Andrew Glennerster
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ag3dvr.bsky.social
Andrew Glennerster
@ag3dvr.bsky.social
80 followers 220 following 24 posts
3D vision

http://www.personal.reading.ac.uk/~sxs05ag/
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ag3dvr.bsky.social
The set of saccades that take the fovea between points in the scene can be described either as an egocentric representation or a ‘policy’, a set of context-dependent actions. When the observer moves, the most enduring part of the representation is the set of angles between distant points.
In the centre is a yellow plane. This represents the set of all egocentric representations, where neighbouring points on the surface correspond to the egocentric representations for neighbouring locations in space. The large beige region shows that the egocentric representations barely change over a large region of the yellow plane when the scene consists only of mountains. This is because the angles between mountains barely change as the observer moves. The light brown region lies within the beige region. This shows that adding in a forest in the middle distance constrains the set of egocentric representations more precisely. Finally, adding in a picnic table (and all the angles between the picnic table and other object in the scene) constrains the possible location of the observer even more tightly within the overall set of egocentric locations.
September 2, 2025 at 7:07 AM
ag3dvr.bsky.social
One element of the argument concerns the way that we (and most animals) move. We fixate on a point and move relative to that. The dorsal stream is well set up to control movements in this way.
On the left is a grid-like coordinate frame and four locations (O1 to O4). On the right are the same four locations (O1 to O4) but now, instad of a grid coordinate frame, there are three fixation points, A, B and C. The observer fixates on one of these as they move and then makes a sudden eye rotation (saccade) to a new fixation point.
September 2, 2025 at 7:07 AM
ag3dvr.bsky.social
Here is preprint corresponding to the talk I gave at #iNav2024: 'Navigating image space' doi.org/10.31234/osf.... No data, but some thoughts about the difference between Cartesian (grid-like) reference frames and an image-based frame for navigation.
Fig 2 from the paper. It shows an observer/eye moving while fixating a point and then making an eye movement to fixate a new object. Sub-panels show how the image changes during this movement and how responses in the ventral and dorsal streams relate to this movement across image space.
January 17, 2025 at 2:05 PM
ag3dvr.bsky.social
These points are relevant for hippocampal as well as PPC cells.
Text from Discussion. Paraphrasing: "We extend the interpretation to hippocampal cells. In both PPC and HPC, cues processed during fixation impacted the cells strongly"
December 6, 2024 at 5:06 PM
ag3dvr.bsky.social
Visual responses can be ‘erroneously interpreted as place codes’:
Text from Discussion. Paraphrasing: "Visual stimulation of PPC resulted in spatial selectivity that could be mistaken for 'place' codes akin to place cells found in rodent HPC cells."
December 6, 2024 at 5:06 PM
ag3dvr.bsky.social
Conclusion: Overall, PPC and HPC responses were remarkably similar. Certainly, the original adage that PPC encodes egocentric and HPC allocentric coordinate frames seems inconsistent with these results.
Part of Fig 7, showing responses of PPC and HPC cells aligned according to the time a landmark appears.
December 6, 2024 at 5:06 PM
ag3dvr.bsky.social
By contrast, there was very little information about the camera location.
Figure from Muryy et al (Vision Research 174, 79-93) showing a tSNE projection of the DRL representation generated by an agent navigating towards a rewarded goal. it shows clustering according to the target image but very little structure in relation to the camera location ('distance').
November 27, 2024 at 11:27 AM