DATA SET 8: Mike Land's Jigsaw Puzzle Data SetEXPERIMENT DESCRIPTION
Figure1 illustrates an interesting 30 s episode during which the player has two loose pieces (a & b) which he eventually joins and fits to the completed part of the puzzle. The pattern of fixations allows us to reconstruct his thought patterns with some confidence. In the first few seconds, between 1 and 2 piece a is rotated anti-clockwise in three stages (i). While this is happening the glances to the completed part of the puzzle are all to region x, indicating that the player is trying to fit a to this region. However by 2 it is clear that this will not work. He consults the picture on the lid and thereafter directs gaze on the puzzle itself to region y. About a second later (ii) he moves piece a to the right of piece b, probably having also noticed that the right hand side is a straight edge. Interestingly, this move is completed while the eyes are looking at the picture about 20º above, so presumably its trajectory was set up during the previous fixation. Between 3 and 4 the player concentrates on piece b. He moves a and b to the left (iii, iv) and just before 4 he rotates b (v) so that its new right hand profile matches the left profile of a. Just after 4 piece b is lifted and joined to a (vi). After 5 there is quite long period when both pieces, now joined, and the profile of the completed section are fixated and presumably appraised for goodness of fit. The two pieces are lifted together and finally joined to the rest of the puzzle (vii).
This episode illustrates a number of general points. First, the eyes only fixate the parts of the field that are important – the two pieces, the relevant regions of the part-completed puzzle, and on two occasions the relevant region of the picture. When looking at the individual pieces a and b fixation is accurate: the mean fixation distance from the centre of each piece (approximately 2 by 3º) was 1.4º. Second, during the various movements of the pieces they are either fixated during the move, or during the half second before the move. This seems to bear out both the ‘do it where I’m looking’ and the ‘just in time’ rules of Ballard et al. Third, comparisons between patterns and outlines are mostly made by looking from one element to the next and back again, rather than sizing up the situation from a single gaze location. This is particularly clear between 1 and 2 where gaze moves repeatedly from a to the completed part of the puzzle and back again as a is rotated. This leads to the rejection of the hypothesis that a can fit to x, and the development of the new idea that it might fit near y, which is then checked by consulting the picture. Similar ‘aha’ moments precede the move at (vi), again accompanied by much
Fig 1: Gaze movements during a 30 s except from a jigsaw puzzle. Upper part shows the gaze shifts between two pieces (a & b), the part completed puzzle, and the picture on the box. Numbers refer to the sketches below, and roman numerals to the seven movements of the pieces. All the gaze shifts are made with single saccades, and other saccades within each area are shown by short vertical lines. Hand contacts resulting in movement of the pieces are shown by upward (contact) and downward (release) arrows. The lower part of the figure shows details of the movements of the pieces. The movements shown refer to movements made between each illustration and the next.
SCANPATH (EYE-TRACKER) DATA