McLuhan

We tend to think of visual information as instantaneous or simultaneous, and audio as time-based, linear, successive. I do, at any rate.

To underscore this assumption, let's say I'm reviewing a designer's portfolio. I can "read" a visual image almost in a moment -- I make a snap judgement much like that analyzed in Malcolm Gladwell's Blink.

I see a cassette, video tape, quicktime file, or what have you, however, and its a different story -- I know I need to make a time investment. I immediately have expectations for what I want to get out of it. Call it experience economy "ROI". Actually, Bruce Sterling, who incidentally will be speaking at OCAD on October 2 (yes, you heard right), puts it best in Shaping Things: he says in an age of 'Gizmos', our relationship with objects is governed by the "opportunity costs" and "cognitive load" of the user.