Thursday, August 28, 2008

Noticing is remembering

In last week's post on fan color appearance, I wrote that in low light conditions today's top cameras do not reproduce faithfully color appearance because they remain photopic, in opposition to the human visual system which becomes scotopic. The result shown in the photographs was that while we humans see the crowd achromatic and the LED fans chromatic, the camera reproduced the fans achromatically and the crowd chromatically.

Reality is always more complex. For the camera, the image is flat, i.e., each photosite or pixel has the same importance. However, for the human visual system an object that attracts attention by being bright, colorful, and rapidly moving gets more memory resources allocated, i.e., it is more memorable. This fact makes the photopic/photopic confusion more striking for the photographers themselves than for viewers not present at the event.

The lesson is actually more general. Color scientists who are serious about their research still do psychophysics experiments. When designing these experiments, it is important not to overstretch the observer's memory capacity, because it might skew the experiment.

For more on this topic, the recent paper Dynamic Shifts of Limited Working Memory Resources in Human Vision by Paul M. Bays and Masud Husain in Science 8 August 2008: Vol. 321. no. 5890, pp. 851-854 presents the results of recent research on visual memory. Here is the editor's summary:

The dominant model of human visual working memory allows for the simultaneous representation of only three or four objects. With what precision is each visual object stored as a function of the number of items in a scene? Bays and Husain tested the ability of human subjects to remember the location and orientation of multiple visual items after a brief disappearance of the stimulus array, and found that visual working memory is a flexibly allocated resource. Making an eye movement toward an object, or directing covert attention to it, caused a greater proportion of memory resources to be allocated to that object, allowing the memory of its presence to be retained with far greater precision than other objects in the scene.