Retroactive enhancement of a skin sensation by a delayed cortical stimulus in man: Evidence for delay of a conscious sensory experience

Sensation elicited by a skin stimulus (S) was subjectively reported to feel stronger when followed by a stimulus to somatosensory cerebral cortex (C), even when C was delayed by up to 400 ms or more. This expands the potentiality for retroactive effects beyond that previously known as backward masking. It also demonstrates that the content of a sensory experience can be altered by another cerebral input introduced after the sensory signal arrives at the cortex. The long effective S-C intervals support the thesis that a duration of cortical activity of up to 0.5 s is required before awareness of a sensory stimulus is developed.