Iconic memory: Fallacies persist (?)

Two recent papers (Coltheart, 1980; Long, 1980) have evaluated literature on the relationship between "iconic memory" and "visible persistence." In doing this, both writers focused on methods of measurement of these phenomena and the influence on them of luminance and duration. On the basis of his literature review, Coltheart (p. 210) concluded "the distinction between iconic memory and visible persistence is not merely terminological: they are actually different psychological processes." In comparison, Long concluded (p.814) that "the appealing parsimony of equating visible persistence and iconic memory, which has been the traditional view (e.g., Neisser, 1967), need not be abandoned." The present paper evaluates the strength of Long's arguments, and concludes that: (1) conflict arises over problems of definition; (2) the data from experiments using methods considered inappropriate by Long are very consistent and yield useful information about visible persistence; (3) it consequently cannot be claimed that the bulk of the evidence supports a positive relationship between stimulus intensity (or duration) and persistence duration; (4) it is misleading to claim that Long's data, usually collected under a specific combination of somewhat extreme experimental conditions, is representative of data in the area; and (5) iconic memory and visible persistence cannot be readily equated. Long (1980) examined various methods of measuring visible persistence. Results of studies investigating luminance and/or duration effects were then evaluated from the consideration that some persistence measurement methods are more valid than others. Those methods regarded by Long as being less valid are considered to involve the measurement of effects in addition to persistence, or of phenomena that are only marginally related to it. Methods thought to be most inappropriate include persistence-of-form studies (e.g., Bowling, Lovegrove, & Mapperson, 1979; Meyer & Maguire, 1977) and duration-of-stimulus procedures (e.g., Efron, 1970a, 1970b, 1970c; Haber & Standing, 1970). The successive-field paradigm is considered to be the most effective, although different forms of this method also yield inconsistent results (Long, 1980, p. 810). Studies demonstrating an inverse persistence-intensity (or duration) relationship are rejected on the grounds that these studies employed the least valid methods. The remaining studies are considered to strongly support a positive relationship, and consequently the theory that iconic memory has a retinal basis. These conclusions are the opposite of those reached by Coltheart (1980), who considered the evidence for inverse persistence-intensity and persistence-duration relationships to be substantial, and that visible persistence is not the sole determinant of iconic memory.