The “What” and
“Where” Pathways
William W. Crissman
02/08/13
Study Question Overview
1. How have the two cortical pathways historically been
modeled by the like of Ungerleider, Mishkin, Goodale,
and Milner?
2. How does the de Haan and Cowey (2011) differ from
the previous model?
3. What evidence is there to support a more patchworklike model of cortical info-processing?
4. What does heading disorientation (HD) a
characteristically unique form of topographical
disorientation?
5. What area of the brain has been heavily implicated in
the integration of information about objects in space
based on your own frame of reference and changes
you make in body direction?
Historical Perspectives
• Lissauer (19th century)
• Electrophysiological studies
with animals and
neuroimaging studies with
humans (20th century)
• Ungerleider and Mishkin
– 1st to suggest organization of
2 major paths from V1
• Ventral and dorsal paths
Historical Perspectives con.’t
• The Dual-Pathway paradigm (Goodale and Milner, 1995)
– Reconceptualized framework in terms of WHAT
the visual info is USED for, rather the KIND of
information is relayed
• Thus, the same info is being used differently, rather
than different info going to different directions
– Ventral info terminating in the MTL, hippocampus,
and amygdala used for visual recognition,
memory, and emotional content
– Dorsal info feeds into motor cortex of frontal lobe
and uses visual information for action
The Patchwork Model
• Challenges previous model in terms of…
– Whether a pathway model is more parsimonious than
a patchwork model?
• Latter fails to account for the an organizational structure that
consists of many interrelations b/t different visual maps
– Whether there is sufficient evidence to support a
model that suggests strict hierarchical processing of
visual information?
Evolution and Innate Design
• Visual architecture and gross organization of
visual maps
– Both very well-defined
– little variability in humans (total extent of striate
cortex)
• HOW did the architecture and organization
develop in terms of evolution and natural
selection”?
– In “one sweep,” or more independently, haphazard
manner?
• Evolution supports a patchwork model
– Previous model assumes too elaborate of a
“Darwinistic step”
Neural Wiring
• Issue on white matter tracts
– Very little systematic evidence, but overall picture
does not support linear path model
– If no internal organization, then connections should
be equally strong b/t all possible nodes
– If organized into hierarchical pathways,
• Then connections within a path would be stronger than
connections between the paths,
• And shorter connections would be stronger than more longrange connections
• V1 and V2 > V1 and V3?
– Very little systematic evidence concerning this issue
Two Streams (Or are there?)
• Hierarchical model works well to conceptualize ventral
“what” stream
– Color, orientation, and brightness enable perceptions of objects,
places, and faces
• Not so much with dorsal “where/how” stream
– In space, what qualifies are basic or advanced features?
– Position feed into depth, or vice versa?
– At present, three paths have been postulated in parietal lobe
• Parieto-prefrontal path – top-down eye movements, spatial WM
• Parieto-premotor path – visually-guided actions
• Parieto-medial temporal path – visuo-spatial navigation info, spatial LT
memory
– Four, if we add path from LGN to area MT
– Five, if we add path for processing temporal order (“when”
path)
Two Streams (Or are there?)
Too much Cross-talk
• How can two paths with fundamentally
content communicate?
• Why even have two paths given the
continuous and meaningful cross-talk?
• How is the strict division in terms of conscious
perception continually maintained, given the
extensive cross-talk?
• How can we explain certain aspects of dorsal
processing that can reach conscious
awareness?
Integration of Features
• If hierarchical organization, then basic features
processed during early stages are integrated in
subsequent stages
– Maybe at the local, micro-circuit level, in a single area
– “End-stopped cells” in V2 integrate orientation and
position/length info
• Is this really integration? Or an implicit assumption?
– Theoretically, face recognition, a higher-order process,
would call for important visual features that are
processed in more posterior visual areas
• Role of various visual parameters in face recognition have
shown modest effects at best
Complexity
• Hierarchical model also assumes that the
complexity of information increases
progressively and systematically as it is
processed further down stream (“cascade
specification”)
• Is color processing really more “basic,” in
terms of complexity and processing
characteristics, than reading or face
recognition?
Color Perception and Recognition
• Involves numerous separate stages (maps)
• Concerns a stimulus-specific perception
system
• Involves categorical perception
• Leads to conscious perception
• Part of processing occurs subconsciously
• Heredity does influence ontological
development
Authors’ Concluding Remarks
• Prevailing view makes more elaborate assumptions
about evolution of visual system than evidence
currently warrants
• Pathway model are not supported by physiological
neural wiring between different visual maps
• It is not clear why there should only be two paths
• In new model, there are no functional highways, nor
presupposed hierarchy between different visual
abilities
• Allows more flexibility in the role of the visual system
and visual information from different visual areas
• Not advocating to “throw the baby out with the bath
water,” rather reserve hierarchical processing for the
columnar and microcircuit level
• Hasimoto, R., Tanaka, Y., Nakano, I. (2010).
Heading disorientation: A new test and
possible underlying mechanism. European
Neurology, 63, 87 – 93.
• http://www.youtube.com/watch?v=uF7AxleI_0&feature=endscreen
Topographical Disorientation
• Inability to orient one’s self within large-scale,
locomotor environments
• Oftentimes the result of diffuse brain damage
via stroke, dementia, Alzheimer’s disease, etc.
– Also, implicated in focal brain damage as
suggested here
– Four unique varieties
Types of TD
• Egocentric Disorientation
– Implicated in damage to posterior parietal lobe
– Marked inability to represent the location of
objects with respect to one’s self
• Unable to reach out and grab objects, point to locations
of objects, or state the spatial relationship between
objects (above, below, left, right, near, far),
• Pt. GW would turn the wrong way when greeted by
someone she was not facing towards
Types of TD cont.
• Landmark Agnosia
– Implicated in damage to bilateral lingual gyrus
– Inability to recognize salient environmental stimuli for
purposes of orientation
• Anterograde disorientation
– Implicated in damage to parahippocampal gyrus
– Inability to orient in novel environments
• Pt.’s often able to recall spatial layout of known places
before becoming amnestic
– Findings suggest the MTL is not necessary for forming
LT declarative memories, such as spatial maps,
learned prior to injury
Types of TD cont.
• Anterograde disorientation
– Implicated in damage to parahippocampal gyrus
– Inability to orient in new environments
– Pt.’s often able to recall spatial layout of known
places before becoming amnestic, but nothing
about new places after injury
– Findings suggest the MTL is not necessary for
forming LT declarative memories, such as spatial
maps, learned prior to injury
• More ab the hippocampus and its surrounding areas
Heading Disorientation (HD)
• Inability to represent direction of orientation
with respect to external environment
• No visuo-spatial agnosia, nor landmark
agnosia, but still unable to derive orienting
info based on salient environmental cues
• Unable to draw maps or describe routes b/t
familiar places
Review of Cases Reports
• Patient 1
– 67 yr old man that
became lost while
driving his usual
route home
• Patient 2
– 72 yr old man that
became lost while
riding his bicycle
• Patient 3
– 67 yr old man that
kept forgetting
where his hospital
room was
R
L
Card-Placing Test (CPT)
• Two-part performance-based test designed to
examine individuals’ ability to represent
spatial locations of surrounding objects placed
on the floor
• DEMO
Card-Placing Test (CPT)
Age ± SD
CPT part A
(mean ±
SD)
full scores;
#correct/30
trials
CPT part B
(mean ±
SD)
full scores;
#correct/30
trials
Controls (n = 9)
65.4 ±
4.8
27.6 ± 3.0
25.0 ± 4.3
Pt. 1
67
28
4
Pt. 2
72
26
12
Pt. 3
67
26
17
Discussion
• Common damage
– 3 cases, same
localized damage
to right
retrospenial area
– Damage to left
retrospenial
reportedly
associated with
impaired episodic
memory, rather HD
Discussion con.’t
• Common symptoms
– Inability to derive directional info from environmental
cues
– TD in novel AND familiar environments
– Mild to moderate visual memory impairment
– Absence of prominent visuospatial disorientation
•
•
•
•
Preserved tapping span
Absence of hemispatial neglect
Intact constructional abilities
Fairly well-preserved general intellectual functioning
• Underlying mechanism of HD?
– Anterograde visual memory impairment?
– Poor egocentric frame of reference?
– Integration of information on changes in body
direction?
Discussion con.’t
• Converging sources of evidence
– Rat studies
• Excision of retrospenial cortex shows impairment of
spatial navigation
– Human research via PET and MRI
• Retrospenial area active during large-scale navigation
tasks
– Head direction cells
• Excited when rats maintain a certain heading or
orientation in the environment
• Found in retrospenial cortex and many other structures
that may be implicated in the functional circuit of
directional information to the self
Study Questions Revisit
1. How have the two cortical pathways historically been
modeled by the like of Ungerleider, Mishkin, Goodale,
and Milner?
–
As hierarchically organized paths – the ventral “what”
path which is involved in object recognition and memory,
and the dorsal “where” path which is involved in action
2. How does the de Haan and Cowey (2011) model differ
from previous ones?
–
Their patchwork model that does not assume an internal
organizing structure consisting of 2 independent paths,
rather a network of connections within the visual maps.
3. What evidence is there to support a more patchworklike model of cortical info-processing?
–
More than 2 streams, too much cross-talk, integration,
shared complexity, etc.
Study Questions Revisit
4. What makes heading disorientation (HD) a
characteristically unique form of topographical
disorientation?
– The inability to navigate both novel and familiar
environments through the derivation of directional
info from landmarks and changes in body direction,
despite normal visuospatial functioning and the
absence of landmark agnosia
5. What area of the brain has been heavily
implicated in the integration of information
about objects in space based on your own frame
of reference and changes you make in body
direction?
– Right retrospenial cortex