Combined analysis of EEG and eye movements in perception research: application to change blindness
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1
KU Leuven, Laboratory for Perceptual Dynamics, Belgium
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2
University of Geneva, Switzerland
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3
RIKEN Brain Science Institute, Japan
The simultaneous analysis of electrical brain activity and eye movements has primarily been used as a tool for studying the mechanisms of eye movements. However eye movement also provides a natural way of segmenting behavior and related brain activity. Eye-movement-based segmentation is essential for the study of ongoing brain activity, which lacks external markers like stimulus presentations or responses. Therefore the combined analysis of electrical brain activity and eye movements is a valuable tool for exploring perceptual processes.
We applied such an approach to change blindness; this is when observers fail to notice seemingly obvious changes between subsequent views of a scene. In a typical change blindness paradigm, two displays with multiple objects are presented in succession. Observers have to encode into memory the first display and search for a change in the second display. Failure to report a change may arise, among other things, from a failure in encoding of the first display. We proposed that encoding failures in free viewing of natural scenes are resulting from a discrepancy between the control of eye movements and attention.
We tested our hypothesis in a task, in which observers first studied a photographic image of a natural scene during 20 s of free viewing. After a 1 s presentation of a mask, they were to find the part of the scene in which the color or location of an object had been changed or the object deleted. During free viewing, while observers encoded the display in anticipation of a change in the next display, we jointly recorded EEG and eye movements, and extracted eye fixation-related potentials (EFRP). We analyzed EFRP at the encoding stage in four fixation locations relative to the region where the change was going to occur.
We compared eye-movement measures and EFRP amplitudes between scenes in which a change was correctly detected and those in which the observer failed to detect the change. Neither saccades nor fixation durations differentiated between detection success and failure. However, there was a prominent difference in the amplitude of EFRP time-locked to the saccade onset. The difference occurred in the time intervals assigned to saccade preparation and execution and was observed in two out of four types of fixation locations: those inside a candidate change region and those outside the candidate change region on the last fixation before the gaze entered the candidate change region. In both types of fixation locations the following saccade leads inside the change region and therefore these locations were crucial for scrutinizing and selection the region, respectively. During saccade preparation (in the interval -200-20 ms), in case of correct detection the EFRP amplitude mirrored the pattern of eye movements, suggesting a deployment of attention which was matched to the extent of the saccades. In case of detection failure, EFRP amplitude did not correspond that of eye movements.
When deployment of attention does not coincide with the direction of a saccade, it may lead to inability to select and, subsequently, to encode the target region. Thus, the deviation between eye movements and attention causes change blindness. The result is relevant to the mechanism of spatial selection for visual working memory encoding. We are more likely to retain information that we both pay attention to and keep our eyes fixated on.
Keywords:
EEG,
eye fixation-related potentials,
Eye Movements,
change detection,
Attention
Conference:
Belgian Brain Council, Liège, Belgium, 27 Oct - 27 Oct, 2012.
Presentation Type:
Poster Presentation
Topic:
Higher Brain Functions in health and disease: cognition and memory
Citation:
Nikolaev
AR,
Nakatani
C,
Plomp
G,
Jurica
P and
Van Leeuwen
C
(2012). Combined analysis of EEG and eye movements in perception research: application to change blindness.
Conference Abstract:
Belgian Brain Council.
doi: 10.3389/conf.fnhum.2012.210.00089
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Received:
29 Aug 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Dr. Andrey R Nikolaev, KU Leuven, Laboratory for Perceptual Dynamics, Leuven, B-3000, Belgium, andrey.nikolaev@psy.lu.se