Can you point me to some data?

I am working with a client who is creating a small application in which a
person can manipulate objects in order to show importance, intensity, and
relationships. The objects will be shapes or icons. The question has arisen
about whether people already assign meaning to objects based on size, color,
or opacity. We certainly see from tag clouds that there is an assumption
that a larger size indicates a greater value, but part of the question is
what value? Of particular contention is what meaning do people associate
with opacity?

I have spent the past several hours doing a literature search about visual
rhetoric, interaction design, icons, visualization, and some other choice
words, but have yet to locate something that is not just opinion and
indicates that there is a known, documented convention that we might refer
to. If I cannot resolve the issue via a literature search, I need to do some
user testing, fast.

Does anyone have a pointer to the perfect article? Or book title?

-- 
Mary Deaton
Deaton Interactive Design

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