What change blindness says about memory

In change blindness some part of a scene is changed and the change is not noticed by the observer. This can happen when the change is not happening on the retina in a stable condition. It can happen when there is a mask (a blank screen to fast to see), a blink, an eye movement, a change in point of view, an interruption in a action and so on, anything disrupts the continuity of the retina image.

There was some questions of whether change blindness could happen with objects that were at the center of attention. Surely, if you were engaged in a conversation with someone, they could not be replaced with another person without the change being noticed. But they can as Simons and Levin showed in their paper (see citation).

What does this say about our memories? Simon and Levin say:

If we constantly noticed such changes, they would likely detract from our ability to focus on other, more important aspects of our visual world. Change detection as a method relies on the tendency of our visual system to assume an unchanging world. The fact that we do not expect one person to be replaced by another during an interaction may contribute to our inability to detect such changes. … Taken together, these experiments show that even substantial changes to the objects with which we are directly interacting will often go unnoticed. Our visual system does not automatically compare the features of a visual scene from one instant to the next in order to form a continuous representation; we do not form a detailed visual representation of our world. Instead, our abstract expectations about a situation allow us to focus on a small subset of the available information that we can use to check for consistency from one instant to the next.

In effect we delude ourselves as to the completeness of our immediate memory. We remember the unexpected if we notice but there is no guarantee that we will notice.


Simons D.J., & Levin D.T. (1998). Failure to detect changes to people during a real-world interaction Psychonomic Bulletin and Review, 5, 644-649

2 thoughts on “What change blindness says about memory

  1. Curious. I would expect “change” to be equivalent to “motion”, and would expect us to detect motion quickly as a survival technique.


    JK: Thanks for the comment. I would agree with you that motion is so important to survival that it is hard to imagine that it would be ‘missed’ very often. So I would think that change is dealt with differently from motion - probably. In this case it was one person taking the place of another in the middle of a conversation. A person on the street was stopped and asked for directions. During the conversation, two people with a large sheet of wood passed between the two and the asker was replaced during the sheet passing between the two talkers. Although the subject was in a conversation and remembered the conversation (carried on in fact), they often did not have a clear memory of the person and just assumed it was the same person. My impression is that the identification of motion does not depend on short term memory, although it may depend on some sort of sensory memory on the retina or the primary visual cortex.

  2. Blind people with undamaged eyes may still register light non-visually for the purpose of circadian entrainment to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract and are not affected by optic nerve damage beyond where the retinohypothalamic tract exits….’*

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