Animals assess one another using assessment signals in a range of contexts that are critically important for survival and reproduction, from mate choice to agonistic encounters. The receiver’s interpretation of assessment signals is dependent upon both perceptual processes and the signaling environment, yet current research is largely limited to understanding how sensory organs process information. We know little about how information from the sensory organs is processed in the brain in non-human animals, i.e. how the physical attributes of a signal are linked to behavioural outcomes. Thus far, my research in this area has focused on perceptual processes by which continuous variation in signal form may not actually be perceived continuously by a signal receiver.
Proportional Processing of Stimulus Magnitude in Swordtail Fish
Animals, including humans, generally compare stimuli based on proportional rather than absolute differences in stimulus magnitude. This is known as proportional processing, and it adheres to Weber’s Law. Weber’s Law describes the ability of a sensory system to distinguish between the magnitude of two stimuli based on their proportional difference. Proportional processing has important implications for animal behavior, because it impacts of understanding of discrimination thresholds. Additionally, many animals use signals to choose mates or assess rivals that involve assessing the magnitude of two stimuli (for example the length, width, or area of a signaling trait). The often implicit assumption is that recievers continuously perceive continuous variation in signaling trait. However, this assumption is rarely tested.
As a Marie Sklodowska-Curie Postdoctoral Fellow at Exeter working with Dr. Laura Kelley, I will be examining the behavioural and ecological implications of continuous variation in a visual signal, the tail (sword) length of male swordtail fish Xiphophorus helleri, being treated as a non-continuous signal by the receiver. Stay tuned for project updates! |
Categorical Perception of Color Signals in Zebra Finches
We have used food reward protocols to test how birds perceive colors. Birds are trained to locate food rewards beneath discs they perceive as comprising two colors. By varying the colors on each half of the disc, we can test whether two colors are perceived as "same" or "different." Photo by Ryan Huang, Terra Communications LLC.
|
As a post-doctoral associate in the lab of Steve Nowicki at Duke University, I examined how perceptual processes affect the perception of visual stimuli and signals, focusing on categorical perception, in which a receiver’s perceptual system sorts a continuously varying stimulus into discrete categories. That is, although variation in the physical stimulus is continuous, the resulting percept is not. Using measures of zebra finch vision to create stimuli, and behavioral training on a food reward protocol, my collaborators and I demonstrated that female zebra finches exhibit categorical perception of an orange-red color range corresponding to the carotenoid-based coloration of male zebra finch beaks (Caves and Green et al, Nature 2018), an important signal in mate choice. This was the first demonstration of categorical perception of a visual signal. We also demonstrated categorical perception in zebra finch females along a blue to green color range, which has no known signaling function in this species (Zipple and Caves et al., ProcB, 2019). This suggests that categorical perception may be a general feature of avian color perception, rather than being specific to signal perception. Categorical perception of signaling traits has been demonstrated in systems ranging from human speech to frog vocalizations and now to color perception in birds, suggesting that it may be widespread across taxa and modalities and thus warrants further study.
|