Human optokinetic responses under quasi-open and closed loop conditions

The human optokinetic response to a horizontally moving striped pattern surrounding the subject was investigated under quasi-open and closed loop conditions. Open loop conditions were produced by the addition of an external signal from measured slow phase eye velocity to stripe velocity. A comparison of open and closed loop responses to step and sinusoidal changes of stripe velocity indicates that the central nervous system controlling slow phase optokinetic following can be described as a simple first order lag (Ka/(s+a)) where K is 4.7 and the time constant, 1/a, is 1.25 s.     

用红外方法对蝇翅视动行为的探索

本文报告了利用红外装置对蝇翅视动行为实验研究的初步结果及其分析:1.在红外探测器探测到的信号中找到了一个能反映蝇翅拍动幅度的参数.2.双侧、单侧刺激域的宽度及刺激域的高度对视动反应发生几率在一定范围内正相关,当超过一阈值(即饱和阈值)后,即出现稳定的视动反应,它们的饱和阈值分别为60°,30°,40°刺激条纹的亮度生有类似情况.刺激条纹的运动速度在一定范围内对视动反应无影响.3.当刺激没有达到饱和时,蝇翅出现断续的典型的视动反应,即“0-1波动反应”.4.单侧条纹由前向后运动时,蝇翅出现典型反应,而条纹从后向前运动时,不出现典型的视动反应或反应很弱.双侧刺激时,条纹向前运动几乎不诱发反应;条纹向后运动诱发明显的蝇翅视动反应,且蝇翅平面的方向在拍动过程中发生变化.     

Linear Relations between Stimulus Amplitudes and Amplitudes of Retinal Action Potentials from the Eye of the Wolf Spider

Incremental photic stimuli have been used to elicit small amplitude retinal action potentials from light-adapted ocelli of the wolf spider, Lycosa baltimoriana (Keyserling) in order to see whether or not the amplitudes of these potentials are linearly related to the stimulus amplitudes. Sine wave variations of light intensity around a mean elicit sine wave variations in potential which contain inappreciable harmonics of the stimulus frequency and whose amplitudes are linearly related to the stimulus amplitudes. Likewise, the responses to the first two periodic Fourier components of incremental rectangular wave stimuli of variable duty cycle are directly proportional to the amplitudes of these components and have phases dependent only on the frequencies and phases of these components. Thirdly, a linear transfer function can be found which describes the amplitudes and phases of responses recorded at different frequencies of sine wave stimulation and this transfer function is sufficient to predict the responses to incremental step stimuli. Finally, it is shown that flash response amplitudes are linearly related to incremental flash intensities at all levels of adaptation. The relations of these linear responses to non-linear responses and to physiological mechanisms of the eye are discussed.     

Scototaxis and target perception in the camel tickHyalomma dromedarii

The camel tick,Hyalomma dromedarii, exhibited positive scototaxis in an arena, e.g. it oriented towards a black or grey target in front of a white background. The degree of the scototactic response varied with the size and the elevation of the target, with its luminance contrast, with its shape and with the speed by which the target was moved: (1) the response to stationary and moving targets increased with increasing target size; (2) presentation of the targets at an elevation of 11^o–15^o induced the highest response; (3) the response decreased with decreasing luminance contrast of the target; (4) targets with the shape of a disk, a triangle standing on a vertex, a vertical bar or a silhouette of a dromedary caused high responses; a low response was observed when the target was a horizontal bar and there was no response to a striped pattern; (5) the smaller the size of a disk, the faster it had to be moved to elicit an optimum response.The smallest disk which elicited a significant response appeared under a visual angle of 4.8^o for a thick at the starting point. The smallest dromedary-shaped silhouette which elicited a significant response corresponded to the silhouette of a real dromedary at a distance of 18 m.     

Level dependent signal flow in the light pupil reflex

Latency of pupillary responses to light stimuli are smaller for larger steps of light, and larger for smaller steps of light (Alpern 1954; Lowenstein et al. 1964; Lee et al. 1969; Terdiman et al. 1969; Cibis et al. 1977; and many others). Miller and Thompson (1978), however, reported negligible change in pupil cycle time (period of high gain instability oscillations) with increased mean brightness. Sandberg and Stark (1968) reportd a negligible reduction in phase lag of pupillary responses to sinusoidal light stimuli as the modulation coefficient (m) increased. To resolve the inconsistency between the well-documented dependence of latency upon brightness, and the apparent absence of level dependence in the phase characteristics (as reflected directly in the responses to sinusoidal stimuli and indirectly in pupil cycle time experiments) we measured: 1. Latency to step stimuli of light, 2. Phase of responses to sinusoidal light stimuli and 3. Period (pupil cycle time) of high gain instability oscillations. The dependence of pupillary latency upon stimulus level (both light and accommodation) and the interaction between accommodation and light responses were investigated. We show that most of the level dependence of light-pupil latency resides in the afferent path. In the companion papers, we demonstrate that: 1. Phase of pupillary response to sinusoidal light stimuli is reduced by increased mean light level, but is independent of pupil size and accommodative stimulus level; and 2. The period of high gain oscillations is shown to decrease with increased mean light level. Taken together, these results imply the existence of a Level Dependent Signal Flow (LDSF) operator that resides in the light-pupil pathway, but not in the accommodation-pupil pathway. We propose a systems model of this operator in which the neural signals controlling pupil size are treated as waves whose phase velocity increases in response to brighter stimuli, and decreases in response to dimmer stimuli. When parameters of the model are adjusted to fit measured pupillary latency over a range of light levels, the model exhibits reduced phase lag in response to increased mean light level in the sinusoidal paradigm, and it exhibits reduced pupil cycle time in the high-gain oscillation paradigm. The model exhibits saturation of the LDSF effect in all paradigms at high light levels, as do experimental results. It simulates directional asymmetry of pupillary response to positive and negative steps of light, with constriction more rapid than dilatation. Finally, it simulates tonic pupillary constriction in response to modulation of a light simulus without changing average light level (Varju 1964; Troelstra 1968). All of these stimulated results are in accord with experimental observation.     

The adaptive significance of colour pattern polymorphism in the Australian scincid lizard Lampropholis delicata

Females of Lampropholis delicata are dimorphic for colour pattern, the difference between morphs being the presence or absence of a distinct white mid-lateral stripe. A less distinct striped morph occurs also in males. We evaluated alternative hypotheses for the maintenance of this polymorphism by examining temporal and spatial variation in morph frequency, testing for differential selection among morphs using data on body size and reproductive traits from preserved specimens, and experimentally manipulating colour pattern in free-ranging lizards of both sexes, to assess the influence of the lateral stripe on survival rates. We found that the relative frequency of striped individuals varied among populations and decreased from north to south in both sexes, coincident with an increasing incidence of regenerated tails. Morph frequencies did not change through time within a population. Striped gravid females appeared to survive better and produced larger clutches than did non-striped females. In our experimental study, the relationship between survival and colour morph differed between the two sexes; males painted with a white lateral stripe had lower survival than control (brown stripe) males, but survival did not differ between striped and control females. The different response in the two sexes may be due partly to differences in temperature and microhabitat selection. We propose that the white lateral stripe decreases susceptibility to predators in gravid females but increases risk of predation in males, especially in combination with low temperatures. The polymorphism might be maintained by: (1) opposing fitness consequences of the stripe in males and females; (2) sex-specific habitat selection; and (3) gene flow in combination with spatial variation in relative fitness of the two morphs.     

Fast and slow flight torque responses in flies and their possible role in visual orientation behaviour

The flight torque responses of tethered flying houseflies to motion and presentation or removal of a vertical dark stripe on a bright background were recorded in real time. Motion with constant speed of 100° s^-1 from front to back elicits a strong fast response following the diraction of the stimulus motion. Motion from back to front elicits a weaker response. Instantaneous presentation and removal of a stationary stripe elicit weak, slow response. Apparent motion from front to back and from back to front elicit weak responses with a fast, directionally selective, transient peak followed by a slow response component oriented towards the stripes position. The fast transient peak response is not elicited if the animals were stimulated before with real movement of the stripe. The results are discussed and an earlier proposed model for free flight tracking and fixation is extended.     

Flight-phase and visual-field related optomotor yaw responses in gregarious desert locusts during tethered flight

Tethered flying desert locusts, Schistocerca gregaria, generate yaw-torque in response to rotation of a radial grating located beneath them. By screening parts of the pattern, rotation of the unscreened grating turned out to induce a compensatory steering (by pattern motion within transversally oriented 90° wide sectors) as well as an upwind/downwind turning response (by pattern motion within the anterior ventral 90° wide sector). The strength and polarity of responses upon the unscreened grating results from a linear superposition of these two response components. The results are discussed with regard to a functional specialization of eye regions.In a typical experiment, 3 consecutive flight-phases, assumed to mirror start, long-range flight, and landing of a free-flying locust, were distinguished. They may result from a time dependent variation of the polarity and relative strength of upwind/downwind turning and compensatory steering responses. Starting and landing phases were under strong optomotor control and were dominated by the high-gain compensatory steering. In contrast, the phase of long-range flight was under weak optomotor control resulting from a low gain in both of the two response components. The biological significance of this variable strength of optomotor control on free flight orientation of swarming locusts is discussed.     

不同繁殖状态雌性黑线仓鼠对植物血凝素的反应模式

由植物血凝素（Phytohemagglutinin,ＰＨＡ） 诱导产生的肿胀反应是生态免疫学中被广泛使用的免疫学参数,通过注射部位的肿胀程度大体上可反映细胞介导的免疫和天然免疫的综合变化情况。为探讨小型哺乳动物不同繁殖状态对ＰＨＡ 的反应模式,以非繁殖期、妊娠期、哺乳期和断乳期的雌性黑线仓鼠为研究对象,测定了注射ＰＨＡ 和生理盐水前（０ ｈ）及注射后６ ｈ、１２ ｈ 和２４ ｈ 注射部位皮肤组织的增厚程度。结果显示：（１）黑线仓鼠对ＰＨＡ 的反应有两种模式：非繁殖期、妊娠期和断乳期对ＰＨＡ 的反应模式相似,都在注射后６ ｈ 最高,１２ ｈ 和２４ ｈ 后逐渐下降;哺乳期对ＰＨＡ 的反应在注射后６ ｈ、１２ ｈ 和２４ ｈ 接近,彼此间的差异均不显著。（２）哺乳期黑线仓鼠的ＰＨＡ 反应高峰值有下降趋势,但与非繁殖期、妊娠期和断乳期高峰值之间的差异不显著。结果表明,黑线仓鼠在哺乳期对ＰＨＡ 的反应模式不同于其他繁殖阶段,且反应的高峰值被延迟,这对其存活可能有害,但有助于繁殖进程的延续和后代的生长发育。     

Sources of variation in rapidly inducible responses to leaf damage in the mountain birch-insect herbivore system

Summary Studies on rapidly inducible resistance in trees against insect herbivores show substantial variation in the strength of responses. Here we report the results of a study which examined causes of this variation. We bioassayed the quality of leaves of two developmental phases (young vs. mature) of the mountain birch Betula pubescens ssp. tortuosa by measuring the growth of two instars of Epirrita autumnata larvae. We used only short shoot leaves from trees of a natural stand, uniform in size and age. Damage was caused by larvae and artificial tearing of leaf lamina, varying the scale and time. We separated seasonal changes in plants from instar-dependent effects of the animals by testing experimental larvae in two subsequent growth trials. We found that only larval-made damage induced responses in leaves that made the leaves significantly poorer quality for the test larvae. Artificial damage induced only weak responses, and artificial canopy-wide damage even caused slight improvement of leaf quality. Cumulative leaf damage did not strengthen birch responses. Leaves that were in the expansion phase responded to damage while fully-expanded, mature leaves showed no response. The pattern of responses indicated that there might be physiological constraints: small-scale damage induced resistance against the larvae but largescale damage did not. Prevalent weather conditions might have modified these responses. Larvae of two instars and sexes, of low- and high-density populations responded to leaf damage similarly. However, prior experience of larvae with the host plant may have affected subsequent larval performance. Variation in rapidly inducible responses in birches was caused by plant characters rather than by test animals.     

Neural networks with constrained inputs as models for pattern formation in primate visual cortex

We present a neural network model for the formation of ocular dominance stripes on primate visual cortex and examine the generic phase behavior and dynamics of the model. The dynamical equation of ocular dominance development can be identified with a class of Langevin equations with a nonconserved order parameter. We first set up and examine an Ising model with long-range interactions in an external field, which is equivalent to the model described by the Langevin equation. We use both mean-field theory and Monte-Carlo simulations to study the equilibrium phase diagram of this equivalent Ising model. The phase diagram comprises three phases: a striped phase, a hexagonal bubble phase, and a uniform paramagnetic phase. We then examine the dynamics of the striped phase by solving the Langevin equation both numerically and by singular perturbation theory. Finally, we compare the results of the model with physiological data. The typical striped structure of the ocular dominance columns corresponds to the zero-field configurations of the model. Monocular deprivation can be simulated by allowing the system to evolve in the absence of an external field at early times and then continuing the simulation in the presence of an external field. The physical and physiological applications of our model are discussed in the conclusion.     

Experimental design as a tool when evaluating stationary phases for the capillary electrochromatographic separation of basic peptides

Two different capillary electrochromatography (CEC) stationary phases, Hypersil phenyl and Hypersil C(18), have been characterised with respect to their ability to separate the four basic peptides H-Tyr-(D)Ala-Phe-Phe-NH(2) (TAPP), H-Tyr-(D)Ala-Phe-NH(2) (TAP), H-Phe-Phe-NH(2) (PP) and H-Phe-NH(2) (P). Optimal separation conditions were first established separately for the two phases by applying experimental design in a stepwise procedure. The first step comprised a study to acquire basic knowledge about the variables, their influence on the response and their respective experimental domains for each of the two stationary phases. The second step was screening the significant variables and the third step was an optimisation with response surface modelling (RSM) to locate the optimum separation conditions for each stationary phase. The experimental procedure was identical for both stationary phases, but their respective experimental domains were different. The response functions were peak resolution and peak efficiency. This procedure enables specific optimal experimental conditions to be identified for each of the two stationary phases. The optimal conditions identified for the separation on the phenyl stationary phase were to use 50% ACN, 20% 50 mM Tris(hydroxymethyl)aminomethane (TRIS) pH 7.5, 30% H(2)O as BGE, operating at 20 degrees C and 20 kV high voltage. For the C(18) stationary phase optimal separation was achieved using a BGE with 80% ACN, 20% 30 mM TRIS pH 8.5, again operating at 20 degrees C and 20 kV high voltage. Results show that the phenyl stationary phase is better suited for the separation of basic, hydrophilic peptides.     

Effect of behavioral history on subsequent responding: experiments using rotary fixed-ratio schedules

The present study proposes a novel experimental approach to examine the effect of previous schedule history on subsequent responses. College students used a three-button device to indicate their choice of response. We performed two experiments. Each experiment consisted of three phases. In experiment I, fixed-ratio 10 (FR 10) reinforcement schedule was employed in phases 1 and 3. Phase 2 employed "Rotary-FR 10" schedule: after obtaining a point produced by pressing one of three specified buttons in a triangular array 10 times, the effective button changed to another in a clockwise direction. Optimal response pattern for Rotary-FR 10 was analyzed. Two types of behavior, referred to as "consecutive" and "scatter" were observed in phase 1. The mean number of optimal responses in consecutive type was significantly higher than scatter type in phases 2 and 3. In experiment II, two schedules were used in phase 1, and the same protocol used in experiment I was followed. We found that the reinforcement schedule used in phase 1 affected acquisition of the optimal response in phase 2. These results suggest that the earlier behavioral tendencies play an important role in determining subsequent behavior and that such behavioral tendency can be modified by specifically designed protocols.     

The relationship between absolute disparity and ocular vergence

The relationship between disparity and ocular vergence was investigated under closed-loop as well as under open-loop viewing conditions. First we examined whether vergence responded similarly to disparity presented under open-loop and closed-loop conditions. Similar response were observed in both conditions. The direct relationship between disparity and vergence was examined by presenting constant disparities between 0.2° and 4° under open-loop viewing conditions. Such vergence responses are described as the outputs of first-order low-pass filters with different filter characteristics for each amplitude of disparity. By analyzing the latency of vergence responses induced by constant disparities with help of the transfer function of disparitycontrolled vergence, the time delay of disparity processing in the vergence loop was estimated. We suggested that the time delay was approximately between 80 and 120 ms instead of 160 ms as is generally assumed. The relationship between the rate of disparity change and vergence was examined by comparing responses to ramp and stepwise changes in target vergence. From the similar responses to ramp and staircase changes in disparity we concluded that vergence is not sensitive to the velocity of target vergence as such. On the basis of these findings we developed a model of disparity-controlled vergence. In this model disparity is processed through several parallel, imperfect integrators with slightly different low-pass filter characteristics, each of them susceptible to a limited range of disparities. Gains as well as phase lags of vergence responses to sinusoidal disparities are accurately simulated by this model. As a consequence of the limited working range of the low-pass filters, the model correctly simulates the alterations of fast and slow phases in response to step and ramps of target vergence, which are characteristic of real vergence responses.     

Learning receptive field properties of complex cells in V1

There are two distinct classes of cells in the primary visual cortex (V1): simple cells and complex cells. One defining feature of complex cells is their spatial phase invariance; they respond strongly to oriented grating stimuli with a preferred orientation but with a wide range of spatial phases. A classical model of complete spatial phase invariance in complex cells is the energy model, in which the responses are the sum of the squared outputs of two linear spatially phase-shifted filters. However, recent experimental studies have shown that complex cells have a diverse range of spatial phase invariance and only a subset can be characterized by the energy model. While several models have been proposed to explain how complex cells could learn to be selective to orientation but invariant to spatial phase, most existing models overlook many biologically important details. We propose a biologically plausible model for complex cells that learns to pool inputs from simple cells based on the presentation of natural scene stimuli. The model is a three-layer network with rate-based neurons that describes the activities of LGN cells (layer 1), V1 simple cells (layer 2), and V1 complex cells (layer 3). The first two layers implement a recently proposed simple cell model that is biologically plausible and accounts for many experimental phenomena. The neural dynamics of the complex cells is modeled as the integration of simple cells inputs along with response normalization. Connections between LGN and simple cells are learned using Hebbian and anti-Hebbian plasticity. Connections between simple and complex cells are learned using a modified version of the Bienenstock, Cooper, and Munro (BCM) rule. Our results demonstrate that the learning rule can describe a diversity of complex cells, similar to those observed experimentally.     

Regulation of Transpiration in Avena. Responses to Red and Blue Light Steps

The transpiration responses of primary Arena leaves to red and blue light steps were investigated. The response to a red light step was a so-called slow response (with a rise time of about 8 min). The response to a blue light step consisted of both a slow, and a rapid response (with a rise time of about 2 min). CO₂-free air outside the leaf eliminated only the slow response, i.e. in CO₂-free ait the plant responded to blue light steps but not to red ones. A short exposure of red light prior to a blue light step enhanced the rapid response. The same enhancement of the rapid response could be achieved by means of a temporary pretreatment with CO₂-free air. The magnitude of the rapid response was dependent on the blue light irradiance and no threshold effects could be detected. — The experimental results are discussed by means of a model, based on stomatal regulation by, ion transport between the subsidiary cells and the guard cells. It is suggested that the slow transpiration response is due to CO₂-regulation of the stomatal aperture and that the rapid response reflect a CO₂-independent blue light sensitive process, which acts directly on the ion transport through the subsidiary and guard cell membranes.     

Age‐0 striped bass,Morone saxatilis (Walbaum, 1792), response to immunostimulation

Young‐of‐the‐year (age‐0) striped bass, Morone saxatilis, were studied to characterize their responses to inflammatory stimuli. There were two studies, with the hypotheses that (i) <5 g striped bass would respond to inflammatory insult within 6 h, and (ii) response to antigens would be maintained for >24 h in larger fish. Study I was conducted to understand the cytokine expression pattern (IL‐1β, TNF‐α, Nramp and TGF‐β) in response to lipopolysaccharide (LPS) or Freund's complete adjuvant (FCA) stimulation in age‐0 striped bass (3.44 ± 1.68 g, 70.6 ± 10.3 mm fork length) up to 24 h post injection (hpi). Study II was similar to Study I, but striped bass were sampled over a longer time frame (by 48 hpi) and larger age‐0 striped bass were used (20.6 ± 5.9 g, 129.2 ± 10.9 mm fork length). It was confirmed that immunostimulants such as LPS and FCA induce production of inflammatory cytokines and Nramp, which are important in innate immune response to bacterial infection. The responses were rapidly stimulated with LPS (IL‐1β, TNF‐α, TGF‐β >3‐fold increase, compared to PBS) or FCA (IL‐1β >3‐fold and TGF‐β >2‐fold, compared to PBS) within 6 hpi and maintained in most cases 48 hpi (spleen Nramp and TGF‐β 2‐fold >PBS, at 24 and 48 h), similar to other teleosts. Intraperitoneal injection with PBS also simulated inflammatory gene expression, but was delayed (IL‐1β, TNF‐α, TGF‐β and Nramp, FCA and LPS< at 6 h; 24 h >LPS and PBS) in comparison to LPS and FCA, suggesting that this procedure and possibly the volume used can be stimulatory and potentially harmful in age‐0 fish. Therefore, this study suggests that age‐0 striped bass are capable of strong cytokine induction in response to immunological stimulation within a very short period of time.     

Dorsal pattern polymorphism in female Iberian wall lizards: differences in morphology,dorsal coloration,immune response,and reproductive investment

Sex‐specific colour polymorphisms have been extensively documented in many different taxa. When polymorphism in colour pattern is restricted to females, the condition is known as female‐limited pattern polymorphism (FPP), which has been less commonly addressed in vertebrates. FPP is present in several lizard species, although most research on lizards has focused on carotenoid‐ and pteridine‐based coloration and not on melanin‐based polymorphisms. In the present study, we focus on Iberian wall lizards, Podarcis hispanicus, where two female melanin‐based dorsal patterns can be clearly distinguished: striped and reticulated‐blotched. We indirectly tested the hypothesis that selection acts differentially among P. hispanicus female morphs to create alternative morph‐specific phenotypic optima at different levels by investigating whether morphs differ in fitness proxies. We specifically examined whether the two female dorsal pattern morphs differed in adult morphology, dorsal coloration, immune response, reproductive investment, and growth. We did not find a relationship between melanin‐based coloration and hatchling growth and immune response, despite a correlation between these traits possibly being expected as a result of pleiotropy in the melanocortin system. However, our results show that female dorsal morphs in P. hispanicus differ in terms of adult morphology, dorsal coloration, and reproductive investment. Reticulated‐blotched P. hispanicus females had deeper heads and longer femora, less melanin, and more brownish coloration, and also had larger and heavier hatchlings than striped females.     

The three-dimensional optomotor torque system ofDrosophila melanogaster

Summary The well known optomotor yaw torque response in flies is part of a 3-dimensional system. Optomotor responses around the longitudinal and transversal body axes (roll and pitch) with strinkingly similar properties to the optomotor yaw response are described here forDrosophila melanogaster. Stimulated by visual motion from a striped drum rotating around an axis aligned with the measuring axis, a fly responds with torque of the same polarity as that of the rotation of the pattern. In this stimulus situation the optomotor responses for yaw, pitch and roll torque have about the same amplitudes and dynamic properties (Fig. 2). Pronounced negative responses are measured with periodic gratings of low pattern wavelengths due to geometrical interference (Fig. 3). The responses depend upon the contrast frequency rather than the angular velocity of the pattern (Fig. 4). Like the optomotor yaw response, roll and pitch responses can be elicited by small field motion in most parts of the visual field; only for motion below and behind the fly roll and pitch responses have low sensitivity.The mutantoptomotor-blind ^H31 (omb ^H31) in which the giant neurones of the lobula plate are missing or severely reduced, is impaired in all 3 optomotor torque responses (Fig. 5) whereas other visual responses like the optomotor lift/thrust response and the landing response (elicited by horizontal front-to-back motion) are not affected (Heisenberg et al. 1978).We propose that the lobula plate giant neurons mediate optomotor torque responses and that the VS-cells in particular are involved in roll and pitch but not in lift/thrust control. This hypothesis accommodates various electrophysiological and anatomical observations about these neurons in large flies.Abbreviation EMD elementary movement detector     

Comparison between the movement detection systems underlying the optomotor and the landing response in the housefly

Flies evaluate movement within their visual field in order to control the course of flight and to elicit landing manoeuvres. Although the motor output of the two types of responses is quite different, both systems can be compared with respect to the underlying movement detection systems. For a quantitative comparison, both responses were measured during tethered flight under identical conditions. The stimulus was a sinusoidal periodic pattern of vertical stripes presented bilaterally in the fronto-lateral eye region of the fly. To release the landing response, the pattern was moved on either side from front to back. The latency of the response depends on the stimulus conditions and was measured by means of an infrared light-beam that was interrupted whenever the fly lifted its forelegs to assume a preprogrammed landing posture (Borst and Bahde 1986). As an optomotor stimulus the pattern moved on one side from front to back and on the other side in the opposite direction. The induced turning tendency was measured by a torque meter (Götz 1964). The response values which will be compared are the inverse latencies of the landing response and the amplitude of the yaw torque.

1. Optomotor course-control is more sensitive to pattern movement at small spatial wavelengths (10° and 20°) than the landing response (Fig. 1a and b). This suggests that elementary movement detectors (EMDs, Buchner 1976) with large detection base (the distance between interacting visual elements) contribute more strongly to the landing than to the optomotor system.
2. The optimum contrast frequencies of the different responses obtained at a comparatively high pattern contrast of about 0.6 was found to be between 1 and 10 Hz for the optomotor response, and around 20 Hz for the landing response (Fig. 2a and b). This discrepancy can be explained by the fact that the optomotor response was tested under stationary conditions (several seconds of stimulation) while for the landing response transient response characteristics of the movement detectors have to be taken into account (landing occurs under these conditions within less than 100 ms after onset of the movement stimulus). To test the landing system under more stationary conditions, the pattern contrast had to be reduced to low values. This led to latencies of several seconds. Then the optimum of the landing response is around 4 Hz. This is in the optimum range of the optomotor course-control response. The result suggests the same filter time constants for the movement detectors of both systems.
3. The dependence of both responses on the position and the size of the pattern was examined. The landing response has its optimum sensitivity more ventrally than the optomotor response (Fig. 3a and b). Both response amplitudes increase with the size of the pattern in a similar progression (Fig. 3c and d).

In first approximation, the present results are compatible with the assumption of a common set of movement detectors for both the optomotor course-control and the landing system. Movement detectors with different sampling bases and at different positions in the visual field seem to contribute with different gain to both responses. Accordingly, the control systems underlying both behaviors are likely to be independent already at the level of spatial integration of the detector output.