Basic principles of visual processing Flashcards

Question

A pessimistic estimate of the time required for an eye to evolve (Nilsson and Pelger, 1994) research

Answer 1

Maclver et al. (2017) Kumar (2019)

Answer 2

The evolution of terrestrial vertebrates, starting around 385 million years ago, is an iconic moment in evolution that brings to mind images of fish transforming into four-legged animals. Here, we show that this radical change in body shape was preceded by an equally dramatic change in sensory abilities akin to transitioning from seeing over short distances in a dense fog to seeing over long distances on a clear day. Measurements of eye sockets and simulations of their evolution show that eyes nearly tripled in size just before vertebrates began living on land. Computational simulations of these animal’s visual ecology show that for viewing objects through water, the increase in eye size provided a negligible increase in performance. However, when viewing objects through air, the increase in eye size provided a large increase in performance. The jump in eye size was, therefore, unlikely to have arisen for seeing through water and instead points to an unexpected hybrid of seeing through air while still primarily inhabiting water. Our results and several anatomical innovations arising at the same time suggest lifestyle similarity to crocodiles. The consequent combination of the increase in eye size and vision through air would have conferred a 1 million-fold increase in the amount of space within which objects could be seen. The “buena vista” hypothesis that our data suggest is that seeing opportunities from afar played a role in the subsequent evolution of fully terrestrial limbs as well as the emergence of elaborated action sequences through planning circuits in the nervous system.

Answer 3

Eye evolution is far from resolved and despite the considerable interest and decades of study, many questions remain on the evolutionary scenarios of eyes and photoreceptor cells. While examining their ultrastructure has been an important way for comparative studies, the high degree of variation of eye structures/complexities within species (and closely related species) calls for more detailed studies at the molecular level. As with many lophotrochozoan taxa, annelids also display simple to elaborate eye structures. Although general homology of the cerebral rhabdomeric eyes is assumed, this has not been firmly established leaving the scene in the annelid ancestor unanswered. To gain an understanding of the situation in a long pelagic annelid larva, we studied Malacoceros fuliginosus. The larvae possess multiple eyespots and therefore suitable for studies on how different eyespots develop and integrate into the nervous system. We used ultrastructure and gene expression studies to understand the eyespot structure and development. Our phylogenetic analysis of annelid r-opsins revealed the existence of two r-opsin paralogs - r-opsin1 and r-opsin3 within the two main annelid groups - sedentaria and errantia, whereas in basal branching annelids only a single r-opsin type is present. In comparison with the well-studied annelid Platynereis dumerilii, we find that the rhabdomeric eyes have several similarities in terms of spatial and temporal development, r-opsin expression dynamics and axonal connectivity. This suggests homology of the two rhabdomeric eyes and the more complex dorsal eyes in P. dumerilii is likely a case of augmentation of a simple eyespot. Apart from visual r-opsins, the eye PRCs in M. fuliginosus also expresses the newly classified opsin type, xenopsin. Inspection of the eye structure also revealed the existence of a prominent cilium in both rhabdomeric eyes. Additionally, we also identified a c-opsin in an extraocular cell type thereby making it the only species so far having both c-opsin and xenopsin. Taken together, our data provide insights into the eye organization of the annelid ancestor and adds information on how eye evolution is shaped by opsin gain and loss. The second topic of interest is the nervous system development in the M. fuliginosus larva. The evolution of the bilaterian nervous system is a topic of long-standing debate inciting the need for studies at multiple levels along with broader species sampling. A major question is whether the centralized nervous system seen across taxa is derived from a common ancestor or independently originated multiple times. Characterization of the nervous system has been mainly done at the level of gene expression patterns along the major body axes, anterior-posterior and dorsal-ventral. One aspect that has been overlooked particularly in lophotrochozoans is the development of pioneer neurons that give rise to the early neuronal scaffold. In M. fuliginosus, we identify at least three pioneer neurons that are responsible to form the complete early neuronal scaffold. While a posterior neuron pioneers the path for the ventral nerve cord, pair of neurons form the prototroch ring nerve and a ganglion cell near the apical organ with descending axons prefigures the central ganglia. Here we focused on the development of the posterior pioneer neuron and distinguish it from the rest of the neurons. It is one of the earliest cells to differentiate along with other ciliated cells of apical tuft and prototroch cells which are known to have mosaic development. The posterior neuron does not express the well-characterized proneural genes such as Ascl1, Olig, NeuroD, and Ngn and moreover, they even lack Prox1 and Elav which are represented by most other neurons. From a molecular perspective, the posterior pioneer neuron is indeed distinct from the rest of the neurons and may develop in a cell-autonomous manner.

Answer 4

``` · Spatial resolution o Viewing distances, size and density of relevant features or objects in the visual scene o Density and number of photoreceptors o Eye size and curvature of retina · Light sensitivity o Intensity range in which receptors operate (dim or bright light) o Eye size o Size of the lens(es) o Decreases with higher spatial resolution · Temporal resolution o Speed of movements Fast or slow photoreceptors ```

Answer 5

``` 1 = humans · 2 = peregrine falcon · 13 = honeybee · 18 = drosophila · 8 = Myotis (bat) 17 = Metaphidippus (jumping spider, better vision than bat) ``` see notes

Answer 6

Bagheri et al. (2020) Pusch et al. (2013)

Answer 7

Visual systems play a vital role in guiding the behaviour of animals. Understanding the visual information animals are able to acquire is therefore key to understanding their visually mediated decision making. Compound eyes, the dominant eye type in arthropods, are inherently low-resolution structures. Their ability to resolve spatial detail depends on sampling resolution (interommatidial angle) and the quality of ommatidial optics. Current techniques for estimating interommatidial angles are difficult, and generally require in vivo measurements. Here, we present a new method for estimating interommatidial angles based on the detailed analysis of 3D micro-computed tomography images of fixed samples. Using custom-made MATLAB software, we determined the optical axes of individual ommatidia and projected these axes into the 3D space around the animal. The combined viewing directions of all ommatidia, estimated from geometrical optics, allowed us to estimate interommatidial angles and map the animal's sampling resolution across its entire visual field. The resulting topographic representations of visual acuity match very closely the previously published data obtained from both fiddler and grapsid crabs. However, the new method provides additional detail that was not previously detectable and reveals that fiddler crabs, rather than having a single horizontal visual streak as is common in flat-world inhabitants, probably have two parallel streaks located just above and belowthe visual horizon. A key advantage of our approach is that it can be used on appropriately preserved specimens, allowing the technique to be applied to animals such as deep-sea crustaceans that are inaccessible or unsuitable for in vivo approaches.

Answer 8

The retina of the weakly electric fish Gnathonemus petersii is a so-called grouped retina where photoreceptors are bundled. These bundles are regarded as functional units and this type of retinal specialization is uniquely found in teleosts. To understand how this anatomical organization influences visual information processing we investigated the morphology and distribution of retinal ganglion cells (GCs) and the response properties of retinal afferents terminating in the major retinorecipient area, the optic tectum. GCs were classified based on their dendritic morphology (dendritic field diameters <90-100 m: narrow-field GCs; 110-280 m: widefield GCs; >280 m: giant GCs). Within these classes subtypes were distinguished based on the ramification patterns of the dendrites in the sublaminae of the inner plexiform layer. Properties of presumed optic nerve terminals were investigated in the optic tectum using extracellular recordings. Physiological classes could be observed based on their response to visual stimuli (on; off; on-off, and fast units). Receptive field sizes and spatiotemporal properties were classified and the topographical representation of the visual space was mapped in the tectum. Gratings of low spatial frequencies were best responded to and followed up to high temporal frequencies (>30 Hz). Most of the recorded units were directionally selective. No evidence of distorted topographies in the tectum was found, i.e., no overrepresentation of the retina was seen in the tectum opticum. The grouped retina of G. petersii seems to be optimized for the detection of large, fast objects in an environment of low optical quality

Answer 9

· Single lens eye : resolution scales linearly with size | Compound eye: eye radius is proportional to square of required resolution – If we had this would have to be 1m diameter

Answer 10

Kiltie (2001) Gundi et al. (2020)

Answer 11

1. Kirschfeld (1976) suggested that visual acuity is directly proportional to body length across a wide range of animal species. A survey of eye size, visual acuity and body size of birds and mammals that is consistent with Kirschfeld's suggestion is reported. Hypoallometry (scaling factor 1) for acuity vs eye size to produce roughly linear scaling between acuity and body size. 2. Kirschfeld (1976) also suggested that the distance at which important objects are typically viewed is a linear function of body length. ‘Subjective distance’ (viewing distance/body length) was therefore thought to be independent of body size across species. However, for prey detection by mammalian and avian predators, it is doubtful that subjective visual distances are size independent because prey size and visual acuity both scale by factors > 0·5 with predator body size; hence, detection distance should scale with size by a factor > 1. Scaling analyses also suggest that subjective visual distances for intraspecific social interactions are size dependent. 3. A positive association between body size and viewing distance has implications for the scaling of coat pattern features. In environments with fractal visual backgrounds (in which perceived sizes of background pattern elements do not change as distance from the background changes), larger animal species should have larger coat patches than smaller species if they are adapted to be cryptic at greater viewing distances than smaller species are.

Answer 12

Crustacean larvae are usually recognised as small organisms, below one millimeter body size. However, in different crustacean groups such as Stomatopoda, Polychelida, or Achelata, also very large larvae occur with sizes of 20 mm and beyond. Also from few meiuran species ("short-tailed" crustaceans, including crabs, hermit crabs, or squat lobsters), rather large larvae are known, though still considerably smaller than 20 mm. We present here two specimens of anomalan meiuran larvae, each with a total length of 24 mm, which by far exceed the previously known/reported maximum sizes of meiuran larvae. Yet, both specimens exhibit characters that indicate their identity as zoea larvae (first larval phase with several stages), most likely shortly before the metamorphosis to the megalopa (second larval phase with one stage). Due to this early developmental state, it is difficult to provide a narrower systematic identification of the larvae. In addition to the description of the developmental status of all appendages, we also investigated the gizzard and especially the compound eyes. The latter possess a mixture of hexagonal, intermediate, and square-shaped facets in an unusual arrangement. We documented the exact arrangement of the facets in both specimens and discuss the possible re-structuring during metamorphosis. The arrangement of the different types of facets indicates that transformation to an adult eye structure takes place over several moults and that the facets are being rearranged in this process. The findings demonstrate that also meiuran larvae contribute to the fraction of the macro-plankton.

Answer 13

To resolve more details in the patterns of flower, bees have to come close to a flower see notes

Answer 14

van der Kooi et al. (2016) Ne'eman and Ne'eman (2017)

Answer 15

The coloration of flowers is due to the wavelength-selective absorption by pigments of light backscattered by structures inside the petals. We investigated the optical properties of flowers using (micro)spectrophotometry and anatomical methods. To assess the contribution of different structures to the overall visual signal of flowers, we used an optical model, where a petal is considered as a stack of differently pigmented and structured layers and we interpreted the visual signals of the model petals with insect vision models. We show that the reflectance depends, in addition to the pigmentation, on the petal's thickness and the inhomogeneity of its interior. We find large between-species differences in floral pigments, pigment concentration and localization, as well as floral interior structure. The fractions of reflected and transmitted light are remarkably similar between the studied species, suggesting common selective pressures of pollinator visual systems. Our optical model highlights that pigment localization crucially determines the efficiency of pigmentary filtering and thereby the chromatic contrast and saturation of the visual signal. The strongest visual signal occurs with deposition of pigments only on the side of viewing. Our systematic approach and optical modelling open new perspectives on the virtues of flower colour.

Answer 16

Plants use visual signals to attract pollinators and direct them to their flowers. Visual capabilities of bees have been extensively studied mostly using artificial paper models. However, there is no empirical determination of the maximal detection distance (MDD) or minimal subtended visual angle (MSVA) of real flowers. Using a six armed radial maze, we tested MDD and MSVA of 12 types of natural and manipulated real flowers by bumble bee (Bombus terrestris ) workers. Bees were initially trained to obtain sugar solution at target flowers that were presented at close range on a mobile divider at the back of one of the six arms. Bees were individually marked and tested. For bees that passed the short range test, we gradually increased the distance of the target flower, until the number of successful choices reached chance level, indicating that they could not see the target flowers. The results show that MSVA of flowers is correlated with flower diameter but not with MDD. The variation in MDD to natural flowers by bumble bee workers can be best predicted by: MDD = flower coloured area / (contour line * green contrast). Contour line length determines flower dissectedness. Full circular flowers can be detected from longer distance than dissected flowers with identical diameter. We hypothesize that dissected flower shapes might be compensated by their higher attractiveness for bees. Empirical determination of real flower MDD and MSVA is important for studying bee foraging behaviour, pollinator induced evolution of flower traits and validation of neurophysiological visual models.

Answer 17

1. Reduce the distance to the object or feature (move closer or bring the image closer to you – less of the scene is now seen but more details start to appear) 2. Accommodation of the lens (humans, mammals) or cornea (diving sea birds) 3. Move the lens or retina inside the eye (fish, jumping spiders)

Answer 18

· Coding information is costly · Most useful info are in the patterns of contrasts o Change in visual intensities · Better to extract important information The function of vision is extraction of info, not to form a copy of the external world

Answer 19

Zhong et al. (2020) Gao et al. (2019)

Answer 20

Mantis shrimp have complex visual sensors, and thus, they have both color vision and polarization vision, and are adept at using polarization information for visual tasks, such as finding prey. In addition, mantis shrimp, almost unique among animals, can perform three-axis eye movements, such as pitch, yaw, and roll. With this behavior, polarization contrast in their field of view can be adjusted in real time. Inspired by this, we propose a bionic model that can adaptively enhance contrast vision. In this model, a pixel array is used to simulate a compound eye array, and the angle of polarization (AoP) is used as an adjustment mechanism. The polarization information is pre-processed by adjusting the direction of the photosensitive axis point-to-point. Experiments were performed around scenes where the color of the target and the background were similar, or the visibility of the target was low. The influence of the pre-processing model on traditional feature components of polarized light was analyzed. The results show that the model can effectively improve the contrast between the object and the background in the AoP image, enhance the significance of the object, and have important research significance for applications, such as contrast-based object detection.

Answer 21

Adaptation aftereffects are generally stronger for peripheral than for foveal viewing. We examined whether there are also differences in the dynamics of visual adaptation in central and peripheral vision. We tracked the time course of contrast adaptation to binocularly presented Gabor patterns in both the central visual field (within 58) and in the periphery (beyond 108 eccentricity) using a yes/no detection task to monitor contrast thresholds. Consistent with previous studies, sensitivity losses were stronger in the periphery than in the center when adapting to equivalent high contrast (90% contrast) patterns. The time course of the threshold changes was fitted with separate exponential functions to estimate the time constants during the adapt and post-adapt phases. When adapting to equivalent high contrast, adaptation effects built up and decayed more slowly in the periphery compared with central adaptation. Surprisingly, the aftereffect in the periphery did not decay completely to the baseline within the monitored post-adapt period (400 s), and instead asymptoted to a higher level than for central adaptation. Even when contrast was reduced to one-third (30% contrast) of the central contrast, peripheral adaptation remained stronger and decayed more slowly. This slower dynamic was also confirmed at suprathreshold test contrasts by tracking tilt-aftereffects with a 2AFC orientation discrimination task. Our results indicate that the dynamics of contrast adaptation differ between central and peripheral vision, with the periphery adapting not only more strongly but also more slowly, and provide another example of potential qualitative processing differences between central and peripheral vision.

Answer 22

· Excitatory and inhib connections form different receptive fields · Serial processing: photoreceptor – bipolar cell – ganglion cell (retinotopic arrangement – correspondence between photoreceptos that look at particular part of visual field and bipolar cells and ganglion cells) – signal travels in this direction Stage 1 – absorption of light by photoreceptors Horizontal cells connect photoreceptors and collect info from them and pass on to bipolar cells Amacrine cells connect bipolar cells and ganglion cells Filtering can work by connecting neurons through excitatory and inhib synapses Lateral inhib (within each layer, via horizontal and amacrine cells) changes the signal as it is transmitted to the ganglion cell see notes A bipolar and ganglion cell with centre-surround receptive field is sensitive to edge contrasts (edges, bar lines, small spots) imaged by the photoreceptors see notes · No. receptor cells converging onto bipolar · Light in centre/surround = excitatory/inhib response · Centre surround receptive field – on centre and off surround · Light on centre = excitatory – spike goes up Periphery = response goes down

Answer 23

Beaudot (1996) Turner et al. (2018) Malavita et al. (2017)

Answer 24

We propose a theoretical framework of the adaptive control of visual sensitivity performed by the vertebrate retina. Instead of a logarithmic function, the photoreceptor transfer function is modelled with a MichaelisMenten law which has a more plausible biophysical correlate. We show that the neural and functional architecture of the retina supports the requirements for an optimal transcoding of non-stationary visual information: This control of visual sensitivity is done by using an adaptive transfer function whose parameters are spatiotemporally and locally estimated by the subsequent retinal circuit and fed back at the level of photoreceptors. Although the use of the resulting model remains limited in the context of digital image processing, it provides a good structural framework for an analog VLSI implementation of an adaptive spatiotemporal neuromorphic retina.

Answer 25

Antagonistic receptive field surrounds are a near-universal property of early sensory processing. A key assumption in many models for retinal ganglion cell encoding is that receptive field surrounds are added only to the fully formed center signal. But anatomical and functional observations indicate that surrounds are added before the summation of signals across receptive field subunits that creates the center. Here, we show that this receptive field architecture has an important consequence for spatial contrast encoding in the macaque monkey retina: the surround can control sensitivity to fine spatial structure by changing the way the center integrates visual information over space. The impact of the surround is particularly prominent when center and surround signals are correlated, as they are in natural stimuli. This effect of the surround differs substantially from classic center-surround models and raises the possibility that the surround plays unappreciated roles in shaping ganglion cell sensitivity to natural inputs.

Answer 26

o Purpose : Perceptual surround suppression has been extensively studied as an analogue of cortical excitatory and inhibitory mechanisms in humans. Contrast detection thresholds of a central target can be either facilitated or suppressed depending on the contrast, orientation and spatial frequency of the surround. However, such effects on surround suppression have been rarely studied in the visual periphery. The specific purpose of this study was to study the orientation dependency of centre-surround interactions outside of the fovea. Specifically, we hypothesised that centre-surround orientation interactions in peripheral vision depend not only on the relationship of the orientation between the centre and surround but also on the retinotopic location of the centre-surround stimulus. o Methods : Contrast detection thresholds were estimated for radially and tangentially oriented centre targets with parallel, oblique (45°) and orthogonal surrounding annuli in nasal, inferior and infero-temporal visual field locations at 6° and 15° eccentricities. Two experienced and one naïve (mean age= 27.3 years) psychophysical observers participated in the study. Suppression ratio was calculated as the ratio between the detection threshold with a surround and without a surround. o Results : We find that at 6° and for the parallel centre-surround orientation, greatest suppression is seen for the horizontal compared to vertical configuration (RM-ANOVA; df = 1, p=0.006) and this effect disappears at 15° (RM-ANOVA; df =1, p=0.29). There was no bias for orientation at 15° (RM-ANOVA; df =1, p=0.19). Further, the magnitude of suppression was dramatically reduced with 45° centre-surround orientation difference on a radially oriented centre but not for a tangentially oriented centre, indicating a difference in the orientation tuning bandwidth between these conditions. Conclusions : We suggest this change in the orientation anisotropy with eccentricity reflects a link between surround suppression and visual field retinotopy. Orientation tuning properties may be different for centre-surround orientations with respect to visual field location and eccentricity.

Answer 27

see notes · Light spot has diff sizes · Receptive field/connectivity arranged across retina and can have diff sizes – more fine grained (small spots of light) or larger · Fovea à periphery – receptive field size increases – spatial res higher in fovea · Combination of receptive fields · Can be overlapping depending on what visual system need · Fovea = small size RF Ganglion cells = larger

Answer 28

· The responses of cells with centre-surround receptive fields (also called classical RFs) in the vertebrate retina can be described by the Differences of Gaussians model (or simpler said by the summation of excitatory and inhib inputs) · Figure shows responses of centre and surround and their sum for an On-centre/OFF-surround receptive field when a spot is moved across the receptive field · Because of the shape, the resulting curve is also known as ‘Mexican-hat’ function · Basic receptive-field model for linear retinal ganglion cells · Two mechanisms with own linear spatio-temporal sensitivities · Ex and inhib process – slightly overlapping · Diff between processes = what signal is generated · When reaches centre of RF = excitation · Filters our bright spots on dark background and vice versa Question whether mor einstances of cells that have centre-surround RF see notes

Answer 29

Muller et al. (2006) Baruch and Goldfarb (2020) Kawasetsu et al. (2018)

Answer 30

We assessed the interference by distracter letters on target discrimination as a function of the distance between incompatible distracters and target. The slope of the response time—distance function supports a Mexican hat pattern of attentional modulation in the visual field. We relate the results to our recent finding of neural activity suppression in primary visual cortex coding locations in the vicinity of an attended region [Müller, N. G., & Kleinschmidt, A. (2004). The attentional ‘spotlight’s’ penumbra: Center-surround modulation in striate cortex. Neuroreport, 15(6), 977–980]. As behavioral performance parallels activity modulation of primary visual cortex but not other areas we propose that perceptual capacities are determined by attentional response properties of V1.

Answer 31

Classical models of exogenous attention suggest that attentional enhancement at the focus of attention degrades gradually with distance from the attended location. On the other hand, the Attentional Attraction Field (AAF) model (Baruch and Yeshurun, 2014) suggests that the shift of receptive fields toward the attended location, reported by several physiological studies, leads to a decreased density of RFs at the attentional surrounds and hence the model predicts that the modulation of performance by spatial attention may have the shape of a Mexican Hat. Motivated by these theories, this study presents behavioral evidence in support of a Mexican Hat shaped modulation in exogenous spatial tasks that appears only at short latencies. In two experiments participants had to decide the location of a small gap in a target circle that was preceded by a non-informative attention capturing cue. The distance between cue and target and the latency between their onsets were varied. At short SOAs the performance curves were cubic and only at longer SOAs- this trend turned linear. Our results suggest that a rapid Mexican Hat modulation is an inherent property of the mechanism underlying exogenous attention and that a monotonically degrading trend, such as advocated by classical models, develops only at later stages of processing. The involvements of bottom-up processes such as the attraction of RFs to the focus of attention are further discussed.

Answer 32

A significant challenge in robotics is providing a sense of touch to robots. Even though several types of flexible tactile sensors have been proposed, they still have various technical issues such as a large amount of deformation that fractures the sensing elements, a poor maintainability and a deterioration in the sensitivity caused by the presence of a thick and soft covering. As one solution for these issues, we proposed a flexible tactile sensor composed of a magnet, magnetic transducer and dual-layer elastomer, which consists of a magnetorheological and nonmagnetic elastomer sheet. In this study, we first investigated the sensitivity of the sensor, which was found to be high (approximately 161 mV/N with a signal-to-noise ratio of 42.2 dB); however, the sensor has a speed-dependent hysteresis in its sensor response curve. Then, we investigated the spatial response and observed the following results: (1) the sensor response was a distorted Mexican-hat-like bipolar shape, namely a negative response area was observed around the positive response area; (2) the negative response area disappeared when we used a compressible sponge sheet instead of the incompressible nonmagnetic elastomer. We concluded that the characteristic negative response in the Mexican-hat-like response is derived from the incompressibility of the nonmagnetic elastomer.

Answer 33

see notes · Excitatory and inhib connections - particularly in the lamina · Mostly retinotopic projections · Serial processing o Photoreceptors – lamina – medulla – Lobula o Lamina interneurons form the lamina cartridges (columnar arrangements of neurons) each of which is located under an ommatidium · Eye is compound – contains ommatidia · Project onto lamina – each cartridge associated with ommatidium Similar to vertebrate retina

Answer 34

Friedrich et al. (2011) Gleadall et al. (1989)

Answer 35

The canonical number of eight photoreceptors and their arrangement in the ommatidia of insect compound eyes is very conserved. However significant variations exist in selective groups, such as the Lepidoptera and Hymenoptera, which independently evolved additional photoreceptors. For this and historical reasons, heterogeneous labeling conventions have been in use for photoreceptor subtypes, despite developmentally and structurally well-defined homologies. Extending earlier efforts, we introduce a universal photoreceptor subtype classification key that relates to the Drosophila numbering system. Its application is demonstrated in major insect orders, with detailed information on the relationship to previous conventions. We then discuss new insights that result from the improved understanding of photoreceptor subtype homologies. This includes evidence of functionally imposed ground rules of differential opsin expression, the underappreciated role of R8 as ancestral color receptor, the causes and consequences of parallel R7 photoreceptor addition in Hymenoptera and Lepidoptera, and the ancestral subfunctionalization of outer photoreceptors cells, which may be only developmentally recapitulated in Drosophila. We conclude with pointing out the need for opsin expression data from a wider range of insect orders.

Answer 36

o A new survey, by HPLC, of the visual pigment chromophores in the compound eye of Japanese insects was made during the Summer and Autumn of 1988. The results largely conformed to those of previous studies (in Europe, Japan and the U.S.A.), except for the discovery of several coleopterans unusual in containing both retinal (A1) and 3-hydroxyretinal (A3). o The chromophores of five coleopteran families are described for the first time: the Gyrinidae, Hydrophilidae and Lampyridae contain both A1 and A3: while in the Lucanidae and Melandryidae only A1 was detected. Of the Family Cerambycidae (the only insect family so far discovered to contain members with different chromophore types), one of the two major subfamilies not previously investigated, the Lepturinae, yielded only A1. Newly-tested species from the Prioninae conformed to earlier findings (A1 only). Additional data (Vogt, previously unpublished) suggest that the Cantharidae, Cicindelidae, Dermestidae and Tenebrionidae also utilize only A1. o The distribution of A1 and A3 among the insects is discussed in terms of phylogeny, diet, and the photic environment. The coleopterans utilizing both A1 and A3 are widely separated, phylogenetically, but most are carnivorous and associated with an aquatic environment. The co-incidence of these features also in the Odonata, which generally utilize both A1 and A3, suggests that chromophore content in both groups may well be environmentally related. These findings are compared with the seasonal and environment-related occurrence of A1 and A2 (3-dehydroretinal) reported for fishes, amphibians and crustaceans. The data now accumulated for compound eye chromophore content of the Insecta are listed. Included are first mentions of the Dermaptera (the earwig Anisolabis maritima) and Megaloptera (Sialis lutaria), which contain only A1. Exceptions to the previously apparent, general phylogenetic trends are now known in the Orders Coleoptera, Diptera, Neuroptera and Odonata.

Answer 37

· Large monopolar cells (LMC) (form the cartridges) in the lamina respond to contrast respond to contrast – record from intracellular recordings – can do at the same time as photoreceptors – looks different depending on where inserted – depolarisation · Sensitive to small fluctuations in light intensity about an average value · Their signal depends also on the contrast between light falling on ‘own’ photoreceptor(s) and on neighbouring ommatidia · Cell responds to change and then adapts to rest again · Inhib syanpses between photoreceptor and LMCs · Signal of LMS influced by light shone onto photoreceptors associated with LMS/neighbouring ommatidium · Differences in responses · Photoreceptor detects light and will respond to light as long as it is on. LMC responds to onset and offset of light see notes

Answer 38

Srinivasan et al. (1990) Coombe et al. (1989)

Answer 39

At high levels of ambient light, large monopolar cells (LMCS) display spatially antagonistic receptive fields and a biphasic response to a brief flash of light from an axially positioned point source. In low ambient light the response becomes monophasic everywhere within the receptive field. Using the theory of matched filters, we infer that the LMCS are optimal for the detection of moving edges at high light levels, and for ‘blobs’ in low ambient light. The spatio-temporal properties predicted by the theory are in agreement with experimental observation. At high light levels, the strong temporal inhibition, the weak, diffuse lateral inhibition, and the non-separability of the receptive field in space and time are all properties that promote the sensitivity to a moving edge. At low light levels, the lack of spatial or temporal antagonism enhances the sensitivity to a blob. Our hypothesis is reinforced by the observation that flies tend to walk toward the edges of a broad, dark vertical stripe at high light levels, but uniformly toward all regions within the stripe in low ambient light.

Answer 40

Evidence is presented here from experiments on the visual system of the fly that questions participation of the large monopolar cells (LMCs) in the optomotor response. 1. The response of a directionally-selective motiondetecting neuron (HI) in the lobula plate to small sudden jumps of a grating is directionally-selective (Fig. 1), indicating that at least one of the inputs to each of the elementary movement detectors (EMD) that feed into H1 must deliver a tonic signal. The responses of LMCs to the same stimulus are, however, entirely phasic (Fig. 2). 2. In dual electrode experiments on Eristalis, injection of current into an LMC does not change the spiking rate of H1. Induction of spiking activity, or injection of current into an LMC, which alters the cell's response to a flash of light from a point source, does not affect the response of HI to the same flash (Figs. 3, 4). 3. The temporal properties of LMCs differ markedly from those of the optomotor response and of directionally-selective movement - detecting neurons in the lobula plate (Figs. 6, 9). 4. There is poor correlation between LMC degeneration and the strength of the optomotor response in a mutant of Drosophila (Fig. 8). 5. The optomotor response of Drosophila is strongly polarization sensitive, but Drosophila LMCs show no polarization sensitivity (Fig. 11). While our results do not exclude the participation of the LMCs in the optomotor response, they do indicate that at least one other lamina channel that is tonic and/ or polarization sensitive must be involved.

Answer 41

· Photoreceptor and LMS respond differently to light flicker that slowly increases in intensity · Filtering: subtraction of background illumination · Amplification of the contrast signal: small changes are detected and discriminated against noise · Vary level of light · Increase light intensity · Receptor follows strength og light – measures intensity of light and respond to increase and decrease with light and relative changes as well as over stimulation · LMS follows rhythm of wave – independent of intensity of light First processing stage in LMC – filter and subtract background illumination and amplify contrast – small changes detected effectivyt and discriminated against the background see notes

Answer 42

Ke et al. (2014) Laughlin et al. (1987) Adesnik (2017)

Answer 43

Rod photoreceptors contribute to vision over an ∼6-log-unit range of light intensities. The wide dynamic range of rod vision is thought to depend upon light intensity-dependent switching between two parallel pathways linking rods to ganglion cells: a rod→rod bipolar (RB) cell pathway that operates at dim backgrounds and a rod→cone→cone bipolar cell pathway that operates at brighter backgrounds. We evaluated this conventional model of rod vision by recording rod-mediated light responses from ganglion and AII amacrine cells and by recording RB-mediated synaptic currents from AII amacrine cells in mouse retina. Contrary to the conventional model, we found that the RB pathway functioned at backgrounds sufficient to activate the rod→cone pathway. As background light intensity increased, the RB’s role changed from encoding the absorption of single photons to encoding contrast modulations around mean luminance. This transition is explained by the intrinsic dynamics of transmission from RB synapses.

Answer 44

We investigate the effects of synaptic transmission on early visual processing by examining the passage of signals from photoreceptors to second order neurons (LMCS). We concentrate on the roles played by three properties of synaptic transmission: (1) the shape of the characteristic curve, relating pre- and postsynaptic signal amplitudes, (2) the dynamics of synaptic transmission and (3) the noise introduced during transmission. The characteristic curve is sigmoidal and follows a simple model of synaptic transmission (Appendix) in which transmitter release rises exponentially with presynaptic potential. According to this model a presynaptic depolarization of 1.50–1.86 mV produces an e-fold increase in postsynaptic conductance. The characteristic curve generates a sigmoidal relation between postsynaptic (LMC) response amplitude and stimulus contrast. The shape and slope of the characteristic curve is unaffected by the state of light adaptation. Retinal antagonism adjusts the characteristic curve to keep it centred on the mean level of receptor response generated by the background. Thus the photoreceptor synapses operate in the mid-region of the curve, where the slope or gain is highest and equals approximately 6. The dynamics of transmission of a signal from photoreceptor to second-order neuron approximates to the sum of two processes with exponential time courses. A momentary receptor depolarization generates a postsynaptic hyperpolarization of time constant 0.5–1.0 ms, followed by a slower and weaker depolarization. Light adaptation increases the relative amplitude of the depolarizing process and reduces its time constant from 80 ms to 1.5 ms. The hyperpolarizing process is too rapid to bandlimit receptor signals. The noise introduced during the passage of the signal from receptor to second-order neuron is measured by comparing signal: noise ratios and noise power spectra in the two cell types. Under daylight conditions from 50 to 70% of the total noise power is generated by events associated with the transmission of photoreceptor signals and the generation of LMC responses. According to the exponential model of transmitter release, the effects of synaptic noise are minimized when synaptic gain is maximized. Moreover, both retinal antagonism and the sigmoidal shape of the characteristic curve promote synaptic gain. We conclude that retinal antagonism and nonlinear synaptic amplification act in concert to protect receptor signals from contamination by synaptic noise. This action may explain the widespread occurrence of these processes in early visual processing.

Answer 45

The synaptic mechanisms of feature coding in the visual cortex are poorly understood, particularly in awake animals. The ratio between excitation (E) and inhibition (I) might be constant across stimulus space, controlling only the gain and timing of neuronal responses, or it might change, directly contributing to feature coding. Whole-cell recordings in L2/3 of awake mice revealed that the E/I ratio systematically declines with increasing stimulus contrast or size. Suppressing somatostatin (SOM) neurons enhanced the E and I underlying size tuning, explaining SOM neurons’ role in surround suppression. These data imply that contrast and size tuning result from a combination of a changing E/I ratio and the tuning of total synaptic input. Furthermore, they provide experimental support in awake animals for the “Stabilized Supralinear Network,” a model that explains diverse cortical phenomena, and suggest that a decreasing E/I ratio with increasing cortical drive could contribute to many different cortical computations.

Answer 46

· Signal from neighbouring cartridges is subtracted from the signal of the cartridge of a central ommatidium A tiny spot elicits high response in LMC, whereas uniform illumination doesn’t see notes · Decrease if in periphery – across RF – increase and then decrease – followed by inhibition · Big light spot (whole RF) = no response · Signal from LMS influcnec buy other neurons that form its RF Shape of function suggess it has centre surround RF

Answer 47

Zettler and Jarviletho (1979) Yuan et al. (2020)

Answer 48

Intracellular light-evoked potentials were measured from both visual cells and secondary neurons (monopolar neurons type I) in the eye of Calliphora at varying angles of light-incidence. From these measurements and from the characteristic curves we obtained a relationship between the effective light intensity and the angle of incidence of the light stimulus for both cell types. These curves must be identical for the two cell types in the absence of a lateral information processing as a theoretical reflection shows. From the experimental results that the curve (effective light intensity versus light angle of incidence) of the monopolar neurons was considerably narrower as that of the visual cells, it was concluded that a lateral inhibition in the first optic ganglion of the fly retina exists. Although the information coding in the secondary neurons of the fly retina was completely different (graded potentials) from that of corresponding neurons in the Limulus eye (spikes), it appeared that the same principles of information processing existed in both instances.

Answer 49

Natural scenes contain complex visual cues with specific features, including color, motion, flicker, and position. It is critical to understand how different visual features are processed at the early stages of visual perception to elicit appropriate cellular responses, and even behavioral output. Here, we studied the visual orientation response induced by flickering stripes in a novel behavioral paradigm in Drosophila melanogaster. We found that free walking flies exhibited bandpass orientation response to flickering stripes of different frequencies. The most sensitive frequency spectrum was confined to low frequencies of 2–4 Hz. Through genetic silencing, we showed that lamina L1 and L2 neurons, which receive visual inputs from R1 to R6 neurons, were the main components in mediating flicker‐induced orientation behavior. Moreover, specific blocking of different types of lamina feedback neurons Lawf1, Lawf2, C2, C3, and T1 modulated orientation responses to flickering stripes of particular frequencies, suggesting that bandpass orientation response was generated through cooperative modulation of lamina feedback neurons. Furthermore, we found that lamina feedback neurons Lawf1 were glutamatergic. Thermal activation of Lawf1 neurons could suppress neural activities in L1 and L2 neurons, which could be blocked by the glutamate‐gated chloride channel inhibitor picrotoxin (PTX). In summary, lamina monopolar neurons L1 and L2 are the primary components in mediating flicker‐induced orientation response. Meanwhile, lamina feedback neurons cooperatively modulate the orientation response in a frequency‐dependent way, which might be achieved through modulating neural activities of L1 and L2 neurons.

Answer 50

Receptor signals are distributed spatially in continuous, noisy patterns – a threshold is required to detect contrasts see notes ``` Contrast edges (areas of change) contain information · Visual system relies heavily on edges · Retina decomposes visual image into most basic elements · Continuous imahe with lots diff values of light intensity and wavelength = many overlapping signals = blurry · Nee decision making mechanism that puts boundaries between diff areas · Detects edge where have sufficient change and decides where edge os What centre surround RF does ```

Answer 51

Yildirim and Kacar (2020) Venkataramani et al. (2014)

Answer 52

In this paper, a novel analog retinomorphic block performing the edge enhancing and edge detection caused by lateral inhibition phenomenon is proposed. This phenomenon, which occurs in human retina, causes the visual acuity to improve in the edge regions of the object. In contrast to the negative meaning of the word "inhibition", this type of behavior causes the human eye to act as an analogue image processing chip. The reason for that is the edges of object are enhanced and the contrast ratios in the edge regions of an object are increased owing to the lateral inhibition. We adapt the process of convolution and the concept of image masking used in digital image signal processing method to analog image signal processing method. Our proposed circuit, which exhibits edge enhancing behavior thanks to lateral inhibition, consists of only current mirrors and current subtractor circuits. We obtain the analysis results via a simple circuit design having lateral inhibition feature and the results are quite similar to that occurring in human retina. In addition to the ability of lateral inhibition, we utilize from the masking property of the lateral inhibition circuit and change the coefficients of the mask in order to obtain an edge detecting circuit. For this purpose, we use a mask whose sum of the coefficients is equal to zero. Two different 500 x 500 pixel silicon networks are designed for both edge enhancement and edge detection circuits. We have analyzed an image with the helped of both edge enhancement and edge detection circuits. Analyses results reveal that our suggested block, which is set up using only MOS transistors, can enable edge enhancement and edge detection in grayscale image and lateral inhibition behavior of the human retina can be provided using a simple electronic circuit design which has the ability of performing convolution operation. TSMC CMOS 0.18 mu m process model is utilized to simulate proposed two analog circuit networks

Answer 53

This paper examines the role of inhibition in generating the receptive-field properties of local edge detector (LED) ganglion cells in the rabbit retina. We confirm that the feed-forward inhibition is largely glycinergic but, contrary to a recent report, our data demonstrate that the glycinergic inhibition contributes to temporal tuning for the OFF and ON inputs to the LEDs by delaying the onset of spiking; this delay was more pronounced for the ON inputs (similar to 340 ms) than the OFF inputs (similar to 12 ms). Blocking glycinergic transmission reduced the delay to spike onset and increased the responses to flickering stimuli at high frequencies. Analysis of the synaptic conductances indicates that glycinergic amacrine cells affect temporal tuning through both postsynaptic inhibition of the LEDs and presynaptic modulation of the bipolar cells that drive the LEDs. The results also confirm that presynaptic GABAergic transmission contributes significantly to the concentric surround antagonism in LEDs; however, unlike presumed LEDs in the mouse retina, the surround is only partly generated by spiking amacrine cells.