And a very complementary pair they are. The more recent of the two, "Lives without imagery – congenital aphantasia" (in Cortex) by Adam Zeman of Exeter and co-authors, discusses the complete, lifelong, absence of voluntary mental images, for which it coins the term aphantasia. The paper is not open access, but a nice summary has been given by Rolf Degen:
Zeman and his colleagues now propose the use of the term ‘aphantasia’ to refer to a condition of reduced or absent voluntary imagery. In the journal "Cortex", they describe, for the first time, the features of their condition, elicited by a questionnaire. Participants typically became aware of their condition in their teens or twenties when, through conversation or reading, they realized that most people who ‘saw things in the mind’s eye’, unlike themselves, enjoyed a quasi-visual experience. 19 of the 21 subjects were male, possibly a tribute to the readership of Discover magazine. 5 reported affected relatives, while 10 stated that all moralities of imagery were affected. More than half of the respondents suffered from impairments of autobiographical memory. The same number identified compensatory strengths in verbal, mathematical and logical domains.
Despite their substantial or complete deficit in voluntary visual imagery, the majority of participants was at times stricken by involuntary imagery. This could occur during wakefulness, usually in the form of ‘flashes’ and/or during dreams. When the subjects had to perform task that normally would commandeer imagery - such as ‘count how many windows there are in your house or apartment’ - they succeeded by drawing on what they described as ‘knowledge’, ‘memory’ and ‘subvisual’ models.
"Skeptics could claim that aphantasia is itself a mere fantasy: describing our inner lives is difficult and undoubtedly liable to error. We suspect, however, that aphantasia will prove to be a variant of neuropsychological functioning akin to synaesthesia." The latter is usually associated with heightened scores at tests of imagination. How commonly does congenital aphantasia occur? Existing data suggest a frequency of around 2 percent but there is no fully reported large scale study. "We are optimistic that modern structural and functional brain imaging may help to answer questions about the nature of visual imagery that were first posed in ancient Greece and first quantified at Sir Francis Galton’s breakfast table over a hundred years ago."
The other (open acess in Neuropsychologia), by Daniela Palombo of Boston University and her co-authors, is about the combination of the absence of images (both voluntary and involuntary) AND the lack of episodic memory, a condition for which it proposes the term "Severely Deficient Autobiographical Memory (SDAM)".
On the face of it, SDAM is a subset of aphantasia, as some of Zeman et al's respondents had episodic memory impairments and some didn't.
