VIEWS: 7 PAGES: 20 POSTED ON: 9/8/2011
Stephanie Fishel Jennifer Pappas Jason Moss Jacob Hicks Teri Leech Objective 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 them. • 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 o Pilot • Once again, possible failure to notice warning alerts/icons on display Background 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 event Background 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 quality. • 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 peripheral vision. Hypotheses o This study will attempt to confirm the subjective data from previous studies related to inattentional blindness, with objective data collected through eye tracking o Hypotheses: • 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 the ROI • 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. Equipment o Tobii 1750 eye-tracker o Display driven by dual processor xeon Linux computer 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 Experimental Design o Stimulus: • 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 seconds o Participants: • 19 undergraduate students at Clemson University • 10 males and 9 females • Mean age = 19.42 years (SD = 1.43 years) o Design: • 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. Procedure 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 explain. • Have you previously participated in an experiment similar to this or have you ever heard of such an experiment or the general phenomenon? Analysis 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 the ROI Results 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. Results 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 Results 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 ROI 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. Results 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. Discussion 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. o Improvements: • 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 see. Conclusion 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. ANY QUESTIONS? References 1. Caters, K., Chalmers, A., Ledda, P. (2002). Selective quality rendering by exploiting human inattentional blindness: Looking but not Seeing. Proceedings of VRST’02, Hong Kong. 2. Caters, K., Chalmers, A., & Ward, G. (2003). Detail to attention: Exploiting visual tasks for selective rendering. Eurographics Symposium on Rendering, Leuven, Belgium. 3. Henderson, J.M. & Hollingworth, A. (2003). Global transsaccadic change blindness during scene perception. Psychological Science, 14, 493-497. 4. Mack, A. (2003). Inattentional blindness: Looking without seeing. Current Directions in Psychological Science, 12, 180-184. 5. Moore, C.M. (2001). Inattentional blindness: Perception or memory and what does it matter. Psyche, 7, NP. 6. Most, S.B., Simons, D.J., Scholl, B.J., & Chabris, C.F. (2000). Sustained inattentional blindness: The role of location in the detection of unexpected dynamic events. An Interdisciplinary Journal of Research on Consciousness, 6(14), NP. 7. Most, S.B., Simons, D.J., Scholl, B.J., Jimenez, R., Clifford, E., & Chabris, C.F. (2001). How not to be seen: The contribution of similarity and selective ignoring to sustained inattentional blindness. Psychological Science, 12, 9-17. 8. Neisser, U. (1979). The control of information pickup in selective looking in Perception and its Development: A tribute to Eleanor J Gibson Ed. A D Pick (Hillsdale, NJ: Lawrence Erlbaum Associates), pp 201-219. 9. Neisser, U., Becklen, R. (1975). Selective looking: Attending to visually specified events. Cognitive Psychology, 7, 480-494. 10. Newby, E.A., & Rock, I. (1998). Inattentional blindness as a function of proximity to the focus of attention. Perception, 27, 1025-1040. 11. Simons, D.J., & Chabris, C.F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28, 1059-1074. 12. Tobii User Manual. (2003.) Tobii, Stockholm, Sweden. http://www.tobii.com/ Version 2.1.
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