Analysis of Soft Data for Mass Provision of Stereoacuity Testing Through a Serious Game for Health by Ushaw G, Sharp S, Hugill J, Rafiq S, Black C, Casanova T, Vancleef K, Read JCA, Morgan G, UshawSharpHugillRafiqBlackCasanovaVancleefReadMorgan2017.pdf (1.7 MiB) - Mass provision of healthcare through a digital medium can be greatly enhanced by the use of serious games. The accessibility and engagement provided by a serious game to the subject can significantly increase participation. The commercial games industry employs numerous techniques to analyse soft data collected from early users of an application to evolve the application itself and improve the experience of playing it. A game for mass stereoacuity testing of young children is used as a case study in this paper, to illustrate how soft feedback can be used to improve the effectiveness of a clinical trial. The key to the approach is identified as rapid incremental evolution of the application and trial protocol in a manner which increases the amount and usefulness of soft data collected, and reacts to issues identified in the soft data in a timely fashion. It is hoped that the approach can be adopted for a wide range of digital applications for mass health provision.
Stereopsis in animals: evolution, function and mechanisms by Nityananda V, Read JCA, NityanandaRead2017.pdf (0.8 MiB) - Stereopsis is the computation of depth information from views
acquired simultaneously from different points in space. For many
years, stereopsis was thought to be confined to primates and other
mammals with front-facing eyes. However, stereopsis has now been
demonstrated in many other animals, including lateral-eyed prey
mammals, birds, amphibians and invertebrates. The diversity of
animals known to have stereo vision allows us to begin to investigate
ideas about its evolution and the underlying selective pressures in
different animals. It also further prompts the question of whether all
animals have evolved essentially the same algorithms to implement
stereopsis. If so, this must be the best way to do stereo vision, and
should be implemented by engineers in machine stereopsis.
Conversely, if animals have evolved a range of stereo algorithms in
response to different pressures, that could inspire novel forms of
machine stereopsis appropriate for distinct environments, tasks or
constraints. As a first step towards addressing these ideas, we here
review our current knowledge of stereo vision in animals, with a view
towards outlining common principles about the evolution, function
and mechanisms of stereo vision across the animal kingdom. We
conclude by outlining avenues for future work, including research into
possible new mechanisms of stereo vision, with implications for
machine vision and the role of stereopsis in the evolution of
camouflage.
Visual Perception: Neural Networks for Stereopsis by Read JCA, Cumming BG, ReadCumming2017.pdf (0.4 MiB) - This is a comment article on Welchman and Goncalves (2017): ‘‘What not’’ detectors help the brain see in depth. Curr. Biol. 27, 1403–1412.
True stereoscopic 3D cannot be simulated by shifting 2D content off the screen plane by Hands P, Read JCA, HandsRead2017.pdf (0.9 MiB) - money by including brief sections of 2D content displayed with a uniform disparity, i.e. the 2D image is
geometrically shifted behind the screen plane. This manipulation is believed to produce an illusion of
depth which, while not as powerful as true S3D, is nevertheless more compelling than simple 2D. Our
study examined whether this belief is correct. 30 s clips from a nature documentary were shown in
the original S3D, in ordinary 2D and in shifted versions of S3D and 2D. Participants were asked to determine
the impression of depth on a 7 point Likert scale. There was a clear and highly significant difference
between the S3D depth perception (mean 6.03) and the shifted 2D depth perception (mean 4.13)
(P = 0.002, ANOVA). There was no difference between ordinary 2D presented on the screen plane, and
the shifted 2D. We conclude that the shifted 2D method not only fails to mimic the depth effect of true
S3D, it in fact has no benefit over ordinary 2D in terms of the depth illusion created. This could impact
viewing habits of people who notice the difference in depth quality.
Overestimation of stereo thresholds by the TNO stereotest is not due to global stereopsis. by Vancleef K, Read JCA, Herbert W, Goodship N, Woodhouse M, Serrano-Pedraza I, VancleefReadHerbertGoodshipWoodhouseSerranoPedraza2017_2.pdf (18 KiB) - Purpose
It has been repeatedly shown that the TNO stereotest overestimates stereo threshold compared to other clinical stereotests. In the current study, we test whether this overestimation can be attributed to a distinction between ‘global’ (or ‘cyclopean’) and ‘local’ (feature or contour-based) stereopsis.
Methods
We compared stereo thresholds of a global (TNO) and a local clinical stereotest (Randot Circles). In addition, a global and a local psychophysical stereotest were added to the design. One hundred and forty-nine children between 4 and 16 years old were included in the study.
Results
Stereo threshold estimates with TNO were a factor of two higher than with any of the other stereotests. No significant differences were found between the other tests. Bland-Altman analyses also indicated low agreement between TNO and the other stereotests, especially for higher stereo threshold estimates. Simulations indicated that the TNO test protocol and test disparities can account for part of this effect.
Discussion
The results indicate that the global – local distinction is an unlikely explanation for the overestimated thresholds of TNO. Test protocol and disparities are one contributing factor. Potential additional factors include the nature of the task (TNO requires depth discrimination rather than detection) and the use of anaglyph red/green 3D glasses rather than polarizing filters, which may reduce binocular fusion.
Assessment of epilepsy using noninvasive visual psychophysics tests of surround suppression by Yazdani P, Read JCA, Whittaker RG, Trevelyan AJ, YazdaniReadWhittakerTrevelyan2017.pdf (2.1 MiB) - Powerful endogenous inhibitory mechanisms are thought to restrict the spread of epileptic discharges in cortical networks. Similar inhibitory mechanisms also influence physiological processing. We reasoned, therefore, that useful information about the quality of inhibitory restraint in individuals with epilepsy may be gleaned from psychophysical assays of these physiological processes. We derived a psychophysical measure of cortical inhibition, the motion surround suppression index (SSI), in 54 patients with epilepsy and 146 control subjects. Multivariate regression analyses showed that SSI was predicted strongly by age and seizure type, but not by seizure frequency. Specifically, we found that patients with exclusively focal epilepsy, and no history of generalization, showed significantly stronger cortical inhibition as measured by the SSI compared to all other groups, including controls. In contrast, patients with focal seizures evolving into generalized seizures, and patients with generalized genetic epilepsy, showed similar levels of cortical inhibition to controls. The presumptive focus, when one could be identified, was rarely found in visual cortex, meaning that the relationship with the epilepsy subtype is likely to reflect some global difference in inhibition in these subjects. This is the first reported instance of raised SSI in any patient cohort, and appears to differentiate between patients with respect to the likelihood of their experiencing generalization of their seizures. These results suggest that such simple psychophysical assays may provide useful aids to clinical management, particularly at the time of diagnosis.
The optomotor response of the praying mantis is driven predominantly by the central visual field by Nityananda V, Tarawneh G, Errington S, Serrano-Pedraza I, Read JCA, NityanandaTarawnehErringtonSerranoPedrazaRead.pdf (1.9 MiB) - The optomotor response has been widely used to
investigate insect sensitivity to contrast and motion. Several
studies have revealed the sensitivity of this response
to frequency and contrast, but we know less about the
spatial integration underlying this response. Specifically,
few studies have investigated how the horizontal angular
extent of stimuli influences the optomotor response. We
presented mantises with moving gratings of varying horizontal
extents at three different contrasts in the central or
peripheral regions of their visual fields. We assessed the
relative effectivity of different regions to elicit the optomotor
response and modelled the dependency of the response
on the angular extent subtended by stimuli at these different
regions. Our results show that the optomotor response
is governed by stimuli in the central visual field and not
in the periphery. The model also shows that in the central
region, the probability of response increases linearly with
increase in horizontal extent up to a saturation point. Furthermore,
the dependency of the optomotor response on the
angular extent of the stimulus is modulated by contrast. We
discuss the implications of our results for different modes
of stimulus presentation and for models of the underlying
mechanisms of motion detection in the mantis.
Unravelling the illusion of flicker fusion by Umeton D, Read JCA, Rowe C, UmetonReadRowe2017.pdf (0.7 MiB) - For over 150 years, researchers have investigated the anti-predator function of animal patterns. However, this work has mainly focused on when prey remain still, and has only recently started to incorporate motion into the study of defensive coloration. As motion breaks camouflage, a new challenge is to understand how prey avoid predators while moving around their environment, and if a moving prey can ever be camouflaged. We propose that there is a solution to this, in that a ‘flicker fusion effect’ can change the appearance of the prey in the eyes of their predators to reduce the chances of initial detection. This effect occurs when a high contrast pattern blurs at speed, changing the appearance of the prey, which may help them better match their background. Despite being widely discussed in the literature, the flicker fusion effect is poorly described, there is no clear theoretical framework for testing how it might reduce predation, and the terminology describing it is, at best, rather confusing. Our review addresses these three key issues to enable researchers to formulate precise predictions about when the flicker fusion effect occurs, and to test how it can reduce predation.
Blindness to background: an inbuilt bias for visual objects by O'Hanlon, CG and Read JCA, OHanlonRead2016.pdf (1.6 MiB) - Sixty-eight 2- to 12-year-olds and 30 adults were shown colorful displays on a touchscreen monitor and trained to point to the location of a named color. Participants located targets near-perfectly when presented with four abutting colored patches. When presented with three colored patches on a colored background, toddlers failed to locate targets in the background. Eye tracking demonstrated that the effect was partially mediated by a tendency not to fixate the background. However, the effect was
abolished when the targets were named as nouns, whilst the change to nouns had little impact on eye movement patterns. Our results imply a powerful, inbuilt tendency to attend to objects, which may slow the development of color concepts and acquisition of color words.
Avoiding monocular artifacts in clinical stereotests presented on column-interleaved digital stereoscopic displays by Serrano-Pedraza I, Vancleef K, Read JCA, SerranoPedrazaVancleefRead.pdf (1.5 MiB) - New forms of stereoscopic 3-D technology offer vision
scientists new opportunities for research, but also
come with distinct problems. Here we consider
autostereo displays where the two eyes’ images are
spatially interleaved in alternating columns of pixels
and no glasses or special optics are required. Columninterleaved
displays produce an excellent stereoscopic
effect, but subtle changes in the angle of view can
increase cross talk or even interchange the left and
right eyes’ images. This creates several challenges to
the presentation of cyclopean stereograms (containing
structure which is only detectable by binocular vision).
We discuss the potential artifacts, including one that is
unique to column-interleaved displays, whereby scene
elements such as dots in a random-dot stereogram
appear wider or narrower depending on the sign of
their disparity. We derive an algorithm for creating
stimuli which are free from this artifact.We show that
this and other artifacts can be avoided by (a) using a
task which is robust to disparity-sign inversion—for
example, a disparity-detection rather than
discrimination task—(b) using our proposed algorithm
to ensure that parallax is applied symmetrically on the
column-interleaved display, and (c) using a dynamic
stimulus to avoid monocular artifacts from motion
parallax. In order to test our recommendations, we
performed two experiments using a stereoacuity task
implemented with a parallax-barrier tablet. Our
results confirm that these recommendations eliminate
the artifacts. We believe that these recommendations
will be useful to vision scientists interested in running
stereo psychophysics experiments using parallaxbarrier
and other column-interleaved digital displays
