1. I always heard that neglect typically follows right hemisphere damage, rather than left (unlike damage to early sensory areas that have retinotopic organization). Why might the areas involved in neglect be lateralized? What could lateralization tell us about the function and circuitry of areas like LIP?

2. Perception of Space Perception of 3 D structure - static observer
– stereo, motion parallax, geometric cues etc
Representation of structure and location of objects – moving observer
Need to interact with objects – aiming movements
Need to get from one place to another in large scale space – Navigation, wayfinding

3. Moving observer: Self motion generated optic flow.
Point of heading indicated by “focus
of expansion”
Humans can locate FOE within a few
degrees (Warren)
A bit problematic is S is fixating off the
FOE
Later: Simon Rushton – use of visual
direction to control heading
Warren – both are used.
Note Srinivasan – bees
Also flow influences walking speed.
Flow is not necessary for estimating distance
travelled. Blind walking very accurate - Loomis
Vestibular + proprioception/efference copy. These
Are usually highly correlated. A cue conflict induces
re-calibration eg treadmill walking.

4. Need to take account of self-motion.

5. Systematic distortions of perceived visual speed during walking enhance perceptual
precision in the measurement of visual speed
Precision more important than accuracy (?)

6. By slowing down the apparent rate of visual flow during self-motion, our
visual system is able to perceive differences between actual and
expected flow more precisely.
This is useful in the control of action. Eg intercepting a moving object while walking ((??)
Cf Barlow – subtracting mean improves discrimination.
Previously, apparent slowing of optic flow during walking had been interpreted
as a suppression of flow to promote the perception of a stable world.

7. Optic flow “parsing” – flow generated by ego motion separated from that generated by
object motion

8. Stationary observer: cloud of limited lifetime dots.
Note this is a cue conflict situation. No vestibular signal.

9. Effect of optic flow is mediated by global not local effects.

10. Simulate ground plane plus
sky
Discounting background flow despite lack of overlap. The magnitude of the effect in the
Opposite condition appears to be around 60%–70% of that in the Full condition.

11. Proprioceptive, efferent commands, intertial (vestibular) cues.
Fajen & Matthis: What is the contribution of non-visual factors about self-motion
to flow parsing..
Proprioceptive, efferent commands, intertial (vestibular) cues.
Figure 1. Optic flow field and decomposition into self-motion and object-motion components.
Fajen BR, Matthis JS (2013) Visual and Non-Visual Contributions to the Perception of Object Motion during Self-Motion. PLoS ONE 8(2): e doi: /journal.pone

12. Use HMD in VR – normal walking
Use HMD in VR – normal walking. Subject judges whether he/she could pass
through the aperture formed by two converging objects if walking as fast as
possible.

13. On catch trials manipulate gain between actual walking speed and speed of flow field.
This dissociates non-visual from visual cues.
Retinal motion generated by moving objects remains same.
Result: Gain influences judgment, but not as much as expected from visual manipulation
Only 20% of predicted effect. Therefore non-visual influence on self-motion perception
contributes to flow parsing.

14. However, is flow parsing necessary for interception of moving objects
during self-motion?
Can use constant bearing angle strategy.
Unresolved
Calibration and prediction is another possibility.

15. Areas implicated??
MSTd (note vestibular input))
Also V7a VIP CSv
Note – Angelaki – Bayesian combination of visual and vestibular information
for evaluation of self motion (ie cues are added, weighted by their reliability)

16. Angelaki et al

18. Multiple object tracking

19. Wolbers et al NN 2008 Spatial Updating
Because egocentric object locations constantly change as we
move through an environment, only continuous updating enables us to
effectively act on objects or to avoid getting lost. This process has been
termed spatial updating, and it is of major importance whenever
objects go out of view, when people walk with little vision in the dark.
Successful spatial updating requires an observer to perceive the initial
spatial positions of external objects and to create a corresponding internal representation.
Subdivisions of the posterior parietal cortex code for spatial location in
multiple body-based reference frames.
Such locational cues form the basis of an egocentric map of the surrounding space that critically depends on the precuneus and connected inferior and superior parietal areas.
Unknown how the human brain continuously integrates the wealth of incoming
information during complete body displacements.

21. Only the precuneus and the left dorsal precentral gyrus showed a combination
of both main effects in the delay phase (middle); not only were BOLD responses elevated during updating as compared with static trials, but they also showed a linear increase related to the number of objects.
This indicates that both regions are sensitive to working memory load and the presence of optic flow, suggesting a prominent role for spatial updating.

22. Humans can update up to four spatial positions during simulated self-motion.
Pointing errors and reaction times increased with increasing working memory load
And were elevated when self-motion cues were present.
Activation in the precuneus and the dorsal precentral gyrus closely followed both experimental manipulations, thus suggesting their importance for the updating process.
Only the Pre-cuneus involved when pointing response required. Support for the existence of transient spatial maps in medial parietal cortex.
Visual spatial updating linked to the interplay of self-motion processing with the construction of updated representations in the precuneus and the context-dependent
planning of potential motor actions in dorsal precentral gyrus.
When navigating in familiar environments or over longer durations, humans predominantly monitor changes in orientation and position using path integration and later reconstruct object locations from enduring allocentric representations. Medial prefrontal cortex and hippocampus - involved in visual path integration.
Spatial updating over short time scales in novel environments operates on transient, egocentric representations, in which the relationship between each object and the observer must be constantly updated as the observer move

23. Electrocortical stimulation in the precuneus can induce the sensation of translational
self-motion and BOLD responses in this structure correlate with the subjective experience
of self-motion
Updating of the stored egocentric object vectors
mediated by dense connections between area MST and the precuneus,
providing the latter with crucial information about translational self motion
may contain a human homolog of the monkey parietal reach region
the storing and updating of egocentric representations of space, independent of potential
actions, constitutes the most parsimonious interpretation of the activation in the precuneus
Dorsal pre-motor:
whenever subjects responded by pointing, the egocentric spatial map in the precuneus was
transformed into corre- sponding vectors for pointing movements in PMd,
which could be accomplished via direct connections between both regions.