Orientation detectors in insects

Naturwissenschaften, 1993

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1998

Honeybees Apis mellifera were trained to enter a Y-maze and choose the arm with a rewarded disc presented against a grey background. The alternative arm displayed the unrewarded grey background alone. Training and testing were performed with the rewarding disc subtending dierent visual angles. The training disc was either achromatic and provided green contrast, or chromatic and provided the same amount of green contrast as the achromatic one. The bee-achromatic disc could be learned and detected by the bees whenever it subtended 5°or 10°, but not if it subtended 30°. The chromatic disc was learned well and detected at all three visual angles. However, at 5°the maximum level of correct choices was ca. 75% with the achromatic disc whilst it was ca. 90% with the chromatic one. Thus, the presence of chromatic contrast enhances considerably the level of correct choices for the same amount of green contrast. The lower threshold of achromatic target detection lies between 3.7°and 5°; the upper threshold between 15°and 10°. At the upper threshold, detection switches from chromatic-based to achromatic-based. Thus, in the context of target detection, the achromatic green contrast channel specialises in the detection of objects of reduced angular size, whilst the chromatic channels are specialised for objects of large angular size. We suggest that achromatic detectors with a centresurround organisation are involved in the task of detecting achromatic targets.

Journal of Comparative Physiology A, 1990

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Frontiers in Physiology, 2021

Gaze direction is closely coupled with body movement in insects and other animals. If movement patterns interfere with the acquisition of visual information, insects can actively adjust them to seek relevant cues. Alternatively, where multiple visual cues are available, an insect's movements may influence how it perceives a scene. We show that the way a foraging bumblebee approaches a floral pattern could determine what it learns about the pattern. When trained to vertical bicoloured patterns, bumblebees consistently approached from below centre in order to land in the centre of the target where the reward was located. In subsequent tests, the bees preferred the colour of the lower half of the pattern that they predominantly faced during the approach and landing sequence. A predicted change of learning outcomes occurred when the contrast line was moved up or down off-centre: learned preferences again reflected relative frontal exposure to each colour during the approach, independent of the overall ratio of colours. This mechanism may underpin learning strategies in both simple and complex visual discriminations, highlighting that morphology and action patterns determines how animals solve sensory learning tasks. The deterministic effect of movement on visual learning may have substantially influenced the evolution of floral signals, particularly where plants depend on fine-scaled movements of pollinators on flowers.

2001

In three experiments, bumble bees were trained to discriminate between a reinforcing pattern (S+) and a nonreinforcing one (S−) which differed only in the configuration of four artificial petals. They were subsequently tested for recognition of the S+ rotated by 90 • (S + 90). Experiment 1 used petals of four colors, and the other experiments used four symbols. The symbols either remained unchanged when the whole pattern was rotated (e.g., "+" in Experiment 2) or changed appearance (e.g., "<" in Experiment 3). The bees failed to recognize the S + 90 in the first two experiments, but in Experiment 3, the choice proportion for S + 90 in the presence of a New pattern was significantly higher than chance. Bumble bees can recognize a rotated pattern, possibly by using mental rotation, provided that a cue as to the extent of the pattern transformation is given.

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 2002

We investigated pattern discrimination by worker honeybees, Apis mellifera, focusing on the roles of spectral cues and the angular size of patterns. Freeflying bees were trained to discriminate concentric patterns in a Y-maze. The rewarded pattern could be composed of either a cyan and a yellow colour, which presented both different chromatic and achromatic Lreceptor contrast, or an orange and a blue colour, which presented different chromatic cues, but the same L-receptor contrast. The non-rewarded alternative was either a single-coloured disc with the colour of the central disc or the surrounding ring of the pattern, a checkerboard pattern with non-resolvable squares, the reversed pattern, or the elements of the training pattern (disc or ring alone). Bees resolved and learned both colour elements in the rewarded patterns and their spatial properties. When the patterns subtended large visual angles, this discrimination used chromatic cues only. Patterns with yellow or orange central discs were generalised toward the yellow and orange colours, respectively. When the patterns subtended a visual angle close to the detection limit and L-receptor contrast was mediating discrimination, pattern perception was reduced: bees perceived only the pattern element with higher contrast.

PLOS ONE

Simple feature detectors in the visual system, such as edge-detectors, are likely to underlie even the most complex visual processing, so understanding the limits of these systems is crucial for a fuller understanding of visual processing. We investigated the ability of bumblebees (Bombus terrestris) to discriminate between differently angled edges. In a multiple-choice, “meadow-like” scenario, bumblebees successfully discriminated between angled bars with 7° differences, significantly exceeding the previously reported performance of eastern honeybees (Apis cerana, limit: 15°). Neither the rate at which bees learned, nor their final discrimination performance were affected by the angular orientation of the training bars, indicating a uniform performance across the visual field. Previous work has found that, in dual-choice tests, eastern honeybees cannot reliably discriminate between angles with less than 25° difference, suggesting that performance in discrimination tasks is affected...

Journal of Experimental Biology, 2008

To find out how grouping of flowers into patches improves their detectability by hymenopteran pollinators, we trained honeybees and bumblebees to detect groups of three spatially separated disks and compared results with the detection limit for single disks. When the discs presented contrast to the long-wavelength-sensitive (L) receptor, grouping of disks improved the detectability. The disks were optically resolvable for the honeybee eye. The improvement of detectability was stronger for bumblebees than for honeybees. When disks did not present contrast to the L-receptor, the grouping did not improve the detectability, i.e. the detection limit was set by the size of a single disk. We conclude that in bees the neural mechanisms that improve detectability of grouped elements require input from the L-receptor. Our results indicate that grouping of flowers into sparse patches can improve their detectability by bees, even when individual flowers can be optically resolved by the eyes of bees, as long as flowers can be detected by the long-wavelength-sensitive receptor.

Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 1999

Honeybees Apis mellifera detect coloured targets presented to the frontal region of their compound eyes using their colour vision system at larger visual angles (a > 15°), and an achromatic visual system based on the long-wave photoreceptor type at smaller visual angles (5°< a < 15°). Here we examine the capability of the dorsal, ventral and frontal regions of the eye for colour detection. The minimum visual angle a min at which the bees detect a stimulus providing both chromatic contrast and receptor-speci®c contrasts to the three receptor types varies for the dierent regions of the eye: 7.1 0.5°for the ventral region, 8.2 0.6°for the dorsal region and 4.0 0.5°for the frontal region. Flight trajectories show that when the target was presented in the horizontal plane, bees used only the ventral region of their eyes to make their choices. When the targets appeared dorsally, bees used the frontodorsal region. This ®nding suggests that pure dorsal detection of coloured targets is dicult in this context. Furthermore, a min in the ventral plane depends on receptor-speci®c contrasts. The absence of S-receptor contrast does not aect the performance (a min = 5.9 0.5°), whilst the absence of M-and L-receptor contrast sig-ni®cantly impairs the detection task. Minimal visual angles of 10.3 0.9°and 17.6 3°, respectively, are obtained in these cases. Thus, as for many visual tasks, the compound eye of the honeybee shows a regionalisation of colour detection that might be related to peripheral or central specialisations.

Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1999

Honeybees Apis mellifera detect coloured targets presented to the frontal region of their compound eyes using their colour vision system at larger visual angles (a > 15°), and an achromatic visual system based on the long-wave photoreceptor type at smaller visual angles (5°< a < 15°). Here we examine the capability of the dorsal, ventral and frontal regions of the eye for colour detection. The minimum visual angle a min at which the bees detect a stimulus providing both chromatic contrast and receptor-speci®c contrasts to the three receptor types varies for the dierent regions of the eye: 7.1 0.5°for the ventral region, 8.2 0.6°for the dorsal region and 4.0 0.5°for the frontal region. Flight trajectories show that when the target was presented in the horizontal plane, bees used only the ventral region of their eyes to make their choices. When the targets appeared dorsally, bees used the frontodorsal region. This ®nding suggests that pure dorsal detection of coloured targets is dicult in this context. Furthermore, a min in the ventral plane depends on receptor-speci®c contrasts. The absence of S-receptor contrast does not aect the performance (a min = 5.9 0.5°), whilst the absence of M-and L-receptor contrast sig-ni®cantly impairs the detection task. Minimal visual angles of 10.3 0.9°and 17.6 3°, respectively, are obtained in these cases. Thus, as for many visual tasks, the compound eye of the honeybee shows a regionalisation of colour detection that might be related to peripheral or central specialisations.