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. 2019 Dec 11;30(4):2659–2673. doi: 10.1093/cercor/bhz267

Figure 1.

Figure 1

Visual stimuli and behavioral task. (A) Marmosets were trained to maintain fixation within a window 2° in diameter around a target presented at the center of the screen (1). A random pattern of dots was then presented within a circular aperture 7° in diameter centered on the fixation target (2). The dots moved at a speed of 15°/s in one of eight possible directions equally distributed between 0 and 360°. Coincident with the onset of the random dot pattern, eight small choice targets were presented, equally spaced around a ring, 10.6° in diameter, concentric with the central fixation target. Marmosets received a liquid reward for correctly reporting the direction of motion by making a saccade to one of the choice targets (3). On a proportion of trials, marmosets received an overt cue, consisting of a small high contrast Gabor patch, presented at the location of the correct choice target. On these trials, marmosets could obtain the reward by making an eye movement to the cued target location without integrating the motion stimulus. These cued trials served to ensure a sufficiently high rate of reward to keep the marmosets engaged with the task. Over the course of training, the proportion of cued trials was gradually reduced. (B) Sequence of trial events. After a fixation period of 200–500 ms (1), the random dot pattern appeared (2). Marmosets were required to maintain fixation on the central target for a minimum duration of 100 ms after appearance of the motion stimulus, after which the fixation target dimmed and the marmosets were free to indicate the perceived direction of motion by making an eye movement to one of the choice targets. Both the fixation point and the random dot pattern were extinguished if the marmoset broke fixation or after a maximum period of 600 ms, whichever came first (3). (C) After initial training, the number of possible motion directions was increased from 8 to 50 over the course of several weeks and the discrete choice targets were replaced by a continuous ring. The strength of the motion signal was then varied by assigning to each dot a direction drawn from a uniform generating distribution centered on the target motion direction.