From receptor signal to perception Flashcards

Question

Kang et al. (2015)

Answer 1

Camouflage can be attained via mechanisms such as background matching (resembling the general background) and disruptive coloration (hindering the detection of an animal’s outline). However, despite much conceptual work with artificial stimuli there have to date been few studies of how such camouflage types work in real animals in their natural environments. Here, using avian vision models and image analysis, we tested which concealing mechanisms operate to provide camouflage during behavioral choice of a resting position in 2 bark-resting moths, Hypomecis roboraria and Jankowskia fuscaria . Our results suggest that both species reinforced their crypticity in terms of both background matching and disruptive coloration. However, the detailed mechanisms (such as achromatic/chromatic matching or pattern direction matching) that each species exploits differed between the 2 species. Our results demonstrate that an appropriate behavioral choice of background and body orientation is important to improve camouflage against natural predators, and highlight the mechanisms that confer camouflage to cryptic animals in their natural habitats.

Answer 2

Camouflage is driven by matching the visual environment, yet natural habitats are rarely uniform and comprise many backgrounds. Therefore, species often exhibit adaptive traits to maintain crypsis, including colour change and behavioural choice of substrates. However, previous work largely considered these solutions in isolation, whereas many species may use a combination of behaviour and appearance to facilitate concealment. Here we show that green and red chameleon prawns (Hippolyte varians) closely resemble their associated seaweed substrates to the vision of predatory fish, and that they can change colour to effectively match new backgrounds. Prawns also select colour-matching substrates when offered a choice. However, colour change occurs over weeks, consistent with seasonal changes in algal cover, whereas behavioural choice of matching substrates occurs in the short-term, facilitating matches within heterogeneous environments. We demonstrate how colour change and behaviour combine to facilitate camouflage against different substrates in environments varying spatially and temporally.

Answer 3

• Train bees to do more artificial tasks • Reward with sucrose solution • New pattern every time get sucrose • Change in orientation or change in stripe thickness • Can learn symmetry and asymmetry as feature • Test with novel stim • If can extract that isn't pattern that matters but orientation - choose correctly previously rewarded even if never seen stim Perf not great with rectangles but can still recognise orientation see notes

Answer 4

Giurfa et al. (1996) Roper et al. (2017)

Answer 5

SYMMETRICAL visual patterns have a salient status in human perception, as evinced by their prevalent occurrence in art1, and also in animal perception, where they may be an indicator of phenotypic and genotypic quality2–4. Symmetry perception has been demonstrated in humans5–8, birds9–11, dolphins12 and apes13. Here we show that bees trained to discriminate bilaterally symmetrical from non-symmetrical patterns learn the task and transfer it appropriately to novel stimuli, thus demonstrating a capacity to detect and generalize symmetry or asymmetry. We conclude that bees, and possibly flower-visiting insects in general, can acquire a generalized preference towards symmetrical or, alternatively, asymmetrical patterns depending on experience, and that symmetry detection is preformed or can be learned as a perceptual category by insects, because it can be extracted as an independent visual pattern feature. Bees show a predisposition for learning and generalizing symmetry because, if trained to it, they choose it more frequently, come closer to and hover longer in front of the novel symmetrical stimuli than the bees trained for asymmetry do for the novel asymmetrical stimuli. Thus, even organisms with comparatively small nervous systems can generalize about symmetry, and favour symmetrical over asymmetrical patterns.

Answer 6

The ability to generalize over naturally occurring variation in cues indicating food or predation risk is highly useful for efficient decision-making in many animals. Honeybees have remarkable visual cognitive abilities, allowing them to classify visual patterns by common features despite having a relatively miniature brain. Here we ask the question whether generalization requires complex visual recognition or whether it can also be achieved with relatively simple neuronal mechanisms. We produced several simple models inspired by the known anatomical structures and neuronal responses within the bee brain and subsequently compared their ability to generalize achromatic patterns to the observed behavioural performance of honeybees on these cues. Neural networks with just eight large-field orientation-sensitive input neurons from the optic ganglia and a single layer of simple neuronal connectivity within the mushroom bodies (learning centres) show performances remarkably similar to a large proportion of the empirical results without requiring any form of learning, or fine-tuning of neuronal parameters to replicate these results. Indeed, a model simply combining sensory input from both eyes onto single mushroom body neurons returned correct discriminations even with partial occlusion of the patterns and an impressive invariance to the location of the test patterns on the eyes. This model also replicated surprising failures of bees to discriminate certain seemingly highly different patterns, providing novel and useful insights into the inner workings facilitating and limiting the utilisation of visual cues in honeybees. Our results reveal that reliable generalization of visual information can be achieved through simple neuronal circuitry that is biologically plausible and can easily be accommodated in a tiny insect brain.

Answer 7

• Early 20th century, School of Gestalt (shape or form) psychology proposed that shape and object perception is underpinned by processes in the mind that are characterised by the Gestalt laws, for example, proximity or similarity (e.g. in colour or size) • Local information (dots and blobs) is integrated across long distances in the image - illusory edges form global features • Is slow - requires a lot more computations and eye scanning's of the whole scene to make sense of the world and resolve ambiguities After a while visual system becomes primed see notes

Answer 8

Adding motion enhances the recognition of shape and action see notes • fMRI experiments in humans with point-light biological motion animations show strong activation of lateral and inferior temporal cortex ('what' visual stream) but also inferior frontal cortex known to be activated by action observation • Can also flicker them and gives the same effect • Adding motion enhances the recognition of shape and action • From way lights move our brain can make a lot of sense of sparse scene • Lateral and inferior temp cortex concerned with making sense of world • Frontal cortex imp which we know where mirror neurons located for observing action Also activate part of brain when observing action not perf it see notes

Answer 9

Blake and Shiffrar (2007) Sokolov et al. (2018)

Answer 10

Humans, being highly social creatures, rely heavily on the ability to perceive what others are doing and to infer from gestures and expressions what others may be intending to do. These perceptual skills are easily mastered by most, but not all, people, in large part because human action readily communicates intentions and feelings. In recent years, remarkable advances have been made in our understanding of the visual, motoric, and affective influences on perception of human action, as well as in the elucidation of the neural concomitants of perception of human action. This article reviews those advances and, where possible, draws links among those findings.

Answer 11

Visual perception of body motion is of substantial value for social cognition and everyday life. By using an integrative approach to brain connectivity, the study sheds light on architecture and functional principles of the underlying cerebro-cerebellar network. This circuity is organized in a parallel rather than hierarchical fashion. This may explain why body-language reading is rather resilient to focal brain damage but severely affected in neuropsychiatric conditions with distributed network alterations. Furthermore, visual sensitivity to body motion is best predicted by specific top-down feedback to the early visual cortex, as well as functional communication (effective connectivity) and presence of white-matter pathways between the right fusiform gyrus and superior temporal sulcus. The findings allow better understanding of the social brain.

Answer 12

• Psychophysics - links variation in stim w/ changes in behav (e.g. eye and body responses, verbal responses, task acquisition and execution) • Neuroanatomy - provides info about connectivity in the sensory organs, brain and motor systems • Theory, philosophy and computational modelling - proposes concepts and tests mechanistic and functional hypotheses, formulates mathematical algorithms to show how neurons do or may interact within and between brain areas Functional neurophysiology and neurogenics - links neural response patterns to connectivity or to behaviour, tests concepts and algorithms

Answer 13

``` • LGN (cortical pathway) ○ Processes visual info ○ Ganglion cells form optic nerve, which leaves eye through blind spot and transfer signal between back of eye and thalamus in base of brain • Subcortical pathways ○ Pretectum § Mediates pupillary reflex ○ Superior colliculus Controls saccadic eye movements ``` see notes

Answer 14

• High input - 10000 ganglion axons • Thalamus gates and modulates the flow of info to cortex • Info from diff sensory modalities and processed in diff areas of thal • Opportunity for multi sensory modulation and interactions • Not all info reaches cerebral cortex • LGN composed of several layers ○ Receive input from magnocellular ganglion cells - magnocellular laminae - large cell bodies and receive input from right and left eye ○ Retinoptopic mapping as well as origin of info from each eye retained in LGN Further layers which receive input from retina are parvocellular layers - subdivisions for right and left eye see notes

Answer 15

• A and B ○ Filed sign analysis of retinotopic cortical visual areas from right and left hemispheres in a single subject ○ In A, anterior is to the left, and posterior to the right ○ In B, this is reversed ○ The field sign maps are based on 2 scans measuring polar angle (rotating thin ray stim) and 2 scans measuring eccentricity (expanding thin ring stim), acquired from echo-planar images in a 3-T scanner, using a bilateral, send-receive quadrature coil ○ Both stim extended 18-25 degree in eccentricity • C and D ○ Same data, in cortically 'inflated' format, now viewed from a more posterior-inferior vantage point ○ The left panel shows the right hem ○ Human retinotopic areas revealed by the field sign analysis have been labelled (V1 etc.) ○ Cortical areas with a visual field sign (polarity) similar to that in the actual visual field are coded blue, and those areas showing a mirror-reversed field polarity are coded yellow ○ Also labelled is the foveal representation in V1 (black *) ○ Gyri and sulci in the folded state (e.g. A and B) are coded in lighter and darker shades of grey in the inflated format ○ Area V1 is larger than normal, extending well past the lips of the calcarine fissure ○ As in most subjects, the V1 representation of the extrafoveal horizontal meridian lies near the fundus of the calcarine fissure V1 imp for conscious vision see notes

Answer 16

Kamitani and Tong (2005) Wenliang and Seitz (2018)

Answer 17

The potential for human neuroimaging to read out the detailed contents of a person's mental state has yet to be fully explored. We investigated whether the perception of edge orientation, a fundamental visual feature, can be decoded from human brain activity measured with functional magnetic resonance imaging (fMRI). Using statistical algorithms to classify brain states, we found that ensemble fMRI signals in early visual areas could reliably predict on individual trials which of eight stimulus orientations the subject was seeing. Moreover, when subjects had to attend to one of two overlapping orthogonal gratings, feature-based attention strongly biased ensemble activity toward the attended orientation. These results demonstrate that fMRI activity patterns in early visual areas, including primary visual cortex (V1), contain detailed orientation information that can reliably predict subjective perception. Our approach provides a framework for the readout of fine-tuned representations in the human brain and their subjective contents.

Answer 18

Understanding visual perceptual learning (VPL) has become increasingly more challenging as new phenomena are discovered with novel stimuli and training paradigms. Although existing models aid our knowledge of critical aspects of VPL, the connections shown by these models between behavioral learning and plasticity across different brain areas are typically superficial. Most models explain VPL as readout from simple perceptual representations to decision areas and are not easily adaptable to explain new findings. Here, we show that a well -known instance of deep neural network (DNN), whereas not designed specifically for VPL, provides a computational model of VPL with enough complexity to be studied at many levels of analyses. After learning a Gabor orientation discrimination task, the DNN model reproduced key behavioral results, including increasing specificity with higher task precision, and also suggested that learning precise discriminations could transfer asymmetrically to coarse discriminations when the stimulus conditions varied. Consistent with the behavioral findings, the distribution of plasticity moved toward lower layers when task precision increased and this distribution was also modulated by tasks with different stimulus types. Furthermore, learning in the network units demonstrated close resemblance to extant electrophysiological recordings in monkey visual areas. Altogether, the DNN fulfilled predictions of existing theories regarding specificity and plasticity and reproduced findings of tuning changes in neurons of the primate visual areas. Although the comparisons were mostly qualitative, the DNN provides a new method of studying VPL, can serve as a test bed for theories, and assists in generating predictions for physiological investigations.

Answer 19

see notes • Ganglion cells co-located - similar area in visual field and process incoming light info at same time but project along diff pathways • Parallel processing • Signal travels across several layers • V1 projections more complex - interconnect diff layers Hierarchical arrangement also called serial processing - happens sequentially in time

Answer 20

Atilgan et al. (2020) Hall and McAnany (2017)

Answer 21

The crowding effect, defined as the detrimental effects of nearby items on visual object recognition, has been extensively investigated. Previous studies have primarily focused on finding the stage(s) in the visual hierarchy where crowding starts to limit target processing, while little attention has been focused on potential differences between the parvocellular (P) and magnocellular (M) pathways in crowding mechanisms. Here, we investigated the crowding effect in these parallel visual pathways. In Experiment 1, stimuli were designed to separately engage the P or M pathway, by tuning stimulus and background features (e.g., temporal frequency and color) to activate the targeted pathway and saturate the other pathway, respectively. Results showed that at the same eccentricity and with the same tasks, targets processed in the M pathway appeared to be more vulnerable to crowding effect. In Experiment 2, crowding effects were studied using three different types of stimuli and visual tasks (form, color, and motion), presumably with different degrees of dependence on the P and M pathways. Results revealed that color, motion, and form discrimination were increasingly more affected by crowding. We conclude that processing in the M and P pathways are differentially impacted by crowding; and importantly, crowding seems to affect processing of spatial forms more than other stimulus properties.

Answer 22

This study evaluated the extent to which different types of luminance noise can be used to target selectively the inferred magnocellular (MC) and parvocellular (PC) visual pathways. Letter contrast sensitivity (CS) was measured for three visually normal subjects for letters of different size (0.8 degrees-5.3 degrees) under established paradigms intended to target the MC pathway (steady-pedestal paradigm) and PC pathway (pulsed-pedestal paradigm). Results obtained under these paradigms were compared to those obtained in asynchronous static noise (a field of unchanging luminance noise) and asynchronous dynamic noise (a field of randomly changing luminance noise). CS was measured for letters that were high-and low-pass filtered using a range of filter cutoffs to quantify the object frequency information (cycles per letter) mediating letter identification, which was used as an index of the pathway mediating CS. A follow-up experiment was performed to determine the range of letter duration over which MC and PC pathway CS can be targeted. Analysis of variance indicated that the object frequencies measured under the static noise and steady-pedestal paradigms did not differ significantly (p >= 0.065), but differed considerably from those measured under the dynamic noise (both p < 0.001) and pulsed-pedestal (both p < 0.001) paradigms. The object frequencies mediating letter identification increased as duration increased under the steady-pedestal paradigm, but were independent of target duration (50-800 ms) under the pulsed-pedestal paradigm, in static noise, and in dynamic noise. These data suggest that the spatiotemporal characteristics of noise can be manipulated to target the inferred MC (static noise) and PC (dynamic noise) pathways. The results also suggest that CS within these pathways can be measured at long stimulus durations, which has potential importance in the design of future clinical CS tests.

Answer 23

• Retinotopic: the relative position of the object in the visual field is preserved in the retina • Then it is also preserved in the LGN and the primary visual cortex • But ○ The map is upside down (due to focusing by lens and cornea) - minor issue The map is disproportionate: more cells are devoted to processing info from central visual areas (dark red and yellow) - cortical magnification - more neurons activated - less space for peripheral visual field see notes

Answer 24

Griffis et al. (2017) | 2015

Answer 25

Psychophysical and neurobiological evidence suggests that central and peripheral vision are specialized for different functions. This specialization of function might be expected to lead to differences in the large-scale functional interactions of early cortical areas that represent central and peripheral visual space. Here, we characterize differences in whole-brain functional connectivity among sectors in primary visual cortex (V1) corresponding to central, near-peripheral, and far-peripheral vision during resting fixation. Importantly, our analyses reveal that eccentricity sectors in V1 have different functional connectivity with non-visual areas associated with large-scale brain networks. Regions associated with the fronto-parietal control network are most strongly connected with central sectors of V1, regions associated with the cingulo-opercular control network are most strongly connected with near-peripheral sectors of V1, and regions associated with the default mode and auditory networks are most strongly connected with far-peripheral sectors of V1. Additional analyses suggest that similar patterns are present during eyes-closed rest. These results suggest that different types of visual information may be prioritized by large-scale brain networks with distinct functional profiles, and provide insights into how the small-scale functional specialization within early visual regions such as V1 relates to the large-scale organization of functionally distinct whole-brain networks.

Answer 26

Attention facilitates the processing of task-relevant visual information and suppresses interference from task-irrelevant information. Modulations of neural activity in visual cortex depend on attention, and likely result from signals originating in fronto-parietal and cingulo-opercular regions of cortex. Here, we tested the hypothesis that attentional facilitation of visual processing is accomplished in part by changes in how brain networks involved in attentional control interact with sectors of V1 that represent different retinal eccentricities. We measured the strength of background connectivity between frontoparietal and cingulo-opercular regions with different eccentricity sectors in V1 using functional MRI data that were collected while participants performed tasks involving attention to either a centrally presented visual stimulus or a simultaneously presented auditory stimulus. We found that when the visual stimulus was attended, background connectivity between V1 and the left frontal eye fields (FEF), left intraparietal sulcus (IPS), and right IPS varied strongly across different eccentricity sectors in V1 so that foveal sectors were more strongly connected than peripheral sectors. This retinotopic gradient was weaker when the visual stimulus was ignored, indicating that it was driven by attentional effects. Greater task-driven differences between foveal and peripheral sectors in background connectivity to these regions were associated with better performance on the visual task and faster response times on correct trials. These findings are consistent with the notion that attention drives the configuration of task-specific functional pathways that enable the prioritized processing of task-relevant visual information, and show that the prioritization of visual information by attentional processes may be encoded in the retinotopic gradient of connectivty between V1 and fronto-parietal regions.

Answer 27

• Complicated architecture • Analysis of contours and boundaries analysis of objects • Contour enhancement for identifying objects • Cells with large RFs (e.g. simple, complex cells) that code for features of shapes, with some showing positional invariance • Filling-in info about colour and texture of objects - areas between edges don’t have much info and need little info to provide good understanding of properties of object • Initially decomposed image partially reassembled Picture not coloured uniformly but brain can fill in gaps - don’t need to see it all coloured in to see that it is a single coloured coat (Renoir) see notes

Answer 28

Speed et al. (2019) Wohlschlager et al. (2016)

Answer 29

Many factors modulate the state of cortical activity, but the importance of cortical state variability for sensory perception remains debated. We trained mice to detect spatially localized visual stimuli and simultaneously measured local field potentials and excitatory and inhibitory neuron populations across layers of primary visual cortex (V1). Cortical states with low spontaneous firing and correlations in excitatory neurons, and suppression of 3- to 7-Hz oscillations in layer 4, accurately predicted single-trial visual detection. Our results show that cortical states exert strong effects at the initial stage of cortical processing in V1 and can play a prominent role for visual spatial behavior in mice.

Answer 30

The human brain's ongoing activity is characterized by intrinsic networks of coherent fluctuations, measured for example with correlated functional magnetic resonance imaging signals. So far, however, the brain processes underlying this ongoing blood oxygenation level dependent (BOLD) signal orchestration and their direct relevance for human behavior are not sufficiently understood. In this study, we address the question of whether and how ongoing BOLD activity within intrinsic occipital networks impacts on conscious visual perception. To this end, backwardly masked targets were presented in participants' left visual field only, leaving the ipsi-lateral occipital areas entirely free from direct effects of task throughout the experiment. Signal time courses of ipsi-lateral BOLD fluctuations in visual areas V1 and V2 were then used as proxies for the ongoing contra-lateral BOLD activity within the bilateral networks. Magnitude and phase of these fluctuations were compared in trials with and without conscious visual perception, operationalized by means of subjective confidence ratings. Our results show that ipsilateral BOLD magnitudes in V1 were significantly higher at times of peak response when the target was perceived consciously. A significant difference between conscious and non-conscious perception with regard to the pre-target phase of an intrinsic-frequency regime suggests that ongoing V1 fluctuations exert a decisive impact on the access to consciousness already before stimulation. Both effects were absent in V2. These results thus support the notion that ongoing slow BOLD activity within intrinsic networks covering V1 represents localized processes that modulate the degree of readiness for the emergence of visual consciousness.

Answer 31

• V1 cells don’t respond well to single spots of light, but to lines of specific orientations • Simple cells require stim to be in particular position in visual field • Rotate bar to elicit max response • As rotate away from preferred orientation, cell responds less until doesn’t respond at all • Turning curve for orientation selectivity • Only accomplished by more complicated, complex RF • Models how it would originate from retina with CS RFs by combing several of those to feed into one large bar shape Could move bar around in visual field within boundaries of large RFs of cells see notes

Answer 32

Hubel and Wiesel (2015) Kayser et al. (2003)

Answer 33

Over 40 years ago, Hubel and Wiesel gave a preliminary report of the first account of cells in monkey cerebral cortex selective for binocular disparity. The cells were located outside of V-1 within a region referred to then as "area 18." A full-length manuscript never followed, because the demarcation of the visual areas within this region had not been fully worked out. Here, we provide a full description of the physiological experiments and identify the locations of the recorded neurons using a contemporary atlas generated by functional magnetic resonance imaging; we also perform an independent analysis of the location of the neurons relative to an anatomical landmark (the base of the lunate sulcus) that is often coincident with the border between V-2 and V-3. Disparity-tuned cells resided not only in V-2, the area now synonymous with area 18, but also in V-3 and probably within V-3A. The recordings showed that the disparity-tuned cells were biased for near disparities, tended to prefer vertical orientations, clustered by disparity preference, and often required stimulation of both eyes to elicit responses, features strongly suggesting a role in stereoscopic depth perception.

Answer 34

Studies on processing in primary visual areas often use artificial stimuli such as bars or gratings. As a result, little is known about the properties of activity patterns for the natural stimuli processed by the visual system on a daily basis. Furthermore, in the cat, a well-studied model system for visual processing, most results are obtained from anesthetized subjects and little is known about neuronal activations in the alert animal. Addressing these issues, we measure local field potentials (lfp) and multiunit spikes in the primary visual cortex of awake cats. We compare changes in the lfp power spectra and multiunit firing rates for natural movies, movies with modified spatio-temporal correlations as well as gratings. The activity patterns elicited by drifting gratings are qualitatively and quantitatively different from those elicited by natural stimuli and this difference arises from both spatial as well as temporal properties of the stimuli. Furthermore, both local field potentials and multiunit firing rates are most sensitive to the second-order statistics of the stimuli and not to their higher-order properties. Finally, responses to natural movies show a large variability over time because of activity fluctuations induced by rapid stimulus motion. We show that these fluctuations are not dependent on the detailed spatial properties of the stimuli but depend on their temporal jitter. These fluctuations are important characteristics of visual activity under natural conditions and impose limitations on the readout of possible differences in mean activity levels.

Answer 35

• RFs in interneurons of the brain can be varied in many ways to combine info provided within or between visual pathways ○ Cells in serially connected layers directly and simply cause the elements of perception (Barlow, 1972; Barlow, 2009) • 2 major concepts how perceptual info is coded: 1. Grandmother (or gnostic) cells (e.g. face-selective cells in the inferotemporal cortex of monkeys) - sparsely coded representation of an object (requires few neurons) - respond to face stim - preferences to familiar faces and complex shapes - brain can vary economically, code for representation of complex object 2. Distributed networks - represent objects by binding features that are coded in receptive fields across neural centres of the brain, form a distributed representation of an object - sparse coding - when have representation, when matured and coded, number of neurons excited is small • Redundancy reduction, sparse coding and SA keeps energetic cost of processing low (e.g. Lennie, 2003) SA helps direct activity of brain to areas that are involved in current tasks - impossible to process everything at once

Answer 36

Coltheart (2017) Kamal et al. (2016)

Answer 37

A grandmother cell is a neural or cognitive unit that selectively responds to just one particular physical object (one's maternal grandmother, for example, or one's own right hand, or one's own car). Grandmother cells should be distinguished from gnostic units, which are neural or cognitive units that respond selectively to all members of categories of physical objects (all elderly ladies, for example, or all hands, or all cars). Both grandmother cells and gnostic units count as local representations, but not all local representations count as grandmother cells.

Answer 38

Distributed algorithms have recently gained immense popularity. With regards to computer vision applications, distributed multi-target tracking in a camera network is a fundamental problem. The goal is for all cameras to have accurate state estimates for all targets. Distributed estimation algorithms work by exchanging information between sensors that are communication neighbors. Vision-based distributed multi-target state estimation has at least two characteristics that distinguishes it from other applications. First, cameras are directional sensors and often neighboring sensors may not be sensing the same targets, i.e., they are naive with respect to that target. Second, in the presence of clutter and multiple targets, each camera must solve a data association problem. This paper presents an information-weighted, consensus-based, distributed multi-target tracking algorithm referred to as the Multi-target Information Consensus (MTIC) algorithm that is designed to address both the naivety and the data association problems. It converges to the centralized minimum mean square error estimate. The proposed MTIC algorithm and its extensions to non-linear camera models, termed as the Extended MTIC (EMTIC), are robust to false measurements and limited resources like power, bandwidth and the realtime operational requirements. Simulation and experimental analysis are provided to support the theoretical results.

Answer 39

Moore et al. (2020)

Answer 40

Anne Treisman and colleagues developed an influential theoretical framework surrounding the construct of "object files" as a means of understanding the functional need for an episodic representation of objects as they move, change, disappear, and reappear from view (Kahneman, Treisman, & Gibbs, Cognitive Psychology, 24, 175-219, 1992; Treisman, The Quarterly Journal of Experimental Psychology, 40, 201-237, 1988). Within that framework, object files are defined through the process of object correspondence, whereby stimuli are associated with and represented as later instantiations of existing object representations and are used to selectively update those representations. A central assertion of the object file framework is that object correspondence is established on the basis of spatiotemporal continuity, without regard to feature information. We tested this assertion by investigating whether feature information, separate from spatiotemporal information, can determine how object correspondence is resolved. We used the perception of causality in simple dynamic displays, which provides a means of inferring how object correspondence is resolved. We found that, contrary to the spatiotemporal dominance assertion, feature information is used to resolve object correspondence. We suggest that the object-file framework be extended to reflect the importance of both feature and spatiotemporal information in establishing and maintaining episodic object representations.

Answer 41

• Lesioning inferior temp cortex or parietal cortex • Show affected diff visual tasks Objection recog and other handling object and locating it and interacting with object see notes

Answer 42

Ungerleider and Haxby (1994) Long et al. (2018)

Answer 43

Multiple visual areas in the cortex of nonhuman primates are organized into two hierarchically organized and functionally specialized processing pathways, a ‘ventral stream’ for object vision and a ‘dorsal stream’ for spatial vision. Recent findings from positron emission tomography activation studies have localized these pathways within the human brain, yielding insights into cortical hierarchies, specialization of function, and attentional mechanisms

Answer 44

Human object-selective cortex shows a large-scale organization characterized by the high-level properties of both animacy and object size. To what extent are these neural responses explained by primitive perceptual features that distinguish animals from objects and big objects from small objects? To address this question, we used a texture synthesis algorithm to create a class of stimuli—texforms—which preserve some mid-level texture and form information from objects while rendering them unrecognizable. We found that unrecognizable texforms were sufficient to elicit the large-scale organizations of object-selective cortex along the entire ventral pathway. Further, the structure in the neural patterns elicited by texforms was well predicted by curvature features and by intermediate layers of a deep convolutional neural network, supporting the mid-level nature of the representations. These results provide clear evidence that a substantial portion of ventral stream organization can be accounted for by coarse texture and form information without requiring explicit recognition of intact objects.

Answer 45

Schyns and Oliva (1994) Im et al. (2017)

Answer 46

In very fast recognition tasks, scenes are identified as fast as isolated objects How can this efficiency be achieved, considering the large number of component objects and interfering factors, such as cast shadows and occlusions? Scene categories tend to have distinct and typical spatial organizations of their major components If human perceptual structures were tuned to extract this information early in processing, a coarse-to-fine process could account for efficient scene recognition A coarse description of the input scene (oriented “blobs” in a particular spatial organization) would initiate recognition before the identity of the objects is processed We report two experiments that contrast the respective roles of coarse and fine information in fast identification of natural scenes The first experiment investigated whether coarse and fine information were used at different stages of processing The second experiment tested whether coarse-to-fine processing accounts for fast scene categorization The data suggest that recognition occurs at both coarse and fine spatial scales By attending first to the coarse scale, the visual system can get a quick and rough estimate of the input to activate scene schemas in memory, attending to fine information allows refinement, or refutation, of the raw estimate

Answer 47

In crowds, where scrutinizing individual facial expressions is inefficient, humans can make snap judgments about the prevailing mood by reading ‘crowd emotion’. We investigated how the brain accomplishes this feat in a set of behavioural and functional magnetic resonance imaging studies. Participants were asked to either avoid or approach one of two crowds of faces presented in the left and right visual hemifields. Perception of crowd emotion was improved when crowd stimuli contained goal-congruent cues and was highly lateralized to the right hemisphere. The dorsal visual stream was preferentially activated in crowd emotion processing, with activity in the intraparietal sulcus and superior frontal gyrus predicting perceptual accuracy for crowd emotion perception, whereas activity in the fusiform cortex in the ventral stream predicted better perception of individual facial expressions. Our findings thus reveal significant behavioural differences and differential involvement of the hemispheres and the major visual streams in reading crowd versus individual face expressions.

Answer 48

• Thick arrows: main connections ○ Main connections synapse the geniculate nucleus and project to the primary visual cortex ○ V1 sent info to the extrastriate areas (V2, 3, 4 and MT+/V5) ○ Most of the corticocortical (blue) and subcortico-cortical (orange) connections are reciprocal • Thin arrows: many connections are reciprocal ○ The extrageniculostriate pathway belonging to the dorsal visual stream, originates in the retina and synapses in the superior colliculus and in the pulvinar and projects directly to extrastriate areas (in particular MT+/V5) bypassing both V1 and the LGN ○ This pathway has been accounted to mediate action blindsight ○ Another colliculo-pulvinar pathway, associated with the ventral visual stream, synapses in the LGN and projects to extrastriate areas (in particular V4) bypassing V1 ○ This pathway has been accounted to mediate colour and shape residual discrimination ○ Other collicular pathways are represented: the colliculo-pulvinar pathway (between Sc and pulvinar), the pulvino-amygdalar pathway (between pulvinar and amygdala) and the colliculo-pulvino-amygdalar pathway (between the SC, the pulvinar and the amygdala) ○ These pathways have been accounted to mediate affective blindsight Pathways that bypass V1 have been accounted to mediate blin see notes

Answer 49

Hadid and Lepore (2017) Tran et al. (2019)

Answer 50

Homonymous hemianopia (HH) is the most common cortical visual impairment leading to blindness in the contralateral hemifield. It is associated with many inconveniences and daily restrictions such as exploration and visual orientation difficulties. However, patients with HH can preserve the remarkable ability to unconsciously perceive visual stimuli presented in their blindfield, a phenomenon known as blindsight. Unfortunately, the nature of this captivating residual ability is still misunderstood and the rehabilitation strategies in terms of visual training have been insufficiently exploited. This article discusses type I and type II blindsight in a neuronal framework of altered global workspace, resulting from inefficient perception, attention and conscious networks. To enhance synchronization and create global availability for residual abilities to reach visual consciousness, rehabilitation tools need to stimulate subcortical extrastriate pathways through V5/MT. Multisensory bottom-up compensation combined with top-down restitution training could target pre-existing and new neuronal mechanisms to recreate a framework for potential functionality.

Answer 51

Brain imaging offers a valuable tool to observe functional brain plasticity by showing how sensory inputs reshape cortical activations after a visual impairment. Following a unilateral post-chiasmatic lesion affecting the visual cortex, patients may suffer a contralateral visual loss referred to homonymous hemianopia. Nevertheless, these patients preserve the ability to unconsciously detect, localize and discriminate visual stimuli presented in their impaired visual field. To investigate this paradox, known as blindsight, we conducted a study using functional magnetic resonance imaging (fMRI) to evaluate the structural and functional impact of such lesion in a 33-year old patient (ML), who suffers a complete right hemianopia without macular sparing and showing strong evidences of blindsight. We thus performed whole brain and sliced thalamic fMRI scan sequences during an event-related motion detection task. We provided evidence of the neuronal fingerprint of blindsight by acquiring and associating neural correlates, specific structures and functional networks of the midbrain during blindsight performances which may help to better understand this condition. Accurate performance demonstrated the presence of residual vision and the ability to unconsciously perceive motion presented in the blind hemifield, although her reaction time was significantly higher in her blind-field. When the normal hemifield was stimulated, we observed significant contralateral activations in primary and secondary visual areas as well as motion specific areas, such as the supramarginal gyrus and middle temporal area. We also demonstrated sub-thalamic activations within the superior colliculi (SC) and the pulvinar. These results suggest a role of secondary subcortical structures in normal spontaneous motion detection. In a similar way, when the lesioned hemifield was stimulated, we observed contralateral activity in extrastriate areas with no activation of the primary lesioned visual cortex. Moreover, we observed activations within the SC when the blind hemifield was stimulated. However, we observed unexpected ipsilateral activations within the same motion specific areas, as well as bilateral frontal activations. These results highlight the importance of abnormal secondary pathways bypassing the primary visual area (V1) in residual vision. This reorganization in the structure and function of the visual pathways correlates with behavioral changes, thus offering a plausible explanation for the blindsight phenomenon. Our results may potentially impact the development of rehabilitation strategies to target subcortical pathways.

Answer 52

• Interneurons in the retina and LGN are segregated in parallel pathways ○ P ganglion cells project to the parvocellular layer in the LGN - small RFs, small axons, high acuity, poor response to transient stim, colour sensitive - insensitive to contrast M ganglion cells project to magnocellular layer in LGN - large RFs, bigger axons (faster conduction), sensitive to motion, low acuity, no colour discrim - only sees brightness - detect small contrasts

Answer 53

• Colour vision: ability to discrim light stim by their spectral content (colour cue) and not their intensity (brightness cue) • Variation of light in nature • Pathways that compute colour - chromatic pathways - achromatic system that rely on the analysis of intensity diffs Trichromatic colour vision - detect fruit better

Answer 54

Werner et al. (2020) Szatko et al. (2020)

Answer 55

For over 150 years, spectrally selective filters have been proposed to improve the vision of observers with color vision deficiencies [1]. About 6% of males and <1% of females have anomalies in their gene arrays coded on the X chromosome that result in significantly decreased spectral separation between their middle(M-) and long- (L-) wave sensitive cone photoreceptors [2]. These shifts alter individuals' color-matching and chromatic discrimination such that they are classified as anomalous trichromats [3, 4]. Broad-band spectrally selective filters proposed to improve the vision of color-deficient observers principally modify the illuminant and are largely ineffective in enhancing discrimination or perception because they do not sufficiently change the relative activity of M- and L-photoreceptors [5, 6]. Properly tailored notch filters, by contrast, might increase the difference of anomalous M- and L-cone signals. Here, we evaluated the effects of long-term usage of a commercial filter designed for this purpose on luminance and chromatic contrast response, estimated with a signal detection-based scaling method. We found that sustained use over two weeks was accompanied by increased chromatic contrast response in anomalous trichromats. Importantly, these improvements were observed when tested without the filters, thereby demonstrating an adaptive visual response. Normal observers and a placebo control showed no such changes in contrast response. These findings demonstrate a boosted chromatic response from exposure to enhanced chromatic contrasts in observers with reduced spectral discrimination. They invite the suggestion that modifications of photoreceptor signals activate a plastic post-receptoral substrate that could potentially be exploited for visual rehabilitation.

Answer 56

Color vision is essential for an animal's survival. It starts in the retina, where signals from different photoreceptor types are locally compared by neural circuits. Mice, like most mammals, are dichromatic with two cone types. They can discriminate colors only in their upper visual field. In the corresponding ventral retina, however, most cones display the same spectral preference, thereby presumably impairing spectral comparisons. In this study, we systematically investigated the retinal circuits underlying mouse color vision by recording light responses from cones, bipolar and ganglion cells. Surprisingly, most color-opponent cells are located in the ventral retina, with rod photoreceptors likely being involved. Here, the complexity of chromatic processing increases from cones towards the retinal output, where non-linear center-surround interactions create specific color-opponent output channels to the brain. This suggests that neural circuits in the mouse retina are tuned to extract color from the upper visual field, aiding robust detection of predators and ensuring the animal's survival.

Answer 57

see notes • 3 cones in colour coding • Usually have 4 cones - extended colour space • Eyes (lens and optic apparatus) cuts out UV • Short-wavelength receptor sensitive to UV • Don’t perceive light in UV - blind to diffs in contrasts • Bees - less sensitive in long-wavelengths - red appears black • Our ancestors in mammalian lines have lost cones (2 of 4 cones) - short and long wavelength receptor Few primates added third due to gene duplication - selection pressures

Answer 58

Garbers and Wachtler (2016) Jacobs (2013)

Answer 59

Among the five photoreceptor opsins in the eye of Drosophila, Rhodopsin 1 (Rh1) is expressed in the six outer photoreceptors. In a previous study that combined behavioral genetics with computational modeling, we demonstrated that flies can use the signals from Rh1 for color vision. Here, we provide an in-depth computational analysis of wildtype Drosophila wavelength discrimination specifically considering the consequences of different choices of computations in the preprocessing of the behavioral data. The results support the conclusion that Drosophila wavelength discrimination behavior can best be explained by a contribution of Rh1. These findings are corroborated by results of an information-theoretical analysis that shows that Rh1 provides information for discrimination of natural reflectance spectra.

Answer 60

All mammalian cone photopigments are derived from the operation of representatives from two opsin gene families (SWS1 and LWS in marsupial and eutherian mammals; SWS2 and LWS in monotremes), a process that produces cone pigments with respective peak sensitivities in the short and middle-to-long wavelengths. With the exception of a number of primate taxa, the modal pattern for mammals is to have two types of cone photopigment, one drawn from each of the gene families. In recent years, it has been discovered that the SWS1 opsin genes of a widely divergent collection of eutherian mammals have accumulated mutational changes that render them nonfunctional. This alteration reduces the retinal complements of these species to a single cone type, thus rendering ordinary color vision impossible. At present, several dozen species from five mammalian orders have been identified as falling into this category, but the total number of mammalian species that have lost short-wavelength cones in this way is certain to be much larger, perhaps reaching as high as 10% of all species. A number of circumstances that might be used to explain this widespread cone loss can be identified. Among these, the single consistent fact is that the species so affected are nocturnal or, if they are not technically nocturnal, they at least feature retinal organizations that are typically associated with that lifestyle. At the same time, however, there are many nocturnal mammals that retain functional short-wavelength cones. Nocturnality thus appears to set the stage for loss of functional SWS1 opsin genes in mammals, but it cannot be the sole circumstance.

Answer 61

see notes • Assign primary colour to short, middle and long wavelength receptor of bee • Measure (inc UV) using UV sensitive cameras • Transfrom signals into 3 primary colours and create false colour image which shows single coloured flower actually has 2 colours - one in surround that reflects UV and long wavelengths and anothet colour that reflects only long wavelengths Bees can discrim colours well

Answer 62

Davies et al. (2013) Verhoeven et al. (2018)

Answer 63

echnological developments in municipal lighting are altering the spectral characteristics of artificially lit habitats. Little is yet known of the biological consequences of such changes, although a variety of animal behaviours are dependent on detecting the spectral signature of light reflected from objects. Using previously published wavelengths of peak visual pigment absorbance, we compared how four alternative street lamp technologies affect the visual abilities of 213 species of arachnid, insect, bird, reptile and mammal by producing different wavelength ranges of light to which they are visually sensitive. The proportion of the visually detectable region of the light spectrum emitted by each lamp was compared to provide an indication of how different technologies are likely to facilitate visually guided behaviours such as detecting objects in the environment. Compared to narrow spectrum lamps, broad spectrum technologies enable animals to detect objects that reflect light over more of the spectrum to which they are sensitive and, importantly, create greater disparities in this ability between major taxonomic groups. The introduction of broad spectrum street lamps could therefore alter the balance of species interactions in the artificially lit environment

Answer 64

The colour vision system of bees and humans differs mainly in that, contrary to humans, bees are sensitive to ultraviolet light and insensitive to red light. The synopsis of a colour picture and a UV picture is inappropriate to illustrate the bee view of flowers, since the colour picture does not exclude red light. In this study false-colour pictures in bee view are assembled from digital photos taken through a UV, a blue, and a green filter matching the spectral sensitivity of the bees’ photoreceptors. False-colour pictures demonstrate small-sized colour patterns in flowers, e.g. based on pollen grains, anthers, filamental hairs, and other tiny structures that are inaccessible to spectrophotometry. Moreover, false-colour pictures are suited to demonstrate flowers and floral parts that are conspicuous or inconspicuous to bees. False-colour pictures also direct the attention to other ranges of wavelength besides ultraviolet demonstrating for example blue and yellow bulls’ eyes in addition to UV bulls’ eyes which previously have been overlooked. False-colour photography

Answer 65

• Most mammals have also only 2 spectral types of photoreceptors like 'colour-blind' humans • Marine mammals are truly colour-blind (have only 1 spectral type of photoreceptor) • True colour blindness - miss one of cones • Most freq long wavelength cones quite freq and middle wavelength cones and vary rarely short wavelength cones Other mammals have dichromatic vision like colour blind humans - short wavelength receptor and another sensitive in middle or longer wavelength part of spectrum see notes

Answer 66

Hart (2020) Angechekar et al. (2017)

Answer 67

The visual sense of elasmobranch fishes is poorly studied compared to their bony cousins, the teleosts. Nevertheless, the elasmobranch eye features numerous specialisations that have no doubt facilitated the diversification and evolutionary success of this fascinating taxon. In this review, I highlight recent discoveries on the nature and phylogenetic distribution of visual pigments in sharks and rays. Whereas most rays appear to be cone dichromats, all sharks studied to date are cone monochromats and, as a group, have likely abandoned colour vision on multiple occasions. This situation in sharks mirrors that seen in other large marine predators, the pinnipeds and cetaceans, which leads us to reassess the costs and benefits of multiple cone pigments and wavelength discrimination in the marine environment.

Answer 68

Color Blindness which can be also referred as Color Vision Deficiency (CVD) is one of the biggest scaling defect in humans which is still under the research for its accurate detection and cure measures & strategies. Color Blindness is the decreased ability to sight the distinctive colors instantly under normal lighting conditions. There are approximately 250 million individuals who suffer from Color Blindness. So it is need of an hour to understand all the important aspects of the Problem CVD and take the necessary measures to help the People who are knowingly or unknowingly suffering from CVD. In this paper we are going to put light on how exactly color blindness is genetically transferred to children, types in color vision deficiency i.e. Anomalous Trichromacy (protanomaly, deuteranomaly, tritanomaly), Monochromacy and how exactly person sees the normal image under respective CVD and finally put light on few algorithms and strategies which with the help of re-coloring and wavelength shifting actually help the color vision deficient to view and sight all the colors of the actual image distinctively.

Answer 69

• Ability to recognise colours under diff illuminations • Sun light is slightly coloured during dusk and dawn • Visual system compensates for such slow changes by global adaptation • During visual search in a natural scene, the visual system can also adapt quickly by within the spatially restricted area(s) of visual search - local adaptation system • Colour constancy = perceptions stable despite changing physical conditions • Visualise diff pictures by shining light on white background and see colour of background changes because diff wavelengths reflected from white paper because illuminated them w/ diff coloured light • Colours in fruit bowl don’t change dramatically If shown pictures in succession with some breaks, eyes would adapt and wouldn’t notice diffs see notes Purves and Lotto (2005) see notes • Background black and homogeneous Context varies between two patches - see diff colours of shapes - brain interps patches as belonging to 2 diff objects - little sense to show they're physically same

Answer 70

Teixeira et al. (2020) Hurlbert (2019) Shapiro and Hedjar (2019) Chetverikov et al. (2017) Arikawa (2003) Yonekura et al. (2020)

Answer 71

○ Introduction: Color constancy, a property of conscious color experience, maintains object color appearance across illuminant changes. We investigated the neural correlates of subliminal vs. conscious stimulus deviations of color constancy manipulations. ○ Methods: Behavioral and Oddball EEG/ERP experiments were conducted (n = 20). Psychophysical illuminant variation discrimination thresholds were first estimated, to establish individual perceptual awareness ranges, allowing for simulation of natural daylight spectral and spatial variations on colored surfaces, at different ambiguity levels. ○ Results: Behavioral results validated illuminant choice. ERPs showed a significant modulation of posterior P1 component specifically for the subliminal global uniform deviation condition, respecting color constancy. Neural correlates of conscious percepts were identified at posterior N2-P3 latencies, parietal (P3b) and frontal regions. Conclusions: We identified an early subliminal correlate of low-level illuminant change, which reflects automatic unconscious detection of global color constancy deviations. Its suppression under conscious perception is probably due to top-down suppression according to prediction error models.

Answer 72

Color constancy is a prime example of a perceptual constancy, giving stability to mental representations of objects in an unstable world. Yet color constancy is highly variable, depending on the illumination, the object and its context, and the viewer. Color constancy is particularly challenged by artificial lights that differ from the natural illuminations under which human vision evolved. The rapid developments in solid-state lighting technologies revive the need to scrutinise the limits of color constancy, to understand whether and how it is optimised for natural illuminations, and, in turn, to optimise novel lighting technologies for human color perception. For these goals, a deeper collaboration between the disciplines of human vision science and color science is needed.

Answer 73

Illusions are often considered to be a misperception of the physical world. We present a different framework for illusions: in non-illusory conditions, healthy brains construct a single, consistent representation from the physiological processes that encode the world; illusions, in contrast, are conditions where the brain constructs conflicting representations of the world. We contend that the conditions for illusions often arise for color vision because of the multifaceted aspects of color in relation to space, and that many color illusions arise from the juxtaposition and selective recombination (i.e. the binding) of these aspects of color/spatial information. We discuss three spatial aspects of color: modes of appearance, color versus color contrast, and information at different spatial scales

Answer 74

What are the building blocks of our visual representations? Whatever we look at, the things we see will have some feature variability: even snow is not purely white but has a range of shades of white. However, in most studies investigating visual perception, homogeneous displays with all stimuli having a very limited range of features have been used. In contrast, recent studies using heterogeneous displays have shown that our perceptual system encodes surprisingly detailed information about stimuli, representing parameters such as the mean, variance, and most importantly the probability density functions of feature distributions. Learning the parameters of the distributions takes time as distribution representations are continuously updated with incoming information. However, the mechanisms guiding this process are not yet known. We will review current knowledge about the sampling and updating of representations of feature distributions in heterogeneous displays and will present new findings providing further insights into this process. Overall, the results show that representations of distributions can be remarkably detailed and shed light on how the information provided affects the learning of feature distributions. Observers’ ability to quickly encode the probability density function of distributions in the environment may potentially provide novel interpretations of a number of well-known phenomena in visual perception.

Answer 75

• Size constancy - honeybees can discrim between objects at diff distances irrespective of their size • Honeybees and the butterfly papilio xuthus have colour constancy • They recognise the rewarded colour in a Mondrian stim under diff coloured illuminations Vary real size and depth - guided by relative diff in size and not height at which flower located - size constancy • Butterflies • Quickly satiated - not interested in food rewarded tasks - one trial per day - lengthy task • Trained butterfly on one colour - then change light of illumination - see where searched for food - wavelengths reflected from surface perceived during training now in wrong patch • Butterfly picks right path - has colour constancy and can correct for changes in illumination • Colour constancy breaks down when illumination very colourful Colour constancy mechanisms have limits within which they can operate and correct, but usually within natural conditions these constancy mechanisms operate very effectively

Answer 76

Srinivasan et al. (1991) Butaois et al. (2018)

Answer 77

When negotiating a narrow gap, honeybees tend to fly through the middle of the gap, balancing the distances to the boundary on either side. To investigate the basis of this “centering response,” bees were trained to fly through a tunnel on their way to a feeding site and back, while their flight trajectories were filmed from above. The wall on either side carried a visual pattern. When the patterns were stationary vertical gratings, bees tended to fly through the middle of the tunnel, i.e. along its longitudinal axis. However, when one of the gratings was in motion, bees flying in the same direction as the moving grating tended to fly closer to while bees flying in the opposite direction tended to fly closer to the stationary grating. This demonstrates, directly and unequivocally, that flying bees estimate the distances of surfaces in terms of the apparent motion of their images. A series of further experiments revealed that the distance to the gratings is gauged in terms of their apparent angular speeds, and that the visual system of the bee is capable of measuring angular speed largely independently of the spatial period, intensity profile, or contrast of the grating. Thus, the motion-sensitive mechanisms mediating range perception appear to be qualitatively different from those that mediate the well-known optomotor response in insects, or those involved in motion detection and ocular tracking in man.

Answer 78

To study visual learning in honey bees, we developed a virtual reality (VR) system in which the movements of a tethered bee walking stationary on a spherical treadmill update the visual panorama presented in front of it (closed-loop conditions), thus creating an experience of immersion within a virtual environment. In parallel, we developed a small Y-maze with interchangeable end-boxes, which allowed replacing repeatedly a freely walking bee into the starting point of the maze for repeated decision recording. Using conditioning and transfer experiments between the VR setup and the Y-maze, we studied the extent to which movement freedom and active vision are crucial for learning a simple color discrimination. Approximately 57% of the bees learned the visual discrimination in both conditions. Transfer from VR to the maze improved significantly the bees’ performances: 75% of bees having chosen the CS+ continued doing so and 100% of bees having chosen the CS− reverted their choice in favor of the CS+. In contrast, no improvement was seen for these two groups of bees during the reciprocal transfer from the Y-maze to VR. In this case, bees exhibited inconsistent choices in the VR setup. The asymmetric transfer between contexts indicates that the information learned in each environment may be different despite the similar learning success. Moreover, it shows that reducing the possibility of active vision and movement freedom in the passage from the maze to the VR impairs the expression of visual learning while increasing them in the reciprocal transfer improves it. Our results underline the active nature of visual processing in bees and allow discussing the developments required for immersive VR experiences in insects.

Answer 79

This review outlines our recent studies on the spectral organization of butterfly compound eyes, with emphasis on the Japanese yellow swallowtail butterfly, Papilio xuthus, which is the most extensively studied species. Papilio has color vision when searching for nectar among flowers, and their compound eyes are furnished with six distinct classes of spectral receptors (UV, violet, blue, green, red, broadband). The compound eyes consist of many ommatidia, each containing nine photoreceptor cells. How are the six classes of spectral receptors arranged in the ommatidia? By studying their electrophysiology, histology, and molecular biology, it was found that the Papilio ommatidia can be divided into three types according to the combination of spectral receptors they contain. Different types of ommatidia are distributed randomly over the retina. Histologically, the heterogeneity appeared to be related to red or yellow pigmentation around the rhabdom. A subset of red-pigmented ommatidia contains 3-hydroxyretinol in the distal portion, fluorescing under UV epi-illumination. The red, yellow and fluorescing pigments all play crucial roles in determining the spectral sensitivities of receptors. Spectral heterogeneity and random array of ommatidia have also been found in other lepidopteran species. Similarities and differences between species are also discussed.

Answer 80

The fruit fly Drosophila melanogaster can process chromatic information for true color vision and spectral preference. Spectral information is initially detected by a few distinct photoreceptor channels with different spectral sensitivities and is processed through the visual circuit. The neuroanatomical bases of the circuit are emerging. However, only little information is available in chromatic response properties of higher visual neurons from this important model organism. We used in vivo whole-cell patch-clamp recordings in response to monochromatic light stimuli ranging from 300 to 650 nm with 25-nm steps. We characterized the chromatic response of 33 higher visual neurons, including their general response type and their wavelength tuning. Color-opponent-type responses that had been typically observed in primates and bees were not identified. Instead, the majority of neurons showed excitatory responses to broadband wavelengths. The UV (300–375 nm) and middle wavelength (425–575 nm) ranges could be separated at the population level owing to neurons that preferentially responded to a specific wavelength range. Our results provide a first mapping of chromatic information processing in higher visual neurons of D. melanogaster that is a suitable model for exploring how color-opponent neural mechanisms are implemented in the visual circuits

Answer 81

• Sensory systems extract info from sensory cues and to generate unconscious and conscious perceptions as required and prioritised for decision-making and task execution in diff areas and system of the brain • Visual info - motion, colour hue and saturation, brightness, edges, shape, spatial and temporal patterns - is computed from photoreceptor signals and processed in various hierarchically organised (serial connectivity) but parallel working pathways • Evidence generated in research often not linked to tasks, studying isolated components of the visual system and bran Incorp comparative approaches and ecological and evolutionary considerations, e.g. by considering the properties of natural visual scenes, the behavioural and ecological needs of humans and animals, can help to better understand the functions and limitations of brain mechanisms