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[Display omitted] • Standard solar collectors' absorber geometry modification by inserting V-grooves. • Optimizing solar collectors based on the geometric modification was demonstrated. • Importance of the absorbing surface geometry combined with spectral selectivity. • Improvement of the efficiency of the collectors despite increasing the thermal losses. • Efficiency improvement up to 5.61%, considering a V-groove opening angle of 60°. Solar energy plays an essential role in the process of the energy transition to renewable sources, and so too do technological innovations for exploring these energy sources, and for improving the thermal efficiency of conventional flat solar collectors. This study set out to model, simulate, and investigate the effect of modifying the geometry of the absorber plate of standard solar collectors for heating liquids, by inserting V corrugations. This leads to making consequent modifications to geometrical and optical parameters that improve the efficiency of the equipment. This paper presents the application of a mathematical-graphical model that seeks an optimum incidence angle to corrugate an absorber plate. This model, based on available optical experimental data, was built to improve the efficiency of solar collectors. During its application, an investigation could be made of the effect of the corrugation on the radiation and on the convection coefficients, the correlations of which were introduced into the mathematical model, and some of them were neither mentioned nor used in previous publications. A case study was carried out to investigate the behavior of three different collectors and the improvement in the efficiency of these collectors. It was shown that by using V grooves the efficiency was improved for all three flat solar collectors studied. As seen, the geometric modification contributes to improving efficiency when associated with selective absorption layers of solar collectors. The combination of both strategies can enhance the thermal efficiency of solar collectors and this can be further explored by researchers and manufacturers. [ABSTRACT FROM AUTHOR]

Block frames called directional analytic discrete cosine frames (DADCFs) are proposed for sparse image representation. In contrast to conventional overlapped frames, the proposed DADCFs require a reduced amount of 1) computational complexity, 2) memory usage, and 3) global memory access. These characteristics are strongly required for current high-resolution image processing. Specifically, we propose two DADCFs based on discrete cosine transform (DCT) and discrete sine transform (DST). The first DADCF is constructed from parallel separable transforms of DCT and DST, where the DST is permuted by row. The second DADCF is also designed based on DCT and DST, while the DST is customized to have no DC leakage property which is a desirable property for image processing. Both DADCFs have rich directional selectivity with slightly different characteristics each other and they can be implemented as non-overlapping block-based transforms, especially they form Parseval block frames with low transform redundancy. We perform experiments to evaluate our DADCFs and compare them with conventional directional block transforms in image recovery.

Abstract This paper presents a novel type of a filter bank for image decomposition that incorporates “singular spectrum analysis” (SSA). SSA is based on “singular value decomposition” (SVD).The presented filter banks provide good directional selectivity. Sub-band images highlight exposed directional features such as 0∘,90∘,+ 45∘, and − 45∘ of the input image. The proposed method can be seen as a tool to separate an image into layers or to present an image as a sum of its high-frequency directional components and a low-frequency approximation.

In all animals the optic tectum (OT) (or superior colliculi in mammals) provides guidance for external attention; this is not the only function of the tectum but is critically important for the development of behavioral visual reactions. In fish, the OT is the main primary visual center. It receives signals from most ganglion cells (GC) of different (known) types in the retina. Knowledge of the properties – both structural and physiological – of the neurons in the OT is important for understanding the mechanisms organizing behavior. We recorded extracellular electrical activity in the OT in living adult fish (Carassius auratus gibelio). Simultaneous recordings were made of the responses of retinal GC (from their axon terminals) and tectal neurons (TN), probably from cell bodies. Four types of TN are described with directional selectivity (DS) (henceforth these neurons are termed DS TN) at different (defined) depths of the OT. In addition to these, rare sporadic spikes lacking DS and arising on stimulation at any locus in a large area were consistently recorded simultaneously (superficially) with the responses of caudorostral DS GC with the electrode in one position. These are presumptively the responses of superficial tectal neurons (superficial inhibitory neurons, SIN). Various different types of stimulation were applied with the aim of obtaining clear SIN responses. Comparison of the results of our electrophysiological studies with published data (most studies in this direction have used calcium imaging in transparent Danio rerio fry) showed that DS TN were identical to glutamatergic periventricular interneurons in the OT, while SIN were identical to GABAergic inhibitory interneurons (SIN). These latter presumptively mediate detection of the main object (pop-out) in the field of vision. [ABSTRACT FROM AUTHOR]

This paper presents a novel type of a filter bank for image decomposition that incorporates "singular spectrum analysis" (SSA). SSA is based on "singular value decomposition" (SVD).The presented filter banks provide good directional selectivity. Sub-band images highlight exposed directional features such as 0∘,90∘,+ 45∘, and − 45∘ of the input image. The proposed method can be seen as a tool to separate an image into layers or to present an image as a sum of its high-frequency directional components and a low-frequency approximation. [ABSTRACT FROM AUTHOR]

The use of allocentric cues for movement guidance is complex because it involves the integration of visual targets and independent landmarks and the conversion of this information into egocentric commands for action. Here, we focus on the mechanisms for encoding reach targets relative to visual landmarks in humans. First, we consider the behavioral results suggesting that both of these cues influence target memory, but are then transformed—at the first opportunity—into egocentric commands for action. We then consider the cortical mechanisms for these behaviors. We discuss different allocentric versus egocentric mechanisms for coding of target directional selectivity in memory (inferior temporal gyrus versus superior occipital gyrus) and distinguish these mechanisms from parieto‐frontal activation for planning egocentric direction of actual reach movements. Then, we consider where and how the former allocentric representations of remembered reach targets are converted into the latter egocentric plans. In particular, our recent neuroimaging study suggests that four areas in the parietal and frontal cortex (right precuneus, bilateral dorsal premotor cortex, and right presupplementary area) participate in this allo‐to‐ego conversion. Finally, we provide a functional overview describing how and why egocentric and landmark‐centered representations are segregated early in the visual system, but then reintegrated in the parieto‐frontal cortex for action. [ABSTRACT FROM AUTHOR]

In flies, the direction of moving ON and OFF features is computed separately. T4 (ON) and T5 (OFF) are the first neurons in their respective pathways to extract a directionally selective response from their non-selective inputs. Our recent study of T4 found that the integration of offset depolarizing and hyperpolarizing inputs is critical for the generation of directional selectivity. However, T5s lack small-field inhibitory inputs, suggesting they may use a different mechanism. Here we used whole-cell recordings of T5 neurons and found a similar receptive field structure: fast depolarization and persistent, spatially offset hyperpolarization. By assaying pairwise interactions of local stimulation across the receptive field, we found no amplifying responses, only suppressive responses to the non-preferred motion direction. We then evaluated passive, biophysical models and found that a model using direct inhibition, but not the removal of excitation, can accurately predict T5 responses to a range of moving stimuli.

The paper aims to analyze the performance of the damage identification algorithms using the directional wavelet transforms, which reveal higher sensitivity for various orientations of spatial damage together with lower susceptibility to noise. In this study, the algorithms based on the dual-tree, the double-density, and the dual-tree double-density wavelet transforms were considered and compared to the algorithm based on the discrete wavelet transform. The performed analyses are based on shearographic experimental tests of a composite plate with artificially introduced damage at various orientations. It was shown that the directional wavelet transforms are characterized by better performance in damage identification problems than the basic discrete wavelet transform. Moreover, the proposed approach based on entropic weights applicable to the resulting sets of the detail coefficients after decomposition of mode shapes can be effectively used for automatic selection and emphasizing those sets of the detail coefficients, which contain relevant diagnostic information about damage. The proposed processing method allows raw experimental results from shearography to be significantly enhanced. The developed algorithms can be successfully implemented in a shearographic testing for enhancement of a sensitivity to damage during routine inspections in various industrial sectors.

A previous study reported that movement directions adapt much better to 60° target displacements (double steps) when target displacements are introduced incrementally and not abruptly. The present study tested whether incremental adaptation to 60° discordances can be explained by specific cognitive abilities. The results showed that an increase of discordance size during adaptation enhanced reaction times. Furthermore, the individual performance in neuropsychological tests measuring sustained attention, figural fluency and perseveration predicted the rate of adaptation at different discordance sizes. These results are discussed with reference to recent models on directional selectivity and modularity during visually guided reaching. [ABSTRACT FROM AUTHOR]

A remembered saccade target could be encoded in egocentric coordinates such as gaze-centered, or relative to some external allocentric landmark that is independent of the target or gaze (landmark-centered). In comparison to egocentric mechanisms, very little is known about such a landmark-centered representation. Here, we used an event-related fMRI design to identify brain areas supporting these two types of spatial coding (i.e., landmark-centered vs. gaze-centered) for target memory during the Delay phase where only target location, not saccade direction, was specified. The paradigm included three tasks with identical display of visual stimuli but different auditory instructions: Landmark Saccade (remember target location relative to a visual landmark, independent of gaze), Control Saccade (remember original target location relative to gaze fixation, independent of the landmark), and a non-spatial control, Color Report (report target color). During the Delay phase, the Control and Landmark Saccade tasks activated overlapping areas in posterior parietal cortex (PPC) and frontal cortex as compared to the color control, but with higher activation in PPC for target coding in the Control Saccade task and higher activation in temporal and occipital cortex for target coding in Landmark Saccade task. Gaze-centered directional selectivity was observed in superior occipital gyrus and inferior occipital gyrus, whereas landmark-centered directional selectivity was observed in precuneus and midposterior intraparietal sulcus. During the Response phase after saccade direction was specified, the parietofrontal network in the left hemisphere showed higher activation for rightward than leftward saccades. Our results suggest that cortical activation for coding saccade target direction relative to a visual landmark differs from gaze-centered directional selectivity for target memory, from the mechanisms for other types of allocentric tasks, and from the directionally selective mechanisms for saccade planning and execution.

Ipsilateral motor areas of cerebral cortex are active during arm movements and even reliably predict movement direction. Is coding similar during ipsilateral and contralateral movements? If so, is it in extrinsic (world-centered) or intrinsic (joint-configuration) coordinates? We addressed these questions by examining the similarity of multivoxel fMRI patterns in visuomotor cortical regions during unilateral reaching movements with both arms. The results of three complementary analyses revealed that fMRI response patterns were similar across right and left arm movements to identical targets (extrinsic coordinates) in visual cortices, and across movements with equivalent joint-angles (intrinsic coordinates) in motor cortices. We interpret this as evidence for the existence of distributed neural populations in multiple motor system areas that encode ipsilateral and contralateral movements in a similar manner: according to their intrinsic/joint coordinates. [ABSTRACT FROM AUTHOR]

The perception of visual motion is critical for animal navigation, and flies are a prominent model system for exploring this neural computation. In Drosophila, the T4 cells of the medulla are directionally selective and necessary for ON motion behavioral responses. To examine the emergence of directional selectivity, we developed genetic driver lines for the neuron types with the most synapses onto T4 cells. Using calcium imaging, we found that these neuron types are not directionally selective and that selectivity arises in the T4 dendrites. By silencing each input neuron type, we identified which neurons are necessary for T4 directional selectivity and ON motion behavioral responses. We then determined the sign of the connections between these neurons and T4 cells using neuronal photoactivation. Our results indicate a computational architecture for motion detection that is a hybrid of classic theoretical models. [ABSTRACT FROM AUTHOR]

Neurons across sensory systems and organisms often display complex patterns of action potentials in response to sensory input. One example of such a pattern is the tendency of neurons to fire packets of action potentials (i.e. a burst) followed by quiescence. While it is well known that multiple mechanisms can generate bursts of action potentials at both the single-neuron and the network level, the functional role of burst firing in sensory processing is not so well understood to date. Here we provide a comprehensive review of the known mechanisms and functions of burst firing in processing of electrosensory stimuli in gymnotiform weakly electric fish. We also present new evidence from existing data showing that bursts and isolated spikes provide distinct information about stimulus variance. It is likely that these functional roles will be generally applicable to other systems and species.

Synaptic circuits for identified behaviors in the Drosophila brain have typically been considered from either a developmental or functional perspective without reference to how the circuits might have been inherited from ancestral forms. For example, two candidate pathways for ON- and OFF-edge motion detection in the visual system act via circuits that use respectively either T4 or T5, two cell types of the fourth neuropil, or lobula plate, that exhibit narrow-field direction-selective responses and provide input to wide-field tangential neurons. T4 or T5 both have four subtypes that terminate one each in the four strata of the lobula plate. Representatives are reported in a wide range of Diptera, and both cell types exhibit various similarities in: 1) the morphology of their dendritic arbors; 2) their four morphological and functional subtypes; 3) their cholinergic profile in Drosophila; 4) their input from the pathways of L3 cells in the first neuropil, or lamina, and by one of a pair of lamina cells, L1 (to the T4 pathway) and L2 (to the T5 pathway); and 5) their innervation by a single, wide-field contralateral tangential neuron from the central brain. Progenitors of both also express the gene atonal early in their proliferation from the inner anlage of the developing optic lobe, being alone among many other cell type progeny to do so. Yet T4 receives input in the second neuropil, or medulla, and T5 in the third neuropil or lobula. Here we suggest that these two cell types were originally one, that their ancestral cell population duplicated and split to innervate separate medulla and lobula neuropils, and that a fiber crossing – the internal chiasma – arose between the two neuropils. The split most plausibly occurred, we suggest, with the formation of the lobula as a new neuropil that formed when it separated from its ancestral neuropil to leave the medulla, suggesting additionally that medulla input neurons to T4 and T5 may also have had a common origin.

Neurons across sensory systems and organisms often display complex patterns of action potentials in response to sensory input. One example of such a pattern is the tendency of neurons to fire packets of action potentials (i.e., a burst) followed by quiescence. While it is well known that multiple mechanisms can generate bursts of action potentials at both the single-neuron and the network level, the functional role of burst firing in sensory processing is not so well understood to date. Here we provide a comprehensive review of the known mechanisms and functions of burst firing in processing of electrosensory stimuli in gymnotiform weakly electric fish. We also present new evidence from existing data showing that bursts and isolated spikes provide distinct information about stimulus variance. It is likely that these functional roles will be generally applicable to other systems and species. [ABSTRACT FROM AUTHOR]

Two key features of sensorimotor adaptation are the directional selectivity of adaptive changes and the interference of adaptations to opposite directions. The present study investigated whether directional selectivity and interference of adaptation are related to executive functions and whether these phenomena differ between two methods for visuomotor adaptation. Subjects adapted at three target directions to clockwise or counterclockwise rotated feedback or to clockwise or counterclockwise target displacements (double steps). Both adaptation methods induce rotations of movement trajectories into the same direction, but provide visual information differently. The results showed that adaptation progressed differently between three targets. When movements adapted clockwise, adaptation was best at the most clockwise located target, and when movements adapted counterclockwise, it was best at the most counterclockwise located target, suggesting that spatial generalization between target directions is related to the direction of motor adaptation. The two adaptation methods produced different adaptation patterns, which indicate a further impact of visual information. A second adaptation to the other and opposite-directed discordance was worse than naive adaptation and washed out the aftereffects from the first adaptation, confirming that both adaptation methods interfered. Executive functions were significant covariate for overall interference and interference of target-specific adaptation. The results suggest that directional selectivity of adaptation is shaped by the direction of motor adaptation and the visual information provided. The interference of both adaptation methods indicates that they share adaptive mechanisms for recalibration. The interference is the lower the better subjects are able to cognitively switch between tasks and to inhibit prepotent responses. Therefore, cognitive functions seem to be involved in the inhibition of non-adequate sensorimotor responses. [ABSTRACT FROM AUTHOR]

Prefrontal neurons exhibit saccade-related activity and pre-saccadic memory-related activity often encodes the directions of forthcoming eye movements, in line with demonstrated prefrontal contribution to flexible control of voluntary eye movements. However, many prefrontal neurons exhibit post-saccadic activity that is initiated well after the initiation of eye movement. Although post-saccadic activity has been observed in the frontal eye field, this activity is thought to be a corollary discharge from oculomotor centers, because this activity shows no directional tuning and is observed whenever the monkeys perform eye movements regardless of goal-directed or not. However, prefrontal post-saccadic activities exhibit directional tunings similar as pre-saccadic activities and show context dependency, such that post-saccadic activity is observed only when monkeys perform goal-directed saccades. Context-dependency of prefrontal post-saccadic activity suggests that this activity is not a result of corollary signals from oculomotor centers, but contributes to other functions of the prefrontal cortex. One function might be the termination of memory-related activity after a behavioral response is done. This is supported by the observation that the termination of memory-related activity coincides with the initiation of post-saccadic activity in population analyses of prefrontal activities. The termination of memory-related activity at the end of the trial ensures that the subjects can prepare to receive new and updated information. Another function might be the monitoring of behavioral performance, since the termination of memory-related activity by post-saccadic activity could be associated with informing the correctness of the response and the termination of the trial. However, further studies are needed to examine the characteristics of saccade-related activities in the prefrontal cortex and their functions in eye movement control and a variety of cognitive functions.

Electrophysiological responses from 91 direction-selective (DS) units located in the basal optic root (nBOR) and the adjacent dorsomedial area have been recorded extracellularly in the frog ( Rana temporaria L.). Based on characteristics of the recorded responses, 23 of the units are considered to be retinal ganglion cells' (RGC; axon terminals). The majority of the remaining 68 units were considered to be DS neurons of the nBOR. The results of our study suggest that in the nBOR area there might be four subtypes of the tegmental and retinal DS units that respond selectively to stimuli moving in the dorso-ventral, ventro-dorsal, caudo-rostral and rostro-caudal directions. The receptive field (RF) sizes of the nBOR DS neurons were estimated to be about 30-, while those for the retinal units were significantly smaller - just 6-. In response to abrupt darkening within the units' RFs, both the nBOR DS neurons and the RGC DS units respond by a weak discharge. Our results indicate that the frog nBOR DS neurons integrate the inputs from the retinal OFF-type DS units over relatively large segments of the visual field. [ABSTRACT FROM AUTHOR]

Stimulus-specific adaptation (SSA) is considered to be the neural underpinning of habituation to frequent stimuli and novelty detection. However, neither the cellular mechanism underlying SSA nor the link between SSA-like neuronal plasticity and behavioral modulation is well understood. The wind-detection system in crickets is one of the best models for investigating the neural basis of SSA. We found that crickets exhibit stimulus-direction-specific adaptation in wind-elicited avoidance behavior. Repetitive air currents inducing this behavioral adaptation reduced firings to the stimulus and the amplitude of excitatory synaptic potentials in wind-sensitive giant interneurons (GIs) related to the avoidance behavior. Injection of a Ca2+ chelator into GIs diminished both the attenuation of firings and the synaptic depression induced by the repetitive stimulation, suggesting that adaptation of GIs induced by this stimulation results in Ca2+-mediated modulation of postsynaptic responses, including postsynaptic short-term depression. Some types of GIs showed specific adaptation to the direction of repetitive stimuli, resulting in an alteration of their directional tuning curves. The types of GIs for which directional tuning was altered displayed heterogeneous direction selectivity in their Ca2+ dynamics that was restricted to a specific area of dendrites. In contrast, other types of GIs with constant directionality exhibited direction-independent global Ca2+elevation throughout the dendritic arbor. These results suggest that depression induced by local Ca2+ accumulation at repetitively activated synapses of key neurons underlies direction-specific behavioral adaptation. This input-selective depression mediated by heterogeneous Ca2+ dynamics could confer the ability to detect novelty at the earliest stages of sensory processing in crickets. [ABSTRACT FROM AUTHOR]

Directional selectivity during visually guided hand movements is a fundamental characteristic of neural populations in multiple motor areas of the primate brain. In the current study, we assessed how directional selectivity changes when reaching movements are dissociated from their visual feedback by rotating the visual field. We recorded simultaneous movement kinematics and fMRI activity while human subjects performed out-and-back movements to four peripheral targets before and after adaptation to a 45° visuomotor rotation. A classification algorithm was trained to identify movement direction according to voxel-by-voxel fMRI patterns in each of several brain areas. The direction of movements was successfully decoded with above-chance accuracy in multiple motor and visual areas when training and testing the classifier on trials within each condition, thereby demonstrating the existence of directionally selective fMRI patterns within each stage of the experiment. Most importantly, when training the classifier on baseline trials and decoding rotated trials, motor brain areas exhibited above-chance decoding according to the original movement direction and visual brain areas exhibited above-chance decoding according to the rotated visual target location, while posterior parietal cortex (PPC) exhibited chance-level decoding according to both. These results reveal that directionally selective fMRI patterns in motor system areas faithfully represent movement direction regardless of visual feedback, while fMRI patterns in visual system areas faithfully represent target location regardless of movement direction. Directionally selective fMRI patterns in PPC, however, were altered following adaptation learning, thereby suggesting that the novel visuomotor mapping, which was learned during visuomotor adaptation, is stored in PPC. [ABSTRACT FROM AUTHOR]

Crickets ( Gryllus bimaculatus ) use the cercal sensory system at the rear of the abdomen to detect air currents and direct predator avoidance behavior. Sensory information regarding the direction and dynamic properties of air currents is processed within the terminal abdominal ganglion, and conveyed by ascending giant interneurons (GIs) to higher centers including the brain. However, the brain region responsible for decoding cercal sensory information has not yet been identified, nor the response properties within the brain characterized. In this study, we performed in vivo Ca 2+ imaging to investigate wind-evoked neural activities within the cricket protocerebrum. Ca 2+ responses to air current stimuli were observed at peripheral regions of the ventrolateral neuropile (VLNP) where projection of GIs’ axon terminals has been observed in larvae. The wind-evoked Ca 2+ response had temporal dynamics and directional sensitivity that varied with different recorded regions displaying transient or sustained Ca 2+ increases. Individual cells showed Ca 2+ elevation in response to air currents from a specific angle, while stimuli from a different angle evoked decreased signals. Removing the antennae reduced the air-current-evoked responses in VLNP, suggesting contribution of sensory inputs from antennae in addition to the cercal inputs. The VLNP is presumably an integrative center for mechanosensory processing from antennae and cerci where directional information is primarily decoded by protocerebral neurons. [ABSTRACT FROM AUTHOR]

A principal loss mechanism for solar receivers in solar-thermal systems is radiation from the absorbing surface. This loss can be reduced by using the concept of directional selectivity in which radiation is suppressed at angles larger than the incident angle of the sunlight striking the absorber. Directional selectivity can achieve efficiencies similar to high solar concentration, without the drawbacks associated with large heat fluxes. A specularly reflective hemispherical cavity placed over the absorber can reflect emitted radiation back to the absorber, effectively suppressing emission losses. An aperture in the cavity will still allow sunlight to reach the absorber surface when used with point focus concentrating systems. In this paper the reduction in radiative losses through the use of a hemispherical cavity is predicted using ray tracing simulations, and the effects of cavity size and absorber alignment are investigated. Simulated results are validated with proof of concept experiments that show reductions in radiative losses of more than 75% from a near blackbody absorber surface. The demonstrated cavity system is shown to be capable of achieving receiver efficiencies comparable to idealized spectrally selective absorbers across a wide range of operating temperatures. [ABSTRACT FROM AUTHOR]

The location of a remembered reach target can be encoded in egocentric and/or allocentric reference frames. Cortical mechanisms for egocentric reach are relatively well described, but the corresponding allocentric representations are essentially unknown. Here, we used an event-related fMRI design to distinguish human brain areas involved in these two types of representation. Our paradigm consisted of three tasks with identical stimulus display but different instructions: egocentric reach (remember absolute target location), allocentric reach (remember target location relative to a visual landmark), and a nonspatial control, color report (report color of target). During the delay phase (when only target location was specified), the egocentric and allocentric tasks elicited widely overlapping regions of cortical activity (relative to the control), but with higher activation in parietofrontal cortex for egocentric task and higher activation in early visual cortex for allocentric tasks. In addition, egocentric directional selectivity (target relative to gaze) was observed in the superior occipital gyrus and the inferior occipital gyrus, whereas allocentric directional selectivity (target relative to a visual landmark) was observed in the inferior temporal gyrus and inferior occipital gyrus. During the response phase (after movement direction had been specified either by reappearance of the visual landmark or a pro-/anti-reach instruction), the parietofrontal network resumed egocentric directional selectivity, showing higher activation for contralateral than ipsilateral reaches. These results show that allocentric and egocentric reach mechanisms use partially overlapping but different cortical substrates and that directional specification is different for target memory versus reach response. [ABSTRACT FROM AUTHOR]

Research in motion analysis is a challenging field and it has a variety of video surveillance applications. For any video surveillance application, background detection and removal plays an important role in segmentation of the moving objects. This study proposes a new method for segmentation of the moving object, which is based on single change detection applied on Daubechies complex wavelet coefficients of two consecutive frames. The authors have chosen Daubechies complex wavelet transform as it is shift invariant and has a better directional selectivity as compared with real‐valued wavelet transforms. Single change detection is a method to obtain video object plane by inter‐frame difference of two consecutive frames, and it provides automatic detection of appearances of new objects. The proposed method does not require any other parameter except wavelet coefficients. Segmentation results of the moving objects after applying the proposed method are compared with those obtained after applying other spatial and wavelet domain segmentation methods in terms of visual performance and a number of quantitative measures viz misclassification penalty, relative position‐based measure, structural content, normalised absolute error and average difference and the proposed method is found better than the other methods. [ABSTRACT FROM AUTHOR]

Pharmacological block of inhibition is often used to determine if inhibition contributes to spike selectivity, in which a preferred stimulus evokes more spikes than a null stimulus. When inhibitory block reduces spike selectivity, a common interpretation is that differences between the preferred- and null-evoked inhibitions created the selectivity from less-selective excitatory inputs. In models based on empirical properties of cells from the inferior colliculus of awake bats, we show that inhibitory differences are not required. Instead, inhibition can enhance spike selectivity by changing the gain, the ratio of output spikes to input current. Within the model, we made preferred stimuli that evoked more spikes than null stimuli using five distinct synaptic mechanisms. In two cases, synaptic selectivity (the differences between the preferred and null inputs) was entirely excitatory, and in two it was entirely inhibitory. In each case, blocking inhibition eliminated spike selectivity. Thus, observing spike rates following inhibitory block did not distinguish among the cases where synaptic selectivity was entirely excitatory or inhibitory. We then did the same modeling experiment using empirical synaptic conductances derived from responses to preferred and null sounds. In most cases, inhibition in the model enhanced spike selectivity mainly by gain modulation and firing rate reduction. Sometimes, inhibition reduced the null gain to zero, eliminating null-evoked spikes. In some cases, inhibition increased the preferred gain more than the null gain, enhancing the difference between the preferred- and null-evoked spikes. Finally, inhibition kept firing rates low. When selectivity is quantified by the selectivity index (SI, the ratio of the difference to the sum of the spikes evoked by the preferred and null stimuli), inhibitory block reduced the SI by increasing overall firing rates. These results are consistent with inhibition shaping spike selectivity by gain control.

Threshold selection is a challenging job for the image denoising in the contourlet domain. In this paper, a new local threshold with adaptive window shrinkage is proposed. According to the anisotropic energy clusters in contourlet subbands, local adaptive elliptic windows are introduced to determine the neighboring coefficients with strong dependencies for each coefficient. Utilizing the maximum likelihood estimator within the adaptive window, the signal variance is estimated from the noisy neighboring coefficients. Based on the signal variance estimation, the new threshold is obtained in the Bayesian framework. Since it makes full use of the captured directional information of images, the threshold extends to the anisotropic spatial adaptability and behaves reliably. Simulation experiments show that the new method exhibits better performance than other outstanding wavelet and contourlet denoising schemes obviously, both in the PSNR value and the visual appearance. [ABSTRACT FROM AUTHOR]

Abstract: Auditory frequency discrimination training can remediate deteriorated frequency representations and temporal information processing in the adult primary auditory cortex induced by early post-natal pulsed noise exposure. In this study, we investigated the neural mechanisms underlying the restoration of directional selectivity by auditory spatial discrimination training. Rats exposed to pulsed noise during a post-natal critical period demonstrated reduced auditory directional selectivity but could be successfully trained to identify a target sound stimulus at a specific azimuth angle using a reward-contingent auditory discrimination task (EXP rats). In contrast, rats passively exposed to the training procedure but no reward for correct identification of the azimuth angle (PNR rats) showed no improvement and behavioral performance remained significantly below EXP rats and control (CON) rats reared under a normal sonic environment. The expression levels of GABAA receptor subunits α1, α3, β2, and β3, and the AMPA GluR2 subunit were significantly altered in the auditory cortex of untrained noise-raised (NR and PNR) rats compared to age-matched CON rats, while trained noise-raised (EXP) rats exhibited levels of expression not significantly different from CON rats. Thus, reward-contingent sound-azimuth discrimination training may remediate directional selectivity by restoring the proper expression profile of neurotransmitter receptor subunits in the auditory cortex, allowing for normal spatial selectivity by cortical neurons. The development of auditory directional selectivity depends on the regulated expression of these excitatory and inhibitory neurotransmitter receptor subunits; early pulsed noise may disrupt the normal development of directional selectivity by interfering with receptor expression. [Copyright &y& Elsevier]

Abstract: Sound localization is one of the most important tasks performed by the auditory system. Studies have shown that intensive training can remediate deteriorated frequency representations and temporal information processing in the adult primary auditory cortex (A1) induced by early post-natal pulsed noise exposure. Here we demonstrate that intensive sound location discrimination training improved the dysfunctional sound azimuth selectivity degraded by early post-natal pulsed noise exposure. Rats exposed to pulsed white noise during a post-natal critical period were successfully trained to identify a target sound stimulus with specific azimuth angle that changed daily on a random schedule. Consistent with recovery of behavioral accuracy for sound-azimuth discriminations, we found that the average angular range (AR) of A1 neuronal azimuth selective curves in trained noise-raised rats was not significantly different from that measured in control rats, while the average AR of A1 neurons in untrained noise-raised rats was significantly higher, indicating that these neurons were less direction selective. Directional selectivity of A1 neurons was normalized by training, thus demonstrating the benefits of sensory discrimination training as a strategy for restoring auditory function in adult mammals damaged by sensory disruption during critical periods of cortical development. [Copyright &y& Elsevier]

In this paper, we found that spatial and temporal asymmetricity of excitatory connections are able to generate directional selectivity which can be enhanced by asymmetrical inhibitory connections by reconstructing a hexagonally-arranged three-layered simulation model of retina by NEURON simulator. Asymmetric excitatory inputs to ganglion cells with randomly arborizing dendrites were able to generate weaker directional selectivity to moving stimuli whose speed was less than 10 μm/msec. By just adding asymmetric inhibitory connections via inhibitory amacrine cells, directional selectivity became stronger to respond to moving stimuli at ten times faster speed (< 100 μm/msec). In conclusion, an excitatory mechanism appeared to generate directional selectivity while asymmetric inhibitory connections enhance directional selectivity in retina. [ABSTRACT FROM AUTHOR]

A reaction-diffusion model is presented to encapsulate calcium-induced calcium release (CICR) as a potential mechanism for somatofugal bias of dendritic calcium movement in starburst amacrine cells. Calcium dynamics involves a simple calcium extrusion (pump) and a buffering mechanism of calcium binding proteins homogeneously distributed over the plasma membrane of the endoplasmic reticulum within starburst amacrine cells. The system of reaction-diffusion equations in the excess buffer (or low calcium concentration) approximation are reformulated as a nonlinear Volterra integral equation which is solved analytically via a regular perturbation series expansion in response to calcium feedback from a continuously and uniformly distributed calcium sources. Calculation of luminal calcium diffusion in the absence of buffering enables a wave to travel at distances of 120 μm from the soma to distal tips of a starburst amacrine cell dendrite in 100 msec, yet in the presence of discretely distributed calcium-binding proteins it is unknown whether the propagating calcium wave-front in the somatofugal direction is further impeded by endogenous buffers. If so, this would indicate CICR to be an unlikely mechanism of retinal direction selectivity in starburst amacrine cells. [ABSTRACT FROM AUTHOR]

Abstract: Using intrinsic optical imaging methods, somatosensory-evoked neural activity was visualized in the rat barrel cortex at high spatial resolution in order to obtain cortical maps of the directional selectivity of whisker deflection. For this task, a special multidirectional mechanical stimulator was developed in our laboratory. The vibrissae were covered with magnetic paint and deflection was performed using a custom-built deflecting device with four small crosswise electromagnets; the whisker was placed at the intersection of the magnet axes. The results show that differences between responses to directional deflection were indicated by a change in the intrinsic optical signal of incident light at 546nm corresponding to an increase in blood volume. Our results provide a preliminary indication that the different regions of the barrel have different directional preference, supporting recent electrophysiological studies suggesting that the barrel might have a fine, directionally-sensitive anatomical structure. [Copyright &y& Elsevier]

Extracellular recordings were made from a directionally selective neuron in the ventral nerve cord of mantises. The neuron’s preferred direction of motion was forward and upward over the compound eye contralateral to its axon at the cervical connective. The neuron was sensitive to wide-field motion stimuli, resistant to habituation, and showed transient excitation in response to light ON and OFF stimuli. Its responses to drifting gratings depended on the temporal frequency and contrast of the stimulus. These results suggest that the neuron receives input from correlation-type motion detectors. [ABSTRACT FROM AUTHOR]

Shift invariance associated with good directional selectivity is important for the use of a wavelet transform (WT) in many fields of image processing. Generally, complex wavelet transforms, e.g., the double-tree complex WI (DTCWT), have these useful properties. In this paper, we propose the use of a recently introduced implementation of such a WI, namely, the hyperanalytic WI (HWT), in association with filtering techniques already used with the discrete WI (DWT). The result is a very simple and fast image denoising algorithm. Some simulation results and comparisons prove the performance obtained using the new method. [ABSTRACT FROM AUTHOR]

Bistratified (BS) ganglion cells have long been recognized in vertebrate retina. Thirty years ago, it became clear that bistratification allows the integration of ON and OFF retinal pathways to produce contrast-independent responses in ganglion cells. Best studied is the type 1 bistratified (BS1) ganglion cell of rabbit retina, the physiologically well-characterized ON-OFF directionally selective (DS) ganglion cell, which is co-stratified with the two types of starburst amacrine (SA) cells in sublaminae a and b of the inner plexiform layer (IPL). DS responses have recently been documented in the latter. In this report, BS1 cells are further studied and are used as ''fiducials'' to characterize a second type of BS ganglion cell. An example of a possible third type is shown to be distinct from examples of BS1 and BS2 cells. All three have two distinct, narrowly stratified arborizations, one in sublamina a and one in sublamina b. All have similar dimensions, except for their dendritic trees, differing also in branching pattern. BS1 cells have compact, regular, highly branched trees; BS2 cells have significantly larger, more sparsely branched, irregular, radiate trees; the proposed BS3 type is intermediate in field size, and its branching pattern is different from the first two. BS2 and BS3 cells are co-stratified, branching nearer to the margins of the IPL, out of range of SA cells. In a previous report by others, illustrating the morphology of intracellularly stained ganglion cells, one example each of both ''orientation-selective'' ganglion cells and ''uniformity detectors'' resembles the BS2 cell. A rationale is presented for correlating BS2 cells with uniformity detectors. [ABSTRACT FROM AUTHOR]

Motion detector interneurons were examined to determine their responsiveness to the motion of polarized light images (i.e. images segmented by spatial variations in e-vector angle). Computer generated images were displayed as intensity contrasts or polarization contrasts on a modified LCD projection panel. The stimuli included the motion of a single stripe (45°–55°/s) and the global motion of a square wave grating (3.3°/s). Neurons were impaled in the medulla interna. Of the neurons which exhibited a directional response to the motion of intensity contrast stimuli, about 2/3 were also directional in the response to polarized light images. Transient (nondirectional) stimuli included looming and jittery motions. The responses to the transient motions of the polarized light images were roughly comparable to those elicited by intensity contrast. The results imply that behavioral responses to polarized light images (i.e. optokinetic and defense reflexes) may have a basis in the polarization sensitivity and synaptic organization of the medulla interna. [ABSTRACT FROM AUTHOR]

Among other sensory modalities, flight stabilization in insects is performed with the aid of visual feedback from three simple eyes (ocelli). It is thought that each ocellus acts as a single wide-field sensor that detects changes in light intensity. We challenge this notion by providing evidence that, when light-adapted, the large retinal L-neurons in the median ocellus of the dragonfly respond in a directional way to upward moving bars and gratings. This ability is pronounced under UV illumination but weak or nonexistent in green light and is optimal at angular velocities of ~750° s-1. Using a reverse-correlation technique, we analyze the functional organization of the receptive fields of the L-neurons. Our results reveal that L-neurons alter the structure of their linear spatiotemporal receptive fields with changes in the illuminating wavelength, becoming more inseparable and directional in UV light than in green. For moving bars and gratings, the strength of directionality predicted from the receptive fields is consistent with the measured values. Our results strongly suggest that, during the day, the retinal circuitry of the dragonfly median ocellus performs an early linear stage of motion processing. The likely advantage of this computation is to enhance pitch control. [ABSTRACT FROM AUTHOR]

Abstract: In the mammalian retina, high levels of the group II metabotropic glutamate receptor (mGluR) subtype are expressed in starburst amacrine cells. A prominent role of starburst amacrine cells is the generation of directional selectivity in ON–OFF directionally selective retinal ganglion cells (DS RGCs). Extracellular microelectrodes were used to study the effects of activation of group II mGluRs on the responses of rabbit ON–OFF DS RGCs to a moving light stimulus. Directionally selective responses in these RGCs were substantially reduced by the selective group II mGluR agonist DCG-IV. DCG-IV brought out a response to movement in the null direction that was similar in magnitude and time course to the response to movement in the preferred direction. This effect of DCG-IV was reversed by the group II mGluR antagonist EGLU. Application of EGLU alone failed to alter directional selectivity in the RGCs but did reduce the response to movement in the preferred direction. To determine whether group II mGluRs modulate the release of the neurotransmitter acetylcholine from starburst amacrine cells, the effect of DCG-IV on ON–OFF DS RGCs was examined in the presence of ambenonium, an acetylcholinesterase inhibitor. When applied alone, ambenonium greatly prolonged the responses of ON–OFF DS RGCs to a light stimulus. This effect of ambenonium was completely abolished upon application of DCG-IV. Overall, the results suggest that postsynaptic group II mGluRs have the potential to influence directional selectivity in RGCs by inhibiting transmitter release from starburst amacrine cells. [Copyright &y& Elsevier]

The present study is the first attempt to make comparisons of the visual response properties between tectal and thalamic neurons with spatially overlapping receptive fields by using extracellular recording and computer mapping techniques. The results show that in neuronal pairs about 70% of thalamic cells have excitatory receptive field alone, whereas 85% of tectal cells possess an excitatory receptive field surrounded by an inhibitory receptive field. In 70% of pairs the tectal cells are selective for direction of motion different from that which the thalamic cells prefer. Most thalamic cells prefer high speeds (80–160°/s), whereas tectal cells prefer intermediate (40°/s) or low (10–20°/s) speeds. Photergic and scotergic cells exist in the thalamus but not in the tectum. These results provide evidence that tectal and thalamic cells extract different visual information from the same region of the visual field. The functional significance of these differences is discussed. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

In our previous study, we have shown that the recovery cycle of most neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, is typically longer at ipsilateral azimuth than at contralateral azimuth under free-field stimulation conditions. The present study is to test the hypothesis that this azimuth-dependent recovery cycle may contribute to the variation of directional selectivity of IC neurons with sequential presented sound pulses within a pulse train. A 300-ms pulse train containing nine sound pulses of 4-ms with an inter-pulse interval of 33.3 ms was delivered at several selected azimuthal angles between ±80° lateral in the frontal auditory space of a bat. A family of nine directional selectivity curves was plotted with a neuron''s number of impulses in response to each individual pulse against the azimuthal angles. The type and sharpness of these directional selectivity curves were then compared in relation to pulse position within the pulse train. All 675 directional selectivity curves obtained from 75 IC neurons could be described as directionally selective (423, 63%), hemifield (220, 32%), or non-directional (32, 5%). The directional selectivity curves of 45 (60%) neurons did not vary with pulse position. However, those of the remaining neurons (30, 40%) changed from one type to another such that the number of neurons with directionally selective curves progressively increased and the number of neurons with hemifield and non-directional selectivity curves decreased with increasing pulse position within the pulse train. Among 68 IC neurons whose directional selectivity curves were compared quantitatively, directional selectivity determined with sequentially presented sound pulses significantly increased in 38 (56%) neurons; decreased in 18 (26%) neurons but did not change in 12 (18%) neurons. This change of directional selectivity was due to the variation in recovery cycle of these IC neurons with azimuthal angle as we hypothesized. [Copyright &y& Elsevier]

Auditory and vestibular functions of otolithic organs vary among vertebrate taxa. The saccule has been considered a major hearing organ in many fishes. However, little is known about the auditory role of the lagena in fishes. In this study we analyzed directional and frequency responses from single lagenar fibers of Dormitator latifrons to linear accelerations that simulate underwater acoustic particle motion. Characteristic frequencies of the lagenar fibers fell into two groups: ≤50 Hz and 80–125 Hz. We observed various temporal response patterns: strong phase-locking, double phase-locking, phase-locked bursting, and non-phase-locked bursting. Some bursting responses have not been previously observed in vertebrate otolithic nerve fibers. Lagenar fibers could respond to accelerations as small as 1.1 mm s-2. Like saccular fibers, lagenar fibers were directionally responsive and decreased directional selectivity with stimulus level. Best response axes of the lagenar fibers clustered around the lagenar longitudinal axis in the horizontal plane, but distributed in a diversity of axes in the mid-sagittal plane, which generally reflect morphological polarizations of hair cells in the lagena. We conclude that the lagena of D. latifrons plays a role in sound localization in elevation, particularly at high stimulus intensities where responses of most saccular fibers are saturated. [ABSTRACT FROM AUTHOR]

Effects of baclofen on the directional selectivity of the inner retinal neurons were studied using conventional intracellular recording techniques and computer simulations. Baclofen suppressed sustained components, but enhanced transient components of third-order neurons in the catfish retina. In addition, directional selectivity of transient neurons was enhanced by the application of baclofen. The simplified network model was tested to account for the details of directional selectivity observed in the inner retina. Results suggest that the directional selectivity in fish retina could be evoked by the asymmetric distribution of GABAergic third-order neurons. [Copyright &y& Elsevier]

This study examined the role of GABAergic inhibition in shaping directional selectivity of neurons in the inferior colliculus of the big brown bat, Eptesicus fuscus. When determined with temporally patterned pulse trains at different pulse repetition rates, 93 inferior colliculus neurons displayed three types of directional selectivity curves. A directionally selective curve always showed a maximum to a certain azimuthal angle (the best angle). A hemifield curve showed a maximum to a range of contralateral azimuthal angles. A non-directional curve did not show a maximum to any particular azimuthal angles. Directional selectivity curves of 42% neurons changed from hemifield or non-directional to directionally selective and the best angles of 16–21% neurons shifted toward the midline with increasing pulse repetition rate of pulse trains. Directional selectivity curves of most (74%) neurons that discharged impulses to each pulse of a pulse train also became sharper with increasing pulse repetition rate of pulse trains. Bicuculline application produced more pronounced broadening of directional selective curves of inferior colliculus neurons at higher than at lower pulse repetition rates. As a result, pulse repetition rate-dependent directional selectivity of inferior colliculus neurons was abolished. Possible mechanisms and biological significance of these findings are discussed. [ABSTRACT FROM AUTHOR]

Cortical networks are dynamical systems whose task is to process information. However, in addition to ‘intended’ dynamical behaviors, the sheer complexity of a cortical network''s structure—regardless of its precise details—should generate additional ‘unintended’ dynamical behaviors. Dynamics observed in cortical network models and in the somatosensory cortex suggest that such spurious dynamical behaviors are likely to be pervasive but relatively simple, contributing to—rather than dominating—a network''s response to stimuli. Spurious dynamics may be responsible for a variety of experimentally observed intriguing features of cortical dynamics. Because of their distributed origins and emergent nature, such dynamical features, while clearly identifiable, will resist attempts at identifying specific mechanisms to explain them. We describe some of the spurious dynamical phenomena associated with somatosensory cortical response to brushing stimulation, to illustrate how spurious dynamics can affect neurons’ functional properties, cortical stimulus representation and, ultimately, perception. [Copyright &y& Elsevier]

Abstract For the detection of a moving object, segregating the object from the background is a necessary first step. This segregation can be achieved by detection of differences in the spatial, temporal and spatio-temporal properties of the object and background. Here we investigate how flicker influences the perception of a moving object in man and monkey, and we examine the neuronal responses in extrastriate medial temporal and medial superior temporal areas (MT and MST) of two rhesus monkeys. The performance of humans and monkeys in a direction discrimination task was impaired in the presence of flicker in the background compared to the static background condition. A similar effect was found in recordings from 155 single units in areas MT and MST during the discrimination task. The discriminability (d ′) of the neuronal responses in preferred and nonpreferred directions was reduced by 33% on average in the presence of a flicker background compared to the static background. This reduction in discriminability was not caused by differences in variance of the neuronal activity for the two background conditions, but was due to a reduction of the difference between the activities in preferred and nonpreferred direction. This reduction in directional selectivity could be traced back to two different mechanisms: in 32 out of 155 neurons (21%), the decrease resulted from an increase in the response to the stimulus moving in the nonpreferred direction; in 62 out of 155 neurons (40%), the reduction in directional selectivity was due to a decrease in the response to the preferred direction. These results give deeper insights into how moving stimuli are processed in the presence of background flicker as present in natural visual scenes. [ABSTRACT FROM AUTHOR]

This paper presents a biologically inspired, hardware-realisable spiking neuron model, which we call the Temporal Noisy-Leaky Integrator (TNLI). The dynamic applications of the model as well as its applications in Computational Neuroscience are demonstrated and a learning algorithm based on postsynaptic delays is proposed. The TNLI incorporates temporal dynamics at the neuron level by modelling both the temporal summation of dendritic postsynaptic currents which have controlled delay and duration and the decay of the somatic potential due to its membrane leak. Moreover, the TNLI models the stochastic neurotransmitter release by real neuron synapses (with probabilistic RAMs at each input) and the firing times including the refractory period and action potential repolarisation. The temporal features of the TNLI make it suitable for use in dynamic time-dependent tasks like its application as a motion and velocity detector system presented in this paper. This is done by modelling the experimental velocity selectivity curve of the motion sensitive H1 neuron of the visual system of the fly. This application of the TNLI indicates its potential applications in artificial vision systems for robots. It is also demonstrated that Hebbian-based learning can be applied in the TNLI for postsynaptic delay training based on coincidence detection, in such a way that an arbitrary temporal pattern can be detected and recognised. The paper also demonstrates that the TNLI can be used to control the firing variability through inhibition; with 80% inhibition to concurrent excitation, firing at high rates is nearly consistent with a Poisson-type firing variability observed in cortical neurons. It is also shown with the TNLI, that the gain of the neuron (slope of its transfer function) can be controlled by the balance between inhibition and excitation, the gain being a decreasing function of the proportion of inhibitory inputs. Finally, in the case of perfect balance between inhibition and excitation, i.e. where the average input current is zero, the neuron can still fire as a result of membrane potential fluctuations. The firing rate is then determined by the average input firing rate. Overall this work illustrates how a hardware-realisable neuron model can capitalise on the unique computational capabilities of biological neurons. [Copyright &y& Elsevier]

The population-vector analysis was applied to visualize neuronal processes of sensory-to-motor transformation in the prefrontal cortex while two monkeys performed two types of oculomotor delayed-response (ODR) tasks. In a standard ODR task, monkeys were required to make a quick eye movement to where thevisual cue had been presented 3 s before, whereas in R-ODR task, monkeys wererequired to make an eye movement 90°clockwise to the direction that the visual cue had been presented. In both tasks, directions of population vectors calculated from cue- and response-period activity were almost the same as cue directions and saccade directions, respectively, indicating that population vectors of cue- and response-period activity represent information of visual inputs and motor outputs, respectively. To visualize neuronal processes of information transformation, population vectors were calculated every 250 ms during a whole trial. In ODR task, population vectors weredirected the same direction as the cue direction during the delay period. However, in R-ODR task, population vector rotated gradually from the direction similar to the cue direction to the saccade direction during the delay period. These results indicate that visual-to-motor transformation occurs during the delay period and that this process can be visualized by the population-vectoranalysis. [ABSTRACT FROM AUTHOR]

The avian ectostriatum is the telencephalic recipient zone of the tectofugal pathway, which may be homologous to the colliculo-pulvinar-cortical pathway in mammals. The present paper studies the visual response properties and receptive field organization of ectostriatal cells in pigeons with extracellular recording and computer mapping techniques. The results indicate that 90% of ectostriatal cells prefer forward, downward and upward motion of visual stimuli at velocities in the range of 16–128° s–1. They respond optimally to small stimuli (1–4° visual angle), mostly preferring a target of 2°. Most cells (78.8%) have one excitatory receptive field that usually possesses one or two hotspots, some cells (13.5%) have two excitatory receptive fields each having one or two hotspots, and a few cells (7.7%) have one excitatory receptive field with an unresponsive region in the center. An inhibitory receptive field is not found surrounding the excitatory receptive field in the ectostriatal cells examined. These response properties and receptive field organization may reflect the possible roles of the ectostriatum in stimulus discrimination and visual cognition. [ABSTRACT FROM AUTHOR]

The present study describes the effects of gamma-aminobutyric acid (GABA) and its antagonists, bicuculline and 2-hydroxysaclofen, on visual responses of neurons in the pigeon nucleus lentiformis mesencephali (nLM). The results indicate that GABA significantly reduces both spontaneous activity and visual responsiveness, and GABAA antagonist bicuculline but not GABAB antagonist 2-hydroxysaclofen enhances visual responses of nLM cells examined. Furthermore, inhibition produced by motion in the null-direction of pretectal neurons is diminished by bicuculline but not by 2-hydroxysaclofen. It is therefore concluded that the null-direction inhibition of directional cells in the pigeon nLM is predominantly mediated by GABA and GABAA receptors. This inhibition may at least in part underlie directional asymmetry of optokinetic responses. [ABSTRACT FROM AUTHOR]

Diverse sensory systems, from audition to thermosensation, feature a separation of inputs into ON (increments) and OFF (decrements) signals. In the Drosophila visual system, separate ON and OFF pathways compute the direction of motion, yet anatomical and functional studies have identified some crosstalk between these channels. We used this well-studied circuit to ask whether the motion computation depends on ON-OFF pathway crosstalk. Using whole-cell electrophysiology, we recorded visual responses of T4 (ON) and T5 (OFF) cells, mapped their composite ON-OFF receptive fields, and found that they share a similar spatiotemporal structure. We fit a biophysical model to these receptive fields that accurately predicts directionally selective T4 and T5 responses to both ON and OFF moving stimuli. This model also provides a detailed mechanistic explanation for the directional preference inversion in response to the prominent reverse-phi illusion. Finally, we used the steering responses of tethered flying flies to validate the model's predicted effects of varying stimulus parameters on the behavioral turning inversion. • Whole-cell recordings of T4 and T5 responses to ON-OFF visual stimuli • T4 and T5 have a similar receptive field but with opposite contrast selectivity • Biophysical model fit to ON and OFF responses predicts directional selectivity • The model explains cellular and behavioral responses to reverse-phi illusion Recording whole-cell responses from ON and OFF cells in the Drosophila motion pathway, Gruntman et al. show that these cells share a receptive field structure for their non-preferred contrast responses. This structure explains the perception of directional inversion to the reverse-phi illusion. [ABSTRACT FROM AUTHOR]

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