| 1. |
- Barnett, Paul, et al.
(author)
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Retinotopic organization of small-field-target-detecting neurons in the insect visual system.
- 2007
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In: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 17:7, s. 569-578
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Journal article (peer-reviewed)abstract
- BackgroundDespite having tiny brains and relatively low-resolution compound eyes, many fly species frequently engage in precisely controlled aerobatic pursuits of conspecifics. Recent investigations into high-order processing in the fly visual system have revealed a class of neurons, coined small-target-motion detectors (STMDs), capable of responding robustly to target motion against the motion of background clutter. Despite limited spatial acuity in the insect eye, these neurons display exquisite sensitivity to small targets. ResultsWe recorded intracellularly from morphologically identified columnar neurons in the lobula complex of the hoverfly Eristalis tenax. We show that these columnar neurons with exquisitely small receptive fields, like their large-field counterparts recently described from both male and female flies, have an extreme selectivity for the motion of small targets. In doing so, we provide the first physiological characterization of small-field neurons in female flies. These retinotopically organized columnar neurons include both direction-selective and nondirection-selective classes covering a large area of visual space. ConclusionsThe retinotopic arrangement of lobula columnar neurons sensitive to the motion of small targets makes a strong case for these neurons as important precursors in the local processing of target motion. Furthermore, the continued response of STMDs with such small receptive fields to the motion of small targets in the presence of moving background clutter places further constraints on the potential mechanisms underlying their small-target tuning.
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| 2. |
- Bolzon, Douglas M, et al.
(author)
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Local and large-range inhibition in feature detection
- 2009
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In: Journal of Neuroscience. - 0270-6474 .- 1529-2401. ; 29:45, s. 14143-14150
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Journal article (peer-reviewed)abstract
- Lateral inhibition is perhaps the most ubiquitous of neuronal mechanisms, having been demonstrated in early stages of processing in many different sensory pathways of both mammals and invertebrates. Recent work challenges the long-standing view that assumes that similar mechanisms operate to tune neuronal responses to higher order properties. Scant evidence for lateral inhibition exists beyond the level of the most peripheral stages of visual processing, leading to suggestions that many features of the tuning of higher order visual neurons can be accounted for by the receptive field and other intrinsic coding properties of visual neurons. Using insect target neurons as a model, we present unequivocal evidence that feature tuning is shaped not by intrinsic properties but by potent spatial lateral inhibition operating well beyond the first stages of visual processing. In addition, we present evidence for a second form of higher-order spatial inhibition--a long-range interocular transfer of information that we argue serves a role in establishing interocular rivalry and thus potentially a neural substrate for directing attention to single targets in the presence of distracters. In so doing, we demonstrate not just one, but two levels of spatial inhibition acting beyond the level of peripheral processing.
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| 3. |
- Nordström, Karin, 1973-, et al.
(author)
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Feature detection and the hypercomplex property in insects.
- 2009
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In: TINS - Trends in Neurosciences. - : Elsevier BV. - 0166-2236 .- 1878-108X. ; 32:7, s. 383-391
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Journal article (peer-reviewed)abstract
- Discerning a target amongst visual ‘clutter’ is a complicated task that has been elegantly solved by flying insects, as evidenced by their mid-air interactions with conspecifics and prey. The neurophysiology of smalltarget motion detectors (STMDs) underlying these complex behaviors has recently been described and suggests that insects use mechanisms similar to those of hypercomplex cells of the mammalian visual cortex to achieve target-specific tuning. Cortical hypercomplex cells are end-stopped, which means that they respond optimally to small moving targets, with responses to extended bars attenuated. We review not only the underlying mechanisms involved in this tuning but also how recently proposed models provide a possible explanation for another remarkable property of these neurons – their ability to respond robustly to the motion of targets even against moving backgrounds.
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| 4. |
- Nordström, Karin, et al.
(author)
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Insect detection of small targets moving in visual clutter.
- 2006
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In: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 4:3, s. e54-
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Journal article (peer-reviewed)abstract
- Detection of targets that move within visual clutter is a common task for animals searching for prey or conspecifics, a task made even more difficult when a moving pursuer needs to analyze targets against the motion of background texture (clutter). Despite the limited optical acuity of the compound eye of insects, this challenging task seems to have been solved by their tiny visual system. Here we describe neurons found in the male hoverfly, Eristalis tenax, that respond selectively to small moving targets. Although many of these target neurons are inhibited by the motion of a background pattern, others respond to target motion within the receptive field under a surprisingly large range of background motion stimuli. Some neurons respond whether or not there is a speed differential between target and background. Analysis of responses to very small targets (smaller than the size of the visual field of single photoreceptors) or those targets with reduced contrast shows that these neurons have extraordinarily high contrast sensitivity. Our data suggest that rejection of background motion may result from extreme selectivity for small targets contrasting against local patches of the background, combined with this high sensitivity, such that background patterns rarely contain features that satisfactorily drive the neuron.
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| 5. |
- Nordström, Karin, 1973-, et al.
(author)
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Sexual dimorphism in the hoverfly motion vision pathway.
- 2008
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In: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 18:9, s. 661-667
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Journal article (peer-reviewed)abstract
- Many insects perform high-speed aerial maneuvers in which they navigate through visually complex surrounds. Among insects, hoverflies stand out, with males switching from stationary hovering to high-speed pursuit at extreme angular velocities [1]. In dipterans, 50-60 large interneurons -- the lobula-plate tangential cells (LPTCs) -- detect changes in optic flow experienced during flight [2-5]. It has been predicted that large LPTC receptive fields are a requirement of accurate "matched filters" of optic flow [6]. Whereas many fly taxa have three horizontal system (HS) LPTC neurons in each hemisphere, hoverflies have four [7], possibly reflecting the more sophisticated flight behavior. We here show that the most dorsal hoverfly neuron (HS north [HSN]) is sexually dimorphic, with the male receptive field substantially smaller than in females or in either sex of blowflies. The (hoverfly-specific) HSN equatorial (HSNE) is, however, sexually isomorphic. Using complex optic flow, we show that HSN, despite its smaller receptive field, codes yaw velocity as well as HSNE. Responses to a target moving against a plain or textured background suggest that the male HSN could potentially play a role in target pursuit under some conditions.
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| 6. |
- Nordström, Karin, et al.
(author)
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Small object detection neurons in female hoverflies.
- 2006
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In: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 273:1591, s. 1211-6
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Journal article (peer-reviewed)abstract
- While predators such as dragonflies are dependent on visual detection of moving prey, social interactions make conspecific detection equally important for many non-predatory insects. Specialized 'acute zones' associated with target detection have evolved in several insect groups and are a prominent male-specific feature in many dipteran flies. The physiology of target selective neurons associated with these specialized eye regions has previously been described only from male flies. We show here that female hoverflies (Eristalis tenax) have several classes of neurons within the third optic ganglion (lobula) capable of detecting moving objects smaller than 1 degrees . These neurons have frontal receptive fields covering a large part of the ipsilateral world and are tuned to a broad range of target speeds and sizes. This could make them suitable for detecting targets under a range of natural conditions such as required during predator avoidance or conspecific interactions.
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| 7. |
- Nordström, Karin, 1973-, et al.
(author)
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The motion after-effect : local and global contributions to contrast sensitivity.
- 2009
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In: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 276:1662, s. 1545-1554
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Journal article (peer-reviewed)abstract
- Motion adaptation is a widespread phenomenon analogous to peripheral sensory adaptation, presumed to play a role in matching responses to prevailing current stimulus parameters and thus to maximize efficiency of motion coding. While several components of motion adaptation (contrast gain reduction, output range reduction and motion after-effect) have been described, previous work is inconclusive as to whether these are separable phenomena and whether they are locally generated. We used intracellular recordings from single horizontal system neurons in the fly to test the effect of local adaptation on the full contrast-response function for stimuli at an unadapted location. We show that contrast gain and output range reductions are primarily local phenomena and are probably associated with spatially distinct synaptic changes, while the antagonistic after-potential operates globally by transferring to previously unadapted locations. Using noise analysis and signal processing techniques to remove 'spikelets', we also characterize a previously undescribed alternating current component of adaptation that can explain several phenomena observed in earlier studies.
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| 8. |
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| 9. |
- Straw, Andrew D., et al.
(author)
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A 'bright zone' in male hoverfly (Eristalis tenax) eyes and associated faster motion detection and increased contrast sensitivity
- 2006
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In: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 209:21, s. 4339-4354
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Journal article (peer-reviewed)abstract
- Eyes of the hoverfly Eristalis tenax are sexually dimorphic such that males have a fronto-dorsal region of large facets. In contrast to other large flies in which large facets are associated with a decreased interommatidial angle to form a dorsal 'acute zone' of increased spatial resolution, we show that a dorsal region of large facets in males appears to form a 'bright zone' of increased light capture without substantially increased spatial resolution. Theoretically, more light allows for increased performance in tasks such as motion detection. To determine the effect of the bright zone on motion detection, local properties of wide field motion detecting neurons were investigated using localized sinusoidal gratings. The pattern of local preferred directions of one class of these cells, the HS cells, in Eristalis is similar to that reported for the blowfly Calliphora. The bright zone seems to contribute to local contrast sensitivity; high contrast sensitivity exists in portions of the receptive field served by large diameter facet lenses of males and is not observed in females. Finally, temporal frequency tuning is also significantly faster in this frontal portion of the world, particularly in males, where it overcompensates for the higher spatial-frequency tuning and shifts the predicted local velocity optimum to higher speeds. These results indicate that increased retinal illuminance due to the bright zone of males is used to enhance contrast sensitivity and speed motion detector responses. Additionally, local neural properties vary across the visual world in a way not expected if HS cells serve purely as matched filters to measure yaw-induced visual motion.
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