Contrast and duration of exposure differentially affect vernier and stereoscopic acuity

Although stereoacuity and vernier acuity both yield comparable thresholds well below the eye's resolution limit, the neural circuits for these two classes of visual responses do not process the signals in an identical manner. It had previously been demonstrated that hyperacuity is more resistant to image blur than stereoacuity and that the zones within which two targets must be placed to achieve the lowest thresholds differ quite radically. Two further differences are reported here: reduced contrast affects stereoacuity more severely than hyperacuity, as also does shortening of exposure into a range of tens of milliseconds, even when the Bunsen-Roscoe-Bloch law has been factored out.