It's an oddly dissatisfying experience visiting the National Portrait Gallery's Self Portrait: Renaissance to Contemporary exhibition. The eminently watchable Matthew Collings has just done a television series on the same subject - Western self-portraiture over the past 500 years - with which the exhibition is loosely associated. But this show fails to serve up catchy observations of the Collings ilk, and the over-intellectualised, frequently tautological essays in the accompanying catalogue contribute to the genre's inherent problems.

Whatever motives art historians attribute to artists' urge to immortalise themselves - self-aggrandisement being the main one - self-portraiture so often remains wrapped in the mystery of the personality that created it.

The frustration of the NPG show is twofold. It fails to rationalise the genre by presenting the works (all oil paintings) in meaningful groups, and the choice of pictures seems unrepresentative.

Self-portraiture is one of those rare areas where cross-historical themes work. There is the oft-repeated practice of artists showing themselves at their easels, for example, or the fondness for role-playing - take Cristofano Allori's use of his own face on the severed head of Holofernes in his biblical image of 1613, say, or Courbet's indolent picture of himself as a wounded man (1844-54).

But here, despite teasing panels pointing out such themes before irritatingly directing you to paintings in four different rooms, there's a plodding chronological presentation that feels like a mishmash. Little links Zoffany's pompous, repellent picture, for instance, with Hogarth's exquisite little record of himself at work, except the century. There is some sense of a gathering introspection as we enter the 1900s, but hadn't Rembrandt already laid bare his soul in the 1640s?