If the stimulus gets so faint that it can no longer be perceived, increase its intensity. If the stimulus is perceived, decrease its intensity. Go back and forth for a preset number of trials and average the intensity of all the stimuli presented. Two alternative forced choice tracking. Fechner s law Fechner began with Weber s law and assumed that all jnds are equal.
Sensitivity refers to the ability of the perceptual system per se to process the stimulus.
Some subjects want to be sure they perceived it to respond yes while others are more generous with their yes responses. The former will seem to have higher thresholds than the latter if their thresholds are in fact equal. The more sensitive to the stimulus the system is, the greater d is. The more conservative the criterion, the greater b is.