Figure 1.

SVV paradigm. (A) SV V measurement with the line stimulus (red) presented at a random orientation in each trial. As a two-alternative forced choice paradigm (2AFC), the task in each trial is to report whether the line is tilted to the right or left of perceived upright orientation. SV V is then determined by fitting a psychometric curve to the responses from all trials, and calculated as the value on the curve at which the probability of left or right responses is 50% (point of subjective equality). The SV V precision is calculated as the slope of the psychometric fit. (B) A sample time course of 100 trials with the participant's responses, with each point representing one trial. The y-axis shows the angle of the line presented and the color indicates the response for that trial. The left tilt responses are shown in blue and the right tilt responses in red. The line angles were presented randomly within a range that started at 360° and then adjusted based on previous responses (illustrated by the top circles with the light gray sectors). At the end of every 10 trials, the center of this range (also shown in light gray shade on the graph) was set as the SV V value calculated from the previous trials. The range was reduced in half every 10 trials until it reached 8° (±4° around the calculated center), after which it was kept constant for the remaining trials.