Visual search during motion perception

Eye movements during motion tracking or smooth pursuit have been widely investigated. However, it is still unclear how eye movements and motion perception system are related. We aim to analyze the pattern of gaze during coherent motion perception in absence of tracking at the very early stage of the motion perception process. Moreover, we would measure if good performances in motion perception are guided by specific gaze pattern. We measured the gaze in twenty-five healthy subjects using eye tracker system (SMI500) during motion perception tasks (coherent motion test), and during visual search of static elements (i.e. searching coloured dots within a group of white dots). The subjects are divided in two groups: good motion perception performers (scoring above the 50% of the total trials) and bad motion performers. The gaze is analyzed by means of specific parameters obtained from the eye movements recordings: the length of the eye movement track plotted on a bidimensional plane, the area of the confidence ellipse of the eye position, the standardized length (obtained by the ratio between the length and the area of the confidence ellipse), the flattening and the slope of the confidence ellipse. Significant differences in gaze patterns are found between motion perception and static visual search tasks. The gaze during motion perception is characterized by stronger flattening of confidence ellipse and longer length of eye movement track. The good performers have significantly longer length and standardized length of the eye movements track as compared to bad performers. These results show that the motion detection requires longer gaze path with respect to static visual search and that the path length is longer in good than in bad performers. In conclusion, the efficiency in motion detection is related to longer length of the gaze path (i.e. mean velocity) more than to the area scanned by the different gaze positions.