This protocol is designed to investigate the spatial deployment of visual attention during saccade programming and it allows to assess what people attempt before they look somewhere. The main advantage of the protocol is that one can analyze visual attention before the execution of so called averaging saccades which land at an intermediate location between two saccade targets. Nina Hanning, a PhD student from our laboratory, will be demonstrating the procedure in the role of a participant.
Begin setup of the experimental materials in a dimly illuminated room consisting of a computer, a Cathode Ray Tube or CRT monitor, a standard keyboard, two loudspeakers, and an eye tracker. Then open the eye tracking software and load a pre-written script that includes all parameters for stimulus presentation and capture of behavioral and eye data. Display all visual stimuli on a CRT screen with a minimal vertical refresh rate of 120 Hertz.
Use the left and right arrow keys on a keyboard to assess the participant's evaluation of the discrimination target orientation either counterclockwise versus clockwise. Ensure the proper display of visual Gabors on the screen. Lastly, set up speakers in order to provide auditory feedback for incorrect manual responses.
Begin by having the participant sit down in a chair in front of the eye tracker. Place their chin on the chin rest and lean their forehead against the bar to restrain head movements. Next, run a calibration procedure by asking the participant to follow a dot moving across different locations on the screen in order to guarantee that the participant's gaze can be accurately tracked within a radius of one degree.
During the experiment, monitor correct fixation at the screen center at the beginning of each trial. Next, instruct the participant to fixate at the center of the screen at the beginning of each trial. Then inform the participant that 24 flickering distractor streams will appear on the screen and that two of them will be cued by white frames which will either be flashed shortly or remain on the screen until the trial end.
Ask the participant to then look as quickly as possible towards the center of one of the two cues. Finally, ask the participant to manually report whether the tilted Gabor was rotated clockwise or counterclockwise relative to the vertical by pressing the right or left arrow on the keyboard respectively. Explain that a sound will be played if the orientation of the tilted Gabor is being reported incorrectly.
Begin the tasks with a fixation target in the form of a black and white bull's eye at the center of the screen. Remove the fixation target from the screen together with the onset of the saccade targets. Display 24 evenly spaced distractor streams at a radius of 10 degrees from the fixation target at the trial start.
Use dynamic stimuli alternating every 25 milliseconds between a vertical Gabor patch and a Gaussian pixel noise mask. Between 300 and 600 milliseconds after the onset of the fixation target present two saccade targets in the form of gray circles surrounding two randomly chosen distractor streams at an angular distance of either 30 degrees or 90 degrees across trials. Ensure to vary the time of saccade target onset from trial to trial to avoid the participants adopt a predictable saccade execution pattern.
Next, randomly present a discrimination target, a tilted Gabor patch rotated clockwise or counterclockwise by 12 degrees relative to the vertical for 25 milliseconds to replace the vertical Gabor patch within the randomly selected distractor stream. Then select the time window for discrimination target presentation to maximize the number of trials in which the discrimination target offset occurred before saccade onset. Erase all stimuli from the screen 500 milliseconds after the onset of the saccade targets such that only the gray background remains.
Finally, wait for the participant to indicate the orientation of the discrimination target via the keyboard by pressing the left arrow for counterclockwise orientations and the right arrow for clockwise orientations and play a feedback sound whenever participants report the discrimination target orientation incorrectly. Automatically launch the next trial once a manual response was given. Results indicate that the saccade endpoint distributions associated with the 90 degree and 30 degree conditions differed substantially.
Further, taking into account saccades of all directions, data showed a selective facilitation of visual sensitivity at the two saccade targets relative to the control locations in both the 90 degree and 30 degree conditions. Visual sensitivity was significantly enhanced at the endpoint of accurate saccades in both the 90 degree and 30 degree conditions. In contrast, before averaging saccades, visual sensitivity was not enhanced at the saccade endpoint but slightly reduced.
Lastly, no significant benefit was observed at the endpoint of corrective saccades following an averaging saccade which supports the interpretation that attentional selection was not resolved before averaging saccades. Make sure to measure visual attention during saccade preparation. To do so, only include those trials in the analysis in which the discrimination target actually appeared before the onset of the saccade.
Applying concurrent neurophysiological recordings from areas such as the frontal eye fields or the superior caliculi could extend insights on the coupling between attention and saccadic eye movements at the neuronal level.
