On the encoding of movement vectors by honeybees. Are distance and direction represented independently?

Honeybees flying repeatedly over the same trajectory link it to an associated visual stimulus such that on viewing the stimulus they perform a trajectory in the habitual direction. To test if trajectory length can also be linked to a visual stimulus, bees were trained to fly through a multi-comparmented maze. Bees flew through a multi-compartmented maze. In one compartment a short trajectory could be linked to a stripe pattern oriented at 45° to the horizontal. In another compartment a longer trajectory could be linked to 135° stripes. Bees made both associations: their trajectories were short when viewing 45° stripes and longer when viewing 135° stripes. 90° stripes evoked trajectories of intermediate length.To test if distance and direction are linked independently to stripe orientation, a bee's trajectory was linked to 135° stripes in one compartment and to 45° stripes in another. These trajectories were the same length but differed in their horizontal direction by 60° or by 120°. 90° stripes evoked trajectories of intermediate direction which were shorter than those elicited by either training pattern. Bees were also trained to generate one long and one short trajectory with directions 120° apart. The trajectories elicited by 90° stripes were then biased towards the direction of the long training vector. Length and direction are not treated separately. The rules for combining trajectories resemble those of vector averaging.     

Learnt sensori-motor mappings in honeybees: interpolation and its possible relevance to navigation

We investigated the ability of bees to associate a motor parameter with a sensory one. Foragers were trained to fly along a prescribed route through a large box which was partitioned into compartments. Access from one compartment to the next was through a hole in each partition. In two of the compartments, the back wall was covered with a grating of black and white stripes. Stripe orientations and the required trajectories differed in the two compartments so giving bees the opportunity to learn that one stripe orientation signalled the need to fly leftwards and the other rightwards.We videotaped the bees' trajectories through one of these compartments in tests with the grating on the back wall in one of four possible orientations. Flight trajectories to stripes in the training orientations were appropriately to the left or to the right implying that bees had linked a given flight direction to a given stripe orientation. With gratings oriented between the training values, flight directions were, under some conditions, intermediate between the training directions. This interpolation indicates that the training regime had induced a continuous mapping between stripe orientation and trajectory direction and thus suggests that trajectory direction is a motor parameter which is encoded explicitly within the brain. We describe a simple network that interpolates much like bees and we consider how interpolation may contribute to the ability of bees to navigate flexibly within a familiar environment.     

Orientation by polarized light in the crayfish dorsal light reflex: behavioral and neurophysiological studies

In decapod crustaceans, the dorsal light reflex rotates the eyestalk so that the dorsal retina faces the brightest segment of dorsal visual space. Stepwise displacements of white stripes elicit eyestalk rotations in the same direction as that of the stripe. Conversely, stepwise displacements of black stripes on a white background elicit eyestalk rotations in the opposite direction as that of the stripe. The reversal of the response with contrast inversion distinguishes the dorsal light reflex from an optokinetic reflex. When the visual scene is composed of polarized light, segmented by variations in e-vector orientation, displacement of segments containing near vertical e-vectors elicit responses similar to those elicited by a white stripe. Displacement of polarized stripes containing near horizontal e-vectors elicit eyestalk rotations similar to those elicited by a black stripe. The results are consistent with the use of polarized light in orientation. The stimulus conditions described above were also applied to visual interneurons (sustaining fibers) and oculomotor neurons and the results were generally in accord with the behavior. In the neural studies, it was possible to show that responses to polarized stripe displacements are predictable from the receptive field location and the neuron’s polarization tuning function. John P. Schroeter deceased on September 14, 2006.     

Pattern recognition in honeybees: eidetic imagery and orientation discrimination

The roles of eidetic imagery and orientational cues, respectively, in the discrimination of visual patterns by honeybees (Apis mellifera) were evaluated by training the bees to discriminate between patterns consisting of periodic, black and white square wave gratings. Training and tests with a number of different pairs of patterns revealed that bees use orientational cues almost exclusively, if such are present, and make use of eidetic images only when orientational cues are not available. On the other hand, if a pattern carries strong orientational cues, bees learn the orientation even if it is irrelevant to the discrimination task on which they are trained.     

Analysis of emergent patterns in crossing flows of pedestrians reveals an invariant of ‘stripe’ formation in human data

When two streams of pedestrians cross at an angle, striped patterns spontaneously emerge as a result of local pedestrian interactions. This clear case of self-organized pattern formation remains to be elucidated. In counterflows, with a crossing angle of 180°, alternating lanes of traffic are commonly observed moving in opposite directions, whereas in crossing flows at an angle of 90°, diagonal stripes have been reported. Naka (1977) hypothesized that stripe orientation is perpendicular to the bisector of the crossing angle. However, studies of crossing flows at acute and obtuse angles remain underdeveloped. We tested the bisector hypothesis in experiments on small groups (18-19 participants each) crossing at seven angles (30° intervals), and analyzed the geometric properties of stripes. We present two novel computational methods for analyzing striped patterns in pedestrian data: (i) an edge-cutting algorithm, which detects the dynamic formation of stripes and allows us to measure local properties of individual stripes; and (ii) a pattern-matching technique, based on the Gabor function, which allows us to estimate global properties (orientation and wavelength) of the striped pattern at a time T. We find an invariant property: stripes in the two groups are parallel and perpendicular to the bisector at all crossing angles. In contrast, other properties depend on the crossing angle: stripe spacing (wavelength), stripe size (number of pedestrians per stripe), and crossing time all decrease as the crossing angle increases from 30° to 180°, whereas the number of stripes increases with crossing angle. We also observe that the width of individual stripes is dynamically squeezed as the two groups cross each other. The findings thus support the bisector hypothesis at a wide range of crossing angles, although the theoretical reasons for this invariant remain unclear. The present results provide empirical constraints on theoretical studies and computational models of crossing flows.     

The interaction of edge-fixation and negative phototaxis in the orientation of walking gypsy moths,Lymantria dispar

Summary The visual orientation towards single black stripes and more complex patterns, comprising smooth gradients of brightness was studied in walking gypsy moths. Depending on the width of a black stripe, up to three walking directions are preferred within one stimulus situation: towards the centre of the stripe and towards a region within the stripe closer to each edge. The observed responses are explained by a compromise between edge-fixation and negative phototaxis. This hypothesis turned out to be also applicable to more complex patterns.     

The number of stripes on the compound eyes reflects each instar in <Emphasis Type="Italic">Acromantis satsumensis</Emphasis> (Mantodea: Hymenopodidae)

The praying mantis genus Acromantis is characterized by its compound eyes with stripe patterns in the Japanese Mantodea. In the laboratory, we observed that the 1st instar nymphs of Acromantis satsumensis Matsumura had a single stripe on their compound eyes, and one more stripe appeared on both of their compound eyes when they became 2nd instar nymphs. Likewise, the 3rd instars had 3 stripes, the 4th instars had 4 stripes, and so on. These results suggest that the stripe patterns on the compound eyes increase one by one with each molt in A. satsumensis.     

Discrimination training with multimodal stimuli changes activity in the mushroom body of the hawkmoth Manduca sexta

Background

The mushroom bodies of the insect brain play an important role in olfactory processing, associative learning and memory. The mushroom bodies show odor-specific spatial patterns of activity and are also influenced by visual stimuli.

Methodology/Principal Findings

Functional imaging was used to investigate changes in the in vivo responses of the mushroom body of the hawkmoth Manduca sexta during multimodal discrimination training. A visual and an odour stimulus were presented either together or individually. Initially, mushroom body activation patterns were identical to the odour stimulus and the multimodal stimulus. After training, however, the mushroom body response to the rewarded multimodal stimulus was significantly lower than the response to the unrewarded unimodal odour stimulus, indicating that the coding of the stimuli had changed as a result of training. The opposite pattern was seen when only the unimodal odour stimulus was rewarded. In this case, the mushroom body was more strongly activated by the multimodal stimuli after training. When no stimuli were rewarded, the mushroom body activity decreased for both the multimodal and unimodal odour stimuli. There was no measurable response to the unimodal visual stimulus in any of the experiments. These results can be explained using a connectionist model where the mushroom body is assumed to be excited by olfactory stimulus components, and suppressed by multimodal configurations.

Conclusions

Discrimination training with multimodal stimuli consisting of visual and odour cues leads to stimulus specific changes in the in vivo responses of the mushroom body of the hawkmoth.     

THE VARIABILITY OF INTENSITY DISCRIMINATION BY THE HONEY BEE IN RELATION TO VISUAL ACUITY

Variation in the determined magnitudes of the difference in brightness between alternating members of a system of stripes requisite for the elicitation of a threshold response in bees shows that the intensity of excitation, as a function of width of stripe and of intensity of illumination, is determined by the intensity of illumination and by the frequency of occurrence of divisions between bright and less bright bars. The variation of ΔI is limited by the intensity of excitation, so that the curves relating P.E. (ΔI/I) have the same form in relation to I as do the curves for ΔI/I. The limiting rule according to which P.E. ΔI is a power function of I for stripes of maximum usable width is departed from more and more markedly, for lower intensities, as narrower stripes are employed.     

Features effective in course control during object fixation by walking Colorado beetles

A test paradigm is designed to determine which features of viewed objects (a disk 10° in diameter) are responsible for preferential fixation by Colorado beetles (Leptinotarsa decemlineata). The beetle walks on a locomotion compensator that permits free choice of direction in a visual surround containing three different objects. The beetles use both colour and contrast information in these choice experiments. The preferred colours are yellow and orange; their attractiveness is considerably enhanced when they appear in a pattern with highly contrasting features such as stripes. In its optimal form, the object amounts to a dummy beetle, with a pattern that resembles the markings on the elytra of this species. Since the beetles appear to employ a contact pheromone for sex recognition, the function of orientation to these patterns is unclear. However, the patterns might accelerate the identification of conspecifics or be effective at a distance. The reaction to the dummies is telotactic — that is, the beetles walk towards the dummy. One other object, a 10°-wide black stripe, elicits menotactic orientation, in which the beetle maintains a stable course at an angle to the object.     

Places and patterns — a study of context learning in honeybees

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.     

Visual detection of wind-drift by high-flying insects at night: a laboratory study

Summary Locusta migratoria were tethered on a yaw-torque balance and flown in a wind tunnel of diamond-shaped cross-section. Slowly moving stripes of very low luminance were projected onto the two lower faces of the tunnel and a turning stimulus was generated by reversing the direction of stripe movement on one face relative to the other. It was found that the lower the pattern speed, the higher the luminance required to maintain a torque response. When our results were plotted together with optomotor thresholds taken or inferred from the data of other workers, a threshold curve extending over a luminance range from 10^–8 to 1 Lamberts (1 Lambert (L) = 3183 cd/m²), and a pattern speed range from 10^–2 to 1 °/s² °/s could be constructed. An implication of this threshold curve is thatLocusta flying in bright moonlight and as high as 2000 m could, in principle, detect the drift induced by a cross-wind of only 2.5 m/s. However, in the absence of the moon, this sensitivity to drift would be much reduced and it seems to be inadequate to explain some cases of down-wind orientation that have been observed by radar on moonless nights.     

Intracellular activity of morphologically identified neurons of the grass frog's optic tectum in response to moving configurational visual stimuli

Summary In the grass frogRana temporaria, various classes of tectal neurons were identified by means of intracellular recording and iontophoretic staining using potassium-citrate/Co³⁺-lysine-filled micropipettes, which have been defined previously by extracellular recording methods. Class T5(1) neurons had receptive fields (RF) of 33°±5° diameter. In response to a moving 8°×8° square (S), a 2°×16° worm-like (W), or a 16°×2° antiworm-like (A) moving stripe, these cells showed excitatory postsynaptic potentials (EPSPs) and spikes which were interrupted occasionally by small inhibitory postsynaptic potentials (IPSPs). The excitatory responses (R) were strongest towards the square (R_S) and less to the worm (R_W). For the antiworm (R_A) the responses were smallest or equal to the worm stimulus yielding the relationship R_S>R_WR_A. Some of these cells were identified as pear-shaped or large ganglionic neurons, whose somata were located in the tectal cell layer 8. The somata of other large ganglionic neurons were found in layer 7 and the somata of other pear-shaped neurons at the top of layer 6, both displaying T5(1) properties. Class T5(2) neurons (RF=34°±3°) responded with large EPSPs and spikes, often interrupted by small IPSPs, when their RF was traversed by the square stimulus. The excitatory activity was somewhat less to the worm stimulus, whereas no activity at all, or only IPSPs, were recorded in response to the antiworm-stimulus; thus yielding the relationship for the excitatory activity R_S>R_W>R_A 0. Such a cell was identified as pyramidal neuron; the soma was located at the top of layer 6, with the long axon travelling into layer 7 to the medulla oblongata. Class T5(3) neurons (RF=29°±6°) showing EPSPs and spikes according to the relationship R_S>R_A>R_W have been identified as large ganglionic neurons. Their somata were located in layer 8. Class T5(4) neurons (RF=24±7°) responded only to the square stimulus with EPSPs and spikes, sometimes interrupted by IPSPs and yielding the relationship R_S>R_AR_W0. The somata of these large ganglionic or pear-shaped neurons were located in layer 8. Class T1(1) neurons (RF=30°–40°) were most responsive to stimuli moving at a relatively long distance in the binocular visual field, and have been identified as pear-shaped neurons. Their somata were located in layer 6.Further neurons are described and morphologically identified which have not yet been classified by extracellular recording methods. For example,IPSP neurons (RF=20°–30°) responded (R) with IPSPs only according to the relationship R_S>R_A R_W. The somata of these pear-shaped neurons were located in layer 6.The properties of tectal cells in response to electrical stimulation of the optic tract and to brisk changes of diffuse illumination suggest certain neuronal connectivity patterns. The results support the idea ofintegrative functional units (assemblies) of connected cells which are involved in various perceptual processes, such as configurational prey selection expressed by T5(2) prey-selective neurons.Abbreviations A antiworm-like 16°×2° stripe stimulus with long axis perpendicular to the direction of movement - W wormlike 2°×16° stripe stimulus with long axis oriented parallel to the direction of movement - S square 8°×8° moving stimulus - ERF excitatory receptive field - IRF inhibitory receptive field - RF receptive field - EPSP excitatory postsynaptic potential - IPSP inhibitory postsynaptic potential     

Thorax vibrations of a stingless bee (<Emphasis Type="Italic">Melipona seminigra</Emphasis>). I. No influence of visual flow

An important question in stingless bee communication is whether the thorax vibrations produced by foragers of the genus Melipona upon their return to the nest contain spatial information about food sources or not. As previously shown M. seminigra is able to use visual flow to estimate flight distances. The present study investigated whether foraging bees encode the visually measured distance in their thorax vibrations. Bees were trained to collect food in flight tunnels lined with a black-and-white pattern on their side walls and floor, which substantially influenced the image motion they experienced. When the bees had collected inside the tunnels the temporal pattern of their vibrations differed significantly from the pattern after collecting in a natural environment. These changes, however, were not associated with the visual flow experienced inside the tunnel. Bees collecting in tunnels offering little visual flow (stripes parallel to flight direction) modified their vibrations similarly to bees collecting in tunnels with high image motion (cross stripes). A higher energy expenditure due to drastically reduced flight velocities inside the tunnel is suggested to be responsible for changes in the thorax vibrations. The bees' vibrations would thus reflect the overall energetic budget of a foraging trip.     

Chromatic and achromatic stimulus discrimination of long wavelength (red) visual stimuli by the honeybee Apis mellifera

It has long been assumed that bees cannot see red. However, bees visit red flowers, and the visual spectral sensitivity of bees extends into wavelengths to provide sensitivity to such flowers. We thus investigated whether bees can discriminate stimuli reflecting wavelengths above 560 nm, i.e., which appear orange and red to a human observer. Flowers do not reflect monochromatic (single wavelength) light; specifically orange and red flowers have reflectance patterns which are step functions, we thus used colored stimuli with such reflectance patterns. We first conditioned honey bees Apis mellifera to detect six stimuli reflecting light mostly above 560 nm and found that bees learned to detect only stimuli which were perceptually very different from a bee achromatic background. In a second experiment we conditioned bees to discriminate stimuli from a salient, negative (un-rewarded) yellow stimulus. In subsequent unrewarded tests we presented the bees with the trained situation and with five other tests in which the trained stimulus was presented against a novel one. We found that bees learned to discriminate the positive from the negative stimulus, and could unambiguously discriminate eight out of fifteen stimulus pairs. The performance of bees was positively correlated with differences between the trained and the novel stimulus in the receptor contrast for the long-wavelength bee photoreceptor and in the color distance (calculated using two models of the honeybee colors space). We found that the differential conditioning resulted in a concurrent inhibitory conditioning of the negative stimulus, which might have improved discrimination of stimuli which are perceptually similar. These results show that bees can detect long wavelength stimuli which appear reddish to a human observer. The mechanisms underlying discrimination of these stimuli are discussed. Handling Editor: Lars Chittka.     

The interaction of stimulus patterns controlling aggressiveness in the cichild fish Haplochromis burtoni

Readiness to attack is controlled by various stimulus patterns displayed in the context of social behaviour. The effect of such stimulus patterns and their combinations can be measured in terms of behavioural quantities. In search of algorithms, f (a, b), describing the combined effect of two stimulus patterns, a and b, those solutions are of particular interest which represent f as the combination of two terms, f₁(a) and f₂(b), which each depend on one stimulus pattern only. The existence of such solutions supports the assumption of independent processes controlled by a and b respectively. Social communication is viewed as a process in which a ‘sender’ manipulates and controls states of behavioural readiness in a ’receiver’. ‘Threat’ displays, in particular, are suggested to tip the balance between aggressive and submissive tendencies in either direction, with the probability of the outcome largely depending upon the initial disposition of the receiver.     

Sequence learning by honeybees

Bees of several genera make foraging trips on which they visit a series of plants in a fixed order. To help understand how honeybees might acquire such routes, we examined whether (1) bees learn motor sequences, (2) they link motor instructions to visual stimuli, (3) their visual memories are triggered by contextual cues associated with the bees' position in a sequence.

Flight torque and lift responses of the housefly (Musca domestica) to a single stripe moving in different parts of the visual field

Visually evoked torque and lift responses in fixed flying houseflies Musca domestica, were measured under open loop conditions. The visual stimuli were: a) Vertical stripes (60°×5°), moving horizontally in a range±30°. b) Horizontal stripes (60°×5°), moving vertically in a range±30°. c) Vertical stripes (30°×5°), moving horizontally in a range±55° in five different planes relative to the equatorial plane (=0) of the fly's eye. d) Horizontal stripes (30°×5°), moving vertically in a range±45° in seven different planes (=-45°,-30°,-15°, 0°, 15°, 30°, 45°) relative to the symmetry line (=0) between the two compound eyes. e) Periodic gratings displayed by two projectors at each side of the test animals (the middle part was situated at =±50°). The stimulated area was roughly 52°×80° (2000 ommatidia). This stimulus was used only in lift experiments. The results are: 1) The preferred direction of the direction sensitive torque response corresponds with the z-direction (Braitenberg, 1971). 2) The direction sensitive torque response is elicited by stimulating above and below the equatorial plane. 3) The direction insensitive torque response is only elicited by stimulating close to and below the equatorial plane. 4) The preferred direction of the direction sensitive lift response has an angle tilted about 30° to the back relative to the vertical axis in the region described in e). 5) The magnitude of the direction sensitive lift response varies considerably over . 6) The w/ dependence of the direction sensitive lift response corresponds qualitatively to the known w/ dependence of the direction sensitive torque responses. 7) The direction insensitive lift response has its maximum at =±15° and decreases with increasing . 8) The findings reported in 3) and 8) indicate the existence of a two-dimensional potential from which the attraction towards a stripe in the two considered degrees of freedom can be derived. Implications for the visually induced orientation behaviour and connections with electrophysiological experiments are discussed.     

Flying Slower: Floor Pattern Object Size Affects Orthokinetic Responses During Moth Flight to Sex Pheromone

Previous studies with Oriental Fruit Moth (OFM, Grapholita molesta) and Heliothis virescens males flying upwind along a pheromone plume showed that they increased their upwind flight speed as they flew higher above striped floor patterns and, for OFM, to a similar degree over dotted floor patterns. This response pattern has been demonstrated in another moth species, Epiphyas postvittana and in a beetle, Prostephanus truncatus. In all cases the role played by the change in angular size of the wind tunnel’s ventral floor pattern was not assessed. In the present study we specifically addressed this question with a systematic examination of moths’ flight control over different sizes of transverse stripes and dot patterns ranging down by halves from 5 to 0.625 cm and a blank white floor as a control, and showed that OFM males fly faster upwind and along their flight paths over floor patterns of decreasing size. Increased speeds over striped patterns were evident as stripe width decreased below 2.5 cm, whereas moths did not increase their flight speed over dot patterns until dot size had decreased to less than 1.25 cm. Another flight component that the moths can actively control, their course angles, was unchanged above both patterns, except for moths flying over 5 cm stripes. Turning frequency and interturn distances were mostly unchanged or offset each other, negating any effects on upwind progress. As in an earlier study examining flight speeds at three heights above floor patterns of three densities, the moths’ changes in speed appear to be exclusively affected by changes in their orthokinetic response to the size of the floor pattern objects.     

ON THE RELATION BETWEEN MEASUREMENTS OF INTENSITY DISCRIMINATION AND OF VISUAL ACUITY IN THE HONEY BEE

1. Bees respond by a characteristic reflex to a movement of their visual field. By confining the field to a series of parallel stripes of two alternating different brightnesses it is possible to determine for any width of stripe, at any brightness of one of the two sets of stripes, the brightness of the second at which the bee will first respond to a displacement of the field. Thus the relations between visual acuity and intensity discrimination can be studied. 2. For each width of stripe and visual angle subtended by the stripe the discrimination power of the bee''s eye for different brightnesses was studied. For each visual acuity the intensity discrimination varies with illumination in a characteristic, consistent manner. The discrimination is poor at low illuminations; as the intensity of illumination increases the discrimination increases, and reaches a constant level at high illuminations. 3. From the intensity discrimination curves obtained at different visual acuities, visual acuity curves can be reconstructed for different values of ΔI/I. The curves thus obtained are identical in form with the curve found previously by direct test for the relation between visual acuity and illumination.