If the appearances of palatable and unpalatable species are close to each other along some stimulus dimension, such as conspicuousness, predators may develop a perceptual bias which enhances discrimination, known by behaviorists as "peak shift" (not to be confused with evolutionary "peak-shift" via the shifting balance). The conflicting pressures on their perceptual/learning system may lead them to avoid patterns brighter than the norm for the unpalatable species more strongly than they avoid the normal pattern; conspicuous unpalatable variants would then have an advantage over the normal pattern, allowing gradual evolution of greater and greater conspicuousness of the unpalatable species (arrow) (61). It is unclear how the palatable species will evolve; it could be selected for mimicry (to the right), or to greater inconspicuousness (to the left) to avoid detection, even though the latter may be costly due to increased predator attack rate once detected.