Re: SciFi Trivia Query: Blue People?

From: Geraint Rees (
Date: Tue Jan 15 2002 - 11:10:40 MST

On 15/1/02 4:37 pm, "Smigrodzki, Rafal" <> wrote:

> There is actually new data on this phenomenon - the visual system uses
> cached data to maintain the illusion of continuity after a saccade.

Here's the abstract Rafal mentions (Nature 2001, 414:302-5) if anyone is

Illusory perceptions of space and time preserve cross-saccadic perceptual

Yarrow K, Haggard P, Heal R, Brown P, Rothwell JC.
Sobell Department of Neurophysiology, Institute of Neurology, 8-11 Queen
Square, London WC1N 3BG, UK.

When voluntary saccadic eye movements are made to a silently ticking clock,
observers sometimes think that the second hand takes longer than normal to
move to its next position. For a short period, the clock appears to have
stopped (chronostasis). Here we show that the illusion occurs because the
brain extends the percept of the saccadic target backwards in time to just
before the onset of the saccade. This occurs every time we move the eyes but
it is only perceived when an external time reference alerts us to the
phenomenon. The illusion does not seem to depend on the shift of spatial
attention that accompanies the saccade. However, if the target is moved
unpredictably during the saccade, breaking perception of the target's
spatial continuity, then the illusion disappears. We suggest that temporal
extension of the target's percept is one of the mechanisms that 'fill in'
the perceptual 'gap' during saccadic suppression. The effect is critically
linked to perceptual mechanisms that identify a target's spatial stability.



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