Finding the answer in space: the mental whiteboard hypothesis on serial order in working memory

Abstract

Various prominent models on serial order coding in working memory (WM) build on the notion that serial order is achieved by binding the various items to-be-maintained to fixed position markers. Despite being relatively successful in accounting for empirical observations and some recent neuro-imaging support, these models were largely formulated on theoretical grounds and few specifications have been provided with respect to the cognitive and/or neural nature of these position markers. Here we outline a hypothesis on a novel candidate mechanism to substantiate the notion of serial position markers. Specifically, we propose that serial order WM is grounded in the spatial attention system: (I) The position markers that provide multi-item WM with a serial context should be understood as coordinates within an internal, spatially defined system; (II) internal spatial attention is involved in searching through the resulting serial order representation; and (III) retrieval corresponds to selection by spatial attention. We sketch the available empirical support and discuss how the hypothesis may provide a parsimonious framework from which to understand a broad range of observations across behavioral, neural and neuropsychological domains. Finally, we pinpoint what we believe are major questions for future research inspired by the hypothesis.

Space in numerical and ordinal information: A common construct?

“…Some studies have replicated this finding (Abrahamse, van Dijck, Majerus, & Fias, 2014), bolstering the nuisance that arbitrary sequences in general appear ordered in space (Previtali, De Hevia, & Girelli, 2010).…”

The heterogeneity of verbal short-term memory impairment in aphasia

“…A number of studies have linked serial order coding to non-linguistic codes shared with other cognitive domains, such as temporal codes (Brown et al, 2000), numerical codes (Botvinick & Watanabe, 2007) or spatial codes (Ginsburg, van Dijck, Previtali, Fias, & Gevers, 2014;Van Dijck & Fias, 2011;Van Dijck, Abrahamse, Majerus, & Fias, 2013;Abrahamse, van Dijck, Majerus, & Fias, 2014). Neural regions outside the language cortex have been linked to serial order coding, with a consistent implication of dorsolateral prefrontal cortex, cerebellar and intraparietal cortex, and this more predominantly in the right hemisphere (Attout et al, 2014;Henson et al, 2000;Majerus et al, 2010;Marshuetz et al, 2000).…”

Keeping an eye on serial order: Ocular movements bind space and time

“…Indeed, oculomotor routines involved in both reading and writing would result, through repetition, in a preferential directional scanning of the external space (see Rinaldi, Di Luca, Henik, & Girelli, 2014). This directional preference would be reinforced in Western populations, where reading occurs from left-to-right, by the slight leftward bias in visuospatial attention processing (Bowers & Heilman, 1980; see Abrahamse et al, 2014;de Hevia, Girelli, & Macchi Cassia, 2012). On these grounds, we hypothesized that, if serial order is grounded on sensorimotor processes, eye movements concurrent to the retrieval of ordered information should reflect the internal scanning of its spatial representation.…”

“…In particular, according to a predominant class of models (i.e., position marking models) the serial order within WM would follow from the pairing of items with some external representation of their location within the sequence (e.g., Brown, Preece, & Hulme, 2000;Henson, 1998), rather than from a mere pairing between the items themselves (e.g., Lewandowsky & Murdock, 1989). In the wake of the position marking models, Abrahamse, van Dijck, Majerus, and Fias (2014) recently claimed that serial order would be grounded on the spatial attention system. More specifically, the position of ordered elements to be remembered would be translated into internal spatial coordinates and, thus, into a spatial representation .…”