Scientific Discovery Within Data Streams - Ambient Intelligence for Scientific Discovery - page 72

the visual metaphor that ThemeRiver used, the human perceptual processes
that ThemeRiver used to its advantage and the layers of context used to provide
additional information beyond that contained in the source material.

3.1 Visual Metaphor

ThemeRiver draws on the power of the human perceptual system by using fa-
miliar metaphors to help users more easily comprehend the data presented. The
graphic layout was designed to leverage a user's ability to quickly assimilate
information, drawing on research in cognitive science and psychophysics. The
addition of useful contextual information, such as time lines and event anno-
tations, allows the user to connect the patterns in content to events or time
intervals (e.g. seasons).
Ideally, a visual metaphor facilitates discovery by presenting data in an in-
tuitive way that is consistent with the user's perceptual and cognitive abilities.
Lakoff and Johnson [5] argue that metaphors are wired into our understand-
ing of particular concepts, using evidence from common linguistic expressions.
One example they cite is the many English expressions that imply that Anglo-
Americans understand time in terms of motion relative to themselves. Some
figures of speech characterize time as moving (e.g., “the time will come” and
“don't let the opportunity pass”), while others imply that people are the ones
moving through time (e.g., “as we go through the years”). We believe the river
metaphor of theme currents changing over time derives part of its strength from
this cultural understanding.
We use a river metaphor to convey several key notions. The document col-
lection's time evolution, selected thematic content, and thematic strength are
indicated by the river's directed flow, composition, and changing width, respec-
tively. The directed flow from left to right is interpreted as movement through
time. In Fig. 5, the river flows from November 1959 to June 1961. The horizontal
distance between two points on the river defines a time interval. For example, the
time interval represented by the distance between the two vertical dotted lines
is almost two months. Like a histogram, ThemeRiver uses variations in width
to represent variations in strength or degree of representation. At any point in
time, the total vertical distance, or width, of the river indicates the collective
strength of the selected themes. The collective theme strength of the river is
quite strong in March 1961 (near the right side of the figure) where the river is
wide; the collective theme strength is much weaker in June 1961 (the far right
of the figure) where the river is narrow.
Colored 'currents' flowing within the river represent individual themes. A
current's vertical width narrows or broadens to indicate decreases or increases
in the strength of the individual theme at any point in time. In Fig. 5 the cyan
current represents 'weapons'; the weapons theme is relatively weak in November
1959 and relatively strong in December 1959. A current maintains its integrity as
a single entity over time. If a theme ceases to occur in the documents for a period
of time and then recurs, the current likewise disappears and then reappears in
the same color and position relative to the other themes. The weapons theme