An article written by me, my advisor, and another professor at George Mason University just got accepted for publication in the journal Cognition:

Wong, J. H., Peterson, M. S & Thompson, J. C. (in press). Visual working memory for objects from different categories: A face-specific maintenance effect. Cognition.

Abstract: The capacity of visual working memory was examined when complex objects from different categories were remembered. Previous studies have not examined how visual similarity affects object memory, though it has long been known that similar-sounding phonological information interferes with rehearsal in auditory working memory. Here, experiments required memory for two or four objects. Memory capacity was compared between remembering four objects from a single object category to remembering four objects from two different categories. Two-category sets led to increased memory capacity only when upright faces were included. Capacity for face-only sets never exceeded their non-face counterparts, and the advantage for two-category sets when faces were one of the categories disappeared when inverted faces were used. These results suggest that two-category sets which include faces are advantaged in working memory but that faces alone do not lead to a memory capacity advantage.

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So what does this mean? Other research has demonstrated that visual working memory seems to be able to hold more information about faces than other objects such as cars or inverted faces (which are processed in an entirely different manner from faces). This is a sensible conclusion, as faces have been shown to be processed uniquely in terms of perception. However, this is the first evidence that faces are unique in terms of working memory.

Our evidence supports that conclusion but also narrows it down. We found no specific advantage for faces if you have to remember a bunch of faces together or a bunch of other objects together (all houses, butterflies, or bodies in motion). This was seen for remembering two or four objects. However, if you have to remember two objects from two categories – two faces and two houses, for example – your memory was better than for four objects from the same category. Additionally, this only happened when faces were part of the set. Remembering two butterflies and two houses together did not lead to better memory.

Therefore, faces are unique in memory, but an advantage is only seen when faces are remembered with non-face objects. Why? It’s possible that there are distributed (but overlapping) representations of faces and all other objects, almost like a Venn diagram with two partially overlapping circles. When only faces or only other objects are remembered, only one of the two circles is activated in support of memory. When faces and other objects must be remembered, both circles can activate, increasing memory capacity. This theory, however, is for another experiment that we’re working on.

By the way, this is the same research that was presented at the 2008 Vision Sciences Conference held last May. Click the poster image below for the PDF: