Foraging Small White Butterflies, Pieris rapae, Search Flowers Using Color Vision

We demonstrate that the small white butterfly, Pieris rapae, uses color vision when searching flowers for foraging. We first trained newly emerged butterflies in a series of indoor behavioral experiments to take sucrose solution on paper disks, colored either blue, green, yellow, or red. After confirming that the butterflies were trained to visit a certain colored disk, we presented all disks simultaneously. The butterflies selected the disk of trained color, even among an array of disks with different shades of gray. We performed the training using monochromatic lights and measured the action spectrum of the feeding behavior to determine the targets’ Pieris-subjective brightness. We used the subjective brightness information to evaluate the behavioral results and concluded that Pieris rapae butterflies discriminate visual stimuli based on the chromatic content independent of the intensity: they have true color vision. We also found that Pieris butterflies innately prefer blue and yellow disks, which appears to match with their flower preference in the field, at least in part.

Superior Parietal Lobule: A Role in Relative Localization of Multiple Different Elements

Simultanagnosia is an impairment in processing multiple visual elements simultaneously consecutive to bilateral posterior parietal damage, and neuroimaging data have specifically implicated the superior parietal lobule (SPL) in multiple element processing. We previously reported that a patient with focal and bilateral lesions of the SPL performed slower than controls in visual search but only for stimuli consisting of separable lines. Here, we further explored this patient’s visual processing of plain object (colored disk) versus object consisting of separable lines (letter), presented in isolation (single object) versus in triplets. Identification of objects was normal in isolation but dropped to chance level when surrounded by distracters, irrespective of eccentricity and spacing. We speculate that this poor performance reflects a deficit in processing objects’ relative locations within the triplet (for colored disks), aggravated by a deficit in processing the relative location of each separable line (for letters). Confirming this, performance improved when the patient just had to detect the presence of a specific colored disk within the triplets (visual search instruction), while the inability to identify the middle letter was alleviated when the distracters were identical letters that could be grouped, thereby reducing the number of ways individual lines could be bound.

THE DETECTION AND RECOGNITION OF COLOR STIMULI BY HONEYBEES: PERFORMANCE AND MECHANISMS

In a detection paradigm, honeybees Apis mellifera were trained to distinguish between the presence and the absence of a rewarded colored spot, presented on a vertical, achromatic plane in a Y-maze. In a recognition paradigm, bees were trained to distinguish between a trained colored disk and alternative stimuli differing in their green contrast and/or chromatic contrast. Results from the first experimental paradigm allowed the establishment of αmin, the visual angle subtended by a colored target at the bee eye at which the bees detect a given stimulus with a probability Po = 0.6. This angle was 5° for stimuli presenting both chromatic contrast and green contrast, and 15° for stimuli presenting chromatic but no green contrast. Therefore, green contrast contributes decisively to the detection task. Results from the second experimental paradigm showed that chromatic and green contrasts are alternatively used depending on the visual angle subtended by a trained chromatic target and that bees also learn the green-contrast difference between a trained and a nonrewarded alternative. Finally, when trained at different visual angles with an achromatic stimulus providing green contrast, bees were capable of learning and detecting the achromatic target only for visual angles from 10° to 5°. Thus, green-contrast and chromatic-contrast channels are tuned to signals of different angular sizes: the chromatic channel conveys the signals of objects of large angular size, while the green contrast channel conveys those of objects of reduced angular size.