Subliminal Perception: Just How Fast Is The Brain?

Subliminal perception has long been a hot topic. The idea that something (generally an image) could appear and disappear before us so quickly that it escapes conscious perception, and yet affect us subconsciously, is a fascinating (and scary) one. Psychologists and neuroscientists are fairly skeptical of any grand or sinister claims for the power of subliminal advertising or propaganda, but on the other hand, many of them use the technique as a research tool. So what's the absolute speed limit of the brain? What's the minimum time that a stimulus needs to appear in order to trigger a measurable brain response? In a new study, Swiss researchers Holger Sperdin and colleagues say that they've detected neural activity in response to images presented for just 250 microseconds - that's 1/4 of a millisecond, or 1/4000-th of a second. Sperdin et al. say that these ultra-brief stimuli are undetectable on a conscious level, yet still evoke a brain response - albeit a small one. Here's the paper: Submillisecond Unmasked Subliminal Visual Stimuli Evoke Electrical Brain Responses. The authors recorded brain activity using EEG and presented the brief stimuli using a device they invented called the LCD Tachistoscope.