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Archive for 10/01/2011

Change blindness illusion

Jordan Suchow has some illustrations of an illusion (here) that accompany the paper whose citation is below. It an excellent demonstration of change blindness. Here is the abstract:

Loud bangs, bright flashes, and intense shocks capture attention, but other changes – even those of similar magnitude – can go unnoticed. Demonstrations of change blindness have shown that observers fail to detect substantial alterations to a scene when distracted by an irrelevant flash, or when the alteration happen gradually. Here, we show that objects changing in hue, luminance, size, or shape appear to stop changing when they move. This motion induced failure to detect change, silencing, persists even though the observer attends to the objects, knows that they are changing, and can make veridical judgments about their current state. Silencing demonstrates the tight coupling of motion and object appearance.

Illusions are always entertaining but my blog is about consciousness. So what does this paper say about that?

During silencing, rapidly changing objects appear nearly static, which raises an immediate question: What is the perceived state at any given moment? To illustrate, consider an observer who fails to notice an object change gradually from yellow to red. One possibility is that the observer always sees yellow, never updating his percept to incorporate the new hue – this is freezing, erroneously keeping hold of an outdated state. Another possibility is that he always sees the current hue (e.g. yellow, orange, then red) but is unaware of the transition from one to the next – this is implicit updating.

In the one case the color’s change does not attained a cognitive level where it could reach consciousness and it the other case it appears to reach that level but for some reason is not included in the contents of consciousness. The two explanations can be examined by starting with yellow and moving to red and then jumping back to yellow. Is the jump noticed (implicit updating has happened) or not (freezing has happened)? In general the answer is implicit updating. But…

Incidentally, freezing of stationary color changes has been found to last for approximately 200ms, which corresponds to a -10 degrees change in hue in our reversion test. Though the data rule out the possibility that temporal freezing explains silencing, they leave open the possibility that freezing persists within a local window, such that the perceived color consistently lags a bit behind the actual color; this would explain the observed, though not statistically significant, lag.

This is about the time that it would take for a change to be able to reach consciousness. Activity occurring up to 200ms seems not to be distinguishable between conscious and unconscious processing, past that approximate duration the activity builds to reach consciousness at about 300ms or remains unconscious. Thus there is a somewhat paradoxical situation where a perception seems to have been formed and reached (or almost reached) consciousness and yet is not consciously reported although is in some sense it is remembered. Is it only the addition of being suddenly the focus of attention that makes the difference?
Suchow, J., & Alvarez, G. (2011). Motion Silences Awareness of Visual Change Current Biology DOI: 10.1016/j.cub.2010.12.019