DATA SET 10: Mike Land's Table Tennis Data Set

Ripoll et al. (1987) found that international table-tennis players anticipate the bounce and make a saccade to a point close to the bounce point. Land and Furneaux (1997) confirmed this (with more ordinary players). They found that shortly after the opposing player had hit the ball the receiver made a saccade down to a point a few degrees above the bounce point, anticipating the bounce by about 0.2 s (Fig. 1c). At other times the ball was tracked around the table in a normal non-anticipatory way; tracking was almost always by means of saccades rather than smooth pursuit. The reason why players anticipate the bounce is that the location and timing of the bounce are crucial in the formulation of the return shot. Up until the bounce the trajectory of the ball as seen by the receiver is ambiguous. Seen monocularly, the same retinal pattern in space and time would arise from a fast ball on a long trajectory or a slow ball on a short one (Fig. 1a). (Whether either stereopsis or looming information is fast enough to contribute a useful depth signal is still a matter of debate). This ambiguity is removed the instant the timing and position of the bounce are established. Therefore the strategy of the player is to get gaze close to the bounce point (this cannot and need not be exact) before the ball does, and lie in wait. The saccade that affects this is interesting in that it is not driven by a ‘stimulus’, but by the player’s estimate of the location of something that has yet to happen. Much the same thing happens in cricket.

Fig 1: (a) The visual ambiguity in the trajectory of an approaching ball before it bounces. The vertical motion of a slow ball bouncing short, and a faster ball bouncing long will appear similar to an observer. The ambiguity is removed when the ball bounces. (b,c) The locations in the field of view of the receiver of 38 fixations which follow the first saccade after the ball has been struck by the opponent: (b) relative to the table top, and (c) relative to the bounce point. The receiver mainly fixates a point a few degrees above the expected bounce point, independent of where that is on the table.

Method
Eye movement recordings were made with a head-mounted camera that produced a split image in which the top two-thirds showed the scene ahead and the lower third the eye in its socket, imaged via a concave mirror. The location and ellipticity of the iris were used to obtain the coordinates of eye direction, by matching the iris outline to a computer- generated eye model. This was done by hand, frame-by-frame, at 50 f.p.s. The coordinates were used to position a 1º dot on the upper scene view, and each frame re-recorded. Head movements could also be obtained by tracking distant background objects in the scene view. The resulting video contains numerical values (in degrees) of the direction of view of the fovea, a frame counter, and a clock. The videos are reversed left to right as a result of the mirror optical system.

Reference
Land MF, Furneaux S (1997) The knowledge base of the oculomotor system. Phil Trans R Soc Lond B 352: 1231-1239

SCENE/DISPLAY/STIMULI IMAGES/VIDEOS

SCANPATH (EYE-TRACKER) DATA

Amateur Players 1 Preview (9167 KB, DIVX compression)

Amateur Players 1 Full Data Set (uncompressed avi, zipped: 605939 KB)

Amateur Players 2 Preview (16081 KB, DIVX compression)

Amateur Players 2 Full Data Set (uncompressed avi, zipped: 1123599 KB)

Expert Players 1 Preview (12694 KB, DIVX compression)

Expert Players 1 Full Data Set (uncompressed avi, zipped: 808444 KB)