Spatial integration in human smooth pursuit

Abstract

When viewing a moving object, details may appear blurred if the object's motion is not compensated for by the eyes. Smooth pursuit is a voluntary eye movement that is used to stabilize a moving object. Most studies of smooth pursuit have used small, foveal targets as stimuli (e.g. Lisberger SG and Westbrook LE. J Neurosci 1985;5:1662-1673.). However, in the laboratory, smooth pursuit is poorer when a small object is tracked across a background, presumably due to a conflict between the primitive optokinetic reflex and smooth pursuit. Functionally, this could occur if the motion signal arising from the target and its surroundings were averaged, resulting in a smaller net motion signal. We asked if the smooth pursuit system could spatially summate coherent motion, i.e. if its response would improve when motion in the peripheral retina was in the same direction as motion in the fovea. Observers tracked random-dot cinematograms (RDC) which were devoid of consistent position cues to isolate the motion response. Either the height or the density of the display was systematically varied. Eye speed at the end of the open-loop period was greater for cinematograms than for a single spot. In addition, eye acceleration increased and latency decreased as the size of the aperture increased. Changes in the density produced similar but smaller effects on both acceleration and latency. The improved pursuit for larger motion stimuli suggests that neuronal mechanisms subserving smooth pursuit spatially average motion information to obtain a stronger motion signal.

Human ocular following: evidence that responses to large-field stimuli are limited by local and global inhibitory influences

“…Many other studies have examined the so-called smooth pursuit tracking responses to single small moving spots that are obviously not confined to a stationary window. These pursuit responses have latencies that are generally at least twice that of the OFR (e.g., Heinen and Watamaniuk, 1998). Mean horizontal R-L eye velocity profiles for one subject synchronized to the onset of the responses; inset shows dependence of latency on the screen coverage (means ±SD for three subjects); numbers at ends of traces indicate the number of strips making up the grating stimulus; grey trace, grating occupies full screen; dashed trace, grating occupies a single strip.…”

Effect of Stimulus Type on the Eye Movements of Children

“…Collapsed across stimulus step size, saccadic latencies were shorter for pictures than for dots (t (59) ϭ 9.05, P Ͻ 0.001), and this difference diminished as a function of age (r (58) ϭ Ϫ0.60, P Ͻ 0.001) (Fig. 1, bottom right).…”

Temporal contrast sensitivity during smooth pursuit eye movements

“…If the eyes move slower than the target, as is often reported (Rashbass, 1961;Collewijn & Tamminga, 1984;Heinen & Watamaniuk, 1998), the target will move on the retina and this may go along with decreased visibility. Because Ludvigh and Miller did not record eye movements, they could not test their hypothesis.…”