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4.3.3.2.1 Direction discrimination task. The stimulus parameters specified in the motion null task as well as for the EEG motion condition (see Table 6) may not be optimal for all participants. For example, studies have suggested that different aspects of human visual function development, such as contrast sensitivity, spatial frequency discrimination, and temporal

frequency discrimination, occur at different rates (Ellemberg, Lewis, Liu, & Maurer, 1999; Gordon & McCulloch, 1999; Lewis & Maurer, 2005). Additionally, sensitivity thresholds for such aspects of vision as spatial frequency are typically established based on measures obtained from adults with normal vision rather than from children or special populations. Therefore, this behavioral task assessed a participant’s ability to perceive and judge the direction of a drifting luminance-defined Gabor-like patch (moving grating inside a static window with smooth edge)

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at varying spatial and temporal frequencies as well as at two contrast levels. This direction discrimination task established that all participants perceive motion consistent with the

parameters of the motion null task and the EEG motion condition; additionally, it provided some insights into task performance (reaction times) differences between groups.

Stimuli for the direction discrimination task were generated using Psykinematix software (KyberVision, Sendai, Japan, psykinematix.com, 2016) and presented on a LCD monitor. Participants were seated 46” from the monitor and viewed a 2° static circular window with smooth Gaussian edges enveloping a grating of varying spatial and temporal frequencies (see Figure 10) presented center screen against a consistent gray background (mean luminance of 85 cd/m2_{). Participants indicated whether the randomly presented conditions appeared to be}

traversing leftwards or rightwards using arrow keys on a standard computer keyboard. Both accuracy and response time data were collected to confirm that each participant’s accuracy rate was above 80% and to determine whether groups varied significantly in their response times to particular sets of parameters related to the motion null task and/or the EEG motion condition. The task included five different sets of parameters (see Table 7), the first of which simulated the parameters used in the motion null task. Three other sets of parameters explored different combinations of spatial frequencies (6 cpd and 4 cpd) and temporal frequencies (10 cps, used in the EEG motion condition, and 2.5 cps used in motion null task). The first four sets of

parameters were all presented at 20% contrast, the initial contrast-level setting in step one of the motion null task. The final set of parameters replicated the EEG motion condition parameters (1 cpd, 8% contrast, 10 cps).

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cpd 4 cpd 6 cpd

Figure 10. Direction discrimination task

Smooth Gaussian edge, presents at three different spatial frequencies (cpd—cycles per degree). Image to traverse left to right or right to left at three different cycles per second (cps).

Table 7

Parameters for the Direction Discrimination Task Direction Discrimination

Parameters Cycles per degree (cpd) Contrast Cycles per second (cps)

1 – Motion Null Task Parameters 6 cpd 20% 2.5 cps 2 – Same SF as Motion Null/Higher TF 6 cpd 20% 10 cps 3 – Lower SF/Same TF as Motion Null 4 cpd 20% 2.5 cps 4 – Lower SF/Higher TF 4 cpd 20% 10 cps

5 – EEG Motion Condition 1 cpd 8% 10 cps

Accuracy and reaction times will be collected for each set of parameters. Parameters differ in their spatial frequencies (SF) indicated by cycles per degree (cpd) and temporal frequencies (TF) indicated by cycles per second (cps). Parameters 1 and 5 mimic the parameters of the motion null task and EEG motion condition respectively. Conditions 2-4 test a range of parameters that may contribute to performance on the motion null task.

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Each of the conditions was presented randomly in one block 40 times (total 200 presentations), with left/right motion randomly selected for a total of 20 left trials and 20 right trials for each block. This task took approximately 5 minutes to complete.

4.3.3.2.2 Orthographic and homophone choice tasks. Two tasks were used to evaluate orthographic processing, or coding, while minimizing the use of phonological processing in response generation. Standardized measures of orthographic skills typically provide a

comparative measure of the integration of orthographic and phonological skills. However, the Orthographic Choice Task (Olson, Wise, Conners, Rack, & Fulker, 1989; Sperling, 2004; Sperling, Lu, Manis, & Seidenberg, 2006;) and Homophone Choice Task (Olson et al., 1989; Sperling et al., 2006) are non-standardized tasks. The Orthographic Choice Task requires

participants to make lexical decisions to 64 pairs of phonetically matched pseudo- and real words (e.g., tight/tite [exception]; sheep/sheap [regular]). For the Homophone Choice Task, participants select which of a phonetically matched pair of possible answers is appropriate for answering a question (e.g., Which is a color? blue/blew). There are 60 questions (Sperling, 2004; Sperling et al., 2006) (see Appendices E and F for samples). Raw scores from these measures were used for the purposes of group comparison and correlation with neurophysiological measures.

4.3.3.2.3 Nonverbal visual reasoning/memory (Larson, Buethe, & Vitali, 1990;

publisher Slosson Educational Publications, Inc.). This task is a subtest of the Comprehensive Test of Visual Functioning assessment which was modified to improve presentation of the images. Participants were presented with a series of shapes within an 8½" x 11" laminated flipbook format. Participants were asked to remember the sequence of shapes. The flipbook page was then turned, and the participant was asked to recall the sequence of shapes presented among four options. The task builds from two shapes to nine shape sequences. Raw scores from these

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measures were used for the purposes of group comparison and correlation with neuro- physiological measures.

4.3.3.3 ERP experimental stimuli. The stimuli for the EEG experiments (see Figures 11