Theoretical neuronal populations response to a pair of dots.

<p>The green circles illustrate two sample dots presented on a monitor. The red circles represent gaze position relative to the sample dots. The left panel represents a ‘saccade’ trial when an observer foveates the leftward dot and at the same time encodes the rightward dot by peripheral vision. The right panel represents a ‘fixation’ trial when an observer foveates a central cross while both sample dots are encoded by peripheral vision. The empty circles of variable size correspond to receptive fields (RFs) covering visual field. The lower panels characterize neuronal populations responses to the visual stimuli in the ‘saccade’ (left) and the ‘fixate’ (right) conditions. The peaks of responses correspond to the positions of the dots when viewed individually (black lines) and when viewed simultaneously (red lines, representing the sum of the functions in black). The line between the sample dots in the ‘saccade’ condition symbolizes no direct interactions between the neuronal populations (small overlap of RFs). The arrow between the sample dots in the ‘fixation’ condition signifies a repulsive effect in perceived distance (large overlap of RFs).</p

Estimation error as a function of sample distance.

<p><b>A.</b> Absolute estimation error as a function of distance between two sample dots. The two encoding conditions: ‘saccade’ and ‘fixate’ (circles with a solid line and asterisks with a dashed line, respectively). <b>B.</b> Estimation bias as a function of sample distance. The sign of the estimation error indicates bias with negative values denoting an underestimation and positive values corresponding to an overestimation of the sample distance. Conventions are the same as in A. <b>C.</b> Standard deviation of the absolute estimation error as a function of separation between the sample dots. Conventions are the same as in A. Error bars denote <i>SEM</i> (n = 7).</p

Bias in distance estimation based on the RF sizes predictions.

<p>The positive values represent an overestimation of a separation between two dots and the negative values, an underestimation. The difference in the eccentricity-related size of the RFs taxed by the ‘saccade’ (solid line with circles) and ‘fixate’ (dashed line with asterisks) conditions, results in a divergent pattern of distance estimation bias.</p

Consecutive stages of ‘fixate’ and ‘saccade’ trials.

<p>Horizontal separation between two sample dots had to be reproduced after a blank delay period. Distance estimation is based on a stationary reference dot and a movable mouse pointer that appeared on top of each other. The arrows with a depiction of an eye in the ‘saccade’ trial (lower panel) represent eye movements that brought the sample dots onto the fovea. The arrow in the distance estimation phase indicates a shift of the mouse pointer required to reproduce separation between the sample dots.</p

The ratio of separation by eccentricity as a function of that separation.

<p>For the ‘saccade’ (solid line with circles) condition, the eccentricity corresponded directly with the distance between the sample dots. For the ‘fixate’ (dashed line with asterisks) encoding condition, the eccentricity was calculated as the mean eccentricity of the most peripheral dot of a sample pair of dots.</p