Perception of signals under varying conditions: implications of proportional processing of signal magnitude for signal design

Objectif

Individuals evaluate one another during interactions using assessment signals that indicate quality, and these signals vary across individuals, reflecting variation in signaler quality. For example, green swordtail (Xiphophorus helleri) females assess the length of an extended caudal fin (known as a sword) on males, which ranges in length from 10-70mm in nature, during mate choice, and males evaluate one another’s swords during agonistic encounters. Models of signal evolution implicitly assume that signals are perceived continuously, meaning that each change in signal magnitude is both perceived by the receiver and results in a concomitant change in receiver response. Increasing evidence, however, shows that signals across modalities, from acoustic signals to color-based visual signals, can be perceived discontinuously. One mechanism by which stimuli can be perceived discontinuously is called proportional processing, which follows Weber’s law. Under proportional processing, a viewer can more readily discriminate between two stimuli that differ by a certain amount when both of those stimuli are of low magnitude, compared with two stimuli that differ by the same amount but are both high magnitude. Although proportional processing has been shown to operate across a variety of taxa and modalities, no study has yet tested for proportional processing of a visual signal. This project will (1) test whether signal magnitude, i.e. male sword length, is perceived continuously or proportionally by female and male swordtails; (2) assess how perception of stimulus magnitude is affected by variation in environmental conditions, by manipulating both the visual and auditory environment; (3) compare perception of signal-relevant (bars) and signal-irrelevant (circles) stimuli, between a swordtail species that exhibits sexual dimorphism in sword length (X. helleri) with one that does not (X. maculatus), to examine the evolution of perceptual processes; and (4) compare perception of the signal magnitude in swordtails with existing data on length perception in a variety of taxa (including humans), to examine the generality of proportional processing of length across species, and how perception differs between species with very different visual acuities (ability to perceive detail) and signaling behaviours. This project will be the first to examine proportional processing of a visual signaling trait in any non-human animal and will provide the first tests of how viewing conditions and multi-modal stimuli impact perception of signal magnitude in non-primates. By combining my expertise in different mechanisms of discontinuous perception with the expertise of Dr Kelley at Exeter, which spans animal behavior, acoustic signaling, and perceptual processing, we will (1) provide novel insights into the relationship between signal design, behaviour, and environment, (2) increase our understanding of how vision and higher-level perceptual processes interact in the perceptual organisation of stimuli, and (3) provide invaluable training in managing a large project at the forefront of perception research, thus opening a host of career and collaborative opportunities.