Abstract
It has recently been proposed that there may be a ‘universal law of human perception’ governing the relationship between perceptual bias and discriminability (Wei X.-X. & Stocker A.A., 2018, PNAS 114, 10244–10249), namely that bias is proportional to the square of the derivative of discrimination threshold. Here, I critically examine the claim that this relationship holds for biases and changes in discrimination performance induced by adaptation. The proposed relationship was applied to published post-adaptation discrimination data for tilt and direction-of-motion as a function of the angular difference between adaptor and test to generate predictions of the angular tuning function for the tilt and direction aftereffects, respectively. These predictions were found to be inconsistent with published aftereffect data. Most strikingly, large attractive aftereffects were predicted for a range of angles at which large repulsive aftereffects have been empirically observed. For a lawful relationship between bias and discriminability to encompass the effects of adaptation would be a challenge to the view that perceptual aftereffects result from a mismatch between the encoding and decoding stages, the so-called ‘coding catastrophe’. Instead, it appears that adaptation may be a catastrophe not only for sensory coding but also for the universality of the proposed law of human perception.