DATA SET 7: Mike Land's Portrait Drawing Data Set

Description
The task of producing a picture is very different from than simply looking at one. In drawing a portrait the artist has to acquire information from a sitter, formulate a line to be drawn and execute this on the drawing itself. There is thus a repeating sitter—drawing gaze cycle, with vision employed in different ways in each half cycle. In our laboratory we asked a painter and art teacher, Nick Bodimeade, to make some portrait sketches for us, as well as a longer more measured drawing, whilst wearing an eye tracker (resolution 1º) with a head-mounted scene camera that showed both the sitter and the drawings (Fig 1).The sketches took about 40 s and the drawing 4 minutes to complete. Fig 2 shows the whole sequence for one sketch, together with the ‘average cycle’ in which the various timings are indexed to the beginning of each drawn line. The principal findings were that a typical cycle lasted 1.7 s (35 cycles per minute), with 0.8 s on the sitter and 0.9 s on the sketch (Fig. 2b). On average the pen made contact with the paper about 0.1 s after gaze transferred to the sketch, and lasted for the time gaze remained on the sketch. However there was much variation, as Fig. 2a shows, and standard deviations for all these measures (relative to the beginning of the drawn line) were in the range 0.3–0.5 s, so the cycles were far from exact repeats, and no event was absolutely synchronized to any other.

It was possible to work out something of what was happening as the artist formulated his next line. Between one and four fixations were made on the sitter’s face (mean 2.3), and by the last fixation the point to be addressed on the sketch had been selected. When gaze left the sitter, it was transferred accurately (< 2º error) to the corresponding point on the sketch. Interestingly, this was not the point that the next line was to be drawn from, but the point drawn to, i.e. the end of the line (Fig. 3). This surprised both ourselves and the artist. It does, however, make some sense. In a sketch each line is a new entity, almost unrelated to the last. Thus start of the next line must be determined by some process of internal selection by the artist. The course of the line and its end-point, however, are derived from features on the sitter, once the start of the line has been established.

The detailed drawing (Fig 1b) was quite different from the sketch, and more complicated. Unlike the sketches, each line was not independent of the last, and often began where the last left off. There was checking in which no line was drawn and alterations to lines. There was also no clear targeting of the end of each line over the beginning, as there was in sketches. Thus whilst the sketches showed a rather clear progression of thought processes, this was much harder to discern in the more complex drawing.

Fig 1: Frames taken from the eye camera on the artist head of a scene from the production of a sketch (top: fixation spot is on the sketch (right) about 2º below the pencil) and a more detailed drawing (bottom: fixation is close to the sitter’s eye while the artist draws the eye). The sitter (and collaborator) is Genevieve Baker. The fixation spot has a 1º diameter.

Fig 2: Timing of the events in the production of a sketch. a) Complete 45 s record showing alternation between the sketch (stipple) and sitter (open). Bars above show when lines were being drawn. b) Average drawing cycle derived from a) by indexing all events to the beginning of each drawn line. The numbers just below the time-line indicate transitions between the locations shown on the on the diagram of sitter and sketch.

Fig 3: Locations of fixations on sitter and sketch in relation to the beginning (□) and end (■) of the line to be drawn. Start point numbers refer to the locations shown on Fig 2b. Error on the ordinate refers to the angular distance between the fixations and the beginning and end points of the line drawn (fixation locations on the sitter have been transferred to equivalent positions on the sketch; drawing on right shows the meaning of the error scale in relation to the sitter’s face). There is a dramatic decrease in error relative to the end of the line between the first and last fixations on the sitter (2 & 3), indicating that this is when the artist decides on the form of the next line.

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 (2006) Eye movements and the control of actions in everyday life. Prog Retinal & Eye Res 25: 296-324. (section 2.1.5).

SCENE/DISPLAY/STIMULI IMAGES/VIDEOS

SCANPATH (EYE-TRACKER) DATA

Sketch 1 Preview (12062 KB, DIVX compression)

Sketch 1 Full Data Set (uncompressed avi, zipped: 862529 KB)

Sketch 2 Preview (13503 KB, DIVX compression)

Sketch 2 Full Data Set (uncompressed avi, zipped: 935106 KB)

Sketch 3 Preview (13678 KB, DIVX compression)

Sketch 3 Full Data Set (uncompressed avi, zipped: 946620 KB)

Long Detailed Drawing Preview (54249 KB, DIVX compression)

Long Detailed Drawing 1 Full Data Set (uncompressed avi, zipped: 3858949 KB)