Looming Stimuli Research Articles

How Auditory Information Influences Volitional Control in Binocular Rivalry: Modulation of a Top-Down Attentional Effect

Although multistable perception has long been studied, in recent years, paradigms involving ambiguous visual stimuli have been used to assess phenomenal awareness. Indeed, for such stimuli, although the sensory input is invariant, a perceptual decision occurs bringing to awareness only one of the possible interpretations. Moreover, the observer experiences inevitable oscillations between these percepts. Only few studies have tackled bistability for multimodal percepts. Conrad et al. [1] presented dot fields going in opposite direction to each eye, they found that lateral sound motion prolongs the dominance duration of the coherent visual motion percept and not the other. In this study, the volitional control—the capacity to promote a given percept—was not assessed. Van Ee et al. [2] tested how sensory congruency influences volitional control using looming motion stimuli that could be seen, heard or sensed on the hand. They found that attention to the additional modality (sound or touch) has to be engaged ...

Three-dimensional reconstruction of the fast-start swimming kinematics of densely schooling fish

Information transmission via non-verbal cues such as a fright response can be quantified in a fish school by reconstructing individual fish motion in three dimensions. In this paper, we describe an automated tracking framework to reconstruct the full-body trajectories of densely schooling fish using two-dimensional silhouettes in multiple cameras. We model the shape of each fish as a series of elliptical cross sections along a flexible midline. We estimate the size of each ellipse using an iterated extended Kalman filter. The shape model is used in a model-based tracking framework in which simulated annealing is applied at each step to estimate the midline. Results are presented for eight fish with occlusions. The tracking system is currently being used to investigate fast-start behaviour of schooling fish in response to looming stimuli.

Behavioural relevance of polarization sensitivity as a target detection mechanism in cephalopods and fishes.

Aquatic habitats are rich in polarized patterns that could provide valuable information about the environment to an animal with a visual system sensitive to polarization of light. Both cephalopods and fishes have been shown to behaviourally respond to polarized light cues, suggesting that polarization sensitivity (PS) may play a role in improving target detection and/or navigation/orientation. However, while there is general agreement concerning the presence of PS in cephalopods and some fish species, its functional significance remains uncertain. Testing the role of PS in predator or prey detection seems an excellent paradigm with which to study the contribution of PS to the sensory assets of both groups, because such behaviours are critical to survival. We developed a novel experimental set-up to deliver computer-generated, controllable, polarized stimuli to free-swimming cephalopods and fishes with which we tested the behavioural relevance of PS using stimuli that evoke innate responses (such as an escape response from a looming stimulus and a pursuing behaviour of a small prey-like stimulus). We report consistent responses of cephalopods to looming stimuli presented in polarization and luminance contrast; however, none of the fishes tested responded to either the looming or the prey-like stimuli when presented in polarization contrast.

Psychological and Neural Mechanisms of Subjective Time Dilation

For a given physical duration, certain events can be experienced as subjectively longer in duration than others. Try this for yourself: take a quick glance at the second hand of a clock. Immediately, the tick will pause momentarily and appear to be longer than the subsequent ticks. Yet, they all last exactly 1 s. By and large, a deviant or an unexpected stimulus in a series of similar events (same duration, same features) can elicit a relative overestimation of subjective time (or “time dilation”) but, as is shown here, this is not always the case. We conducted an event-related functional magnetic neuroimaging study on the time dilation effect. Participants were presented with a series of five visual discs, all static and of equal duration (standards) except for the fourth one, a looming or a receding target. The duration of the target was systematically varied and participants judged whether it was shorter or longer than all other standards in the sequence. Subjective time dilation was observed for the looming stimulus but not for the receding one, which was estimated to be of equal duration to the standards. The neural activation for targets (looming and receding) contrasted with the standards revealed an increased activation of the anterior insula and of the anterior cingulate cortex. Contrasting the looming with the receding targets (i.e., capturing the time dilation effect proper) revealed a specific activation of cortical midline structures. The implication of midline structures in the time dilation illusion is here interpreted in the context of self-referential processes.

Synchronized Neural Input Shapes Stimulus Selectivity in a Collision-Detecting Neuron

How higher-order sensory neurons generate complex selectivity from their simpler inputs is a fundamental question in neuroscience. The lobula giant movement detector (LGMD) is such a visual neuron in the locust Schistocerca americana that responds selectively to objects approaching on a collision course or their two-dimensional projections, looming stimuli [1-4]. To study how this selectivity arises, we designed an apparatus allowing us to stimulate, individually and independently, a sizable fraction of the ∼15,000 elementary visual inputs impinging retinotopically onto the LGMD's dendritic fan [5-7] (Figure1Ai). We then recorded intracellularly invivo throughout the visual pathway, assessing the LGMD's activity and that of all three successive presynaptic stages conveying local excitatory inputs. Our results suggest that as collision becomes increasingly imminent, the strength of these inputs increases, whereas their latency decreases. This latency decrease favors summation of inputs activated sequentially throughout the looming sequence, making the neuron maximally sensitive to collision-bound trajectories. Thus, the LGMD's selectivity arises partially from presynaptic mechanisms that synchronize a large population of inputs during a looming stimulus and subsequent detection by postsynaptic mechanisms within the neuron itself. Analogous mechanisms are likely to underlie the tuning properties of visual neurons in other species as well.

Neural processing of imminent collision in humans

Detecting a looming object and its imminent collision is imperative to survival. For most humans, it is a fundamental aspect of daily activities such as driving, road crossing and participating in sport, yet little is known about how the brain both detects and responds to such stimuli. Here we use functional magnetic resonance imaging to assess neural response to looming stimuli in comparison with receding stimuli and motion-controlled static stimuli. We demonstrate for the first time that, in the human, the superior colliculus and the pulvinar nucleus of the thalamus respond to looming in addition to cortical regions associated with motor preparation. We also implicate the anterior insula in making timing computations for collision events.

A pair of motion-sensitive neurons in the locust encode approaches of a looming object

Neurons in the locust visual system encode approaches of looming stimuli and are implicated in production of escape behaviours. The lobula giant movement detector (LGMD) and its postsynaptic partner, the descending contralateral movement detector (DCMD) compute characteristics of expanding edges across the locust eye during a loom and DCMD synapses onto motor elements associated with behaviour. We identified another descending interneuron within the locust ventral nerve cord. We named this neuron the late DCMD (LDCMD) as it responds later during an approach, with the firing rate peaking at about the time of collision. LDCMD produced lower amplitude, broader action potentials that were associated with an afterhyperpolarization, whereas DCMD action potentials showed a brief afterhyperpolarization often followed by an afterdepolarization. Within the mesothoracic ganglion, the primary LDCMD axon located adjacent to the DCMD axon, was thinner and lacked collateral projections to the lateral region of the neuropil. When compared with DCMD, LDCMD fired with fewer spikes during a loom and showed weaker habituation to repeated approaches. Coincidence of LDCMD and DCMD firing increased during object approach. Our findings indicate the presence of an additional motion-sensitive descending neuron in the locust that encodes temporally distinct properties of an approaching object.

Neuropsychological evidence for a competitive bias against contracting stimuli

Two experiments examined extinction to stimuli presented either with contracting or expanding motion. Experiment 1 used solid shapes which either increased or decreased in size rapidly, consistent with looming motion. Experiment 2 employed random dots so that stimulus size was not confounded with type of motion. In both experiments extinction was modulated by the type of motion presented, with extinction most evident when a contracting object was in the weaker visual field. In addition, in Experiment 2 there was evidence for grouping modulating extinction, when there were looming stimuli in both fields. The results suggest that looming motion is a powerful determinant of stimulus salience in selective attention.

A modified model for the Lobula Giant Movement Detector and its FPGA implementation

Bio-inspired vision sensors are particularly appropriate candidates for navigation of vehicles or mobile robots due to their computational simplicity, allowing compact hardware implementations with low power dissipation. The Lobula Giant Movement Detector (LGMD) is a wide-field visual neuron located in the Lobula layer of the Locust nervous system. The LGMD increases its firing rate in response to both the velocity of an approaching object and the proximity of this object. It has been found that it can respond to looming stimuli very quickly and trigger avoidance reactions. It has been successfully applied in visual collision avoidance systems for vehicles and robots. This paper introduces a modified neural model for LGMD that provides additional depth direction information for the movement. The proposed model retains the simplicity of the previous model by adding only a few new cells. It has been simplified and implemented on a Field Programmable Gate Array (FPGA), taking advantage of the inherent parallelism exhibited by the LGMD, and tested on real-time video streams. Experimental results demonstrate the effectiveness as a fast motion detector.

Comparing binocular, biocular and monocular cues for time-to-contact

Judgements of time-to-contact (TTC) have been shown to be influenced by both monocular cues, such as looming, and binocular cues, such as changing disparity (Gray & Regan, 1998, Vision Research, 38: 499–512). We investigated the contribution of binocular motion information when presented in conjunction with monocular motion cues in a TTC task. We compared TTC judgements in three conditions, a) combined cue - consistent looming and changing disparity, b) monocular - looming showed to one eye only, c) biocular - both eyes presented with a looming stimulus but no change in disparity. Observers were shown a circular patch of dots which appeared to move directly toward them for 588ms at a constant speed, simulating one of three TTCs (1.8s, 2.5s or 3.2s). The stimulus was then replaced with a blank screen for a variable interval before the screen flashed. Observers were asked whether the stimulus would have contacted them before or after the flash, had it continued in its trajectory. This data was used to determine whether observers could perform a TTC judgement in the present task. Analysis suggested that four of eight observers' responses did not in fact reflect TTC judgements, but were based on other stimulus parameters. For those who based their responses on TTC information, we derived approximations of TTC estimates for each condition. Three of these four observers gave more accurate TTC estimates under the combined cue condition than monocular and biocular. No observer's responses differed between monocular and biocular conditions, suggesting that judgements in these conditions were based on monocular information only. The results lead us to conclude that under present conditions, binocular cues can aid TTC estimation when present and consistent with monocular cues, but no influence occurs when binocular information indicating zero motion is presented alongside monocular motion cues.

Alternation of Sound Location Induces Visual Motion Perception of a Static Object

BackgroundAudition provides important cues with regard to stimulus motion although vision may provide the most salient information. It has been reported that a sound of fixed intensity tends to be judged as decreasing in intensity after adaptation to looming visual stimuli or as increasing in intensity after adaptation to receding visual stimuli. This audiovisual interaction in motion aftereffects indicates that there are multimodal contributions to motion perception at early levels of sensory processing. However, there has been no report that sounds can induce the perception of visual motion.Methodology/Principal FindingsA visual stimulus blinking at a fixed location was perceived to be moving laterally when the flash onset was synchronized to an alternating left-right sound source. This illusory visual motion was strengthened with an increasing retinal eccentricity (2.5 deg to 20 deg) and occurred more frequently when the onsets of the audio and visual stimuli were synchronized.Conclusions/SignificanceWe clearly demonstrated that the alternation of sound location induces illusory visual motion when vision cannot provide accurate spatial information. The present findings strongly suggest that the neural representations of auditory and visual motion processing can bias each other, which yields the best estimates of external events in a complementary manner.

Spatiotemporal receptive field properties of a looming-sensitive neuron in solitarious and gregarious phases of the desert locust.

Desert locusts (Schistocerca gregaria) can transform reversibly between the swarming gregarious phase and a solitarious phase, which avoids other locusts. This transformation entails dramatic changes in morphology, physiology, and behavior. We have used the lobula giant movement detector (LGMD) and its postsynaptic target, the descending contralateral movement detector (DCMD), which are visual interneurons that detect looming objects, to analyze how differences in the visual ecology of the two phases are served by altered neuronal function. Solitarious locusts had larger eyes and a greater degree of binocular overlap than those of gregarious locusts. The receptive field to looming stimuli had a large central region of nearly equal response spanning 120 degrees x 60 degrees in both phases. The DCMDs of gregarious locusts responded more strongly than solitarious locusts and had a small caudolateral focus of even further sensitivity. More peripherally, the response was reduced in both phases, particularly ventrally, with gregarious locusts showing greater proportional decrease. Gregarious locusts showed less habituation to repeated looming stimuli along the eye equator than did solitarious locusts. By contrast, in other parts of the receptive field the degree of habituation was similar in both phases. The receptive field organization to looming stimuli contrasts strongly with the receptive field organization of the same neurons to nonlooming local-motion stimuli, which show much more pronounced regional variation. The DCMDs of both gregarious and solitarious locusts are able to detect approaching objects from across a wide expanse of visual space, but phase-specific changes in the spatiotemporal receptive field are linked to lifestyle changes.

Seeing it coming: infants’ brain responses to looming danger

A fundamental property of most animals is the ability to see whether an object is approaching on a direct collision course and, if so, when it will collide. Using high-density electroencephalography in 5- to 11-month-old infants and a looming stimulus approaching under three different accelerations, we investigated how the young human nervous system extracts and processes information for impending collision. Here, we show that infants' looming related brain activity is characterised by theta oscillations. Source analyses reveal clear localised activity in the visual cortex. Analysing the temporal dynamics of the source waveform, we provide evidence that the temporal structure of different looming stimuli is sustained during processing in the more mature infant brain, providing infants with increasingly veridical time-to-collision information about looming danger as they grow older and become more mobile.

Capture of Attention to Threatening Stimuli without Perceptual Awareness

Visual images that convey threatening information can automatically capture attention. One example is an object looming in the direction of the observer-presumably because such a stimulus signals an impending collision. A critical question for understanding the relationship between attention and conscious awareness is whether awareness is required for this type of prioritized attentional selection. Although it has been suggested that visual spatial attention can only be affected by consciously perceived events, we show that automatic allocation of attention can occur even without conscious awareness of impending threat. We used a visual search task to show that a looming stimulus on a collision path with an observer captures attention but a looming stimulus on a near-miss path does not. Critically, observers were unaware of any difference between collision and near-miss stimuli even when explicitly asked to discriminate between them in separate experiments. These results counter traditional salience-based models of attentional capture, demonstrating that in the absence of perceptual awareness, the visual system can extract behaviorally relevant details from a visual scene and automatically categorize threatening versus nonthreatening images at a level of precision beyond our conscious perceptual capabilities.

Temporal dynamics of travelling theta wave activity in infants responding to visual looming

AbstractA fundamental property of most animals is the ability to see whether an object is approaching on a direct collision course and, if so, when it will collide. Using high-density electroencephalography in 5- to 11-month-old infants and a looming stimulus approaching under three different accelerations, we investigated how the young human nervous system extracts and processes information for impending collision. Here we show that infants' looming related brain activity is characterized by theta oscillations. Source analyses reveal clear localised activity in the visual cortex. Analysing the temporal dynamics of the source waveform, we provide evidence that the temporal structure of different looming stimuli is sustained during processing in the more mature infant brain, providing infants with increasingly veridical time-to-collision information about looming danger as they grow older and become mobile.

Spike frequency adaptation mediates looming stimulus selectivity in a collision-detecting neuron

How active membrane conductance dynamics tunes neurons for specific time-varying stimuli remains poorly understood. We studied the biophysical mechanisms by which spike frequency adaptation shapes visual stimulus selectivity in an identified visual interneuron of the locust. The lobula giant movement detector (LGMD) responds preferentially to objects approaching on a collision course with the locust. Using calcium imaging, pharmacology and modeling, we show that spike frequency adaptation in the LGMD is mediated by a Ca(2+)-dependent potassium conductance closely resembling those associated with 'small-conductance' (SK) channels. Intracellular block of this conductance minimally affected the LGMD's response to approaching stimuli, but substantially increased its response to translating ones. Thus, spike frequency adaptation contributes to the neuron's tuning by selectively decreasing its responses to nonpreferred stimuli. Our results identify a new mechanism by which spike frequency adaptation may tune visual neurons to behaviorally relevant stimuli.

Speed sensitive excitation shapes the tuning of a collision-detecting neuron

Event Abstract Back to Event Speed sensitive excitation shapes the tuning of a collision-detecting neuron Motion detection, an ubiquitous computation performed by visual systems, is used to guide a range of vital behaviors, including escape from threats. The Lobula Giant Movement Detector (LGMD), an identified locust neuron in a neural pathway important for escape responses, has been found to be sensitive to stimulus speed but only weakly directionally selective. Both speed sensitivity and direction selectivity together are hallmarks of motion detection, thus we are interested, in this system, in how speed sensitivity alone is generated. We investigated a mechanism that relies solely upon the activation time-course of peripheral receptors as a speed signal by recording intracellularly at several stages along the visual processing pathway. We found that photoreceptor responses carry information about the speed of a moving edge in the slope their of membrane potential deflections, and that these responses can be well mimicked by stationary luminance changes of varying rate at single facets. Immediately post-synaptic to photoreceptors, large monopolar cells (LMCs) appear to transform variation of response slope to variation in response magnitude and timing, consistent with a high pass filtering of photoreceptor responses. LGMD responses to the same stimuli showed similar modulation in both magnitude and timing, showing that the motion speed sensitivity of the LGMD at least partially arises from changes in activation speed of individual photoreceptors. Since the LGMD integrates input originating from a large number of facets on the compound eye (~7,500), we are building a model to extrapolate from the modulation observed in single facet inputs to the magnitude and timing of excitation received from the population of inputs during more complex visual stimuli. We further investigated if these single facet speed signals could help tune the neuron to certain classes of stimuli. Looming stimuli, generated by objects approaching on a collision-course with the animal, most robustly activate the LGMD. Since both angular speed and the rate of luminance change at single facets increase during such stimuli, the dependence of latency on luminance change rate could help tune the LGMD to looming stimuli by synchronizing the excitatory input into the cell. We tested this idea by presenting pseudo-looming stimuli that excited exactly 45 targeted facets (~9x45°) in a precise spatio-temporal pattern that was either consistent with a looming stimulus edge or temporally shuffled to redistribute the speeds experienced by individual facets. We find that the pseudo-looming stimuli evoked tightly clustered spike responses, resulting in high instantaneous firing rates. The shuffled stimuli, however, evoked lower peak firing rates but often evoked similar numbers of spikes. These results indicate that motion speed dependence imparted by the activation rate of photoreceptors plays a role in tuning the LGMD to looming stimuli. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Speed sensitive excitation shapes the tuning of a collision-detecting neuron. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.159 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Feb 2009; Published Online: 03 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The cardiac response of the crabChasmagnathus granulatusas an index of sensory perception

When an animal's observable behavior remains unaltered, one can be misled in determining whether it is able to sense an environmental cue. By measuring an index of the internal state, additional information about perception may be obtained. We studied the cardiac response of the crab Chasmagnathus to different stimulus modalities: a light pulse, an air puff, virtual looming stimuli and a real visual danger stimulus. The first two did not trigger observable behavior, but the last two elicited a clear escape response. We examined the changes in heart rate upon sensory stimulation. Cardiac response and escape response latencies were also measured and compared during looming stimuli presentation. The cardiac parameters analyzed revealed significant changes (cardio-inhibitory responses) to all the stimuli investigated. We found a clear correlation between escape and cardiac response latencies to different looming stimuli. This study proved useful to examine the perceptual capacity independently of behavior. In addition, the correlation found between escape and cardiac responses support previous results which showed that in the face of impending danger the crab triggers several coordinated defensive reactions. The ability to escape predation or to be alerted to subtle changes in the environment in relation to autonomic control is associated with the complex ability to integrate sensory information as well as motor output to target tissues. This ;fear, fight or flight' response gives support to the idea of an autonomic-like reflexive control in crustaceans.

Responses of descending neurons to looming stimuli in the praying mantis Tenodera aridifolia

Responses to visual stimuli of some neurons that descend the nerve cord from the brain were recorded extracellularly in the mantis Tenodera aridifolia. Most of the recorded neurons showed their largest responses to looming stimuli that simulated a black circle approaching towards the mantis. The neurons showed a transient excitatory response to a gradually darkening or receding circle. The neurons showed sustained excitation to the linearly expanding stimuli, but the spike frequency decreased rapidly. The responses of the neurons were affected by both the diameter and the speed of looming stimuli. Faster or smaller looming stimuli elicited a higher peak frequency. These responses were observed in both recordings from the connective between suboesophageal and prothoracic ganglia and the connective between prothoracic and mesothoracic ganglia. There was a one-to-one correspondence of spike firing between these two recordings with a fixed delay. The neurons had the receptive field on ipsilateral side to its axon at the cervical connective. These results suggest that there is a looming-sensitive descending neuron, with an axon projecting over prothoracic ganglion, in the mantis nervous system.

Selective integration of auditory-visual looming cues by humans

An object's motion relative to an observer can confer ethologically meaningful information. Approaching or looming stimuli can signal threats/collisions to be avoided or prey to be confronted, whereas receding stimuli can signal successful escape or failed pursuit. Using movement detection and subjective ratings, we investigated the multisensory integration of looming and receding auditory and visual information by humans. While prior research has demonstrated a perceptual bias for unisensory and more recently multisensory looming stimuli, none has investigated whether there is integration of looming signals between modalities. Our findings reveal selective integration of multisensory looming stimuli. Performance was significantly enhanced for looming stimuli over all other multisensory conditions. Contrasts with static multisensory conditions indicate that only multisensory looming stimuli resulted in facilitation beyond that induced by the sheer presence of auditory-visual stimuli. Controlling for variation in physical energy replicated the advantage for multisensory looming stimuli. Finally, only looming stimuli exhibited a negative linear relationship between enhancement indices for detection speed and for subjective ratings. Maximal detection speed was attained when motion perception was already robust under unisensory conditions. The preferential integration of multisensory looming stimuli highlights that complex ethologically salient stimuli likely require synergistic cooperation between existing principles of multisensory integration. A new conceptualization of the neurophysiologic mechanisms mediating real-world multisensory perceptions and action is therefore supported.