o This study attempted to objectively support previous claims made about
the inattentional blindness phenomenon using eye tracking data.
o Inattentional blindness: the act of failing to perceive clearly visible and
salient unexpected objects or events in one’s environment when engaged
in a task (Simons & Chabris, 1999).
o Example: Finding a seat in a crowded movie theater.
• Friends may see you enter theater and wave their hands.
• You don’t sit next to them and they are upset because you ignored
• However, you did not ignore them.
• You did not perceive them because you were actively attending to
task of finding an available seat in a crowded theater.
Why Do We Care?
o Processing Control Plant
• Controller attending to display for specific task or changes in display.
• Warning alert or icon appears that needs immediate attention and
controller does not notice it and fails to take proper action
• Once again, possible failure to notice warning alerts/icons on display
o Simon and Chabris (1999)
o Asked participants to view a video of two teams passing a basketball, one
team wearing black and the other wearing white and asked the participants
to count the number of passes made between either team
• After approximately 45 seconds, a woman dressed in a black gorilla suit
walked across the scene.
o Overall, 44% noticed unexpected event of gorilla
o Participants counting the passes made by the black team noticed the gorilla
significantly more often (58%) than participants counting passes for the
white team (27%)
• Similarity of the stimulus (the gorilla) to the attended objects (the black
or the white team) effected whether or not the participants noticed the
o Cater, Chalmers, and Ward (2003)
• Used eye tracking to support the idea that inattentional blindness did
indeed occur and not a degraded use of peripheral vision.
• Showed 2 still images; high rendering quality and low rendering
• Participants instructed to count # of teapots in scene.
• Asked if noticed difference in quality between 2 images.
• 20% unable to differentiate between image qualities even when eye
tracking data confirmed participants fixated on similar objects in
scene to teapots.
• Therefore inattentional blindness occurred and not degraded use of
o This study will attempt to confirm the subjective data from previous
studies related to inattentional blindness, with objective data collected
through eye tracking
• Individuals who see the gorilla will have a critical fixation,
Critical fixation: a significantly longer fixation in the Region of
Interest (ROI) indicating detection of the stimulus
• Those who notice the stimulus will have a longer total dwell time in
• Participants counting passes made by the black team will be more
likely to notice the stimulus
• The critical fixation for the individuals counting black team passes
will occur sooner than those counting white team passes
• The stimulus is more likely to be noticed when the distance between
it and the attended team’s basketball is short.
o Tobii 1750 eye-tracker
o Display driven by dual processor xeon
o System run by a single processor Windows
XP computer that sends gaze data over a
100 MBit network to the Linux computer
o The Tobii eye-tracker calculates gaze
positions automatically on the Windows
computer while the Linux computer
displays the stimulus
o The Tobii allows head motion of about 30 x
15 x 20 cm
o Accuracy up to 0.5 degrees and average
frame rate of 50 Hz
• 31 second video clip originally used in the Simons and Chabris (1999)
study; 5 seconds into the clip a woman in gorilla suit walked across
the screen from right to left paused in the middle and beat her chest
before walking off the screen; stimulus of interest present for 10
• 19 undergraduate students at Clemson University
• 10 males and 9 females
• Mean age = 19.42 years (SD = 1.43 years)
• Between-subjects design
• IV: color of the team the participant was asked to observe
• DVs: fixation duration in the ROI, total dwell time in the ROI, number
of fixations in the ROI, and the time to the critical fixation in the ROI.
o Participants completed an informed consent form
o Calibration of the eye tracker
o View the video clip
• Instructed to count the number of passes made by either the team
wearing white shirts or black shirts
o Questionnaire including demographics questions and the following:
• Which team’s passes were you asked to count?
• How many passes did you count?
• While you were counting, did you notice anything unusual in the
video? If yes, please explain
• Did you notice anything other than the six players? If yes, please
• Have you previously participated in an experiment similar to this or
have you ever heard of such an experiment or the general
o Analyzing the Data
• ROI was approximated as a close fitting rectangle around the gorilla
in each frame
• A hybrid algorithm was used that determined saccades based on the
weighted sum of a 5-tap velocity and a 5-tap acceleration filter.
• The eye events were divided into saccades and non-saccadic events
o Computing the Dependent Variables
• Total dwell time in the ROI was computed by summing all of the de-
noised gaze points contained in the ROI
• Total “fixation” time in the ROI was computed by interpolating the
starting first and ending points over the duration on the event
• An ocular event list was formed of each fixation and smooth pursuit
along with its start and end position, duration, and percent of time in
o 14 participants were included in the final data analysis
o 11 (79%) noticed the stimulus and 3 (21%) did not, X2 = 4.57, p < .05.
o Similarity hypothesis: 100% (6 out of 6) of the individuals assigned to the
black team noticed the gorilla, whereas only 63% (5 out of 8) of the
participants assigned to the white team noticed, X2 = 2.86, p = .091.
o There were very few true fixations present in the data after the analysis.
• For analysis purposes, anything other than a saccade
will be termed a “fixation”
o 2 x 2 mixed factorial ANOVA ran to test critical fixation hypothesis
• Need to see an interaction effect to support hypothesis
• No significant interaction found, F(1,12) = .779, p >.05.
o Second similarity hypothesis: Because there were no observed critical
fixations, the hypothesis that participants counting the black team passes
would notice the gorilla sooner than participants counting the white team
passes was unable to be tested.
• Longest fixation in the ROI for participants counting the black team’s
passes occurred significantly sooner, at frame 593, than the longest
fixation for those counting white team, at frame 675, t(7) = -2.541, p < .05.
o Total dwell time hypothesis: There was no significant difference found for total
dwell time in the ROI between those who noticed and those who didn’t, t(12) = -
1.08, p > .05.
o Proximity hypothesis:
• 43.8% of the fixations in the ROI made by participants counting white team
passes occurred when the ball or a white team player is in the ROI
• 52.8% of the fixations in the ROI made by the participants counting black
team passes occurred when the ball or a black team player is in the ROI
o 2 participants (18%) that noticed the gorilla had NO fixations in the ROI
o 2 participants (67%) that did NOT notice the gorilla, had fixations in the
o Some individuals noticed the gorilla without having it cross the fovea, and
others do not notice the gorilla even when it DID cross the fovea.
• Indicates that inattentional blindness is not a failure of the visual
system, but a failure of some cognitive process.
Scan path for Participant 6, who Scan path for Participant 9, who
counted the black team’s passes and counted the white team’s passes and
did notice the stimulus did not notice the stimulus
o A typical scan path shows only saccades and fixations. These scan paths
integrate smooth pursuits.
o In each picture, the thin magenta lines represent saccades. The thicker lines
represent smooth pursuits. The smooth pursuits start out green and change
to a more cyan color as they spend more time in the ROI.
o Expected to see some individuals (who did NOT see the stimulus) with
fixations in the ROI but no critical fixation.
o Did not expect to have individuals (who DID see the stimulus) with no
fixations at all in the ROI.
o Study lends support to the ideas of other researchers that inattentional
blindness is a failure of the human brain to encode information rather
than a failure of the visual system.
• More participants!
• Eye tracking, a lot more work with dynamic stimuli needs to be done
• Repeat the study with another condition where the individuals simply
watch the video with no previous knowledge of what they are going to
o This study marked the first time objective eye tracking data was applied to
inattentional blindness using a well-known dynamic stimulus.
o It provided the first objective evidence that inattentional blindness is not
simply a result of a failure of the visual perception system.
o It was interesting to find such a lack of fixations during the presentation
of the stimulus. Further studies on dynamic stimuli should be done to
increase eye tracking knowledge in this area.
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