Functional visual streams.

The idea that visual signals relayed by the parvocellular and magnocellular subdivisions of the lateral geniculate nucleus remain segregated in the cerebral cortex has attracted considerable attention. It has been proposed that parvocellular contributions dominate in the temporal visual cortex, and that magnocellular contributions dominate in the parietal cortex. Recent experiments have shown that the organization of primate visual pathways is not this simple.     

Odour boosts visual object approach in flies

Multisensory integration is synergistic—input from one sensory modality might modulate the behavioural response to another. Work in flies has shown that a small visual object presented in the periphery elicits innate aversive steering responses in flight, likely representing an approaching threat. Object aversion is switched to approach when paired with a plume of food odour. The ‘open-loop’ design of prior work facilitated the observation of changing valence. How does odour influence visual object responses when an animal has naturally active control over its visual experience? In this study, we use closed-loop feedback conditions, in which a fly''s steering effort is coupled to the angular velocity of the visual stimulus, to confirm that flies steer toward or ‘fixate’ a long vertical stripe on the visual midline. They tend either to steer away from or ‘antifixate’ a small object or to disengage active visual control, which manifests as uncontrolled object ‘spinning’ within this experimental paradigm. Adding a plume of apple cider vinegar decreases the probability of both antifixation and spinning, while increasing the probability of frontal fixation for objects of any size, including a normally typically aversive small object.     

Retinal lattice,visual field and binocularities in flies

Summary The arrangements of ommatidia are charted and the visual fields of the compound eyes are plotted for both male and female of the dipteran speciesMusca domestica L.,Calliphora erythrocephala M.,Stomoxys calcitrans L.,Syritta pipiens L. andFannia fannia L. At the level of the retina remarkable differences between different species and between the sexes of one species exist. Consequences of the small binocular overlap area with respect to depth perception are discussed.     

Multimodal integration: visual cues help odor-seeking fruit flies

Olfactory stimuli are uniquely devoid of directional information, so that multimodal cues are typically required for their localization. A clever new experimental paradigm with flying Drosophila has shown that accurate heading into an odor plume requires panoramic visual cues.     

The functional organization of male-specific visual neurons in flies

Summary Intracellular recording and Lucifer yellow dye filling of male fleshflies, Sarcophaga bullata, have revealed male-specific neurons in the lobula, the axons of which project to the origin of premotor channels supplying flight motor neurons. Dendrites of male-specific neurons visit areas of the retinotopic mosaic supplied by the retina's acute zone, which is used by males to keep the image of a conspecific female centered during aerial pursuit. Only males engage in high-speed acrobatic chases, and male-specific neurons are suspected to under-lie this behavior. Physiological determination of receptive fields of male-specific neurons substantiates the fields predicted from anatomical studies and demonstrates that they subtend the acute zone. Male-specific neurons respond in a manner predicted on theoretical grounds from observations of tracking behavior. Such properties include directional selectivity to visual motion and higher sensitivity to motion of small images than to wide-field motion. The present account substantiates and extends neuroanatomical evidence that predicts that male-specific lobula neurons comprise a distinct circuit mediating conspecific tracking.     

Modulation of visual physiology by behavioral state in monkeys, mice, and flies

When a monkey attends to a visual stimulus, neurons in visual cortex respond differently to that stimulus than when the monkey attends elsewhere. In the 25 years since the initial discovery, the study of attention in primates has been central to understanding flexible visual processing. Recent experiments demonstrate that visual neurons in mice and fruit flies are modulated by locomotor behaviors, like running and flying, in a manner that resembles attention-based modulations in primates. The similar findings across species argue for a more generalized view of state-dependent sensory processing and for a renewed dialogue among vertebrate and invertebrate research communities.     

Virtual-reality techniques resolve the visual cues used by fruit flies to evaluate object distances

Insects can estimate distance or time-to-contact of surrounding objects from locomotion-induced changes in their retinal position and/or size. Freely walking fruit flies (Drosophila melanogaster) use the received mixture of different distance cues to select the nearest objects for subsequent visits. Conventional methods of behavioral analysis fail to elucidate the underlying data extraction. Here we demonstrate first comprehensive solutions of this problem by substituting virtual for real objects; a tracker-controlled 360 degrees panorama converts a fruit fly's changing coordinates into object illusions that require the perception of specific cues to appear at preselected distances up to infinity. An application reveals the following: (1) en-route sampling of retinal-image changes accounts for distance discrimination within a surprising range of at least 8-80 body lengths (20-200 mm). Stereopsis and peering are not involved. (2) Distance from image translation in the expected direction (motion parallax) outweighs distance from image expansion, which accounts for impact-avoiding flight reactions to looming objects. (3) The ability to discriminate distances is robust to artificially delayed updating of image translation. Fruit flies appear to interrelate self-motion and its visual feedback within a surprisingly long time window of about 2 s. The comparative distance inspection practiced in the small fruit fly deserves utilization in self-moving robots.     

Optomotor course control in flies with largely asymmetric visual input

We have studied freely flying and walking flies as well as flies flying in a flight simulator in order to discover how functionally blinding one of the eyes affects the fly's ability to move straight. It is hard to tell just by observing the animals' movements whether they have been deprived of vision in one eye. Statistical analysis is need to show that there are differences in the locomotory paths of monocular and binocular flies: monocular flies tend to turn slightly towards the side of the seeing eye. It is possible that the superimposed translational and rotational optic flow fields, generated on the trajectory of monocular flies, sum to zero net flow. This overall flow over the retina of the open eye might lead to a state of optomotor equilibrium. Accepted: 11 October 1999     

Some factors affecting pigeons' visual tracking behavior

A novel delayed conditional discrimination procedure was used successfully to investigate some factors affecting pigeons' tracking of visual stimuli. Trials began with the brief illumination of one of the keys (randomly selected) from the left- or right-hand column of a three by three matrix of pecking keys. Then the next key in the same row was briefly lit. Finally, the remaining key in the row was lit along with one (randomly chosen) of the remaining five keys from the left- or right-hand columns. A peck to the former but not the latter key was designated as correct and was rewarded. In Experiment 1 pigeons made correct choices on between 70 and 80 percent of trials, thereby demonstrating an ability to visually track objects. In Experiment 2 tracking accuracy was: a) reduced when either the first or second key in the sequence was omitted, b) improved when the sequence was repeated three times, c) reduced when duration of key illumination was reduced, and d) reduced by delays imposed between keys early but not late in the sequence. It was also found that tracking of vertical and horizontal sequences was approximately equal.     

Reproduction in shark-attacked sea turtles is supported by stress-reduction mechanisms

Vertebrates exhibit varied behavioural and physiological tactics to promote reproductive success. We examined mechanisms that could enable female loggerhead turtles to undertake nesting activities and maintain seasonal reproduction despite recent shark injuries of varying severity. We proposed that endocrinal mechanisms that regulate both a turtle's stress response and reproductive ability are modified to promote successful and continued reproduction. Irrespective of the degree of injury, females did not exhibit increased levels of the stress hormone corticosterone, nor decreased levels of the reproductive steroid testosterone; hormone responses consistent with stress. When exposed to a capture stressor, females with shark injury did not exhibit any greater corticosterone response than controls. In addition, breeding females showed a reduced corticosterone stress response compared to non-breeding females. Reduced endocrinal responses following shark injury, and during breeding in general may, in part, enable females to maintain behavioural and physiological commitment to reproduction.     

Discriminate suckling in pipistrelle bats is supported by DNA fingerprinting

DNA fingerprints were obtained by using Jeffreys' probes 33.6 and 33.15 with DNA extracted from nine mother-young pairs of pipistrelle bats Pipistrellus pipistrellns to investigate the feasibility of this technique for determining relatedness in this species. The bats had mated in the wild and gave birth in captivity. All of nine pairs in which infants were found attached showed band-sharing coefficients higher than those for individuals presumed to be unrelated but run in adjacent lanes of the gels. We therefore conclude that all attached infants were probably true offspring.     

Parallel visual motion processing streams for manipulable objects and human movements

We tested the hypothesis that different regions of lateral temporal cortex are specialized for processing different types of visual motion by studying the cortical responses to moving gratings and to humans and manipulable objects (tools and utensils) that were either stationary or moving with natural or artificially generated motions. Segregated responses to human and tool stimuli were observed in both ventral and lateral regions of posterior temporal cortex. Relative to ventral cortex, lateral temporal cortex showed a larger response for moving compared with static humans and tools. Superior temporal cortex preferred human motion, and middle temporal gyrus preferred tool motion. A greater response was observed in STS to articulated compared with unarticulated human motion. Specificity for different types of complex motion (in combination with visual form) may be an organizing principle in lateral temporal cortex.     

Changing visual responsiveness in pregnant and larvipositing tsetse flies, Glossina morsitans

ABSTRACT. Direct observations on the spontaneous activity and visually-evoked responses of pregnant female Glossina morsitans morsitans Westw. were made hourly during the photophase over the 4 days around larviposition. Visual stimulation was by a 5-wide vertical black stripe moving laterally, 4 times min^-1 at c. 5 s^-1. The numbers of take-offs and the numbers of females taking off were recorded, both in response to the stimulus and spontaneously in its absence. The visual responsiveness paralled both the day-to-day changes and the altered circadian patterns of spontaneous activity reported previously (Brady & Gibson, 1983), being very low for the 48 h before parturition. It did not, however, rise in parallel with the increase in spontaneous activity during the last 3–4 h before parturition, and the proportion of flights oriented towards the moving stripe was also much reduced at that time. The significance of this changing responsiveness to slow movement is discussed, and its potential enhancement of any behavioural avoidance of aerosol, non-residual insecticide spraying during late pregnancy is noted.     

The synaptic organization of visual interneurons in the lobula complex of flies

Summary The synaptic organization of three classes of cobalt-filled and silver-intensified visual interneurons in the lobula complex of the blowfly Calliphora (Col A cells, horizontal cells and vertical cells) was studied electron microscopically. The Col A cells are regularly spaced, columnar, small field neurons of the lobula, which constitute a plexus of arborizations at the posterior surface of the neuropil and the axons of which terminate in the ventrolateral protocerebrum. They show postsynaptic specializations in the distal layer of their lobula-arborizations and additional presynaptic sites in a more proximal layer; their axon terminals are presynaptic to large descending neurons projecting into the thoracic ganglion. The horizontal and vertical cells are giant tangential neurons, the arborizations of which cover the anterior and posterior surface of the lobula plate, respectively, and which terminate in the perioesophageal region of the protocerebrum. Both classes of these giant neurons were found to be postsynaptic in the lobula plate and pre- and postsynaptic at their axon terminals and axon collaterals. The significance of these findings with respect to the functional properties of the neurons investigated is discussed.