Explicit processing of verbal and spatial features during letter-location binding modulates oscillatory activity of a fronto-parietal network

Abstract

Keywords: Binding Working memory Episodic buffer Oscillatory activity Prefrontal cortex MagnetoencephalographyThe present study investigated the binding of verbal and spatial features in immediate memory. In a recent study, we demonstrated incidental and asymmetrical letter-location binding effects when participants attended to letter features (but not when they attended to location features) that were associated with greater oscillatory activity over prefrontal and posterior regions during the retention period. We were interested to investigate whether the patterns of brain activity associated with the incidental binding of letters and locations observed when only the verbal feature is attended differ from those reflecting the binding resulting from the controlled/explicit processing of both verbal and spatial features. To achieve this, neural activity was recorded using magnetoencephalography (MEG) while participants performed two working memory tasks. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the task instructions. One of the tasks required participants to process both letters and locations. In the other, participants were instructed to memorize only the letters, regardless of their location. Time-frequency representation of MEG data based on the wavelet transform of the signals was calculated on a single trial basis during the maintenance period of both tasks. Critically, despite equivalent behavioural binding effects in both tasks, single and dual feature encoding relied on different neuroanatomical and neural oscillatory correlates. We propose that enhanced activation of an anterior-posterior dorsal network observed in the task requiring the processing of both features reflects the necessity for allocating greater resources to intentionally process verbal and spatial features in this task.The capacity to maintain and manipulate information in working memory (WM) is critical to higher cognitive functions. Despite its crucial role in a number of mental skills and abilities, WM capacity is surprisingly limited. Through the integration of individual features into "objects", however, we are capable of processing larger amounts of information. Indeed, recent experimentation suggests the limit of WM capacity to be set at around three to four bound "objects" (Cowan, 2001;Todd & Marois, 2004;Vogel, Woodman, & Luck, 2001). The ability to integrate information involves "the reorganization of bits of information to create more complex but unified representations of previously distributed information" (Wheeler & Treisman, 2002), a phenomenon idenCorresponding author. Tel.: +34 91 549 57 00; fax: +34 91 336 68 28. E-mail addresses: Pcampo@arrakis.es, pcampo@med.ucm.es (P. Campo). These authors contributed equally to the study. tified in the memory literature as 'chunking' (Baddeley, 2000;Ericsson, Chase, & Faloon, 1980;Miller, 1956;Simon, 1974). In visual WM, the integration of different stimulus features into more complex representations or objects...

Asymmetric binding in serial memory for verbal and spatial information

“…Second, Baddeley et al's (2011) revised model predicts no asymmetry, because both letters and locations can be accessed independently. However, asymmetric binding has been observed in numerous studies (see Campo et al, 2010;Jiang et al, 2000;Maybery et al, 2009;Poch et al, 2010), including ours.…”

“…Indeed, Zimmer, Speiser, and Seidler (2003) suggested that different processes might be involved in retaining dynamic spatial information as compared to a static display. In line with this idea, all studies showing that spatial locations were automatically bound to object identity have used simultaneous presentation (see, e.g., Campo et al, 2010;Jiang et al, 2000;Meegan & Honsberger, 2005;Olson & Marshuetz, 2005;Poch et al, 2010;Treisman & Zhang, 2006). This could occur because participants encode the configuration of the display during simultaneous presentation.…”

“…A number of studies on binding have suggested that in memory for visual information, features such as color and shape are automatically bound to their spatial location (see, e.g., Jiang et al, 2000;Olson & Marshuetz, 2005;Poch et al, 2010;Treisman & Zhang, 2006). For instance, Poch et al used a paradigm similar to that used by Prabhakaran et al (2000): Participants were presented with an array of letters in different locations, followed by a probe item that was either intact-the letter in its original location-or recombined-a letter and a location from the memory display that had not been presented together.…”

“…Indeed, some researchers have suggested that features are integrated in such a way that the retrieval of one feature depends on the retrieval of another that can be retained independently. For instance, using a change detection task, Jiang et al (2000) showed that memory for colors and shapes is impaired when the locations of the objects are changed from the memory display to the probe display (see also, e.g., Poch et al, 2010). Memory for the spatial configuration of the display, however, was not influenced by whether or not the colors of the objects remained the same from the memory to the probe display.…”

“…Some studies have suggested that binding can occur automatically as attention is paid to an item (see, e.g., Allen, Baddeley, & Hitch, 2006;Guérard et al, 2009a) and that spatial locations are bound to object identities, even if locations do not have to be retained (see, e.g., Jiang et al, 2000;Olson & Marshuetz, 2005;Poch et al, 2010;Treisman & Zhang, 2006). Maybery et al (2009) suggested that such automatic binding would yield an asymmetry, whereas voluntary binding would yield a symmetric pattern.…”