Discrimination of human faces by archerfish (Toxotes chatareus)

GoFish: A low-cost, open-source platform for closed-loop behavioural experiments on fish

Fish are the most species-rich vertebrate group, displaying vast ecological, anatomical and behavioural diversity, and therefore are of major interest for the study of behaviour and its evolution. However, with respect to other vertebrates, fish are relatively underrepresented in psychological and cognitive research. A greater availability of easily accessible, flexible, open-source experimental platforms that facilitate the automation of task control and data acquisition may help to reduce this bias and improve the scalability and refinement of behavioural experiments in a range of different fish species. Here we present GoFish, a fully automated platform for behavioural experiments in aquatic species. GoFish includes real-time video tracking of subjects, presentation of stimuli in a computer screen, an automatic feeder device, and closed-loop control of task contingencies and data acquisition. The design and software components of the platform are freely available, while the hardware is open-source and relatively inexpensive. The control software, Bonsai, is designed to facilitate rapid development of task workflows and is supported by a growing community of users. As an illustration and test of its use, we present the results of two experiments on discrimination learning, reversal, and choice in goldfish (Carassius auratus). GoFish facilitates the automation of high-throughput protocols and the acquisition of rich behavioural data. Our platform has the potential to become a widely used tool that facilitates complex behavioural experiments in aquatic species.

Prosocial behavior in competitive fish: the case of the archerfish

Humans are social creatures, demonstrate prosocial behaviors, and are sensitive to the actions and consequent payoff of others. This social sensitivity has also been found in many other species, though not in all. Research has suggested that prosocial tendencies are more pronounced in naturally cooperative species whose social structure requires a high level of interdependence and allomaternal care. The present study challenges this assumption by demonstrating, in a laboratory setting, that archerfish, competitive by nature, preferred targets rewarding both themselves and their tankmates, but only when the payoff was equal. With no tankmate on the other side of the partition, they exhibited no obvious preference. Finding evidence for prosocial behavior and negative responses to unequal distribution of reward to the advantage of the other fish suggests that in a competitive social environment, being prosocial may be the most adaptive strategy for personal survival, even if it benefits others as well.

Cleaner fish recognize self in a mirror via self-face recognition like humans

Some animals have the remarkable capacity for mirror self-recognition (MSR), yet any implications for self-awareness remain uncertain and controversial. This is largely because explicit tests of the two potential mechanisms underlying MSR are still lacking: mental image of the self and kinesthetic visual matching. Here, we test the hypothesis that MSR ability in cleaner fish, Labroides dimidiatus, is associated with a mental image of the self, in particular the self-face, like in humans. Mirror-naive fish initially attacked photograph models of both themselves and unfamiliar strangers. In contrast, after all fish had passed the mirror mark test, fish did not attack their own (motionless) images, but still frequently attacked those of unfamiliar individuals. When fish were exposed to composite photographs, the self-face/unfamiliar body were not attacked, but photographs of unfamiliar face/self-body were attacked, demonstrating that cleaner fish with MSR capacity recognize their own facial characteristics in photographs. Additionally, when presented with self-photographs with a mark placed on the throat, unmarked mirror-experienced cleaner fish demonstrated throat-scraping behaviors. When combined, our results provide clear evidence that cleaner fish recognize themselves in photographs and that the likely mechanism for MSR is associated with a mental image of the self-face, not a kinesthetic visual-matching model. Humans are also capable of having a mental image of the self-face, which is considered an example of private self-awareness. We demonstrate that combining mirror test experiments with photographs has enormous potential to further our understanding of the evolution of cognitive processes and private self-awareness across nonhuman animals.

Communication from the Zoo: Reports from Zoological Facilities of the Impact of COVID-19 Closures on Animals

Zoos engaged in a range of communication types with prospective visitors during the temporary closures necessitated by the COVID-19 pandemic. This study sought to (1) investigate social media reports and public responses to zoo-animal-related posts over a one-year period during COVID-19 lockdowns; (2) understand the use of reporting language in news articles concerning animal responses during zoo closures, and to investigate whether this differed across species; and (3) investigate how keepers perceived general animal behavior, and how they perceived animal behavior in keeper–animal interactions, during the COVID-19 facility closures. Data were collected from BIAZA-accredited zoos’ Facebook pages (March 2020 to March 2021) and news reports (Google search outputs from 20 March to 5 April 2021). Keeper perceptions were captured via questionnaires (May to August 2021). Data were collected on taxa, the reported behavioral changes and the language used in media communications. In Facebook posts and news reports, mammals were more frequently represented than was expected (p < 0.05). Behavioral responses were more frequently negative (p < 0.05) and less frequently positive or neutral (p < 0.05). Keepers reported overall behavioral changes, as well as changes during their own interactions with animals. On Facebook, mammals were described using a combination of behavioral descriptions and anthropomorphic terms, which were used more frequently than was expected (p < 0.05). In the news reports concerning primate species, anthropomorphic descriptions were used more frequently than expected (p < 0.05), while behavioral descriptions were used less frequently than expected (p < 0.05). The reports regarding the Carnivora were the reverse of this. This study enabled an understanding of the impact of the temporary closures on the animals, and how this impact was communicated to the public. The findings may reflect the relationships that humans have with animals and the need for communication methods that will capture visitors’ interest and induce empathy with the various species.

Face perception: computational insights from phylogeny

Studies of face perception in primates elucidate the psychological and neural mechanisms that support this critical and complex ability. Recent progress in characterizing face perception across species, for example in insects and reptiles, has highlighted the ubiquity over phylogeny of this key ability for social interactions and survival. Here, we review the competence in face perception across species and the types of computation that support this behavior. We conclude that the computational complexity of face perception evinced by a species is not related to phylogenetic status and is, instead, largely a product of environmental context and social and adaptive pressures. Integrating findings across evolutionary data permits the derivation of computational principles that shed further light on primate face perception.

Visual discrimination and amodal completion in zebrafish

While zebrafish represent an important model for the study of the visual system, visual perception in this species is still less investigated than in other teleost fish. In this work, we validated for zebrafish two versions of a visual discrimination learning task, which is based on the motivation to reach food and companions. Using this task, we investigated zebrafish ability to discriminate between two different shape pairs (i.e., disk vs. cross and full vs. amputated disk). Once zebrafish were successfully trained to discriminate a full from an amputated disk, we also tested their ability to visually complete partially occluded objects (amodal completion). After training, animals were presented with two amputated disks. In these test stimuli, another shape was either exactly juxtaposed or only placed close to the missing sectors of the disk. Only the former stimulus should elicit amodal completion. In human observers, this stimulus causes the impression that the other shape is occluding the missing sector of the disk, which is thus perceived as a complete, although partially hidden, disk. In line with our predictions, fish reinforced on the full disk chose the stimulus eliciting amodal completion, while fish reinforced on the amputated disk chose the other stimulus. This represents the first demonstration of amodal completion perception in zebrafish. Moreover, our results also indicated that a specific shape pair (disk vs. cross) might be particularly difficult to discriminate for this species, confirming previous reports obtained with different procedures.

Recognition of natural objects in the archerfish

Recognition of individual objects and their categorization is a complex computational task. Nevertheless, visual systems can perform this task in a rapid and accurate manner. Humans and other animals can efficiently recognize objects despite countless variations in their projection on the retina due to different viewing angles, distance, illumination conditions and other parameters. To gain a better understanding of the recognition process in teleosts, we explored it in archerfish, a species that hunts by shooting a jet of water at aerial targets and thus can benefit from ecologically relevant recognition of natural objects. We found that archerfish not only can categorize objects into relevant classes but also can do so for novel objects, and additionally they can recognize an individual object presented under different conditions. To understand the mechanisms underlying this capability, we developed a computational model based on object features and a machine learning classifier. The analysis of the model revealed that a small number of features was sufficient for categorization, and the fish were more sensitive to object contours than textures. We tested these predictions in additional behavioral experiments and validated them. Our findings suggest the existence of a complex visual process in the archerfish visual system that enables object recognition and categorization.

Highlighted Article: Archerfish are capable of natural object recognition and categorization based on a small number of visual features.

Preference and discrimination of facial expressions of humans, rats, and mice by C57 mice

Social animals likely recognize emotional expressions in other animals. Recent studies suggest that mice can visually perceive emotional expressions of other mice. In the first experiment, we measured the preference of mice for two different facial expressions (a normal facial expression and an expression of negative emotion such as pain) of rats, mice, and humans. Results revealed that mice showed a slight preference for the normal expression over the face expressing pain in the case of rats, but no preference in the case of others. In the second experiment, we trained mice to discriminate between the two facial expressions in an operant chamber with a touch screen. They could discriminate facial expressions of mice and rats, but they did not show discrimination of human facial expressions. Principal component analysis of the images of stimuli reveals negative correlation between pixel-based dissimilarity of training stimuli and the number of sessions to criterion. The mice showed generalization to novel images of the mouse faces with and without pain but did not maintain their discriminative behavior when new rat faces were shown. These results suggest that mice display category discrimination of conspecific facial expressions but not of other species.

Five Breakthroughs: A First Approximation of Brain Evolution From Early Bilaterians to Humans

Retracing the evolutionary steps by which human brains evolved can offer insights into the underlying mechanisms of human brain function as well as the phylogenetic origin of various features of human behavior. To this end, this article presents a model for interpreting the physical and behavioral modifications throughout major milestones in human brain evolution. This model introduces the concept of a "breakthrough" as a useful tool for interpreting suites of brain modifications and the various adaptive behaviors these modifications enabled. This offers a unique view into the ordered steps by which human brains evolved and suggests several unique hypotheses on the mechanisms of human brain function.

Automated Operant Conditioning Devices for Fish. Do They Work?

Simple Summary

Automated training devices are commonly used for investigating learning, memory, and other cognitive functions in warm-blood vertebrates, whereas manual training procedures are the standard in fish and other lower vertebrates, thus limiting comparison among species. Here, we directly compared the two different approaches to training in guppies (Poecilia reticulata) by administering numerical discrimination tasks of increasing difficulty. The automated device group showed a much lower performance compared to the traditionally-trained group. We modified some features of the automated device in order to improve its efficiency. Increasing the decision time or inter-trial interval was ineffective, while reducing the cognitive load and allowing subjects to reside in the test tank improved numerical performance. Yet, in no case did subjects match the performance of traditionally-trained subjects, suggesting that small teleosts may be limited in their capacity to cope with operant conditioning devices.

Abstract

The growing use of teleosts in comparative cognition and in neurobiological research has prompted many researchers to develop automated conditioning devices for fish. These techniques can make research less expensive and fully comparable with research on warm-blooded species, in which automated devices have been used for more than a century. Tested with a recently developed automated device, guppies (Poecilia reticulata) easily performed 80 reinforced trials per session, exceeding 80% accuracy in color or shape discrimination tasks after only 3–4 training session, though they exhibit unexpectedly poor performance in numerical discrimination tasks. As several pieces of evidence indicate, guppies possess excellent numerical abilities. In the first part of this study, we benchmarked the automated training device with a standard manual training procedure by administering the same set of tasks, which consisted of numerical discriminations of increasing difficulty. All manually-trained guppies quickly learned the easiest discriminations and a substantial percentage learned the more difficult ones, such as 4 vs. 5 items. No fish trained with the automated conditioning device reached the learning criterion for even the easiest discriminations. In the second part of the study, we introduced a series of modifications to the conditioning chamber and to the procedure in an attempt to improve its efficiency. Increasing the decision time, inter-trial interval, or visibility of the stimuli did not produce an appreciable improvement. Reducing the cognitive load of the task by training subjects first to use the device with shape and color discriminations, significantly improved their numerical performance. Allowing the subjects to reside in the test chamber, which likely reduced the amount of attentional resources subtracted to task execution, also led to an improvement, although in no case did subjects match the performance of fish trained with the standard procedure. Our results highlight limitations in the capacity of small laboratory teleosts to cope with operant conditioning automation that was not observed in laboratory mammals and birds and that currently prevent an easy and straightforward comparison with other vertebrates.

An Evolutionary Microcircuit Approach to the Neural Basis of High Dimensional Sensory Processing in Olfaction

Odor stimuli consist of thousands of possible molecules, each molecule with many different properties, each property a dimension of the stimulus. Processing these high dimensional stimuli would appear to require many stages in the brain to reach odor perception, yet, in mammals, after the sensory receptors this is accomplished through only two regions, the olfactory bulb and olfactory cortex. We take a first step toward a fundamental understanding by identifying the sequence of local operations carried out by microcircuits in the pathway. Parallel research provided strong evidence that processed odor information is spatial representations of odor molecules that constitute odor images in the olfactory bulb and odor objects in olfactory cortex. Paleontology provides a unique advantage with evolutionary insights providing evidence that the basic architecture of the olfactory pathway almost from the start ∼330 million years ago (mya) has included an overwhelming input from olfactory sensory neurons combined with a large olfactory bulb and olfactory cortex to process that input, driven by olfactory receptor gene duplications. We identify a sequence of over 20 microcircuits that are involved, and expand on results of research on several microcircuits that give the best insights thus far into the nature of the high dimensional processing.

Dog-human social relationship: representation of human face familiarity and emotions in the dog brain

This study investigated the behavioral and neural indices of detecting facial familiarity and facial emotions in human faces by dogs. Awake canine fMRI was used to evaluate dogs' neural response to pictures and videos of familiar and unfamiliar human faces, which contained positive, neutral, and negative emotional expressions. The dog-human relationship was behaviorally characterized out-of-scanner using an unsolvable task. The caudate, hippocampus, and amygdala, mainly implicated in reward, familiarity and emotion processing, respectively, were activated in dogs when viewing familiar and emotionally salient human faces. Further, the magnitude of activation in these regions correlated with the duration for which dogs showed human-oriented behavior towards a familiar (as opposed to unfamiliar) person in the unsolvable task. These findings provide a bio-behavioral basis for the underlying markers and functions of human-dog interaction as they relate to familiarity and emotion in human faces.

Fish Behavior for the Exotic Pet Practitioner

Interpreting fish behavior is an important component of providing veterinary care. There are over 28,000 species of fish and while only a handful are commonly encountered by exotic pet and public display veterinarians, there are still hundreds of species to consider. Three models-natural history (species typical modal action patterns), medical (disease state), and learning experience (classical and operant conditioning)-are useful for taking an actionable, holistic approach to interpreting behavior. Models help clinicians formulate appropriate differentials, ensuring they do not exclusively consider disease, particularly in unfamiliar species.

Categorical face perception in fish: How a fish brain warps reality to dissociate "same" from "different"

Categorical perception (CP) is the phenomenon by which a smoothly varying stimulus property undergoes a nonlinear transformation during processing in the brain. Consequently, the stimuli are perceived as belonging to distinct categories separated by a sharp boundary. Originally thought to be largely innate, the discovery of CP in tasks such as novel image discrimination has piqued the interest of cognitive scientists because it provides compelling evidence that learning can shape a category's perceptual boundaries. CP has been particularly closely studied in human face perception. In nonprimates, there is evidence for CP for sound and color discrimination, but not for image or face discrimination. Here, we investigate the potential for learned CP in a lower vertebrate, the damselfish Pomacentrus amboinensis. Specifically, we tested whether the ability of these fish to discriminate complex facial patterns tracked categorical rather than metric differences in the stimuli. We first trained the fish to discriminate sets of two facial patterns. Next, we morphed between these patterns and determined the just noticeable difference (JND) between a morph and original image. Finally, we tested for CP by analyzing the discrimination ability of the fish for pairs of JND stimuli along the spectrum of morphs between two original images. Discrimination performance was significant for the image pair straddling the boundary between categories, and chance for equivalent stimulus pairs on either side, thus producing the classic "category boundary" effect. Our results reveal how perception can be influenced in a top-down manner even in the absence of a visual cortex.

Jumping archer fish exhibit multiple modes of fin-fin interaction

Aquatic organisms jumping for aerial prey require high-performance propulsion, accurate aim, and trajectory control to succeed. Archer fish, capable of jumping up to twice their body length out of the water, address these considerations through multifaceted fin and body kinematics. In this study, we utilized 3D synthetic aperture particle image velocimetry to visualize the wakes of archer fish throughout the jumping process. We found that multiple modes of interaction between the anal and caudal fins occur during jump behaviors. Time-resolved volumetric measurements presented herein illustrate the hydrodynamics of each interaction mode in detail. Additionally, regardless of which fin uses and interactions were exhibited during a jump, we found similar relationships between the cumulative impulse of multiple propulsive vortices in the wake and the instantaneous ballistic momentum of the fish. Our results suggests that fin use may compensate for variations in individual kinematic events and in the aiming posture assumed prior to jumping and highlight how interactions between tailbeats and other fins help the archer fish reach necessary prey heights in a spatially- and visually-constrained environment. In the broader context of bioinspired propulsion, the archer fish exemplifies that multiple beneficial hydrodynamic interactions can be generated in a high-performance scenario using a single set of actuators.

Representation of edges, head direction, and swimming kinematics in the brain of freely-navigating fish

Like most animals, the survival of fish depends on navigation in space. This capacity has been documented in behavioral studies that have revealed navigation strategies. However, little is known about how freely swimming fish represent space and locomotion in the brain to enable successful navigation. Using a wireless neural recording system, we measured the activity of single neurons in the goldfish lateral pallium, a brain region known to be involved in spatial memory and navigation, while the fish swam freely in a two-dimensional water tank. We found that cells in the lateral pallium of the goldfish encode the edges of the environment, the fish head direction, the fish swimming speed, and the fish swimming velocity-vector. This study sheds light on how information related to navigation is represented in the brain of fish and addresses the fundamental question of the neural basis of navigation in this group of vertebrates.

The devil is in the detail: Zebrafish learn to discriminate visual stimuli only if salient

Due to their unique characteristics, the zebrafish plays a key role in the comprehension of neurobiology of cognition and its pathologies, such as neurodegenerative diseases. More and more molecular tools for this aim are being developed, but our knowledge about the cognitive abilities of zebrafish remains extremely scarce compared to other teleost fish. We aimed to investigate the complex cognitive abilities of zebrafish using a tracking-based automated conditioning chamber that allowed precise experimental control, avoided potential cueing provided by the observer (Clever Hans phenomenon), and was shown to considerably improve learning in other teleosts. A computer presented two visual stimuli in two sectors of the chamber, and zebrafish had to enter the correct sector to obtain a food reward. Zebrafish quickly learned to use the conditioning device and easily performed up to 80 trials per day. In Experiment 1, zebrafish efficiently discriminated between two differently coloured sides, reaching a 75 % accuracy in only 10 training sessions. Surprisingly, zebrafish failed to choose the correct chamber when the stimuli were two shapes, a small circle and a small triangle, even when, in Experiment 2, training on shape discrimination was prolonged for up to 30 sessions. In Experiment 3, we tested the hypothesis that simultaneously learning to use the conditioning chamber and learning discrimination imposes a too-high cognitive load. However, zebrafish that first successfully learned how the conditioning chamber functioned (in the colour discrimination) subsequently failed in the shape discrimination. Conversely, zebrafish that firstly failed the shape discrimination subsequently learned colour discrimination. In Experiment 4, zebrafish showed some evidence of learning when the stimuli were two large shapes, suggesting that zebrafish did not discriminate between the shapes of the previous experiments because they were not salient enough. Altogether, results suggest constraints in the discrimination learning abilities of zebrafish, which should be taken into account when developing cognitive tasks for this species.

Inhibitory control in zebrafish, Danio rerio

We assessed whether zebrafish, Danio rerio, display inhibitory control using a simple and rapid behavioural test. Zebrafish were exposed to a prey stimulus placed inside a transparent tube, which initially elicited attack behaviour. However, zebrafish showed a rapid reduction in the number of attacks towards the prey, which indicated the ability to inhibit their foraging behaviour. Zebrafish also exhibited mnemonic retention of foraging inhibition, as indicated by a reduced number of attacks in a subsequent exposure to the unreachable prey. The ability to inhibit the foraging behaviour varied across three genetically separated wild-type strains and across different individuals within strains, suggesting that zebrafish show heritable within-species differences in inhibitory control. Our behavioural test might be suitable for screening large zebrafish populations in mutational studies and assessing the effects of pharmacologically active substances on inhibitory control.

Archerfish vision: Visual challenges faced by a predator with a unique hunting technique

Archerfish are well-known for their ballistic hunting behaviour, in which they shoot down aerial prey with a well-aimed jet of water. This unique hunting strategy poses several challenges for visual systems. Archerfish face significant distortion to the appearance of targets due to refraction at the air/water interface, they search for prey against a complex background of foliage, they change prey targeting behaviour as conditions change, and they must make high speed decisions to avoid competition. By studying how archerfish have overcome these challenges, we have been able to understand more about fundamental problems faced by visual systems and the mechanisms used to solve them. In some cases, such as when searching for targets, the visual capabilities of archerfish are functionally similar to those of humans, despite significant differences in neuroanatomy. In other cases, the particular challenge faced by archerfish magnifies fundamental problems generally faced by visual systems, such as recognizing objects given strong viewpoint dependent changes to appearance. The efficiency of archerfish retrieving fallen prey to avoid kleptoparasitism, demonstrates that their visual processing excels in both speed and accuracy. In this review, we attempt to provide an overview of the many facets of visually driven behaviour of archerfish, and how they have been studied. In addition to their hunting technique, archerfish are ideal for visual processing experiments as they can be quickly trained to perform a range of non-ecologically relevant tasks. Their behavioural flexibility moreover, introduces the opportunity to study how experience-dependence and choice affects visual processing.

Cellular and Network Mechanisms May Generate Sparse Coding of Sequential Object Encounters in Hippocampal-Like Circuits

The localization of distinct landmarks plays a crucial role in encoding new spatial memories. In mammals, this function is performed by hippocampal neurons that sparsely encode an animal’s location relative to surrounding objects. Similarly, the dorsolateral pallium (DL) is essential for spatial learning in teleost fish. The DL of weakly electric gymnotiform fish receives both electrosensory and visual input from the preglomerular nucleus (PG), which has been hypothesized to encode the temporal sequence of electrosensory or visual landmark/food encounters. Here, we show that DL neurons in the Apteronotid fish and in the Carassius auratus (goldfish) have a hyperpolarized resting membrane potential (RMP) combined with a high and dynamic spike threshold that increases following each spike. Current-evoked spikes in DL cells are followed by a strong small-conductance calcium-activated potassium channel (SK)-mediated after-hyperpolarizing potential (AHP). Together, these properties prevent high frequency and continuous spiking. The resulting sparseness of discharge and dynamic threshold suggest that DL neurons meet theoretical requirements for generating spatial memory engrams by decoding the landmark/food encounter sequences encoded by PG neurons. Thus, DL neurons in teleost fish may provide a promising, simple system to study the core cell and network mechanisms underlying spatial memory.

Long-range neural inhibition and stimulus competition in the archerfish optic tectum

The archerfish, which is unique in its ability to hunt insects above the water level by shooting a jet of water at its prey, operates in a complex visual environment. The fish needs to quickly select one object from among many others. In animals other than the archerfish, long-range inhibition is considered to drive selection. As a result of long-range inhibition, a potential target outside a neuron's receptive field suppresses the activity elicited by another potential target within the receptive field. We tested whether a similar mechanism operates in the archerfish by recording the activity of neurons in the optic tectum while presenting a target stimulus inside the receptive field and a competing stimulus outside the receptive field. We held the features of the target constant while varying the size, speed, and distance of the competing stimulus. We found cells that exhibit long-range inhibition; i.e., inhibition that extends to a significant part of the entire visual field of the animal. The competing stimulus depressed the firing rate. In some neurons, this effect was dependent on the features of the competing stimulus. These findings suggest that long-range inhibition may play a crucial role in the target selection process in the archerfish.

Hunting in archerfish - an ecological perspective on a remarkable combination of skills

Archerfish are well known for using jets of water to dislodge distant aerial prey from twigs or leaves. This Review gives a brief overview of a number of skills that the fish need to secure prey with their shooting technique. Archerfish are opportunistic hunters and, even in the wild, shoot at artificial objects to determine whether these are rewarding. They can detect non-moving targets and use efficient search strategies with characteristics of human visual search. Their learning of how to engage targets can be remarkably efficient and can show impressive degrees of generalization, including learning from observation. In other cases, however, the fish seem unable to learn and it requires some understanding of the ecological and biophysical constraints to appreciate why. The act of shooting has turned out not to be of a simple all-or-none character. Rather, the fish adjust the volume of water fired according to target size and use fine adjustments in the timing of their mouth opening and closing manoeuvre to adjust the hydrodynamic stability of their jets to target distance. As soon as prey is dislodged and starts falling, the fish make rapid and yet sophisticated multi-dimensional decisions to secure their prey against many intraspecific and interspecific competitors. Although it is not known why and how archerfish evolved an ability to shoot in the first place, I suggest that the evolution of shooting has strongly pushed the co-evolution of diverse other skills that are needed to secure a catch.

Does Holistic Processing Require a Large Brain? Insights From Honeybees and Wasps in Fine Visual Recognition Tasks

The expertise of humans for recognizing faces is largely based on holistic processing mechanism, a sophisticated cognitive process that develops with visual experience. The various visual features of a face are thus glued together and treated by the brain as a unique stimulus, facilitating robust recognition. Holistic processing is known to facilitate fine discrimination of highly similar visual stimuli, and involves specialized brain areas in humans and other primates. Although holistic processing is most typically employed with face stimuli, subjects can also learn to apply similar image analysis mechanisms when gaining expertise in discriminating novel visual objects, like becoming experts in recognizing birds or cars. Here, we ask if holistic processing with expertise might be a mechanism employed by the comparatively miniature brains of insects. We thus test whether honeybees (Apis mellifera) and/or wasps (Vespula vulgaris) can use holistic-like processing with experience to recognize images of human faces, or Navon-like parameterized-stimuli. These insect species are excellent visual learners and have previously shown ability to discriminate human face stimuli using configural type processing. Freely flying bees and wasps were consequently confronted with classical tests for holistic processing, the part-whole effect and the composite-face effect. Both species could learn similar faces from a standard face recognition test used for humans, and their performance in transfer tests was consistent with holistic processing as defined for studies on humans. Tests with parameterized stimuli also revealed a capacity of honeybees, but not wasps, to process complex visual information in a holistic way, suggesting that such sophisticated visual processing may be far more spread within the animal kingdom than previously thought, although may depend on ecological constraints.

New encoding concepts for shape recognition are needed

Models designed to explain how shapes are perceived and stored by the nervous system commonly emphasize encoding of contour features, especially orientation, curvature, and linear extent. A number of experiments from my laboratory provide evidence that contours deliver a multitude of location markers, and shapes can be identified when relatively few of the markers are displayed. The emphasis on filtering for orientation and other contour features has directed attention away from full and effective examination of how the location information is registered and used for summarizing shapes. Neural network (connectionist) models try to deal with location information by modifying linkage among neuronal populations through training trials. Connections that are initially diffuse and not useful in achieving recognition get eliminated or changed in strength, resulting in selective response to a given shape. But results from my laboratory, reviewed here, demonstrate that unknown shapes that are displayed only once can be identified using a matching task. These findings show that our visual system can immediately encode shape information with no requirement for training trials. This encoding might be accomplished by neuronal circuits in the retina.

What a predator can teach us about visual processing: a lesson from the archerfish

The archerfish is a predator with highly unusual visually guided behavior. It is most famous for its ability to hunt by shooting water jets at static or dynamic insect prey, up to two meters above the water's surface. In the lab, the archerfish can learn to distinguish and shoot at artificial targets presented on a computer screen, thus enabling well-controlled experiments. In recent years, these capacities have turned the archerfish into a model animal for studying a variety of visual functions, from visual saliency and visual search, through fast visually guided prediction, and all the way to higher level visual processing such as face recognition. Here we review these recent developments and show how they fall into two emerging lines of research on this animal model. The first is ethologically motivated and emphasizes how the natural environment and habitat of the archerfish interact with its visual processing during predation. The second is driven by parallels to the primate brain and aims to determine whether the latter's characteristic visual information processing capacities can also be found in the qualitatively different fish brain, thereby underscoring the functional universality of certain visual processes. We discuss the differences between these two lines of research and possible future directions.

Triggerfish uses chromaticity and lightness for object segregation

Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is asked to detect a pattern made up of dots of similar colour with variable lightness against a background of dots made from different colour(s) and lightness. To find out if fish use colour for object segregation in a similar manner to humans, we used stimuli inspired by the Ishihara test. Triggerfish (Rhinecanthus aculeatus) were trained to detect a cross constructed from similarly coloured dots against various backgrounds. Fish detected this cross even when it was camouflaged using either achromatic or chromatic noise, but fish relied more on chromatic cues for shape segregation. It remains unknown whether fish may switch to rely primarily on achromatic cues in scenarios where target objects have higher achromatic contrast and lower chromatic contrast. Fish were also able to generalize between stimuli of different colours, suggesting that colour and shape are processed by fish independently.

Endogenous orienting in the archer fish

The literature has long emphasized the neocortex's role in volitional processes. In this work, we examined endogenous orienting in an evolutionarily older species, the archer fish, which lacks neocortex-like cells. We used Posner's classic endogenous cuing task, in which a centrally presented, spatially informative cue is followed by a target. The fish responded to the target by shooting a stream of water at it. Interestingly, the fish demonstrated a human-like "volitional" facilitation effect: their reaction times to targets that appeared on the side indicated by the precue were faster than their reaction times to targets on the opposite side. The fish also exhibited inhibition of return, an aftermath of orienting that commonly emerges only in reflexive orienting tasks in human participants. We believe that this pattern demonstrates the acquisition of an arbitrary connection between spatial orienting and a nonspatial feature of a centrally presented stimulus in nonprimate species. In the literature on human attention, orienting in response to such contingencies has been strongly associated with volitional control. We discuss the implications of these results for the evolution of orienting, and for the study of volitional processes in all species, including humans.

Archer fish jumping prey capture: kinematics and hydrodynamics

Smallscale archer fish, Toxotes microlepis, are best known for spitting jets of water to capture prey, but also hunt by jumping out of the water to heights of up to 2.5 body lengths. In this study, high-speed imaging and particle image velocimetry were used to characterize the kinematics and hydrodynamics of this jumping behavior. Jumping used a set of kinematics distinct from those of in-water feeding strikes and was segmented into three phases: (1) hovering to sight prey at the surface, (2) rapid upward thrust production and (3) gliding to the prey once out of the water. The number of propulsive tail strokes positively correlated with the height of the bait, as did the peak body velocity observed during a jump. During the gliding stage, the fish traveled ballistically; the kinetic energy when the fish left the water balanced with the change in potential energy from water exit to the maximum jump height. The ballistic estimate of the mechanical energy required to jump was comparable with the estimated mechanical energy requirements of spitting a jet with sufficient momentum to down prey and subsequently pursuing the prey in water. Particle image velocimetry showed that, in addition to the caudal fin, the wakes of the anal, pectoral and dorsal fins were of nontrivial strength, especially at the onset of thrust production. During jump initiation, these fins were used to produce as much vertical acceleration as possible given the spatial constraint of starting directly at the water's surface to aim.