> For the complete documentation index, see [llms.txt](https://manymanys.gitbook.io/mm1-lab-manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://manymanys.gitbook.io/mm1-lab-manual/method/stimuli.md).
# Stimuli
Stimuli consist of Lego® or Duplo® bricks, which can be assembled into a wide variety of objects that differ in shape and color. This approach offers both versatility in stimulus design and standardization across testing sites and species.
Within a given species, stimuli are kept approximately consistent in size; however, dimensions may vary across species to accommodate differences in body size, visual acuity, and motor capabilities. Each lab/team/site must decide on the stimuli shape and color and report their selection to the MM1 Leadership Team. Labs/teams/sites are encouraged to take into account species’ perceptual capabilities and ecological context and avoid colors that fall outside the species’ visible spectrum, colors subject to species-specific biases, colors that may be associated with threats or predators, and shapes that resemble aversive objects.
For your information, the most recent survey results indicated circle (89%) and triangle (78%) as the most appropriate shapes, followed by square and star (67% each). Regarding color, blue (94%) and yellow (83%) seem to be the most preferred, followed by purple/magenta (72%) and orange (61%).
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Multiple studies suggest that dogs prefer yellow to blue. In addition, some species may perceive orange and yellow as aversive stimuli (e.g., associated with venomous or poisonous animals/plants). Therefore, color and shape selection should be carefully planned to minimize known or potential biases or aversive responses.
{% endhint %}
Size. The dimensions of the stimuli are scaled relative to the size of the species being tested. For species with an average body length between five and 80 centimeters, each stimulus is half of the body length of the animal (based on results collated from \~30 articles; see Figure 2 below). For species outside this range, stimulus size may differ from this ratio for the purposes of feasibility. Note that researchers working with species outside of this range should contact the MM1 Leadership Team to discuss an appropriate stimulus size prior to beginning experimentation.
Positioning. The two stimuli are placed equidistant from the focal individual, at a distance scaled relative to the body size of the animal. For species that move their whole body freely towards the stimuli to make a choice (typically small size), the stimuli are placed at a distance of two times the average body length of the species (Figure 2). For species that reach with their limbs (typically large size), the stimuli are placed just beyond one arm length distance from the subjects so that they cannot grab/grasp/hold on the stimuli. In both cases, the two stimuli are positioned one body length apart from each other. Note that the stimuli must be positioned at a species-appropriate height and depth that match routine feeding locations where applicable (e.g., for flying, arboreal, or swimming species). Stimulus height and depth must remain consistent across all trials and subjects. Distances should be kept consistent within species across labs/teams/sites.
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Figure 2. Schematic of stimulus setup. The stimuli are half of the body length of the animal and placed equidistant from the subject. For species that move their whole body to make a choice, the stimuli are placed at a distance of two times the average body length of the species and positioned one body length apart from each other. Image credit: Grace Blackburn.
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