An illusion is any signal that actively distorts the perception of the receiver. In humans, illusions such as the Ebbinghaus illusion are common and can distort perception by making objects appear larger or smaller than they actually are. This Ebbinghaus illusion occurs when the perceived size of an object depends on the size of the surrounding objects, and may be important to comparative mate evaluation, when males display in groups that allow the choosing female to compare multiple males simultaneously. Perceptual biases present in the receiver can create an inaccurate or incomplete perception of the environment, leading to sub-optimal decision-making. In mate choice, males can take advantage of this biased cognitive perception by creating illusions in mating signals to which females are susceptible. I tested this using the sailfin molly (Poecilia latipinna) where the males show significant variation in body size and females prefer the largest males. If males were able to adaptively choose who they associate with, and strategically position themselves within a social group, they may increase their mating success. I predicted that males are able to do this by creating a deceptive illusion to make them appear larger, and therefore more attractive. I used a preference function test to quantify the change in female preference for a male by sequentially presenting the same male in different social contexts and environmental treatments, and measuring both the female’s and male’s response. I will present data from experiments testing female preference for males in different social contexts, mimicking the Ebbinghaus illusion, by using both live stimulus males and clay models.