Figure 2.

Performance. A–C, Data (points) and decision model fits (solid lines; see Eqs. 1–4) from individual sessions for monkey At. Percentage of correct responses is plotted versus motion strength. Grayscale values correspond to different viewing times (three equally spaced bins between 100 and 800 ms, with darker symbols for longer times). More trials with lower coherences and shorter viewing times were added as training progressed and sensitivity improved to maintain an approximately constant overall percentage of correct responses per session. Dashed lines indicate threshold (percentage coherence corresponding to 82% correct at long viewing times, corrected for lapses as in Eq. 4). D, E, Lapse rate (errors for high-coherence, long-duration stimuli; gray triangles, right ordinate) and discrimination threshold (black symbols, left ordinate with a logarithmic scale) as a function of session for At (D) and Av (E). Error bars are SEM. Lines are weighted fits to a decaying single-exponential function. F, G, Degradation of perceptual sensitivity for unfamiliar axes of motion for At (F) and Av (G). The residuals to the exponential fits to threshold (in logarithmic units) in D and E, respectively, are plotted as a function of the familiarity of the axis of motion (the average, angular difference between the current axis of motion and the axes of motion from all previous sessions; larger values indicate less familiar axes). Only sessions with zero lapse rates were used. Lines are weighted linear fits. Positive slopes (H₀: slope = 0, p < 0.01 in both panels) indicate that perceptual sensitivity tended to be worse than the current trend for less familiar axes of motion.