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Twenty participants (10 female, mean age = 26.0, SD = 11.2) volunteered for the present study. All participants were free of memory problems and uncorrected vision problems. Participants were randomly assigned to one of two age- and sex-matched groups: the experimental group (5 female, mean age = 27.3, SD = 11.2) or the control group (5 female, mean age = 24.8, SD = 11.7). These groups were exposed to two different training conditions, which are illustrated in Figure 1 for the eye exercise group and in Figure 2 for the control group.
Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0059244.g001 Experimental design for the eye exercise group.Following a 10 minute RSVP task, subjects in the eye exercise group were instructed to follow a moving box on the screen, effectively performing numerous saccadic eye movements, before being assessed in a second RSVP task. Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0059244.g002 Experimental design for the control group.Following a 10 minute RSVP task, subjects were asked to fixate on a movie clip presented in a very small box on the screen, effectively performing a very limited amount of eye movements, before being assessed in a second RSVP task. The present study was approved by the York University Human Subjects Review Board and conducted in accordance with the Declaration of Helsinki. All participants provided signed consent prior to taking part in the study, and were free to withdraw at any time with no consequences.
Rapid Serial Visual Presentation (RSVP): For both eye exercise and control groups, participants were assessed using RSVP before and after their respective training conditions. In RSVP, all 26 letters of the English alphabet are randomly presented in either black (RGB: 0, 0, 0) or white (RGB: 255, 255, 255) within a 30×30 pixel grey box (RGB: 128, 128, 128) at the center of the screen. Black letters are non-target letters while white letters represent the target to which subjects responded by button press on a computer keyboard. Each letter is presented for 33 ms followed by a 50 ms blank box. A trial starts with the presentation of 5 to 10 non-target letters followed by a target letter. Following presentation of the first target letter, another 0 to 4 non-target letters are shown before the next target letter. Either 2 or 3 target letters are shown per session before concluding with 14 non-target letters. This sequence is repeated a total of 10 times to constitute one trial. Our subjects were exposed to 12 trials in total. Our RSVP task replicates the one used by Joseph and colleagues [32], except our paradigm includes second and third additional target letters that are randomly presented in the trials within each session. This was meant to ensure that each session randomly presented 2 or 3 target letters and participants were unable to predict how many times they were required to respond. The total experiment consists of 12 trials, each consisting of 10 sessions (1 session = 5−10 non target, target, [0–4 non target, target]×1 or 2 randomized, 14 non target) (Figure 3). Total time for the entire experiment of the modified RSVP task is approximately 10 minutes. We were interested in measuring three aspects of subjects’ performance in the RSVP task: reaction time to responding to target letters, accuracy in responding to target letters, and accuracy in identifying the final target letter in every tenth session.
Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0059244.g003 Experimental paradigm for the modified RSVP task.All letters were presented at central fixation, with target letters appearing in white and non-target letters appearing in black font. Expanding upon the RSVP task presented by Joseph et al. [32] we incorporated an instruction to identify the target letters observed during every tenth session. Participants were prompted by an instructional screen to indicate the letters presented, and were given extra time (15 sec) to indicate the letters using the computer keyboard. The purpose of this evaluation was to determine whether eye exercise facilitated improvements in visual working memory as measured by letter identification, and specifically, with the number of correct responses. Overall, letter identification was required 12 times, once after the final session of every trial (Figure 3).
The experimental condition had ten participants perform an active eye exercise task, which involved following a white square on a black background through a series of paths described as follows. The participants were expected to make saccadic eye movements while following the square through a course of 5 horizontal figure eights, 5 large rectangles outlining the edge of the screen, 5 vertical figure eights and 5 small rectangular paths. This cycle was repeated 4 times. The square would move to a new position every 150 ms. The duration of the eye exercises was 18.5 minutes. Overall, following the square would have resulted in the performance of 7,740 saccadic eye movements, thus maximizing the amount of eye movements performed. The eyes of the subjects were observed by the experimenter during the entire task to ensure that subjects were actively participating in the task. All subjects complied with the instructions and were included in the analysis.
The control group had a training condition that intended to minimize the amount of eye movements, or exercise, that the participants engaged in. As such, the control task involved participants’ passive observation of an 18.5-minute clip of a movie (Shrek 3) without sound. This clip was displayed within a 50×50 pixel sized box surrounded by a white screen. The dimensions were purposefully small to minimize saccadic eye movements. Any changes found in the control group were expected to be due to effects of the RSVP task and thus can be used to factor out the practice effects from the experimental group. The eyes of the subjects were observed by the experimenter to ensure that the subjects were actively participating in the task.
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