Notes: [Auszug] Bees trained to forage at a place specified by landmarks do not construct a cartesian map of the arrangement of landmarks and food source. Instead they store something like a two-dimensional snapshot of their surroundings taken from the food source. To return there, bees move so as to reduce ...

Notes: Abstract To investigate the priming of memories by contextual cues, bees were trained to negotiate two mazes in different places 25 m apart. In the first maze, bees flew leftwards when the inner wall of the maze was covered with 45° stripes or rightwards when the inner wall was coloured yellow. In the second maze, bees flew rightwards on viewing 135° diagonal stripes or leftwards on viewing blue. The trajectories evoked by 45° or 135° stripes were similar in both mazes. However, vertical stripes were treated like 45° stripes in maze 1 and like 135° stripes in maze 2. Contextual cues prime the response to stripes that are oriented in the training condition for that site so influencing responses to stripes in closely neighbouring orientations. What objects in a bee's surroundings determine its sense of place? Bees were trained to different visual patterns at two sites 40 m apart (A+ versus A– at site A, and E+ versus E– at site E). A+ was preferred over A– and E+ was preferred over E– at both training sites. A preference for A+ over E+ exhibited at site A dropped gradually with distance to suggest that spatial context includes both close and distant objects.

Notes: Summary 1. Chases in which male flies (Fannia canicularis) pursue other flies were studied by filming such encounters from directly below. Males will start to chase whenever a second fly comes within 10–15 cm (Fig. 3). 2. Throughout these chases there was a continuous relationship between the angle (θ e ) made by the leading fly and the direction of flight of the chasing fly, and the angular velocity of the chasing fly (ω f ). This relation was approximately linear, with a slope of 20 ° s−1 per degree θ e (Figs. 4–7). 3. The maximum correlation between ω f and θite occurs after a lag of approximately 30 ms, which represents the total delay in the system (Fig. 8). 4. In the region close to the chasing fly's axis (θite less than about 35 °) a second mechanism exists in which the angular velocity of the chasing fly (ω f ) is controlled by the relative angular velocity of the leading fly (ω e ), rather than its relative position. The ratio of ω f to ω e in this region is approximately 0.7. 5. Using the results in 2–4 above, and an empirically determined relation between the angular and forward velocities of the chasing fly, it was possible to simulate the flight path of the chasing fly, given that of the leading fly (Fig. 11). Because these simulations predict correctly the manoeuvres and outcomes of quite complicated chases, it is concluded that the control system actually used by the fly is accurately described by conclusions 2–4. 6. The physiological implications of this behaviour, and the possible function of chasing, are discussed.

Notes: Abstract In order to analyse how landmarks guide the last stages of an insect's approach to a goal, we recorded many flights of individual wasps and honeybees as they flew to an inconspicuous feeder on the ground that was marked by one or by two nearby landmarks. An individual tends to approach the feeder from a constant direction, flying close to the ground. Its body is oriented in roughly the same horizontal direction during the approach so that the feeder and landmarks are viewed over a narrow range of directions. Consequently, when the insect arrives at the feeder, the landmarks take up a standard position on the retina. Three navigational strategies govern the final approach. The insect first aims at a landmark, treating it as a beacon. Secondly, bees learn the appearance of a landmark with frontal retina and they associate with this stored view a motor trajectory which brings them from the landmark sufficiently close to the goal that it can be reached by image matching. Insects then move so as to put the landmark in its standard retinal position. Image matching is shown to be accomplished by a control system which has as set points the standard retinal position of the landmark and some parameter related to its retinal size.

Notes: Summary 1. The visually guided flight behaviour of groups of male and femaleSyritta pipiens was filmed at 50 f.p.s. and analysed frame by frame. Sometimes the flies cruise around ignoring each other. At other times males but not females track other flies closely, during which the body axis points accurately towards the leading fly. 2. The eyes of males but not females have a forward directed region of enlarged facets where the resolution is 2 to 3 times greater than elsewhere. The inter-ommatidial angle in this “fovea” is 0.6°. 3. Targets outside the fovea are fixated by accurately directed, intermittent, open-loop body saccades. Fixation of moving targets within the fovea is maintained by “continuous” tracking in which the angular position of the target on the retina (Θ e) is continuously translated into the angular velocity of the tracking fly ( $$\dot \Phi _p $$ ) with a latency of roughly 20 ms ( $$\dot \Phi _p = k \Theta _e $$ , wherek≏30 s−1). 4. The tracking fly maintains a roughly constant distance (in the range 5–15 cm) from the target. If the distance between the two flies is more than some set value the fly moves forwards, if it is less the fly moves backwards. The forward or backward velocity ( $$\dot F_p $$ ) increases with the difference (D-D 0) between the actual and desired distance ( $$\dot F_p = k^\prime (D - D_0 )$$ ), wherek′=10 to 20 s−1). It is argued that the fly computes distance by measuring the vertical substense of the target image on the retina. 5. Angular tracking is sometimes, at the tracking fly's choice,supplemented by changes in sideways velocity. The fly predicts a suitable sideways velocity probably on the basis of a running averageΘ e , but not its instantaneous value. Alternatively, when the target is almost stationary, angular tracking may bereplaced by sideways tracking. In this case the sideways velocity ( $$\dot S$$ ) is related toΘ e about 30 ms earlier ( $$\dot S_p = k\prime \prime \Theta _e $$ , wherek″=2.5 cm · s−1 · deg−1), and the angular tracking system is inoperative. 6. When the leading fly settles the tracking fly often moves rapidly sideways in an arc centred on the leading fly. During thesevoluntary sideways movements the male continues to point his head at the target. He does this not by correctingΘ e , which is usually zero, but by predicting the angular velocity needed to maintain fixation. This prediction requires knowledge of both the distance between the flies and the tracking fly's sideways velocity. It is shown that the fly tends to over-estimate distance by about 20%. 7. When two males meet head on during tracking the pursuit may be cut short as a result of vigorous sideways oscillations of both flies. These side-to-side movements are synchronised so that the males move in opposite directions, and the oscillations usually grow in size until the males separate. The angular tracking system is active during “wobbling” and it is shown that to synchronise the two flies the sideways tracking system must also be operative. The combined action of both systems in the two flies leads to instability and so provides a simple way of automatically separating two males. 8. Tracking is probably sexual in function and often culminates in a rapid dart towards the leading fly, after the latter has settled. During these “rapes” the male accelerates continuously at about 500 cm · s−2, turning just before it lands so that it is in the copulatory position. The male rapes flies of either sex indicating that successful copulation involves more trial and error than recognition. 9. During cruising flight the angular velocity of the fly is zero except for brief saccadic turns. There is often a sideways component to flight which means that the body axis is not necessarily in the direction of flight. Changes in flight direction are made either by means of saccades or by adjusting the ratio of sideways to forward velocity ( $$\dot S/\dot F$$ ). Changes in body axis are frequently made without any change in the direction of flight. On these occasions, when the fly makes an angular saccade, it simultaneously adjusts $$\dot S/\dot F$$ by an appropriate amount. 10. Flies change course when they approach flowers using the same variety of mechanisms: a series of saccades, adjustments to $$\dot S/\dot F$$ , or by a mixture of the two. 11. The optomotor response, which tends to prevent rotation except during saccades, is active both during cruising and tracking flight.

Notes: Summary 1. MaleSyritta pipiens have been filmed tracking other flies within a rotating drum in order to analyse the interaction between the optomotor and smooth tracking systems. Males have a forwardly directed region of enlarged facets with enhanced spatial resolution, and smooth angular tracking operates to keep targets on this fovea. The male's angular velocity (φ) is driven by the angular position of the target fly on its retina (θe 10 to 20 ms earlier (i.e. φ =k= κθe, where κ is about 30–40s−1). The optomotor system is used for controlling a fly's course. The rotational component of this reflex causes a fly to turn in the same direction as externally generated retinal image motion. When placed within a rotating drum, the angular velocity of freely flyingSyritta follows that of the drum (i.e. φ =Gφdrum, whereG = 0.8 for φdrum〈200 °.s−1). Thus, whenSyritta turns to pursue another fly, the image of its static surroundings will sweep across its retina in the other direction, tending to generate optomotor torque in opposition to that caused by the tracking reflex. Unless arrangements are made to cope with this predictable optomotor input, tracking will be slowed. 2. The angular velocity of a male tracking in a rotating drum has two components: one caused by the drum velocity; the other by the retinal position of the target image (i.e. φ =Gφdrum +kκθe). During tracking, then, the optomotor system is fully active and will minimiseunwanted image motion caused by a disturbance. There are at least three forms of interaction between the two reflexes which in stationary surroundings will allow tracking to operate without interference from an active optomotor system. It is shown that all of them are compatible with the above result. 3. One of these schemes is the follow-up servo in which the tracking system works by injecting a command into the optomotor loop, so changing the latter's set point, thereby inducing an angular velocity greater than zero. This scheme in its simplest form requires that tracking has the same delays and frequency behaviour as the optomotor response. Since the two reflexes probably have different frequency responses, the follow-up servo can be rejected. The gain of the optomotor response (G) measured in an oscillating drum falls steeply between 0.5 Hz and 5 Hz, as it should, if the optomotor response is to be stable. However, there are indications that the constant κ, which relates ϕ to φe during tracking has the same value, if θe oscillates at more than 6 Hz, as it has for very low input frequencies. 4. That the value ofk seems to be limited by stability requirements and is to a first approximation independent of input frequency suggests that the tracking system has indeed been tailored to cope with the optomotor input that must oppose tracking at low frequencies. A simple additive model in which the tracking and optomotor commands first come together at a final common pathway will give the required performance provided that the tracking gain (x in Fig. 9) is enhanced atlow frequencies to allow for the opposing optomotor input. However, a simpler way of eliminating the unwanted optomotor torque is to use the efference copy scheme of von Holst and Mittelstaedt (1950). In this scheme a copy of the tracking command signal is sent to the optomotor input in order to cancel the expected visual consequences of tracking. In general, efference copy is a useful way of mixing two reflexes with different temporal properties. 5. FemaleMusca exhibit behaviour that is somewhat analogous to the smooth tracking of male flies (Reichardt and Poggio, 1976), but is probably concerned, not with chasing small targets, but with maintaining the fixation of large stationary objects. When maintaining fixation of stationary objects, the tracking and optomotor systems will complement each other, rather than acting in opposition, so that the form of interaction between tracking and the optomotor system may be different in the two sexes. Thus the female tracking system need make no provision for the optomotor response, even though the latter is active during tracking (Virsik and Reichardt, 1976).

Notes: Summary 1. Males of many species of hoverfly hover in one spot ready to pursue passing objects, presumably in order to catch a mate. We have filmed two of the larger species as they begin their pursuit of an approaching projectile shot at them from a peashooter. Flies do not turn and fly towards the projectile as they would if they were tracking (Land and Collett, 1974). Instead they adopt an interception path, accelerating at a uniform rate (30–35 m · s−2) approximately in the direction in which the target is moving (Fig. 1). 2. If the projectile is made to reverse direction, the male does not respond to the change in the target's course for about 90 ms (Fig. 2). Thus, in contrast to the situation later (Fig. 3), the start of a pursuit is not under continuous sensory control. The fly selects its course when it first sees the target and maintains its interception path as an open-loop response. 3. Males only need to catch conspecifics and can thus assume that their quarry has a typical speed and, since it is of a uniform size, will be detected at a predetermined distance. These assumptions mean that the approach angle of the target at the moment of first sighting can be specified by the image velocity of the target across the retina ( $$\dot \theta _e $$ ). Since the male also “knows” its own acceleration, the direction of flight which will enable it to intercept the target can also be specified in terms of the initial position (θ e) and velocity ( $$\dot \theta _e $$ ) of the target image (Figs. 6 and 7). 4. We show that interception should occur if the male obeys the simple rule that the size of the turn it makes (Δφ) is given by $$\Delta \phi \simeq \theta _e - 0.1{\text{ }}\dot \theta _e \pm 180^\circ $$ . Our data indicate that the initial turns of the males do obey this rule (Fig. 8), and that males are “designed” to catch females travelling at about 8 m · s−1. 5. If males are calibrated to catch targets of a particular size and speed, they will be unable to intercept projectiles that are very different in these respects. When large, slowly moving projectiles are launched to pass by the fly, its attempted interception path is predictably inappropriate (Fig. 9).

Notes: Summary 1. An open- and closed-loop study of the way ladybirds,Coccinella septempunctata, approach vertical posts emphasizes two features of this reflex. First, ladybirds turn preferentially towards close objects, obtaining the necessary distance information from optic flow. Secondly, once an object has been fixated, movement of its image over frontal retina tends to suppress any response to other laterally viewed targets. 2. Recordings were made of the trajectories followed by ladybirds in an open arena which contained a single, vertical post on the floor. Ladybirds often approached and climbed up the post. Many approaches consisted of straight-line segments interrupted by abrupt turns. These turns are either appropriately sized so that the ladybird faces the post after one turn or, more often, they are too small in which case the ladybird's trajectory is a spiral. The gain of the turn (i.e. the ratio of the size of the turn to the size which is needed to fixate the post) increases slightly as the insect approaches the post. 3. The ladybirds' preference for close objects was examined further on a Y-maze. Insects placed on the trunk of the maze ran towards the fork and down one arm. Each arm of the maze led to a rectangle. Rectangles were placed at various distances from the fork. Their size was adjusted so that viewed from the fork they all subtended 18° horizontally and 63° vertically. Ladybirds chose predominantly the arm which led to the closer rectangle. 4. Open-loop tests indicate that this preference for close objects is caused by the pattern of optic flow resulting from the ladybirds' normal forward locomotion. Insects were fixed in front of a computer screen and carried a small ring which they rotated beneath them. Any attempted turn was manifest in a turn of the ring in the opposite direction. Turns were regularly elicited by small backward movements of a vertical stripe across the retina, as would occur during forward walking. Forward motion of the stripe over the retina rarely evoked turns. Turns increased in frequency and size as the speed of backward image motion was raised from 3°/s to 70°/s. The largest turns were evoked with the stripe placed at an eccentricity of about 90 degs from the midline. Amplitude dropped as the stripe was positioned further frontally or posteriorly. 5. Approaches to a target were modelled using a saccadic system in which gain varied with distance from the target. This simulation generated spiral trajectories. Thus, the spirals described by a ladybird when it walks towards a post may be a consequence of the way the insect uses motion parallax to restrict its attention to nearby objects. 6. Open-loop turns to a stripe moving over peripheral retina are prevented by the concurrent motion of a stripe viewed by frontal retina. This longrange inhibition means that, once a stripe has been fixated, an insect's attention is less likely to be distracted by objects seen peripherally.

Notes: Summary 1. Given the right circumstances, toads will detour round a paling fence to reach their prey on the other side. In programming this manoeuvre, toads take into account both the position of the fence and the distance of the prey (Fig. 1). Should there be a gap in the fence, which offers a more direct approach, toads will aim for that instead (Fig. 2). 2. The argument developed in this paper is that, when a toad decides upon a particular approach, it is guided by the sum of its reactions to several individual features of the situation, such as the length of the fence, the presence or absence of gaps, the gaps' width (Fig. 7) and their proximity to the prey (Fig. 11) and to the toad's long axis (Fig. 10). When there are several possible approaches, toads will select the gap (or edge) which has the most ‘attractive’ combination of features. 3. The relative attraction of gaps can be manipulated and toads will then shift their preference. Normally, toads head for the gap lying closest to the prey and to their long axis (Figs. 9a and 12b). However, if the relative salience of a more peripheral gap is increased the bias towards the closer gap is reduced (Fig. 9b). 4. Toads tend to choose the closest gap even when it is inappropriate to do so. They seem unable to use the spatial information potentially available to them to pick out the shortest, unobstructed path to their prey. The major support for this view comes from the way they treat double fences composed of two rows of palings. With both fences unbroken, toads usually detour around them (Fig. 2d). However, when a gap is inserted in the front fence, they will often aim for that, regardless that the rear fence blocks their subsequent approach (Figs. 2c and 4). If palings are added to join the ends of the two fences, toads continue to aim for the gap, though once they have entered the space between the two fences, all they can do is to retrace their steps. 5. It is not that toads are blind to the rear fence. They can detect gaps in it (Fig. 8a) and their behaviour is influenced by the distance between the rear fence and their prey (Fig. 6). Nonetheless, a gap restricted to the front fence is still treated as a gap, but as less attractive than one extending through both fences (Fig. 8b). And, if such a gap is close to the toad's midline and the prey, then toads are drawn to it, rather than to the ends of the fence.

Notes: Summary 1. In order to analyse the mechanism of accommodation in anurans, drugs (miotic or atropine) were applied to the cornea of anaesthetized animals to change the refractive state of their eyes. During such changes, the lens and cornea were photographed and the refractive state of the eye was measured using laser speckle refractometry. Measurements taken from the photographs confirmed suggestions by Beer (1898) that accommodation is achieved by moving the lens and not by changing the shape of the lens or cornea. The change in refractive state induced by pharmacological manipulation was about 10 diopters with an accompanying shift in lens position of about 150 μm. Calculations based on a schematic eye suggest a disparity between the amount of lens movement theoretically needed to produce a 10 D shift in refractive state and the amount actually observed. 2. The lens is probably moved by two protractor lentis muscles which are positioned so as to pull the lens towards the cornea (Tretjakoff 1906, 1913). Dissection and HRP preparations revealed that these muscles are innervated by fibres of the oculomotor nerve which relay in the ciliary ganglion. InR. esculenta andR. pipiens, the ciliary ganglion consists of only 8 to 12 nerve cells. 3. MS222 anaesthesia and lymphatic injection of curare cause the lens to move away from the cornea, presumably because they destroy the resting tonus of the protractor lentis muscles. We discuss this finding in relation to the frog's ‘resting’ accommodative state, and conclude that unparalysed frogs are likely to be myopic, and not emmetropic as previous work suggests. 4. Prey capture was analysed inR. pipiens after the disruption of accommodation by bilateral section of the oculomotor nerve. Estimates of prey distance remained accurate when vision was binocular. However, during monocular vision, when the oculomotor nerve was sectioned on one side and the other eye was either occluded or had its optic nerve cut, frogs consistently underestimated the distance of their prey. This result suggests, in agreement with earlier evidence, that accommodation is used for judging depth when vision is limited to one eye, but that binocular information predominates when it is available. 5. Atropine applied to the cornea of monocular frogs also causes distance to be underestimated. It is argued from this that frogs assess distance by monitoring the motor commands sent to their accommodative muscles, rather than by using sensory information from the muscles themselves.