Visual Tracking/Saccade Task

PI Name: Scott K. Holland, John Bickle

Email: Scott.Holland@cchmc.org

Areas: V1, V2, V3 visual areas in Occipital Cortex, specifically cuneus, precueus and fusiform gyri

Program: MacStim

Durations: ??????

Special Equipment: MRI compatible video system (goggles preferred)

Description: Subjects execute four cycles of blocks of 2-, 3-, and 4-step saccades, and a baseline sensory-motor task. Table 1 summarizes the timing of presentation for each saccade condition, while the figure illustrates the nature of the visual target stimuli presented during the saccade tasks. The general structure of each saccadic trial is as follows: a trial began with presentation of a centrally located red fixation point (FP) against a black background for 0.5 seconds. After 0.5 seconds the central red dot extinguishes and is followed immediately by a sequence of 2, 3, or 4 yellow dots, each dot positioned at randomly generated locations in one of 8 octants and one of 2 radial distances from the center. Each yellow dot appears for 100 msec against the same black background, and after the final yellow dot, a black screen is presented until the duration of the entire trial is 6.0 seconds. Each trial is repeated 5 times within a block, for a block duration of 30 seconds, and a cycle duration of 2 minutes. For each trial, the subject is instructed to fixate on the red dot initially, and when the yellow dots appeared, to saccade from one target to the next in the correct order of presentation. Due to the short (100ms) duration of each target presentation, the target to be saccaded to must be extinguished prior to saccade initiation, and thus as the number of targets increases, task execution makes increasing demands on working memory (particularly for the 3- and 4-step saccades), and by the 4-step task, subjects report difficulty in task execution, suggesting the limits of working memory are being reached, a condition under which the role of ACC (top down versus bottom up monitoring of working memory) can be probed. The task stimuli are presented using an MRI compatible audiovisual system A bilateral finger tapping task was used as the control condition for the saccades. The diagram below describes the 4-step paradigm timing.