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'Visual memory during pauses between successive saccadesIn 2008 Eileen Kowler along with others from Rutgers University’s Department of psychology and cognitive sciences produced a study about eye movements and how they are closely related to selective attention. Fellow researchers included Timothy M. Gersch, Brian S. Schintzer and Barbara A. Dosher. They aimed to study saccades, which are fast movements of the eye or any part of the human or animal body. They noticed that when the saccaddic goal went at a certain rate at surrounding locations that attention moved. The saccadic patterns could remain ongoing without disrupting the “saccadic goal”. In order to test saccadic goals, Kowler along with her colleagues used color cued paths in order to evaluate attention by visual memory task, they also used random pauses between successive saccades since they believed it had an immense effect on memory.

Intro Saccades are very important when it comes to visual acuity, they help bring sight to the important areas of the eye such as the central fovea (which is the area of the eye that has clearest vision). Another importance that saccadic eye movement plays a role in is identifying and recognizing objects along with remembering. In order for this to occur one must attain direct attention to certain objects or areas that have significance to the task performance that’s being done. Saccadic eye movements also help when it comes to moving attention from one place to another. Kowler and her colleagues have been studying many developments in the saccadic approach when it comes to the relationship between attention and saccades. Their study focused on the manner in which attention helps saccades to connect with target areas when there are competing stimuli.

Methods Kowler and the other researchers used three paid volunteers in the study. Eye movement recording was assessed by stabilizing the subjects head when they measured movements in the right eye. They recorded the movements using a Generation IV SRI Double Purkinjie Image Eyetracker (sensitivity <1 arcmin). Before conducting the experiments they made sure that the subjects were normal and that they all had uncorrected vision. “Stimuli were displayed on a Dell P793 CRT monitor (13 deg 12 deg; viewing distance 115 cm; resolution 1.46 pixels/minarc; refresh rate 75 Hz). Background luminance was 54 cd/m2 and maximum luminance was 108 cd/m2 at the refresh rate used. The display (see Figure 1) was a 5x5 array of 1- diameter outline circles separated by 1.5- (center-to-center). Five of the circles were green (x = 0.280 y = 0.602, luminance = 81.6 cd/m2) and the rest red (x = 0.628 y = 0.338, luminance = 22 cd/m2). The 5x 5 array was bordered by 4 rectangular areas that each held three crosses which served as starting and ending locations for the saccadic sequences. Subjects made saccades to look from one green circle to the next, beginning at the central green cross on one of the 4 sides (chosen randomly) and ending at the central red cross on the opposite side” (Gersch et. al, 2008). The subjects were all gone through the same exact procedure in order to eliminate any factors. The subjects did the following, fixated their vision on a green colored cross and pressed a button in order to begin the trial. Once the trial began the subject would hear a 100 ms (millisecond) beep sound for 50 ms (here was the signal in which sequences of saccades begin). There were 8 different saccadic paths being tested. In order to remove sequence order an on-line algorithm was used to observe eye movement, this was used to help randomize the appearance during pauses of saccades. When this step was finished along with the first trial “the location of the letter was stipulated on a post-trial display by changing color of the circle in the probed location (to either purple or yellow). Sessions were also run in which (1) perceptual performance was tested while steady fixation was maintained at one of the 3 central on-path locations chosen randomly, and (2) saccades were made using the identical stimuli without a letter report taken at the end of the trial. Trials were run in chunks of 60- 100”(Gersch et. al, 2008). Visual memory was also tested. The subject was evaluated by their ability to recognize a display of 25 letters that were randomly chosen and unsystematically flashed during intersaccadic pauses. The 25 letters were randomly chosen from a set of 10 (A to N). When the subject was identifying the observed letter the location was randomly chosen from the central set of 9 letters, this was extremely important to eliminate testing at the edges of the display. “Four frames of the letter array were interleaved with 5 frames of visual noise (13 ms/frame). The noise was a matrix of 20 20 dots (dot size =3  3 pixels) whose luminance levels were Gaussian distributed (SD = 33% maximum display contrast). Interleaved noise was included to maintain consistency with prior work” (Dosher & Lu, 2000; Gersch et al., 2004; Gersch et al., in press). After this the next step was to begin analyzing saccadic characteristics. The characteristics involved distances between fixated positions known as “offset error” and the center of the fixated circle known as “good saccades”.

Result For saccadic sequences the results were presented pretty accurately and they followed the given path. “The on-path saccades landed an average of 18V–24V from the center of the 1 deg diameter target circles. Average intersaccadic pause durations were 200–260 ms, allowing 94.6 of the 6 targets (5 on-path circles + the ending cross) to be looked at during the trials” (Gersch et. al, 2008). Kowler used this saccadic performance to compare to controlled sessions that were observed previously and found that the same sequential patterns of saccades were completed without present memory test. Another important result that was discovered was the differences in offset errors and with no simultaneous task. The results are as followed, findings for JT: t(2865) = 21.09, p G 0.0001; GT: t(1383) = 2.96, p G 0.01; ML: t(1865) = 5.98, p G 0.0001). The results on visual memory performance are as follows. For post-cued letters about 42% for JT, 34% for GT and 38% for ML were recalled correctly during maintained fixation. In order to get these percentages Kowler and her colleagues has to multiply the percentages by the number of locations tested throughout the trials (n=9). When this was calculated on average about 3-4 letters were remembered using visual memory performance. These findings are consistent with short term memory. When vision was fixated, memory for the letters appearing in one of the 3 on-path locations was better than for letters located at off-paths (unfixed locations). The importance of this path result shows that color differences had learned significance and helped influence which letters were to be most likely encoded in memory. Interestingly during intersaccadic pauses fewer letters were remembered as opposed to maintained fixation. Also when letters were shown on a saccadic path they could be remembers even along with locations that were examined prior and off-path performances showed that subjects hardly remembered. Kowler and her colleagues found that at saccadic targets memory was better than at other locations. These findings indicate that the distributions of attention throughout intersaccadic pauses (short delay between eye movements) are due to the product of grouping. This proves that the human visual system has controlled mechanisms that don’t interfere with attention with ongoing saccadic programming.

Discussion Kowler and her colleagues throughout the study began to understand how big of an impact that saccadic eye movement has on visual memory. By looking at targets that had color cued paths it resulted in the dissociation between attention and saccades. When it came to location, memory performance tasks were better than off path locations. Although when we talk about memory it isn’t solely dependent on saccadic plans but also visual cues. Visual cues help assist in attention and memory. Another important reason of this study was to find out what exactly helps facilitate the distribution of attention during saccadic scanning. “The results point to two main processes that operated concurrently to govern the default distribution of attention during saccadic scanning: a ‘top–down’ shift of attention to each saccadic target in sequence and a spread of attention along the saccadic path to locations that shared critical features with the saccadic target” (Gersch et al., 2008). Brought to the attention of researchers was the fact that performance on memory was poorer during scanning and better when saccadic movement was fixated.There is definitely more studies and experiments that can be done in order to learn more about this topic.