Acuity for orientation measured with a sequential recognition task and signal detection methods

An orientation recognition task with two stimuli was employed as the basis of a psychophysical method for measuring sensitivity to orientation. Essentially, this method depends on a subject’s ability to discriminate between two stimuli differing in orientation and presented to the same retinal area in random succession from trial to trial. Advantages of this sequential method over traditional simultaneous matching methods are discussed. Its feasibility is demonstrated in a signal detection analysis of acuity for the orientation of short luminous slits presented foveally on a dark field at seven reference orientations varying between 0° and 90°. In both subjects employed, sensitivity was greater for horizontal and vertical orientations than for other slopes (the oblique effect).