A neuronal correlate of insect stereopsis by Rosner R, von Hadeln J, Tarawneh G, Read JCA, Rosner_et_al-2019-Nature_Communications.pdf (2.9 MiB) - A puzzle for neuroscience-and robotics-is how insects achieve surprisingly complex behaviours with such tiny brains. One example is depth perception via binocular stereopsis in the praying mantis, a predatory insect. Praying mantids use stereopsis, the computation of distances from disparities between the two retinal images, to trigger a raptorial strike of their forelegs when prey is within reach. The neuronal basis of this ability is entirely unknown. Here we show the first evidence that individual neurons in the praying mantis brain are tuned to specific disparities and eccentricities, and thus locations in 3D-space. Like disparity-tuned cortical cells in vertebrates, the responses of these mantis neurons are consistent with linear summation of binocular inputs followed by an output nonlinearity. Our study not only proves the existence of disparity sensitive neurons in an insect brain, it also reveals feedback connections hitherto undiscovered in any animal species.
The psychophysics of stereopsis can be explained without invoking independent ON and OFF channels by Read JCA, Cumming BG, ReadCumming2019.pdf (1.3 MiB) - Early vision proceeds through distinct ON and OFF channels, which encode luminance increments and decrements respectively. It has been argued that these channels also contribute separately to stereoscopic vision. This is based on the fact that observers perform better on a noisy disparity discrimination task when the stimulus is a random-dot pattern consisting of equal numbers of black and white dots (a “mixed-polarity stimulus”, argued to activate both ON and OFF stereo channels), than when it consists of all-white or all-black dots (“same-polarity”, argued to activate only one). However, it is not clear how this theory can be reconciled with our current understanding of disparity encoding. Recently, a binocular convolutional neural network was able to replicate the mixed-polarity advantage shown by human observers, even though it was based on linear filters and contained no mechanisms which would respond separately to black or white dots. Here, we show that a subtle feature of the way the stimuli were constructed in all these experiments can explain the results. The interocular correlation between left and right images is actually lower for the same-polarity stimuli than for mixed-polarity stimuli with the same amount of disparity noise applied to the dots. Since our current theories suggest stereopsis is based on a correlation-like computation in primary visual cortex, this can explain why performance was better for the mixed-polarity stimuli. We conclude that there is currently no evidence supporting separate ON and OFF channels in stereopsis.
Two choices good, four choices better: For measuring stereoacuity in children, a four-alternative forced-choice paradigm is more efficient than two by Vancleef K, Read JCA, Herbert W, Goodship N, Woodhouse M, Serrano-Pedraza I, VancleefReadHerbertGoodshipWoodhouseSerranoPedraza2018.pdf (4.5 MiB) - Purpose
Measuring accurate thresholds in children can be challenging. A typical psychophysical
experiment is usually too long to keep children engaged. However, a reduction in the number of trials decreases the precision of the threshold estimate. We evaluated the efficiency
of forced-choice paradigms with 2 or 4 alternatives (2-AFC, 4-AFC) in a disparity detection
experiment. 4-AFC paradigms are statistically more efficient, but also more cognitively
demanding, which might offset their theoretical advantage in young children.
Methods
We ran simulations evaluating bias and precision of threshold estimates of 2-AFC and 4-
AFC paradigms. In addition, we measured disparity thresholds in 43 children (aged 6 to 17
years) with a 4-AFC paradigm and in 49 children (aged 4 to 17 years) with a 2-AFC paradigm, both using an adaptive weighted one-up one-down staircase.
Results
Simulations indicated a similar bias and precision for a 2-AFC paradigm with double the number of trials as a 4-AFC paradigm. On average, estimated threshold of the simulated data was equal to the model threshold, indicating no bias. The precision was improved with an increasing number of trials. Likewise, our data showed a similar bias and precision for a 2-AFC paradigm with 60 trials as for a 4-AFC paradigm with 30 trials. Trials in the 4-AFC paradigm took slightly longer as participants scanned more alternatives. However, the 4-AFC task still ended up faster for a given precision.
Conclusion
Bias and precision were similar in a 4-AFC task compared to a 2-AFC task with double the number of trials. However, a 4-AFC paradigm was more time efficient and is therefore recommended
ASTEROID: A New Clinical Stereotest on an Autostereo 3D Tablet by Vancleef K, Serrano-Pedraza I, Sharp C, Slack G, Black C, Casanova T, Hugill J, Rafiq S, Burridge J, Puyat V, Ewane Enongue J, Gale H, Akotei H, Collier Z, Haggerty H, Smart K, Powell C, Taylor K, Clarke MP, Morgan G, Read JCA, VancleefEA_ASTEROIDMethods.pdf (1.9 MiB) - Purpose: To describe a new stereotest in the form of a game on an autostereoscopic
tablet computer designed to be suitable for use in the eye clinic and present data on
its reliability and the distribution of stereo thresholds in adults.
Methods: Test stimuli were four dynamic random-dot stereograms, one of which
contained a disparate target. Feedback was given after each trial presentation. A
Bayesian adaptive staircase adjusted target disparity. Threshold was estimated from the
mean of the posterior distribution after 20 responses. Viewing distance was monitored
via a forehead sticker viewed by the tablet’s front camera, and screen parallax was
adjusted dynamically so as to achieve the desired retinal disparity.
Results: The tablet must be viewed at a distance of greater than ~35 cm to produce a
good depth percept. Log thresholds were roughly normally distributed with a mean
of 1.75 log10 arcsec ¼ 56 arcsec and SD of 0.34 log10 arcsec ¼ a factor of 2.2. The
standard deviation agrees with previous studies, but ASTEROID thresholds are
approximately 1.5 times higher than a similar stereotest on stereoscopic 3D TV or on
Randot Preschool stereotests. Pearson correlation between successive tests in same
observer was 0.80. Bland-Altman 95% limits of reliability were 60.64 log10 arcsec ¼ a
factor of 4.3, corresponding to an SD of 0.32 log10 arcsec on individual threshold
estimates. This is similar to other stereotests and close to the statistical limit for 20
responses.
Conclusions: ASTEROID is reliable, easy, and portable and thus well-suited for clinical
stereoacuity measurements.
Translational Relevance: New 3D digital technology means that research-quality
psychophysical measurement of stereoacuity is now feasible in the clinic.
Which Stereotest do You Use? A Survey Research Study in the British Isles, the United States and Canada by Vancleef K, Read JCA, VancleefRead2019.pdf (2.6 MiB) - A wide range of stereotests are available to measure stereopsis. Because each test has its own advantages and disadvantages, opinions differ on which is the preferred test to use in clinical practice. We conducted surveys comparing the use of stereotests in the British Isles and in the United States and Canada.
Two online surveys were developed following consultation with eye care professionals, one for each geographical area. Both surveys included two questions on the frequency of use of different stereotests, two questions on best practice stereotests, and two questions on the usefulness of stereotests. Researchers made distinctions between appointments with children below or above 6 years old for respondents from the British Isles and below or above 5 years old for respondents from the Unites Stated and Canada. The surveys were distributed through professional organisations.
We found Frisby to be the most used stereotest on the British Isles for both age groups. In the US and Canada, Titmus and Randot stereotest are more frequently used. Respondents consider these tests as the best practice stereotests. Eye care professionals agree stereotests are useful in the diagnosis and treatment decision making and even more so in obtaining an accurate measure of stereoacuity, especially with older children.
Apparent Motion Perception in the Praying Mantis: Psychophysics and Modelling by Tarawneh G, Jones L, Nityananda V, Rosner R, Rind C, Read JCA, TarawnehNityanandaJonesNityanandaRosnerRindRead2018.pdf (0.9 MiB) - Apparent motion is the perception of motion created by rapidly presenting still frames in which objects are displaced in space. Observers can reliably discriminate the direction of apparent motion when inter-frame object displacement is below a certain limit, Dmax. Earlier studies of motion perception in humans found that Dmax is lower-bounded at around 15 arcmin, and thereafter scales with the size of the spatial elements in the images. Here, we run corresponding experiments in the praying mantis Sphodromantis lineola to investigate how Dmax scales with the element size. We use random moving chequerboard patterns of varying element and displacement step sizes to elicit the optomotor response, a postural stabilization mechanism that causes mantids to lean in the direction of large-field motion. Subsequently, we calculate Dmax as the displacement step size corresponding to a 50% probability of detecting an optomotor response in the same direction as the stimulus. Our main findings are that the mantis Dmax scales roughly as a square-root of element size and that, in contrast to humans, it is not lower-bounded. We present two models to explain these observations: a simple high-level model based on motion energy in the Fourier domain and a more-detailed one based on the Reichardt Detector. The models present complementary intuitive and physiologically-realistic accounts of how Dmax scales with the element size in insects. We conclude that insect motion perception is limited by only a single stage of spatial filtering, reflecting the optics of the compound eye. In contrast, human motion perception reflects a second stage of spatial filtering, at coarser scales than imposed by human optics, likely corresponding to the magnocellular pathway. After this spatial filtering, mantis and human motion perception and Dmax are qualitatively very similar.
Contrast thresholds reveal different visual masking functions in humans and praying mantises by Tarawneh G, Nityananda V, Rosner R, Errington S, Herbert W, Arranz-Paraíso S, Busby N, Tampin J, Read JCA, Serrano-Pedraza I, TarawnehNityanandaRosnerErringtonHerbertArranzParaisoBusbyTampinSerranoSerranoPedraza2018.pdf (2.3 MiB) - Recently, we showed a novel property of the Hassenstein–Reichardt detector, namely that insect motion detection can be masked by ‘undetectable’ noise, i.e. visual noise presented at spatial frequencies at which coherently moving gratings do not elicit a response (Tarawneh et al., 2017). That study compared the responses of human and insect motion detectors using different ways of quantifying masking (contrast threshold in humans and masking tuning function in insects). In addition, some adjustments in experimental procedure, such as presenting the stimulus at a short viewing distance, were necessary to elicit a response in insects. These differences offer alternative explanations for the observed difference between human and insect responses to visual motion noise. Here, we report the results of new masking experiments in which we test whether differences in experimental paradigm and stimulus presentation between humans and insects can account for the undetectable noise effect reported earlier. We obtained contrast thresholds at two signal and two noise frequencies in both humans and praying mantises (Sphodromantis lineola), and compared contrast threshold differences when noise has the same versus different spatial frequency as the signal. Furthermore, we investigated whether differences in viewing geometry had any qualitative impact on the results. Consistent with our earlier finding, differences in contrast threshold show that visual noise masks much more effectively when presented at signal spatial frequency in humans (compared to a lower or higher spatial frequency), while in insects, noise is roughly equivalently effective when presented at either the signal spatial frequency or lower (compared to a higher spatial frequency). The characteristic difference between human and insect responses was unaffected by correcting for the stimulus distortion caused by short viewing distances in insects. These findings constitute stronger evidence that the undetectable noise effect reported earlier is a genuine difference between human and insect motion processing, and not an artefact caused by differences in experimental paradigms.
A Novel Form of Stereo Vision in the Praying Mantis by Nityananda V, Tarawneh G, Henriksen S, Umeton D, Simmons A, Read JCA , NityanandaTarawnehHenriksenUmetonSimmonsRead2018.pdf (2.5 MiB) - Stereopsis is the ability to estimate distance based on the different views seen in the two eyes. It is an important model perceptual system in neuroscience and a major area of machine vision. Mammalian, avian, and almost all machine stereo algorithms look for similarities between the luminance-defined images in the two eyes, using a series of computations to produce a map showing how depth varies across the scene. Stereopsis has also evolved in at least one invertebrate, the praying mantis. Mantis stereopsis is presumed to be simpler than vertebrates’, but little is currently known about the underlying computations. Here, we show that mantis stereopsis uses a fundamentally different computational algorithm from vertebrate stereopsis --
rather than comparing luminance in the two eyes’ images directly, mantis stereopsis looks for regions of the images where luminance is changing. Thus, while there is no evidence that mantis stereopsis works at all with static images, it successfully reveals the distance to a moving target even in complex visual scenes with targets that are perfectly camouflaged against the background in terms of texture. Strikingly, these insects outperform human observers at judging stereoscopic distance when the pattern of luminance in the two eyes does not match. Insect stereopsis has thus evolved to be computationally efficient while being robust to poor image resolution and to discrepancies in the pattern of luminance between the two eyes.
Thresholds for sine-wave corrugations defined by binocular disparity in random dot stereograms: Factor analysis of individual differences reveals two stereoscopic mechanisms tuned for spatial frequency by Peterzell DH, Serrano-Pedraza I, Widdall M, Read JCA, PeterzellSerranoPedrazaWiddallRead2017.pdf (5 KiB)
Invisible noise obscures visible signal in insect motion detection by Tarawneh G, Nityananda V, Rosner R, Errington S, Herbert W, Cumming BG, Read JCA, Serrano-Pedraza I, TarawnehNityanandaRosnerErringtonHerbertCummingReadSerranoPedraza2017.pdf (2.6 MiB) - The motion energy model is the standard account of motion detection in animals from beetles to
humans. Despite this common basis, we show here that a difference in the early stages of visual
processing between mammals and insects leads this model to make radically different behavioural
predictions. In insects, early filtering is spatially lowpass, which makes the surprising prediction that
motion detection can be impaired by “invisible” noise, i.e. noise at a spatial frequency that elicits
no response when presented on its own as a signal. We confirm this prediction using the optomotor
response of praying mantis Sphodromantis lineola. This does not occur in mammals, where spatially
bandpass early filtering means that linear systems techniques, such as deriving channel sensitivity from
masking functions, remain approximately valid. Counter-intuitive effects such as masking by invisible
noise may occur in neural circuits wherever a nonlinearity is followed by a difference operation.
