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Neural Differences between Covert and Overt Attention Studied using EEG with Simultaneous Remote Eye Tracking

View Article: PubMed Central - PubMed

ABSTRACT

Research on neural mechanisms of attention has generally instructed subjects to direct attention covertly while maintaining a fixed gaze. This study combined simultaneous eye tracking and electroencephalogram (EEG) to measure neural attention responses during exogenous cueing in overt attention shifts (with saccadic eye movements to a target) and compared these with covert attention shifts (responding manually while maintaining central fixation). EEG analysis of the period preceding the saccade latency showed similar occipital response amplitudes for overt and covert shifts, although response latencies differed. However, a frontal positivity was greater during covert attention shifts, possibly reflecting saccade inhibition to maintain fixation. The results show that combined EEG and eye tracking can be successfully used to study natural overt shifts of attention (applicable to non-verbal infants) and that requiring inhibition of saccades can lead to additional frontal responses. Such data can be used to refine current neural models of attention that have been mainly based on covert shifts.

No MeSH data available.


Trial timing. A fixation dot appears in the center of the screen followed by phase reversing bars on the left, right or both sides of the screen. Subjects respond by pressing buttons on a joypad (block 1) or by making eye-movements towards the bars (block 2).
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Figure 1: Trial timing. A fixation dot appears in the center of the screen followed by phase reversing bars on the left, right or both sides of the screen. Subjects respond by pressing buttons on a joypad (block 1) or by making eye-movements towards the bars (block 2).

Mentions: A DELL computer with Linux operating system (Linux Mint 14), with MATLAB [version 7.11.0 (R2010b)] as the presentation program, was used to generate stimuli and present them on a 21.5” (54 cm) LCD monitor (Samsung) that extended over 35.8° × 22.8° of visual angle, running at a frame rate of 60 Hz. Stimuli were presented against a gray background with a mean luminance of 77 cd/m2. A joypad (Saitek USB V pad) was used to monitor participants’ manual responses. A remote eye-tracker, Tobii X120, was used to record the gaze-position of subjects during the experiment at a rate of 60 Hz. The average viewing distance was 65 cm, which approximates the distance at which the eye-tracker receives the best signal. This position was adjusted for each participant until the best possible eye-tracking signal was acquired. Stimulus sizes specified in visual angle are based on this distance. Stimuli were based on the Fixation Shift Paradigm (e.g., Hood and Atkinson, 1993; Kulke et al., 2015a) to facilitate comparison with previous research. At the beginning of each trial, a white dot subtending 0.7° visual angle appeared in the center of the screen for a randomized inter-trial interval between 0.5 s and 2.5 s. When the subject fixated on the dot, target stimuli randomly appeared on the left, right or on both sides of the screen at an eccentricity of 12.9°, while the dot remained present. The target stimuli were phase reversing black and white rectangular bars subtending 3.1° × 13.2°, with a reversal rate of 3 Hz (Figure 1) that appeared until the subject fixated on them for 330 ms (saccade condition) or until the subject made a manual response (manual response condition).


Neural Differences between Covert and Overt Attention Studied using EEG with Simultaneous Remote Eye Tracking
Trial timing. A fixation dot appears in the center of the screen followed by phase reversing bars on the left, right or both sides of the screen. Subjects respond by pressing buttons on a joypad (block 1) or by making eye-movements towards the bars (block 2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120114&req=5

Figure 1: Trial timing. A fixation dot appears in the center of the screen followed by phase reversing bars on the left, right or both sides of the screen. Subjects respond by pressing buttons on a joypad (block 1) or by making eye-movements towards the bars (block 2).
Mentions: A DELL computer with Linux operating system (Linux Mint 14), with MATLAB [version 7.11.0 (R2010b)] as the presentation program, was used to generate stimuli and present them on a 21.5” (54 cm) LCD monitor (Samsung) that extended over 35.8° × 22.8° of visual angle, running at a frame rate of 60 Hz. Stimuli were presented against a gray background with a mean luminance of 77 cd/m2. A joypad (Saitek USB V pad) was used to monitor participants’ manual responses. A remote eye-tracker, Tobii X120, was used to record the gaze-position of subjects during the experiment at a rate of 60 Hz. The average viewing distance was 65 cm, which approximates the distance at which the eye-tracker receives the best signal. This position was adjusted for each participant until the best possible eye-tracking signal was acquired. Stimulus sizes specified in visual angle are based on this distance. Stimuli were based on the Fixation Shift Paradigm (e.g., Hood and Atkinson, 1993; Kulke et al., 2015a) to facilitate comparison with previous research. At the beginning of each trial, a white dot subtending 0.7° visual angle appeared in the center of the screen for a randomized inter-trial interval between 0.5 s and 2.5 s. When the subject fixated on the dot, target stimuli randomly appeared on the left, right or on both sides of the screen at an eccentricity of 12.9°, while the dot remained present. The target stimuli were phase reversing black and white rectangular bars subtending 3.1° × 13.2°, with a reversal rate of 3 Hz (Figure 1) that appeared until the subject fixated on them for 330 ms (saccade condition) or until the subject made a manual response (manual response condition).

View Article: PubMed Central - PubMed

ABSTRACT

Research on neural mechanisms of attention has generally instructed subjects to direct attention covertly while maintaining a fixed gaze. This study combined simultaneous eye tracking and electroencephalogram (EEG) to measure neural attention responses during exogenous cueing in overt attention shifts (with saccadic eye movements to a target) and compared these with covert attention shifts (responding manually while maintaining central fixation). EEG analysis of the period preceding the saccade latency showed similar occipital response amplitudes for overt and covert shifts, although response latencies differed. However, a frontal positivity was greater during covert attention shifts, possibly reflecting saccade inhibition to maintain fixation. The results show that combined EEG and eye tracking can be successfully used to study natural overt shifts of attention (applicable to non-verbal infants) and that requiring inhibition of saccades can lead to additional frontal responses. Such data can be used to refine current neural models of attention that have been mainly based on covert shifts.

No MeSH data available.