Fig. 4.

Population results. A: histogram of modulation in preferred speed (PS) in all 73 neurons. The mean speed modulation is positive and significantly different from 0, indicating a positive correlation between preferred speed and stimulus size in the population. The black, dark gray, and light gray boxes in the histogram indicate the three monkeys. B: differences between normalized preferred speeds for large-medium and medium-small stimuli. All gray symbols indicate the neurons with a negative slope (negative size-dependent modulation) in preferred speed change, and black symbols indicate neurons with a positive slope (positive size-dependent modulation). Insets: schematic representation of the 4 possible alignments of 3 preferred speeds (symbols as in Fig. 3). A majority of the units with positive slopes (positive size dependency) were in the upper right quadrant, indicating that the significance of the data comes mainly from units with a clear increase in preferred speed with stimulus size. The units are sorted in three groups (see legend) according to their preferred speeds for the largest stimulus. Units with preferred speeds above 30°/s (circles) mostly had positive slopes (black circles) and fell in the upper right quadrant (i.e., preferred speed increases with stimulus size). C: regression analysis of log-transformed preferred speeds for the largest and smallest stimulus. The majority of the data points lies below the diagonal, indicating that preferred speeds were slower for smaller stimuli. The equation for the linear regression was y = 0.921x − 0.007. CI, confidence interval.