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In general, humans preferentially look at conspecifics in naturalistic images. However, such group-based effects might conceal systematic individual differences concerning the preference for social information. Here, we investigated to what degree fixations on social features occur consistently within observers and whether this preference generalizes to other measures of social prioritization in the laboratory as well as the real world. Participants carried out a free viewing task, a relevance taps task that required them to actively select image regions that are crucial for understanding a given scene, and they were asked to freely take photographs outside the laboratory that were later classified regarding their social content. We observed stable individual differences in the fixation and active selection of human heads and faces that were correlated across tasks and partly predicted the social content of self-taken photographs. Such relationship was not observed for human bodies indicating that different social elements need to be dissociated. These findings suggest that idiosyncrasies in the visual exploration and interpretation of social features exist and predict real-world behavior. Future studies should further characterize these preferences and elucidate how they shape perception and interpretation of social contexts in healthy participants and patients with mental disorders that affect social functioning.
Different transgenes that can be expressed in neurons to kill or block them were compared. Tetanus neurotoxin blocked chemical synapses very efficiently. Synapses consisting of a chemical and an electrical component were blocked more reliably by expressing a human inwardly rectifying potassium channel. To gain temporal control over neuronal function, three genetic tools have been investigated. None of the systems is without drawbacks, however, the recombination induced tetanus neurotoxin expression is a promising approach. The knowledge gained from the comparative methodological study was used to investigate the role of neurons in sensory systems in processing different sensory informations. Receptor neurons sensitive for chemical or mechanical stimuli were correlated to specific olfactory behaviors or locomotor tasks. The main topic of this thesis is the much discussed question of which neurons are involved in motion processing in the visual system of flies. Neither L2 nor L4 neurons in the first visual neuropil are essential for motion-detection. The results indicate that maybe motion is detected by the network of amacrine cells (a). The vertical motion-sensitive VS cells in the lobula plate are not necessary for behavioral responses to vertical motion. This finding implies that the lack of VS cells in the structural mutant optomotor blind is not causally related to the altered responses to motion stimuli. Other abnormalities in optomotor blind are responsible for this behavioral phenotype. This work shows the potential of the described methods in studying information processing in the Drosophila brain. Groups of neurons were correlated to complex behavioral responses and theories about information processing were tested by behavioral experiments with transgenic flies. The refinement of the genetic tools to interfere with neuronal function will make the Drosophila brain an even better model to study information processing in nervous systems.
Vertebrate and invertebrate visual systems exhibit similarities in early stages of visual processing. For instance, in the human brain, the modalities of color, form and motion are separately processed in parallel neuronal pathways. This basic property is also found in the fly Drosophila melanogaster which has a similar division in color- sensitive and (color blind) motion-sensitive pathways that are determined by two distinct subsets of photoreceptors (the R1-6 and the R7/8 system, respectively). Flies have a highly organized visual system that is characterized by its repetitive, retinotopic organization of four neuropils: the lamina, the medulla, the lobula and the lobula plate. Each of these consists of columns which contain the same set of neurons. In the lamina, axon bundles of six photoreceptors R1-6 that are directed towards the same point in space form columnar structures called cartridges. These are the visual sampling units and are associated with four types of first-order interneuron that receive common input from R1-6: L1, L2, L3 and the amacrine cells (amc, together with their postsynaptic partner T1). They constitute parallel pathways that have been studied in detail at the anatomical level. Little is known, however, about their functional role in processing behaviorally relevant information, e.g. for gaze stabilization, visual course control or the fixation of objects. The availability of a variety of neurogenetic tools for structure-function analysis in Drosophila allowed first steps into the genetic dissection of the neuronal circuitry mediating motion and position detection. In this respect, the choice of the effector turned out to be crucial. Surprisingly, it was found that the clostridial tetanus neurotoxin failed to block mature Drosophila photoreceptor synapses, but caused irreversible damage when expressed during their development. Therefore, the dominant-negative shibire allele shits1 which turned out to be better suited was used for blocking lamina interneurons and thereby analyzing the necessity of the respective pathways. To determine whether the latter were also sufficient for the same behavioral task, the inverse strategy was developed, based on the fact that lamina interneurons express histamine receptors encoded by the ort gene. The specific rescue of ort function in defined channels in an otherwise mutant background allowed studying their sufficiency in a given task. Combining these neurogenetic methods with the optomotor response and object induced orientation behavior as behavioral measures, the aim of the present thesis was to answer the following questions: (a) Which pathways feed into elementary motion detectors and which ones are necessary and/or sufficient for the detection of directional motion? (b) Do pathways exist which specifically mediate responses to unidirectional motion? (c) Which pathways are necessary and/or sufficient for object induced orientation behavior? Some basic properties of the visual circuitry were revealed: The two central cartridge pathways, represented by the large monopolar cells L1 and L2, are key players in motion detection. Under a broad range of stimulatory conditions, the two subsystems are redundant and are able to process motion independently of each other. To detect an impairment when only one of the pathways is intact, one has to drive the system to its operational limits. At low signal to noise ratios, i.e. at low pattern contrast or low background illumination, the L2 pathway has a higher sensitivity. At intermediate pattern contrast, both pathways are specialized in mediating responses to unidirectional motion of opposite stimulus direction. In contrast, neither the L3, nor the amc/T1 pathway is necessary or sufficient for motion detection. While the former may provide position information for orientation, the latter has a modulatory role at intermediate pattern contrast. Orientation behavior turned out to be even more robust than motion vision and may utilize a less sophisticated mechanism, as it does not require a nonlinear comparison of signals from neighboring visual sampling units. The position of objects is processed in several redundant pathways, involving both receptor subsystems. The fixation of objects does not generally require motion vision. However, motion detection improves the fixation of landmarks, especially when these are narrow or have a reduced contrast.
The biogenic amines octopamine and tyramine are important neurotransmitters in insects and other protostomes. They play a pivotal role in the sensory responses, learning and memory and social organisation of honeybees. Generally, octopamine and tyramine are believed to fulfil similar roles as their deuterostome counterparts epinephrine and norepinephrine. In some cases opposing functions of both amines have been observed. In this study, we examined the functions of tyramine and octopamine in honeybee responses to light. As a first step, electroretinography was used to analyse the effect of both amines on sensory sensitivity at the photoreceptor level. Here, the maximum receptor response was increased by octopamine and decreased by tyramine. As a second step, phototaxis experiments were performed to quantify the behavioural responses to light following treatment with either amine. Octopamine increased the walking speed towards different light sources while tyramine decreased it. This was independent of locomotor activity. Our results indicate that tyramine and octopamine act as functional opposites in processing responses to light.
Threat detection plays a vital role in adapting behavior to changing environments. A fundamental function to improve threat detection is learning to differentiate between stimuli predicting danger and safety. Accordingly, aversive learning should lead to enhanced sensory discrimination of danger and safety cues. However, studies investigating the psychophysics of visual and auditory perception after aversive learning show divergent findings, and both enhanced and impaired discrimination after aversive learning have been reported. Therefore, the aim of this web-based study is to examine the impact of aversive learning on a continuous measure of visual discrimination. To this end, 205 participants underwent a differential fear conditioning paradigm before and after completing a visual discrimination task using differently oriented grating stimuli. Participants saw either unpleasant or neutral pictures as unconditioned stimuli (US). Results demonstrated sharpened visual discrimination for the US-associated stimulus (CS+), but not for the unpaired conditioned stimuli (CS-). Importantly, this finding was irrespective of the US's valence. These findings suggest that associative learning results in increased stimulus salience, which facilitates perceptual discrimination in order to prioritize attentional deployment.
Bees have had an intimate relationship with humans for millennia, as pollinators of fruit, vegetable and other crops and suppliers of honey, wax and other products. This relationship has led to an extensive understanding of their ecology and behavior. One of the most comprehensively understood species is the Western honeybee, Apis mellifera. Our understanding of sex-specific investment in other bees, however, has remained superficial. Signals and cues employed in bee foraging and mating behavior are reasonably well understood in only a handful of species and functional adaptations are described in some species. I explored the variety of sensory adaptations in three model systems within the bees. Females share a similar ecology and similar functional morphologies are to be expected. Males, engage mainly in mating behavior. A variety of male mating strategies has been described which differ in their spatiotemporal features and in the signals and cues involved, and thus selection pressures. As a consequence, males’ sensory systems are more diverse than those of females. In the first part I studied adaptations of the visual system in honeybees. I compared sex and caste-specific eye morphology among 5 species (Apis andreniformis, A. cerana, A. dorsata, A. florea, A. mellifera). I found a strong correlation between body size and eye size in both female castes. Queens have a relatively reduced visual system which is in line with the reduced role of visual perception in their life history. Workers differed in eye size and functional morphology, which corresponds to known foraging differences among species. In males, the eyes are conspicuously enlarged in all species, but a disproportionate enlargement was found in two species (A. dorsata, A. florea). I further demonstrate a correlation between male visual parameters and mating flight time, and propose that light intensities play an important role in the species-specific timing of mating flights. In the second study I investigated eye morphology differences among two phenotypes of drones in the Western honeybee. Besides normal-sized drones, smaller drones are reared in the colony, and suffer from reduced reproductive success. My results suggest that the smaller phenotype does not differ in spatial resolution of its visual system, but suffers from reduced light and contrast sensitivity which may exacerbate the reduction in reproductive success caused by other factors. In the third study I investigated the morphology of the visual system in bumblebees. I explored the association between male eye size and mating behavior and investigated the diversity of compound eye morphology among workers, queens and males in 11 species. I identified adaptations of workers that correlate with distinct foraging differences among species. Bumblebee queens must, in contrast to honeybees, fulfill similar tasks as workers in the first part of their life, and correspondingly visual parameters are similar among both female castes. Enlarged male eyes are found in several subgenera and have evolved several times independently within the genus, which I demonstrate using phylogenetic informed statistics. Males of these species engage in visually guided mating behavior. I find similarities in the functional eye morphology among large-eyed males in four subgenera, suggesting convergent evolution as adaptation to similar visual tasks. In the remaining species, males do not differ significantly from workers in their eye morphology. In the fourth study I investigated the sexual dimorphism of the visual system in a solitary bee species. Males of Eucera berlandi patrol nesting sites and compete for first access to virgin females. Males have enlarged eyes and better spatial resolution in their frontal eye region. In a behavioral study, I tested the effect of target size and speed on male mate catching success. 3-D reconstructions of the chasing flights revealed that angular target size is an important parameter in male chasing behavior. I discuss similarities to other insects that face similar problems in visual target detection. In the fifth study I examined the olfactory system of E. berlandi. Males have extremely long antennae. To investigate the anatomical grounds of this elongation I studied antennal morphology in detail in the periphery and follow the sexual dimorphism into the brain. Functional adaptations were found in males (e.g. longer antennae, a multiplication of olfactory sensilla and receptor neurons, hypertrophied macroglomeruli, a numerical reduction of glomeruli in males and sexually dimorphic investment in higher order processing regions in the brain), which were similar to those observed in honeybee drones. The similarities and differences are discussed in the context of solitary vs. eusocial lifestyle and the corresponding consequences for selection acting on males.
Ranging from dwarfs to giants, the species of honeybees show remarkable differences in body size that have placed evolutionary constrains on the size of sensory organs and the brain. Colonies comprise three adult phenotypes, drones and two female castes, the reproductive queen and sterile workers. The phenotypes differ with respect to tasks and thus selection pressures which additionally constrain the shape of sensory systems. In a first step to explore the variability and interaction between species size-limitations and sex and caste-specific selection pressures in sensory and neural structures in honeybees, we compared eye size, ommatidia number and distribution of facet lens diameters in drones, queens and workers of five species (Apis andreniformis, A. florea, A. dorsata, A. mellifera, A. cerana). In these species, male and female eyes show a consistent sex-specific organization with respect to eye size and regional specialization of facet diameters. Drones possess distinctly enlarged eyes with large dorsal facets. Aside from these general patterns, we found signs of unique adaptations in eyes of A. florea and A. dorsata drones. In both species, drone eyes are disproportionately enlarged. In A. dorsata the increased eye size results from enlarged facets, a likely adaptation to crepuscular mating flights. In contrast, the relative enlargement of A. florea drone eyes results from an increase in ommatidia number, suggesting strong selection for high spatial resolution. Comparison of eye morphology and published mating flight times indicates a correlation between overall light sensitivity and species-specific mating flight times. The correlation suggests an important role of ambient light intensities in the regulation of species-specific mating flight times and the evolution of the visual system. Our study further deepens insights into visual adaptations within the genus Apis and opens up future perspectives for research to better understand the timing mechanisms and sensory physiology of mating related signals.