Categorical face perception in fish: How a fish brain warps reality to dissociate "same" from "different".

Categorical perception (CP) is the phenomenon by which a smoothly varying stimulus property undergoes a nonlinear transformation during processing in the brain. Consequently, the stimuli are perceived as belonging to distinct categories separated by a sharp boundary. Originally thought to be largely innate, the discovery of CP in tasks such as novel image discrimination has piqued the interest of cognitive scientists because it provides compelling evidence that learning can shape a category's perceptual boundaries.

Comparison of functional and anatomical estimations of visual acuity in two species of coral reef fish.

The high-contrast, complex patterns typical of many reef fish serve several purposes, including providing disruptive camouflage and a basis for vision-based communication. In trying to understand the role of a specific pattern, it is important to first assess the extent to which an observer can resolve the pattern, itself determined, at least in part, by the observer's visual acuity. Here, we studied the visual acuity of two species of reef fish - and - using both anatomical and behavioural estimates.

A species of reef fish that uses ultraviolet patterns for covert face recognition.

The evolutionary and behavioral significance of an animal's color patterns remains poorly understood [1-4], not least, patterns that reflect ultraviolet (UV) light [5]. The current belief is that UV signals must be broad and bold to be detected because (1) they are prone to scattering in air and water, (2) when present, UV-sensitive cones are generally found in low numbers, and (3) long-wavelength-sensitive cones predominate in form vision in those species tested to date [6]. We report a study of two species of damselfish whose appearance differs only in the fine detail of UV-reflective facial patterns.