Departments of Psychology and Computer Science. University of British Columbia. Vancouver, BC Canada. Ronald A. Rensink. Robust Inattentional Blindness.
Robust Inattentional Blindness Ronald A. Rensink
Departments of Psychology and Computer Science University of British Columbia Vancouver, BC Canada
VISUAL COGNITION LAB
Background Neisser, Becklen, & colleagues (1970s) - count # of times ball is passed between people in white
(Courtesy Dan Simons)
48% of observers did not see the “umbrella woman”
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Simons & Chabris (1999) - count # of times ball is passed between people in white
(Courtesy Dan Simons)
46% of observers did not see person in the gorilla suit
Mack & Rock (1990s) Which line is longer?
hello world
Test stimulus Critical trial (200 ms)
Did you see anything besides the lines?
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Observers often did not see the test stimulus - when items near fixation , blindness rates usually 20% - 30% Explanation: observers did not attend to the test stimulus when it wasn’t expected ⇒ could not see (=experience) its presence ⇒ Inattentional Blindness (IB)
In all these experiments, a critical factor is expectation When observers expect the test stimulus, there exists a divided attention condition. Under these conditions, “…by and large IB no longer occurs.” (Mack & Rock, p.205)
• A lack of expectation is sufficient for IB (Mack & Rock, 1998)
• But is it necessary? (cf. Braun, 2001)
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Are two factors involved (attention, expectation) or just one (attention)?
This issue is important in several ways: 1) Theoretical: Expectation (intention) might be a necessary factor in the setup of particular circuits involved in conscious visual experience. - intention necessary or sufficient for attention? 2) Practical: Eliminating expectation means that only one trial can be carried out per observer - studies can take an extremely long time, requiring many observers (Mack & Rock: 5000 observers!)
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Can inattentional blindness exist even if the observer knows the stimulus might appear?
Methodology Methodology Basic idea: • Present a test stimulus while observer has their attention engaged on some other task • If attention cannot be easily switched, the test stimulus may become “unseeable”, even though it is expected
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“Locked-Onset ” Technique (Experimenter Point of View) The onset of the test stimulus is locked to two events: 1) Appearance of “splats” in the periphery - irrelevant to observer’s task - reduces automatic drawing of attention by transients 2) Beginning of movement of attended items - observer must track these items - need to attend to these to see movement - number attended = 4 ≈ attentional capacity
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“Splats” distract attention during onset of test stimulus
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Observer begins tracking 4 items during onset of test stimulus
Locked Onset - onset of test stimulus is locked to the start of attentional diversion (exogenous & endogenous)
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The offset of the test stimulus is followed by two events: 1) A mask at the location of the test stimulus - irrelevant to observer’s task - reduces chance that attention goes to memory trace of test stimulus after tracking is completed 2) Immediate start of a second attentional task (search) - observer asked for speeded response - if primary task, counterproductive to attend to test stimulus before starting the search
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Is the vowel an A or an E? B H
C
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G E
D K
Locked-Onset Technique (Observer Point of View) Task: pre-condition
main task
- Watch 4 circles move out and back in - Respond to display only if all move out and in (p=2/3) - sometimes only 3 move don’t respond - sometimes 4 move, but only out - sometimes 4 move, but only in
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- Identify whether the letter array contains an “A” or “E” (hit the appropriate key) - When the items move, a test stimulus appears in the center of the display some of the time.
post-task
- If you even slightly suspect it appeared, hit the key again. Otherwise, hit the space bar.
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B H
C
E
D
M
Increasing time
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K X X
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1800 ms
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200 ms
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200 ms
200 ms
Results Results Test stimulus appears for 200 ms; extent = 2º x 2.5º (n = 12; 180 trials per observer)
Pre-condition (continue if valid sequence of tracked items) For all observers, d’ > 1 Main task (vowel A or E ?) Average error < 3% Post-task (report whether or not test stimulus is seen seen = even if they only think they saw it) - remove observers with ≥ 90% “not seen” responses (n=4): Average blindness rate: 27.9%
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Variation among observers
blindness
50 40 30 20 10
Effect of duration of test stimulus Test stimulus appears for 400 ms; extent = 2º x 2.5º (n = 12; 180 trials per observer)
Pre-condition (continue if valid sequence of tracked items) For all observers, d’ > 1 Main task (vowel A or E ?) Average error < 2% Post-task (report whether or not test stimulus is seen seen = even if they only think they saw it) - remove observers with ≥ 90% “not seen” responses (n=2): Average blindness rate: 26.8%
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Effect of size of test stimulus Paired tests (n = 12; 180 per observer trials) Test stimulus appears for 200 ms Extent
2º x 2.5º: Blindness = 30.0% 1º x 1.2º: Blindness = 29.4%
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No effect of size
Cf. Mack & Rock - strength of IB decreases with size - essentially gone at 1.5º - likely due to increased attentional capture For locked onset, attentional capture may not be involved - test stimuli can be even larger?
Conclusions Conclusions IB can exist even when observers expect test stimulus, and have had practice trying to detect it - robust inattentional blindness (RIB) - a considerable degree of blindness (25-30%) can occur - same as “basic IB” (i.e., when IOR not invoked) - no difference between 200 ms and 400 ms durations - same as basic IB - no difference between test stimuli 1º and 2º in extent - different than basic IB - no attentional capture involved?
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⇒ Absence of visual experience (blindness) can occur even if the stimulus is expected and its size, shape, location, and possible moment of appearance are known Locked onset may be a basis for the large-scale investigation into implicit visual perception
Thanks to… Research assistants • Alym Amlani • William Chao • Sandy Chuang • Andrew Synyshyn Supporting agencies • Institute for Robotics and Intelligent Systems • Nissan Motor Co., Ltd • NSERC (Canada)
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