DATA SET 4: Mike Land's Tea Making Data Set

Description
The aim of this study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform. We used a head-mounted eye-movement video camera, which provided a continuous view of the scene ahead, with a dot indicating foveal direction with an accuracy of about 1 deg. A second video camera recorded the subject's activities from across the room. The videos were linked and analysed frame by frame. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. The first object-related fixation typically led the first indication of manipulation by 0.56 s, and vision moved to the next object about 0.61 s before manipulation of the previous object was complete. Each object-related act that did not involve a waiting period lasted an average of 3.3 s and involved about 7 fixations. Roughly a third of all fixations on objects could be definitely identified with one of four monitoring functions: locating objects used later in the process, directing the hand or object in the hand to a new location, guiding the approach of one object to another (eg kettle and lid), and checking the state of some variable (eg water level). We conclude that although the actions of tea-making are ‘automated’ and proceed with little conscious involvement, the eyes closely monitor every step of the process. This type of unconscious attention must be a common phenomenon in everyday life.

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 1 deg 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.

Fig 1: Prints from (a) the activity video, and (b) eye-movement video of the same instant, when the sweetener is dropped into the mug. The head-mounted camera and backpack are shown in (a). In (b) the white dot is the direction of regard of the fovea (into the mug). The eye can be seen in the bottom third of the frame, with a bright ellipse fitting the iris. The angular width of upper part of the frame is approximately 35 deg. Note that (b) is right-left reversed compared with (a) because of the mirror in the camera system

Fig 2: Record of the fixations made by three subjects during the first sequence after the kettle is first detected (0.05 - 0.20 on Fig 3), and during which the kettle is moved from the worktop (left) to the sink (right). Because of the changing viewpoint, the angular relations are only approximate, but fixation positions relative to the objects of regard are accurately represented. Note the associations of fixations with particular objects or other entities - kettle, sink, kettle and lid, taps, water stream - which correspond in time to the actions that relate to them. Note also the rough correspondence in the numbers of fixations that are devoted by each subject to corresponding objects: this gives a good idea of the degree of similarity in scan paths expected when different subjects address the same task.

Fig 3: Records of the actions of the trunk, gaze and hands during the first minute of a four minute tea-making sequence. Typically each ‘object related action’ involves a movement of the body (e.g. from one work surface to another) followed by a gaze shift to the next object to be manipulated, followed by the manipulation itself. This sequence is particularly clear between 0.05 and 0.1 and 0.35 and 0.4 s. The delays involved (trunk-gaze, gaze-manipulation) are typically about 0.6 s. Gaze often moves to the next object in the sequence about half a second before manipulation of the last object is complete, implying that some guidance information is retained in a buffer.

Reference
Land M, Mennie N, Rusted J (1999) The roles of vision and eye movements in the control of activities of everyday living. Perception 28: 1311-1328

SCENE/DISPLAY/STIMULI IMAGES/VIDEOS

SCANPATH (EYE-TRACKER) DATA

Tea Making (ML) Preview (59855 KB, DIVX compression)

Tea Making (ML) Full Data Set (uncompressed avi, zipped: 3818158 KB)