1. Change Detection and
Change Blindness
楊政達
成功大學心理系暨認知科學研究所
視覺認知與數理模型實驗室

2. Outline
 Processes that underlie change detection
 Memory retention
 Memory retrieval
 Comparison and decision
 I will talk about four series of experiments

3. Homework
 After the talk, you have to write 1,000-words
summary, including:
 What you have learned
 The unsolved issues
 New idea and ongoing experiments

4. Change Detection (CD)
 Change detection is a fundamental function of
human vision
 Detecting changes is important
 Successful change detection enables us to perform
proper action
 e.g., dealing with traffic, etc

5. However,
 People may often not detect a large change in the
visual environment
 Change Blindness
 Demo

6. 撲克牌魔術

7. 改變盲的意涵
 The absence of visual representation
 Grand illusion (Noe, 2002)
 “…seeing constitutes an active process of probing the
external environment as though it were a continuously
available external memory.” (O’Regan, 1992)
 Do people not preserve any visual representation in
their brain?

8. Multiple stages in CD
Is there any change?
Change or No change?
Encoding Retention Retrieval and Comparison
Encoding
Time

9. Five possible hypotheses
Simons (2000)

10. In summary, …
 Change blindness may occur because
 Representation-failure: related to encoding and
retention
 Retrieval- and comparison-failure: related to retrieval,
comparison and decision
 Change blindness does not necessarily mean the
absence of visual representation

11. Recent studies showed that …
 Pre-change representation is preserved under
change blindness
 It is more likely that failure of retrieval and
comparison may cause change blindness

12. Overview of the studies
 Issue 1: Is the pre-change representation preserved
under change blindness?
 Issue 2: Does retrieval failure cause change
blindness?
 Issue 3: What is the nature of the retrieval
mechanism?
 Issue 4: What is the nature of the comparison and
decision mechanism?

13. Overview of the studies
 Issue 1: Is the pre-change representation preserved
under change blindness?
 Issue 2: Does retrieval failure cause change
blindness?
 Issue 3: What is the nature of the retrieval
mechanism?
 Issue 4: What is the nature of the comparison and
decision mechanism?

14. Evidence of the dissociation between
change detection and recognition memory
 Examine the existence of the pre-change
representation under change blindness
 Task: change detection task and perceptual
identification task
 Index: repetition priming effect (RPE)
 identifying viewed object is faster and more accurate
than new object
Yeh & Yang (2008)

15. Procedure
1000 ms
2000 ms +
350 ms blank
2000 ms +
350 ms blank
2000 ms
Change
Detection
Perceptual identification task
Experimenter
recorded the
response
Time category

16. Results
 RPE is observed under CD and CB
 Pre-change representation is preserved

17. Dissociation effect as a function of similarity
between pre- and post-change objects
 Manipulating the similarity between pre- and post-
change objects to investigate the effect of similarity
on change detection and recognition memory
 Task: change detection task and recognition
memory task
Yeh & Yang (2008)

18. Procedure and Stimuli
1000 ms
2000 ms +
350 ms blank
2000 ms +
350 ms blank
2000 ms
Change
Detection
2AFC recognition
memory test

19. RM
Results CB
CD
CD

20. In summary, …
 Pre-change representation is preserved under
change blindness
 The dissociation effect
 Similarity ↑ CD↓ RM ↑
 Similarity does not affect the pre-change
representation, it only affects RM
 Similarity benefit occurs because participants use the
similarity as retrieval cues to retrieve the pre-change
representaiton

21. Overview of the studies
 Issue 1: Is the pre-change representation preserved
under change blindness?
 Issue 2: Does retrieval failure cause change
blindness?
 Issue 3: What is the nature of the retrieval
mechanism?
 Issue 4: What is the nature of the comparison and
decision mechanism?

22. Dual processes in recognition memory
 In the literature of recognition memory: two
processes underlie memory recognition
 Recollection and familiarity (Atkinson & Juola, 1973,
1974; Jacoby, 1991; Yonelinas, 1994)
 Recollection: high-threshold model
 Slow, control process and conscious awareness
 Familiarity: signal detection model
 Fast, automatic, and unconscious

23. Dual processes in change detection
 In the context of change detection, it seems that
both processes play roles in detecting changes
 I can recollect information about the pre-change
object: including location, perceptual details, …
 I know that there is something changed, but I cannot
recall any detail about the changed object

24. Purpose
 To examine if retrieval-failure may cause CB
 Retrieval process = recollection process?

25. Process dissociation procedure
 Jacoby (1991) and Yonelinas (1994):
 Study phase (list method)
 List A (interested list); List B (non-interested list)
 Test phase
 Inclusion condition: Is the word from List A?
 Exclusion condition: Is the word from List B?

26.  Inclusion: Is the word from List A?
p(yes | interested list) = P ( R ) + P ( F ) − P ( R ) × P ( F )
 Exclusion: Is the word from List B?
p (yes | interested list) = P ( F ) − P( R) × P( F )
where P ( F ) =φ d '− )
( c
R= Pr(Ex) - Pr(Inc)
F = Pr (Ex) / (1-R)

27. When recognizing the pre-change
object?
Inclusion condition Exclusion condition
“Pre” “Pre/New”
R R
F “Pre” F “Post”
1-R 1-R
“Post/New” “Pre/New”
1-F 1-F
Response

28. Inclusion condition Exclusion condition
Pre-change Pre-change Post-change
Post-
object or New object
change or
New object object

29. Procedure (Inclusion condition)
Fixation
Pre-change display
+
Blank
Post-change display
2000ms
2000 ms Change detection task
350ms
Confidence rating
2000 ms 1 2

30. Data analysis
 WinBUGS: Bayesian analysis
 Chains = 4
 Burn-in = 6000
 Samples = 3000

31. Results
Probability of recollection Probability of familiarity

32. In summary, …
 Although the pre-change representation is
preserved, participants may fail to detect the change
as a result of retrieval failure
 Successful retrieval requires participants to recollect
the pre-change details

33. Overview of the studies
 Issue 1: Is the pre-change representation preserved
under change blindness?
 Issue 2: Does retrieval failure cause change
blindness?
 Issue 3: What is the nature of the retrieval
mechanism?
 Issue 4: What is the nature of the comparison and
decision mechanism?

34. Questions
 Given that both CD and RM require successful
retrieval, why do I observe the dissociation effect?
 What is the nature of the retrieval mechanism?

35. Retrieval blocking hypothesis
 (Yang & Yeh, 2009)
 The retrieval of the post-change object may block
the retrieval of the pre-change object
 A location-based retrieval
 Example

36.  To verify the retrieval blocking hypothesis, I used a false
memory paradigm
 Change blindness may occur because:
 Comparison failure: pre-change representation is intact.
Participants should falsely recognized the pre-change lure as the
pre-change target
 Retrieval blocking hypothesis: ： the retrieval of the post-change
object may block the retrieval of the pre-change object.
Participants should falsely recognized the post-change lure as
the pre-change target

37. Pre-change array 2000 ms
ISI 350 ms
Post-change array 2000 ms
ISI 350 ms
Pre-4-AFC
post-4-AFC

38. Presentation duration for 2 S
Support the retrieval blocking hypothesis
Does this effect occur because pre-change objects
are not completely encoded?
0.8 Target
0.7 Similar to the target
Similar to the alternative target
0.6 Unchanged object
Proportion
0.5
0.4
0.3
0.2
0.1
0
Pre-change Post-change

39. Presentation duration for 3.6 S
Also support the retrieval blocking hypothesis
0.8 Target
Similar to the target
0.7 Similar to the alternative target
Unchanged object
0.6
Proportion
0.5
0.4
0.3
0.2
0.1
0
Pre-change Post-change

40. Discussion
 Retrieval blocking hypothesis
 This effect is not caused by the incompleteness of
the pre-change representation
 However, the result may occur because the
attention is divided when viewing the pre-change
display; the post-change object is under focal
attention
 Divided attention
 The manipulation of the spatial cuing

41. Under divided attention
Memory error of the post-change lure increases,
supporting the retrieval blocking hypothesis
0.7 Target
Similar to the target
0.6
Similar to the alternative target
0.5 Unchanged object
Proportion
0.4
0.3
0.2
0.1
0
Pre-change Post-change

42. The manipulation of the spatial cuing
Memory bias occurs in the INVCD and VCB condition
0.7 Target
Similar to the target
Similar to the alternative target
0.6 Unchanged object
Forget
Proportion
0.5
0.4
0.3
0.2
0.1
0
INVCB INVCD VCB VCD
V: valid cue; INV: invalid cue; CD: correct detection; CB: change blindness

43. The retrieval mechanism
 Adopting a location-based retrieval strategy, the
retrieval of the post-change object may block the
retrieval of the pre-change object for change
detection
 However, this strategy may aid the recognition
memory because similarity between the pre-change
post-change objects can be used as a retrieval cue
 This benefit may be a product of false recognition

44. Overview of the studies
 Issue 1: Is the pre-change representation preserved
under change blindness?
 Issue 2: Does retrieval failure cause change
blindness?
 Issue 3: What is the nature of the retrieval
mechanism?
 Issue 4: What is the nature of the comparison and
decision mechanism?

45. In the visual environment, …
 A change usually contains changes of multiple
features
 E.g., change of hair style (color and length)
 Usually, these changes are not equally salient
 E.g., hair coloring is more salient than hair shortening

46. Questions
 How do people process the concurrent feature-
changes for a decision?
 How do relative salience affect the comparison and
decision processes?

47. Signal detection framework
Signal detection process in
Pre-change Post-change each feature
feature feature
d’
N S+N
Pre-change
object
Feature 1
c
d’
N S+N
∑ D
Feature 2
c
d’
N S+N
Feature 3
Post-change
c
object
...
...
...
...
Relative salience affects the weighting process, rather than the process
characteristics

48. Alternative processes

49. The present study
 Using the systems factorial technology (SFT) to
study the comparison and decision processes
 Examining how relative silence affects the
processes
 Exp1: two features are equally salient
 Exp2: one feature is more salient than the other

50. The SFT
 Double factorial design
 Redundant-target condition

51. Five possibilities of ICSF
Serial self-terminating model (SS)
Serial exhaustive model (SE)
Parallel self-terminating model (PS)
Parallel exhaustive model (PE)
Channel summation model
(coactive model) (C)
See Townsend & Nozawa (1995)

52. Inference of the process characteristics
 Process architecture: serial, parallel, coactive
 Stopping rule: self-terminating, exhaustive

53. Exp 1
 To examine the processes when two features were equally
salient
 Type of changes: frequency/ orientation-change
 Ambiguity: Unambiguous change (100% detection threshold);
Ambiguous change (75 % detection threshold)

54. Results

55. Results

56. Results

57. Summary
 ICM > 0, ICSF > 0
 When the detection thresholds were equated, all
participants adopted parallel self-terminating
processing to detect redundant changes

58. Exp 2
 To examine the processes when one feature was
more salient than the other
Detection threshold F O
Unambiguous change 100% 75%
Ambiguous change 75% 50%

59. Results

60. Results

61. Results

62. Summary
 3 observers: ICM = 0, ICSF = 0; Observer TY: ICM > 0,
ICSF > 0
 When relative salience exists, 3 observers changed
their decision strategy to serial self-terminating
processing; Observer TY remained adopting parallel
self-terminating processing to detect redundant
changes

63. Subjective self-reports
 Exp1: all of them considered that two features were
equally important for a decision
 Exp2
 3 observers detected that frequency was more salient
than orientation
 Although Observer TY detected the relative salience,
she still considered that two features were equally
important for a decision

64. In summary, …
 Relative salience may affect the subjective expected
utility (SEU)
 Participants may change their decision strategy to
detect redundant changes according to the SEU

65. Discussion
 Many factors may cause CB. Therefore, CB does
not necessarily mean the absence of the pre-
change representation
 Failure of retrieval, comparison, and decision may
cause CB
 Change detection and recognition memory are
dissociable

66.  The nature of the retrieval mechanism
 A location-based retrieval strategy
 The nature of the comparison and decision
mechanism
 Not necessarily a coactive process
 Flexible
 Can shift according to the subjective expected utility