Localization of unseen visual stimuli by humans with normal vision

Thirty university students were shown tachistoscopically presented stimuli (half contained an open circle at one of six locations, half were blanks) at four durations. Short durations and a pattern mask reduced subjects' ability to detect the stimuli. For trials on which the subjects reported that the circle was absent, they nevertheless guessed the exact locations of the targets significantly better than chance. A signal detection theory analysis found that subjects were more sensitive for the location decision than for the detection decision. These findings show that the blindsight phenomenon of localization of "unseen" stimuli, previously reported for cortically blind patients, also occurs for humans with normal vision.