Theoretical questions connected with change blindness

1. Theoretical questions connected with change blindness What is internally represented before and after change? How is change detected when it is? What effects does the detection of change have on other information being held in the system?

2. Many situated theorists are anti-representationalists. Why? One picture is radically behaviorist. Attention focuses on certain aspects of the scene, and people respond “automatically” to what they attend to, with no internal representation. A second picture is more moderate: The organism records the stimulus attended to, but this record is not rich enough to count as a representation.

3. But what is a representation? Representations are typically thought to have the following properties: --They are uniquely sensitive to what they represent (they’re detectors) --They contribute to behavior directed toward the thing they represent --They contribute to planning that concerns, and remembering things about, whatever is represented --They can be mistakenly applied (they have conditions of correct applications)

4. Sperling experiment, two rows

5. Silverman and Mack, Exp. 1 -3x3 matrix -standard Sperling report, with and without 500ms delay -identify degraded trigram Results -priming effect of both cued and noncued rows (no diff. between them); held for delayed as well as nondelayed condition (impressive, given the drop off in recall)

7. Experiments 2a and 2b: change is introduced 2a focuses on information about row that was changed later --report whether there was change --cueing and partial report --degraded trigrams are to be decoded

9. Results --Partial cue report much better when change was in the cued row and was detected --When change was not detected, all rows tested have priming effect (equally) --When change was detected the priming effect disappeared!

10. 2b focuses on post-change row Same design as 2a but post-change row trigrams used instead of pre-change row Results same as before: -All tested rows had priming effect (equally) when change is not detected -When change is detected, only changed row (post-change) has priming effect

11. Explanation 1: Overwriting When change is detected the new information overwrites the old But this does not explain the lack of priming of unchanged row And it also leaves it unclear how the mechanism of change-detection works. The overwriting can’t simply be automatic, or the change wouldn’t be detected.

12. Explanation 2: --Information not relevant to a presumed goal (change-detection) was discarded or inhibited. --Note that when interviewed subjects did not think that exposure was meant to help with decoding of degraded trigrams (this is consistent with the idea that the subjects did not think there was any point in preserving information after change was detected)

13. Explanation 3: task demands The failure of priming when change is detected (i.e., the failure of priming in for all rows except the post-change changed row) is a result of task demands. The combination of detecting change and maintaining information for partial report exhausts cognitive resources.

14. Experiments 3a and 3b Similar to 2a and 2b, but without partial report and with some variation in the stimulus changes (to prevent strategic processing) Same pattern of results, which suggests that explanation 2 (inhibition of change-irrelevant information) is correct.

15. Big picture: At least in some cases, change blindness is due to failure of the comparison process, not failure to preserve information. Should the traces carrying this information be considered representations?