds to our perception of composite stimulus motion
where does the middle temporal project to?
the medial superior temporal (the adjacent region)
what does the MT feed into
the main parietal ‘where’ stream
MST cells receptive fields and what this causes
much larger than V5, sums up information from V5
what is responded to beyond V5
- Respond to direction of stimulus motion but can be complex – expansion, contraction, circular or spiral
processes ‘optic flow’
controls ‘smooth pursuit’ eye movements
what is optic flow used for
to calculate direction of heading and distinguish self from motion object
what does the where pathway do?
determine the location of objects in space, relative to ourselves
scientific name for where pathway
dorsal (parietal) pathway
where pathway projections
V1
projects to V2
projects to V4
projects to inferior parietal lobule: areas DP, 7a/b, VIP, LIP
areas of inferior parietal lobule involves in the where pathway
DP, 7a/b, VIP, LIP
why is there strong myelination in the LIP
the signal needs to be conveyed fast
LIP (full name)
Lateral intraparietal cortex
receptive field properties in LIP
Receptive fields are large and retinotopically organised across opposite hemifield
Retinotopic receptive field has a ‘motor field’
what are LIP responses enhanced by?
saccade to target
cells are much more responsive to a stimulus in the receptive field if these are the target of a saccade
saccade
rapid movement of eye between fixation points
what to LIP cells not care about
colour and orientation
relationship between strength of response and starting eye (or head) position
Strength (gain) of response changes linearly with respect to starting eye (or had) position
what is each retinal location represented by in LIP
a population of cells with different field gains
for every region of visual space, there are many cells which represent that location
what does a population of LIP cells code?
positions of objects in space with respect to the body
what connections do LIP cells make
strong callosal connections with the LIP in the other hemisphere as we need a single representation of visual space
feature of LIP cells
have large axonal and dendritic arbours because they need to pool information across large areas
what do LIP cells combine information from?
the retina, eye position, head position and body position
unique feature of LIP cells
LIP cells have memory
what does memory in LIP cells allow
allows LIP cells to decide wat we will look at next
assists in forwards planning, for example in planning saccades
what does the LIP make reciprocal connections with?
the frontal eye fields in the frontal cortex (FEF)
what has memory other than LIP cells?
FEF
what do the FEF and LIP have strong links to? nature of links? importance of links?
strong descending links to the superior colliculus important for decision to make saccades
purpose of the what pathway
to discriminate between objects
scientific name for the what pathway
the ventral (temporal) pathway
what pathway projections
v1
projects to v2
projects to v4
projects to inferior temporal lobule
areas of the inferior temporal lobule involved in the what pathway
anterior, central and anterior parts
-each with dorsal and ventral parts
features of the inferior temporal cortex cells
have very large receptive fields
-may include fovea and both hemifields
what so inferior temporal cortex cell do?
respond to complex stimuli
e.g. hands and faces
how does the inferior temporal cortex respond to faces
cells may be responsive to certain components of faces, expressions etc.
information may be combined to make cells responsive to faces
inferior temporal cortex receptive fields
- Do not normally care about the position or size of the object
- Generally, don’t care about the angle of view
- Responses to specific ‘objects’ will vary according to familiarity
the what and where pathways together
- Higher cortical pathways need to share information
- There are connections between dorsal and ventral pathways:
so that ‘where’ can know where ‘what’ is, and visa versa
