Griffin, M. M. & Robinson, D. H. (2005). Does spatial or visual information in maps facilitate text recall? Reconsidering the conjoint retention hypothesis. Educational Technology Research and Development, 53(1), 23-36.

The conjoint retention hypothesis (CRH) claims that students recall more text information when they study geographic maps in addition to text than when they study text alone, because the maps are encoded spatially (Kulhavy, Lee & Caterino, 1985). This claim was recently challenged by Griffin and Robinson (2000), who found no advantage for maps over feature lists in facilitating text recall. In two experiments, we crossed maps and lists with icons and names (c.f. Griffin & Robinson), and employed materials and methodology very similar to those used in previous CRH studies by Kulhavy, Peterson, Hancock & Verdi, 1995). In addition, we included a concurrent task to measure spatial encoding, as did Griffin and Robinson. No advantages were found for maps over lists in facilitating text recall, nor were maps processed in a more spatial manner than lists. Instead, it appears that the key stimulus feature for facilitating text recall is mimetic icons (i.e., icons that represent features) rather than the spatial characteristics of geographic maps, a finding that supports dual-coding theory (Paivio, 1986), but not the CRH.