User:Angeles90

'''Visual memory during pauses between successive saccades '''          Eye movements are closely linked with selective attention. Before a saccade occured, attention moved to the saccadic goal at the rate of surrounding locations. The present study showed that patterns of saccades could be ongoing without disrupting the saccadic goal, while the attention could be allocated to other locations. Saccades were made in sequence along a color-cued path. Attention was evaluated by a visual memory task accessible during a random pause between successive saccades. It was found that saccadic planning had numerous effects on memory. First being that, fewer letters were remembered during intersaccadic pauses than during maintained fixation. Second, letters appearing on the saccadic path, along with locations that were previously examined, could be remembered; off-path performance was hardly remembered. Thirdly, memory was better at the saccadic target than at all the other locations that were tested, including the currently fixated location. These results show that the distribution of attention during intersaccadic pauses results from the outcome of a grouping of top–down enhancement at the saccadic target tied with a more automatic allocation of attention to selected display locations. This entails that the visual system has mechanisms that can control the distribution of attention without it intruding with ongoing saccadic programming.

Intro Saccades are important for two reasons.The first reason being that visual acuity is keen in the central fovea, saccades are important to bring the line of sight to areas of importance. Also to make sure that selected visual details can be resolved. Secondly, our limits to identifying, recognizing and remembering many objects means that we must obtain sequential "direct attention to those objects or regions that are of immediate relevance to task performance" (Gersch et. al, 2008). Saccades enable carrying attention from one place to another. "This latter role for saccades has encouraged the belief that saccadic eye movements are closely, and perhaps, inextricably, tied to selective perceptual attention" (Gersch et. al, 2008). Many developments in approaches have occurred when studying the links between saccades and attention. There have been many studies about the distinction between perceptual attention and saccades. These studies focused on the way in which attention helps saccades to accurately reach targets when nearby stimuli are competing. Add more goals and approach Methods Eye movement recording. The head was stabilized while movements of the right eye were recorded by a Generation IV SRI Double Purkinjie Image Eyetracker (sensitivity <1 arcmin). The study involved three paid volunteers to be tested. Each subject had normal, I corrected 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). Visual memory was evaluated by the ability to remember and identify a letter from an display of 25 letters that was randomly flashed during a random intersaccadic pause. The letters were chosen at random from a set of 10 (A to N). 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). The location of the examined letter that was to be identified was randomly chosen from the central set of 9, this was done in order to avoid testing at the edges of the display. The procedure goes as follows, the subjects fixated on a green cross and began the trial when they pressed the button. When the subject started they would hear a 100 ms beep sound for 50 ms, which was the signal to begin making the sequence of saccades. Eight different saccadic paths were being tested at the time. An on-line algorithm monitored eye movement data for the incident of saccades, this was used to help randomize the appearance during a pause between saccades. After the first trial finished, 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 on 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 (Gersch et. al, 2008). Trials were run in chunks of 60- 100. Saccadic characteristics were analyzed, first, offset error which is the distance between fixation position and the center of the fixated circle of the “good saccades” (following the prescribed path). Second, the average number of targets hit per trial and third, the average time interval preceding saccades.

Result Visual memory performance was tested and measured when the eye remained directed toward one area for the entire trial on one of the three central on-path locations. the stimuli and procedures used remained the same during the fixation trial as those used in scanning saccades. The percentage of post-cued letters that were recalled correctly (during maintained fixation) was 42% for JT, 34% for GT, and 38% for ML. The percentages were multiplied by the number of locations that were tested throughout the trials (n=9) which when calculated ended up to 3-4 letters remembered. This was consistent with the expected amount of short term memory in the visual mind. The probability of recalling a letter during maintained ﬁxation depended on two things: retinal eccentricity and path status (Figure 2A). Memory for letters appearing in one of the 3 on-path (i.e., ﬁxated) locations was better than for letters at off-path ( (i.e., never ﬁxated) locations at equivalent eccentricities (Gersch et. al, 2008). This result of path shows that either the learned significance of the color differences or the color differences in general, influenced which letters were more likely to be encoded into memory. 	The saccadic sequences were presented accurately. The majority of saccades followed the prescribed 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). This saccadic performance that was just described was comparable to the control sessions that were observed, here the same sequential patterns of saccades were done without existing memory test. One significant finding was the differences in offset errors when scanning and without the concurrent task (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). One of the subjects had longer mean intersaccadic pauses with the concurrent memory (t(3039)= 7.11, p < 0.0001). 	During saccadic scanning, it was observed that performance was best at saccadic target. Memory returned to the usual pattern only when the eye had arrived to the final on-path location.

Discussion