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A single mechanism can account for human perception of depth in mixed correlation random dot stereograms

A single mechanism can account for human perception of depth in mixed correlation random dot stereograms by Henriksen S, Cumming BG, Read JCA, HenriksenCummingRead2016.PDF (0.7 MiB) - Relating neural activity to perception is one of the most challenging tasks in neuroscience.
Stereopsis—the ability of many animals to see in stereoscopic 3D—is a particularly tractable
problem because the computational and geometric challenges faced by the brain are
very well understood. In essence, the brain has to work out which elements in the left eye’s
image correspond to which in the right image. This process is believed to begin in primary
visual cortex (V1). It has long been believed that neurons in V1 achieve this by computing
the correlation between small patches of each eye’s image. However, recent psychophysical
experiments have reported depth perception in stimuli for which this correlation is zero,
suggesting that another mechanism might be responsible for matching the left and right
images in this case. In this article, we show how a simple modification to model neurons
that compute correlation can account for depth perception in these stimuli. Our model
cells mimic the response properties of real cells in the primate brain, and importantly, we
show that a perceptual decision model that uses these cells as its basic elements can capture
the performance of human observers on a series of visual tasks. That is, our computer
model of a brain area, based on experimental data about real neurons and using only a single
type of depth computation, successfully explains and predicts human depth judgments
in novel stimuli. This reconciles the properties of human depth perception with the properties
of neurons in V1, bringing us closer to understanding how neuronal activity causes
perception.

The stereoscopic anisotropy develops during childhood.

The stereoscopic anisotropy develops during childhood. by Serrano-Pedraza I, Herbert W, Villa-Laso L, Widdall M, Vancleef K, Read JCA, SerranoPedrazaHerbertVillaLasoWiddallVancleefRead2016.pdf (1.5 MiB) - PURPOSE:
Human vision has a puzzling stereoscopic anisotropy: horizontal depth corrugations are easier to detect than vertical depth corrugations. To date, little is known about the function or the underlying mechanism responsible for this anisotropy. Here, we aim to find out whether this anisotropy is independent of age. To answer this, we compare detection thresholds for horizontal and vertical depth corrugations as a function of age.
METHODS:
The depth corrugations were defined solely by the horizontal disparity of random dot patterns. The disparities depicted a horizontal or vertical sinusoidal depth corrugation of spatial frequency 0.1 cyc/deg. Detection thresholds were obtained using Bayesian adaptive staircases from a total of 159 subjects aged from 3 to 73 years. For each participant we computed the anisotropy index, defined as the log10-ratio of the detection threshold for vertical corrugations divided by that for horizontal.
RESULTS:
Anisotropy index was highly variable between individuals but was positive in 87% of the participants. There was a significant correlation between anisotropy index and log-age (r = 0.21, P = 0.008) mainly driven by a significant difference between children and adults. In 67 children aged 3 to 13 years, the mean anisotropy index was 0.34 ± 0.38 (mean ± SD, meaning that vertical thresholds were on average 2.2 times the horizontal ones), compared with 0.59 ± 0.55 in 84 adults aged 18 to 73 years (vertical 3.9 times horizontal). This was mainly driven by a decline in the sensitivity to vertical corrugations. Children had poorer stereoacuity than adults, but had similar sensitivity to adults for horizontal corrugations and were actually more sensitive than adults to vertical corrugations.
CONCLUSIONS:
The fact that adults show stronger stereo anisotropy than children raises the possibility that visual experience plays a critical role in developing and strengthening the stereo anisotropy.

Small or far away? Size and distance perception in the praying mantis.

Small or far away? Size and distance perception in the praying mantis. by Nityananda V, Bissianna G, Tarawneh G, Read JCA, Nityananda_et_al2015_PhilTrans_PostReview.pdf (1.5 MiB) - Stereo or '3D' vision is an important but costly process seen in several evolutionarily distinct lineages including primates, birds and insects. Many selective advantages could have led to the evolution of stereo vision, including range finding, camouflage breaking and estimation of object size. In this paper, we investigate the possibility that stereo vision enables praying mantises to estimate the size of prey by using a combination of disparity cues and angular size cues. We used a recently developed insect 3D cinema paradigm to present mantises with virtual prey having differing disparity and angular size cues. We predicted that if they were able to use these cues to gauge the absolute size of objects, we should see evidence for size constancy where they would strike preferentially at prey of a particular physical size, across a range of simulated distances. We found that mantises struck most often when disparity cues implied a prey distance of 2.5 cm; increasing the implied distance caused a significant reduction in the number of strikes. We, however, found no evidence for size constancy. There was a significant interaction effect of the simulated distance and angular size on the number of strikes made by the mantis but this was not in the direction predicted by size constancy. This indicates that mantises do not use their stereo vision to estimate object size. We conclude that other selective advantages, not size constancy, have driven the evolution of stereo vision in the praying mantis.This article is part of the themed issue 'Vision in our three-dimensional world'.

Insect stereopsis demonstrated using a 3D insect cinema

Insect stereopsis demonstrated using a 3D insect cinema by Nityananda V, Tarawneh G, Rosner R, Nicolas J, Crichton S, Read JCA, NityanandaTarawnehRosnerNicolasCrichtonRead2016.pdf (1.2 MiB) - Stereopsis - 3D vision – has become widely used as a model of perception. However, all our knowledge of possible underlying mechanisms comes almost exclusively from vertebrates. While stereopsis has been demonstrated for one invertebrate, the praying mantis, a lack of techniques to probe invertebrate stereopsis has prevented any further progress for three decades. We therefore developed a stereoscopic display system for insects, using miniature 3D glasses to present separate images to each eye, and tested our ability to deliver stereoscopic illusions to praying mantises. We find that while filtering by circular polarization failed due to excessive crosstalk, “anaglyph” filtering by spectral content clearly succeeded in giving the mantis the illusion of 3D depth. We thus definitively demonstrate stereopsis in mantises and also demonstrate that the anaglyph technique can be effectively used to deliver virtual 3D stimuli to insects. This method opens up broad avenues of research into the parallel evolution of stereoscopic computations and possible new algorithms for depth perception.

Viewing 3D TV over two months produces no discernible effects on balance, coordination or eyesight.

Viewing 3D TV over two months produces no discernible effects on balance, coordination or eyesight. by Read JCA, Godfrey A, Bohr I, SImonotto J, Galna B, Smulders TV, ReadGodfreyBohrSimonottoGalnaSmulders2016.pdf (2.2 MiB) - With the rise in stereoscopic 3D media, there has been concern that viewing stereoscopic 3D (S3D) content could have long-term adverse effects, but little data are available. In the first study to address this, 28 households who did not currently own a 3D TV were given a new TV set, either S3D or 2D. The 116 members of these households all underwent tests of balance, coordination and eyesight, both before they received their new TV set, and after they had owned it for 2 months. We did not detect any changes which appeared to be associated with viewing 3D TV. We conclude that viewing 3D TV does not produce detectable effects on balance, coordination or eyesight over the timescale studied. Practitioner Summary: Concern has been expressed over possible long-term effects of stereoscopic 3D (S3D). We looked for any changes in vision, balance and coordination associated with normal home S3D TV viewing in the 2 months after first acquiring a 3D TV. We find no evidence of any changes over this timescale.

Latitude and longitude vertical disparities

Latitude and longitude vertical disparities by Read JCA, Phillipson GP, Glennerster A , ReadPhillipsonGlennerster09.pdf (5.2 MiB) - At around this time I'd been spending a lot of time thinking about vertical disparity, and had been awarded an MRC grant to study it. To begin with, I wasn't even entirely clear what vertical disparity was, and I had difficulty following some of the other papers on it. I realised that a lot of the confusion was occurring because there are actually several different definitions of "vertical disparity" in the literature -- I've identified at least four -- and to make matters worse, different papers aren't always clear about exactly which definition they have in mind. Unsurprisingly, this has caused a lot of confusion about what the properties of vertical disparity actually are. Part of the problem, I think, is that under some circumstances you obtain the same results regardless of whether you define the elevation coordinate as a latitude or a longitude on the retina, and this may have given the impression that it doesn't ever matter -- whereas in fact, under some circumstances, the two definitions give completely different results. So with my PhD student Graeme Phillipson and my old friend and colleague from back in Oxford, Andrew Glennerster, we decided to write a paper really getting into the nitty-gritty of vertical disparity, and laying out clearly what properties follow from different definitions. It may not be the most exciting paper ever, and like many of my papers, it has masses of Appendices filled with equations. But we hoped it would be a useful reference for anyone interested in vertical disparity -- and I did at least try hard to make the pictures pretty.

Extracellular calcium regulates postsynaptic efficacy through group 1 metabotropic glutamate receptors.

Extracellular calcium regulates postsynaptic efficacy through group 1 metabotropic glutamate receptors. by Hardingham NR, Bannister NJ, Read JCA, Fox KD, Hardingham GE, Jack JJB , HardinghamEA06.pdf (0.7 MiB) - This project began when I was in my first neuroscience post-doc, doing a Wellcome Training Fellowship in Mathematical Biology with Julian Jack in Oxford. Julian's lab had done a lot of work on synaptic physiology, in particular developing quantal analysis as a tool to examine central synapses. The physiology underlying quantal analysis is the fact that neurons are generally connected by more than one terminal. When the presynaptic neuron fires an action potential, packets - quanta - of neurotransmitter may be released from all, some or none of these terminals. If each packet of neurotransmitter contributes a similar amount to the postsynaptic depolarisation, then a histogram of the effect produced by each presynaptic action potential will have several peaks, corresponding to the release of 0, 1, 2 ... quanta of neurotransmitter. In principle, this histogram can then be analysed to estimate the effect caused by each quantum, and the probability that a quantum will be released from a terminal given an action potential. In practice, this depends critically on things like whether each quantum really does have a very similar postsynaptic effect, whether the release probability is the same at all terminals, whether these quantities are constant over time and so on. Julian's lab had already developed a lot of sophisticated tools for quantal analysis, and I took this further, developing a still more elaborate fitting algorithm to extract the quantal parameters, and also a battery of statistical tests to decide whether the resulting model of the synapse was adequate. There's quite a lot of sceptism as to how far quantal analysis can be trusted in the central nervous system (as opposed to at the neuromuscular junction, where it was originally developed), so these tests were critical in convincing people that our results were reliable. Neil Hardingham, the first author, who was a Ph.D. student and post-doc in Julian's lab when I was there, used these techniques to examine how the quantal parameters change as a function of extracellular calcium. He was able to show that calcium depletion, as well as reducing release probability, also reduces quantal size. Since calcium levels drop as neurons become active, this represents a novel mechanism for regulating information transfer between neurons.