Attention during pauses between successive saccades
Creators: name: Zhao, Min
Publisher: name: No Publisher Supplied
Year: 2011

description: Perceptual performance is better at the target of a saccade than other locations (e.g. Gersch et al., 2009). To better understand pre-saccadic attention shifts, four experiments were carried out that measured perceptual discrimination and detection across different stimulus contrasts during pauses between successive saccades.     In Experiment 1, displays contained 4 outline squares (1.4° on a side) located at the corners of an imaginary square (3.4° eccentricity from the screen center). Sequences of saccades were made in a V-shaped path from one corner to another.  Perceptual targets (oriented letter T’s) appeared inside each eccentric square when the eye reached the center. The orientation of a randomly-selected T was reported after scanning was completed. Orientation discrimination was poor (&lt; 75% correct) at all test locations other than the saccadic goal, even at the highest contrast. These performance losses could be due to selective decay of visual memory (Gersch et. al., 2008).     Experiment 2 used a single visual target in order to decrease the memory load. The displays contained 13 outlined squares (1.23° on a side, one in the center, 4 at the inner corners and the 8 in the outer loop), which allowed subjects to make a longer sequence of saccades. The eccentricity from the inner corners to the center was 2.5°. In each trial, an oriented Gabor appeared randomly in either the saccadic goal location or the opposite location in the inner group of squares. Perceptual reports were required either frequently (80% of trials) or infrequently (20% of trials). Although the perceptual performances was good at both locations, a small perceptual enhancement at the saccadic goal location was observed regardless whether there was external noise or how frequently a report was required. Durations of pauses between saccades were prolonged when the Gabor was detected at a location other than the saccadic goal, reflecting an attempt to improve perceptual discrimination by delaying the saccade.    Experiment 3 presented two Gabors in each trial, one at the saccadic goal location and one at the opposite location, which prevented subjects from knowing the report location as soon as they detected the Gabor and adjusting their strategy in the trial. Pause durations between saccades were prolonged when a report was required frequently, showing that emphasizing a perceptual task could affect saccadic performance even when there was no location cue. Perceptual enhancement at the saccadic goal location was observed again, and this enhancement was larger when a perceptual report was required infrequently.  The perceptual enhancement at the saccadic goal location still existed with a detection task, which reduced the memory load, in Experiment 4, which tried to find out whether the location difference without external noise condition is due to the attention shift or memory load.    These results show that fixation pause durations were increased by attention to a non-saccadic-goal location, and that perceptual performance was better at the saccadic goal location than at non-goal location, supporting the conclusion that perception and saccades use a common attentional filter.  In contrast to attention shifts controlled by cues during maintained fixation, the pre-saccadic attention shifts were found both with and without the external noise, across the whole range of the stimuli contrasts, and regardless of memory load.  This shows that multiple mechanisms of visual attention must be involved in pre-saccadic attention shifts.