Artificial Stimuli Research Articles

Field experiments on the effectiveness of ‘eyespots’ as predator deterrents

Many potential prey species possess features that falsely convey a risk to the predator. One form of visual signal hypothesized to have this function are the circular features commonly found on the wings of diurnal lepidopterans: ‘eyespots’. Eyespots have been found to reduce predation by intimidating predators before an attack or startling them once an attack has been initiated, and have been proposed to work because predators falsely classify the markings as the eyes of the predators' own enemies. However, this argument lacks unambiguous experimental support because the data are consistent with the hypothesis that eyespots are effective merely because they are highly conspicuous. High contrast concentric circles are liable to be highly effective in stimulating the centre-surround arrangement of receptive fields typical of the vertebrate retina. Here, we use a field technique involving artificial moth-like stimuli, with or without different forms of grey-scale eyespots, to test these two opposing hypotheses. Across five experiments, the consistent effect is that predation risk is reduced by patterns that have high internal pattern contrast and also contrast highly with the target background, irrespective of the specific pattern arrangement. Circles are more effective than less eye-like shapes, but this constitutes only limited support for the eye-mimicry hypothesis because such patterns will also be highly conspicuous to animals with circular receptive fields in their retinae. We conclude that, contrary to popular belief, ‘eyespots’ can be effective predator deterrents without mimicking eyes.

Culture of triploid greenlip abalone ( Haliotis laevigata Donovan) to market size: Commercial implications

Triploid greenlip abalone ( Haliotis laevigata) were produced via a 15 min exposure to 100 μM 6-dimethylaminopurine at 20 min post-fertilization and grown under commercial conditions for up to 48 months. Differential mortality of the ploidy classes resulted in a decline in the proportion of triploid abalone from 83% in trochophores (2 h post-hatch), 55% in post-larvae (29 days post-hatch) and 50% in adults. A random sample of 540 juvenile triploid and diploid abalone from the same cohort were tagged, biopsied (for ploidy determination), weighed and measured at 13 months. Measurements of the tagged abalone for growth were recorded at 17, 25, 32, 36, 39, 42, and 48 months, and sampling for meat yield performed at 36, 42 and 48 months. There were significant differences in the length and weight of diploid and triploid abalone by 13 months, with the latter being impaired by the equivalent of 23 to 25 days growth by this time. Comparisons of growth from 13 to 48 months showed that diploid abalone were consistently 11–15% longer than their triploid siblings. However, larger triploid abalone yielded up to 30% higher meat weight than diploid abalone of comparable length during the spring–summer maturation periods (at 36 and 48 months), making harvesting of triploid abalone for canned product at this time cost effective. Diploid abalone exhibited compensatory growth and had meat weights comparable to those of triploids between the maturation periods (at 42 months). The fatty acid composition of the meat from 48 month old greenlip abalone was not affected by ploidy, maturity or sex. Half of the triploid abalone were male and most of the remainder did not develop gonad. Attempts to spawn triploid abalone were unsuccessful as females did not mature and those males which did mature, failed to respond to artificial spawning stimuli.

Comparative Source Localization of Electrically and Pressure-Stimulated Multichannel Somatosensory Evoked Potentials

The purpose of the study was to determine if there is a difference in the determination of the cortical hand area by dipole source estimation after artificial and natural stimuli. In principle, there are advantages of both methods: pressure stimulation is less invasive and compatible to fMRI, whereas electrical stimulation can be applied with higher stimulus rates and elicits sharper waveforms. Electrical and pressure stimulation was performed simultaneously on the thumb and fifth finger on eight healthy volunteers. The somatosensory evoked potentials after electrical stimulation showed sharper peaks and higher amplitudes than the pressure stimulated potentials. For the two stimulus qualities, cortical source positions of thumb and fifth finger separated significantly in the vertical z-axis. Both methods deliver reliable stimulation and therefore allow separate source localization of thumb and fifth finger. For cortical plasticity studies, peripheral somatosensory stimulation is of great importance. According to these findings, the choice of method, electrical or mechanical stimulation, may depend on practical criteria.

Human Placental Hypoxia-Inducible Factor-1α Expression Correlates with Clinical Outcomes in Chronic Hypoxia in Vivo

Placental hypoxia is causally implicated in fetal growth restriction and preeclampsia, with both occurring more frequently at high altitude (>2700 m; HA). The nuclear transcription factor hypoxia-inducible factor (HIF) may facilitate placental oxygen transport at HA by increasing erythropoiesis and placental angiogenesis. We therefore investigated HIF expression and its regulatory mechanisms in placentas from normal pregnancies at high (3100 m), moderate (1600 m), and sea level (75 m) altitudes. Moderate-altitude and sea level placentas did not differ, but HIF-1alpha and the von Hippel-Lindau tumor suppressor protein were overexpressed in HA placentas. The ability of von Hippel-Lindau tumor suppressor protein to form the E3 ubiquitin protein ligase complex, required for HIF-1alpha degradation, was unaltered in HA placentas. mRNA for factor-inhibiting HIF, a negative modulator of HIF-1alpha transactivation, was increased, but protein levels were diminished. Elevated HIF-1alpha likely contributed to the significant increase we report in HIF-1alpha downstream target proteins, transforming growth factor beta3 in the placenta, and vascular endothelial growth factor and erythropoietin in the maternal circulation. These circulating markers and lowered birth to placental weight ratios correlated with increased HIF-1alpha, thereby linking molecular and systemic physiological data. The HA response to chronic hypoxia resembles preeclampsia in several aspects, illustrating the utility of the HA model in understanding placental pathologies.

Incidental Teaching of Age-Appropriate Social Phrases to Children with Autism

Successful inclusion is facilitated when children with autism fit in and interact in meaningful ways with their typical peers. However, deficits in conversational language likely limit the social attractiveness of children with autism to their classmates. This study evaluated an incidental teaching approach to promoting use of age-appropriate social phrases by three preschool-aged boys with autism. A multiple baseline design demonstrated that introduction of incidental teaching yielded immediate use of the targeted social phrases (“All right” and “You know what?”) during instructional sessions, and children transferred use of the new social phrases to unprompted conditions. Initial instruction required somewhat artificial stimulus—response relationships to compensate for the lack of responsiveness to social consequences that characterizes autism. However, as in other studies in which conversational language was successfully taught to children with autism, systematic fading procedures facilitated transfer of stimulus control from the contrived cues needed to teach a child with autism to say age-appropriate social phrases to conditions that call for comments and queries in everyday situations.

Discrimination of artificial polymorphous categories by rhesus monkeys (Macaca mulatta).

Monkeys (Macaca mulatta) were trained to discriminate between sets of artificial stimuli such as those used by Jitsumori (1993) for pigeons and humans. The stimuli were arrays of symbols differing along three two-valued (positive or negative) dimensions. The discrimination required was between polymorphous categories in which a positive stimulus was defined by possession of any 2 out of 3 positive features. Of the 5 monkeys, 3 learned the discrimination much faster than did pigeons, but transfer to novel stimuli was less impressive than had been shown in pigeons. The 3 monkeys showed high levels of transfer to the stimuli that contained either all 3 positive or all 3 negative features, but 2 of the 3 monkeys failed to show transfer to stimuli that had 1 of the 3 features replaced with a novel one. Analysis of the monkeys' performance raised doubts on the additive integration of features but supported learning of feature combinations as a basis for the discrimination of polymorphous categories by this species.

Enhancement of Visual Responsiveness by Spontaneous Local Network Activity In Vivo

Spontaneous activity within local circuits affects the integrative properties of neurons and networks. We have previously shown that neocortical network activity exhibits a balance between excitatory and inhibitory synaptic potentials, and such activity has significant effects on synaptic transmission, action potential generation, and spike timing. However, whether such activity facilitates or reduces sensory responses has yet to be clearly determined. We examined this hypothesis in the primary visual cortex in vivo during slow oscillations in ketamine-xylazine anesthetized cats. We measured network activity (Up states) with extracellular recording, while simultaneously recording postsynaptic potentials (PSPs) and action potentials in nearby cells. Stimulating the receptive field revealed that spiking responses of both simple and complex cells were significantly enhanced (>2-fold) during network activity, as were spiking responses to intracellular injection of varying amplitude artificial conductance stimuli. Visually evoked PSPs were not significantly different in amplitude during network activity or quiescence; instead, spontaneous depolarization caused by network activity brought these evoked PSPs closer to firing threshold. Further examination revealed that visual responsiveness was gradually enhanced by progressive membrane potential depolarization. These spontaneous depolarizations enhanced responsiveness to stimuli of varying contrasts, resulting in an upward (multiplicative) scaling of the contrast response function. Our results suggest that small increases in ongoing balanced network activity that result in depolarization may provide a rapid and generalized mechanism to control the responsiveness (gain) of cortical neurons, such as occurs during shifts in spatial attention.

Adaptive WTA With an Analog VLSI Neuromorphic Learning Chip

In this paper, we demonstrate how a particular spike-based learning rule (where exact temporal relations between input and output spikes of a spiking model neuron determine the changes of the synaptic weights) can be tuned to express rate-based classical Hebbian learning behavior (where the average input and output spike rates are sufficient to describe the synaptic changes). This shift in behavior is controlled by the input statistic and by a single time constant. The learning rule has been implemented in a neuromorphic very large scale integration (VLSI) chip as part of a neurally inspired spike signal image processing system. The latter is the result of the European Union research project Convolution AER Vision Architecture for Real-Time (CAVIAR). Since it is implemented as a spike-based learning rule (which is most convenient in the overall spike-based system), even if it is tuned to show rate behavior, no explicit long-term average signals are computed on the chip. We show the rule's rate-based Hebbian learning ability in a classification task in both simulation and chip experiment, first with artificial stimuli and then with sensor input from the CAVIAR system.

The duration of the attentional blink in natural scenes depends on stimulus category

Humans comprehend the “gist” of even a complex natural scene within a small fraction of a second. If, however, observers are asked to detect targets in a sequence of rapidly presented items, recognition of a target succeeding another target by about a third of a second is severely impaired, the “attentional blink” (AB) [Raymond, J. E., Shapiro, K. L., & Arnell, K. M. (1992). Temporary suppression of visual processing in an RSVP task: an attentional blink? Journal of Experimental Psychology. Human Perception and Performance, 18, 849–860]. Since most experiments on the AB use well controlled but artificial stimuli, the question arises whether the same phenomenon occurs for complex, natural stimuli, and if so, whether its specifics depend on stimulus category. Here we presented rapid sequences of complex stimuli (photographs of objects, scenes and faces) and asked observers to detect and remember items of a specific category (either faces, watches, or both). We found a consistent AB for both target categories but the duration of the AB depended on the target category.

Sound Transmission and Song Divergence: A Comparison of Urban and Forest Acoustics

AbstractAbstractDegradation of acoustic signals during transmission presents a challenging selection pressure for animals dependent on vocal communication. Sound transmission properties differ among habitats and may drive the evolution of vocal signals in different directions. Urban habitat is expanding worldwide and an increasing number of species, including many birds, must now communicate around buildings and over concrete. Urban habitats are evolutionarily new, although to some extent they may acoustically resemble rocky habitat such as cliffs and canyons. Neither urban nor these natural habitats have been studied in any detail for the selection pressure they may exert on animal communication. Dark-eyed Juncos (Junco hyemalis) commonly inhabit montane pine forests across North America, but for about 25 years an isolated population has been successfully breeding in an urban environment in southern California. We investigated potentially divergent selection pressures on junco songs, using sound transmission experiments with artificial sound stimuli, in natural forest habitat and in this urban habitat. Transmission properties differed significantly, resulting in tails of reflected sound with gradually declining amplitude in the forest and in multiple discrete echoes in the urban environment. We expected environmental selection in urban habitat to favor shorter songs with higher frequencies and slower trill rates. Despite the presence of relatively short urban songs, there was no significant shortening overall. There were also no differences in trill rates, but we did find a significantly higher minimum frequency in the urban junco population compared to three of four forest populations. Although the pattern of song divergence was not consistent and it is difficult to draw firm conclusions from this single urban population, our transmission results suggest that echoes could be important in shaping urban birdsong.

High-altitude hypoxia and preeclampsia

The influence of hypoxia (lowered arterial blood and/or tissue PO2) on fetoplacental development and the role of hypoxia in preeclampsia are major research foci in perinatal biology. While animal and cell models are of utility, we do not know whether artificial hypoxic stimuli mimic the pathological conditions attributed to hypoxic stress in vivo; we cannot distinguish the effects of hypoxia from under- or overlying pathologies. High altitude (>2700 m) is the natural experiment we can use to distinguish pathology from adaptation in human pregnancy. The two best known impacts of high altitude on pregnancy outcome are reduced fetal growth and an increased incidence preeclampsia. This review focuses on the mechanisms by which altitude increases maternal risk for the development of preeclampsia. The review first considers the evidence that placental hypoxia is causally involved in the development of preeclampsia. It then focuses on how data from studies of pregnant women at high altitude support (or do not support) etiological models of preeclampsia. Considered are the theories that reduced uteroplacental blood flow, circulating factors of placental origin, placental oxidative stress and increased maternal vascular reactivity are etiological in preeclampsia. The data suggest that oxidative stress and endothelial dysfunction have pathophysiological origins that are independent of placental hypoxia. We conclude that altitude shifts the individual risk for the development of preeclampsia because of impacts on multiple physiological systems, no one of which can be specifically pointed to as causal.

Sound the alarm: learned association of predation risk with novel auditory stimuli by fathead minnows (Pimephales promelas) and glowlight tetras (Hemigrammus erythrozonus) after single simultaneous pairings with conspecific chemical alarm cues

Fathead minnows, Pimephales promelas, and glowlight tetras, Hemigrammus erythrozonus, were tested for their ability to associate predation risk with novel auditory stimuli after auditory stimuli were presented simultaneously with chemical alarm cues. Minnows and tetras gave a fright response when exposed to skin extract (alarm cue) and an artificial auditory sound stimulus, but no response to water (control) and sound, indicating that they did not have a pre-existing aversion to the auditory stimulus. When retested with sound stimuli alone, minnows and glowlight tetras that had previously been conditioned with water and sound showed no response, but those that had been conditioned with alarm cues and sound exhibited antipredator behaviour (reduced activity) in response to the auditory cue. This is the first known demonstration of learned association of an auditory cue with predation risk, and raises questions about the role of sound in mediating predator-prey interactions in fishes.

The role of presence in virtual reality exposure therapy

A growing body of literature suggests that virtual reality is a successful tool for exposure therapy in the treatment of anxiety disorders. Virtual reality (VR) researchers posit the construct of presence, defined as the interpretation of an artificial stimulus as if it were real, to be a presumed factor that enables anxiety to be felt during virtual reality exposure therapy (VRE). However, a handful of empirical studies on the relation between presence and anxiety in VRE have yielded mixed findings. The current study tested the following hypotheses about the relation between presence and anxiety in VRE with a clinical sample of fearful flyers: (1) presence is related to in-session anxiety; (2) presence mediates the extent that pre-existing (pre-treatment) anxiety is experienced during exposure with VR; (3) presence is positively related to the amount of phobic elements included within the virtual environment; (4) presence is related to treatment outcome. Results supported presence as a factor that contributes to the experience of anxiety in the virtual environment as well as a relation between presence and the phobic elements, but did not support a relation between presence and treatment outcome. The study suggests that presence may be a necessary but insufficient requirement for successful VRE.

The role of functional information for infant categorization

This report examines whether knowledge about function influences the formation of artifact categories in 11–12- month old infants. Using an object-examination task, a set of artificial stimuli was presented that could either be grouped according to overall similarity or according to similarity in one functionally relevant part. Experiment 1 revealed that infants categorized the objects according to overall similarity but not part similarity under control conditions. Experiment 2 showed that after having seen the experimenter demonstrating the functional use of the critical part, infants later categorized the stimuli according to part similarity. When the same actions were performed without producing any effect, infants failed to categorize according to the critical part. This set of findings suggests that 11–12-month old infants use functional information as a cue to categorization.

Heat stress‐induced apoptosis in porcine in vitro fertilized and parthenogenetic preimplantation‐stage embryos

Decades worth of research have consistently shown the adverse effects of elevated temperatures on reproductive parameters of livestock species. The objective of this study was to evaluate the developmental and apoptotic responses of porcine in vitro fertilized (IVF) and parthenogenetically activated (PA) embryos heat stressed at the late 1-cell stage. Embryos were heat stressed (HS) at 42 degrees C for 9 hr starting 22 hr after insemination or artificial activation stimulus. Non heat-stressed (NHS) control embryos were maintained at 39 degrees C for the duration of the experiments. TUNEL staining on Day 5 of development demonstrated that heat stress elicited a significant apoptotic response in IVF embryos (45.6% of HS embryos and 26.7% of NHS embryos were apoptotic; P<0.05), but not in PA embryos (51.1% and 39.9% for HS and NHS embryos, respectively; P>0.1). And, while IVF embryos were highly susceptible to heat-induced developmental perturbations (20.6% and 8.8% development to blastocyst for NHS and HS embryos, respectively; P<0.05), elevated temperatures did not affect blastocyst rates in PA embryos (22.2% for NHS PA embryos and 21.2% for HS PA embryos; P>0.1). These findings indicate that, as in other systems studied, IVF pig embryos are directly affected adversely by heat stress conditions. Parthenogenetic embryos, though, appear to be surprisingly tolerant of the elevated temperatures. The differences between IVF and PA embryos in their response to heat stress warrants further investigation.

Effects of artificial social stimuli on the reproductive schedule and hormone levels of yellow-eyed penguins ( Megadyptes antipodes)

The effects of social stimuli on avian reproductive behaviors such as breeding schedules and courtship behaviors are well known due to numerous field studies. However, studies that have simultaneously examined the effects of social stimuli on reproductive behavior and the mediating endocrine mechanisms have been largely restricted to captive populations, which may not be representative of free-living populations. This study, conducted over two breeding seasons, aimed to simultaneously measure the effects of experimentally increasing auditory stimuli on the breeding schedule and endocrinology (levels of total androgen, estradiol, progesterone and prolactin) on free-living yellow-eyed penguins ( Megadyptes antipodes). The yellow-eyed penguin is the least colonial of all penguins, nesting far apart from each other under dense vegetation, and, therefore, is presumed to experience much lower levels of social stimuli than other penguins. Egg laying was significantly more synchronous and tended to be earlier when birds were exposed to playbacks of the calls of conspecifics in 1 year of the study. We also found that levels of total androgen and estradiol of males in 1 year, and prolactin in another year, were proportionally higher among treated birds compared control birds that received no artificial auditory stimuli. These results show that even among supposedly solitary nesters, social stimuli could still play a role in influencing reproductive behavior and physiology. For the first time in free-living seabirds, we have demonstrated that behavioral responses to increased social stimuli are associated with hormonal changes.

Neural correlates of monocular and binocular depth cues based on natural images: A LORETA analysis

Functional imaging studies investigating perception of depth rely solely on one type of depth cue based on non-natural stimulus material. To overcome these limitations and to provide a more realistic and complete set of depth cues natural stereoscopic images were used in this study. Using slow cortical potentials and source localization we aimed to identify the neural correlates of monocular and binocular depth cues. This study confirms and extends functional imaging studies, showing that natural images provide a good, reliable, and more realistic alternative to artificial stimuli, and demonstrates the possibility to separate the processing of different depth cues.

Behavioural examination of the infrared sensitivity of rattlesnakes (Crotalus atrox)

Pitvipers (Crotalinae) and boid snakes (Boidae) possess highly sensitive infrared (IR) receptors. The ability of these snakes to image IR radiation allows the assessment of the direction and distance of an IR source (such as warm-blooded prey) in the absence of visual cues. The aim of this study was to determine the behavioural threshold of snakes to an IR stimulus. A moving IR source of constant size and temperature was presented to rattlesnakes (Crotalus atrox) at various distances (10-160 cm) from their snout. The snakes' responses were quantified by measuring distinct behavioural changes during stimulus presentation (head jerks, head fixed, freezing, rattling and tongue-flicking). The results revealed that C. atrox can detect an artificial IR stimulus resembling a mouse in temperature and size up to a distance of 100 cm, which corresponds to a radiation density of 3.35 x 10(-3) mW/cm2. These behavioural results reveal a 3.2 times higher sensitivity to IR radiation than earlier electrophysiological investigations.

Vision as Bayesian inference: analysis by synthesis?

We argue that the study of human vision should be aimed at determining how humans perform natural tasks with natural images. Attempts to understand the phenomenology of vision from artificial stimuli, although worthwhile as a starting point, can lead to faulty generalizations about visual systems, because of the enormous complexity of natural images. Dealing with this complexity is daunting, but Bayesian inference on structured probability distributions offers the ability to design theories of vision that can deal with the complexity of natural images, and that use 'analysis by synthesis' strategies with intriguing similarities to the brain. We examine these strategies using recent examples from computer vision, and outline some important implications for cognitive science.

Hierarchical feed-forward network for object detection tasks

Recent research on neocognitron-like neural feed-forward architectures, which have formerly been successfully applied to the recognition of artificial stimuli such as paperclip objects, now also opens up application to more natural stimuli. Such networks exhibit high-recognition performance with respect to translation, rotation, scaling and cluttered surroundings. In this contribution, we introduce a new type of hierarchical model, which is trained using a non-negative matrix factorization algorithm. In contrast to previous work, our approach cannot only classify objects but is also capable of rapid object detection in natural scenes. Thus, the time-consuming and conceptually unsatisfying split-up into a localization stage (e.g., using segmentation) and a subsequent classification can be avoided. The network consists of alternating layers of simple and complex cell planes and incorporates nonlinear processing schemes that have been proposed in recent literature. Learning of receptive field profiles for the lower layers of the network takes place by unsupervised learning whereas a final classification layer is trained supervised. This final layer is then utilized for detection. We test the classification performance of the network on images of natural objects which are systematically distorted. To test the ability to detect objects, cluttered natural background is used.