Oscillatory activity in prefrontal and posterior regions during implicit letter-location binding

Abstract

Many cognitive abilities involve the integration of information from different modalities, a process referred to as "binding." It remains less clear, however, whether the creation of bound representations occurs in an involuntary manner, and whether the links between the constituent features of an object are symmetrical. We used magnetoencephalography to investigate whether oscillatory brain activity related to binding processes would be observed in conditions in which participants maintain one feature only (involuntary binding); and whether this activity varies as a function of the feature attended to by participants (binding asymmetry). Participants performed two probe recognition tasks that were identical in terms of their perceptual characteristics and only differed with respect to the instructions given (to memorize either consonants or locations). MEG data were reconstructed using a current source distribution estimation in the classical frequency bands. We observed implicit verbal-spatial binding only when participants successfully maintained the identity of consonants, which was associated with a selective increase in oscillatory activity over prefrontal regions in all frequency bands during the first half of the retention period and accompanied by increased activity in posterior brain regions. The increase in oscillatory activity in prefrontal areas was only observed during the verbal task, which suggests that this activity might be signaling neural processes specifically involved in cross-code binding. Current results are in agreement with proposals suggesting that the prefrontal cortex function as a "pointer" which indexes the features that belong together within an object.

Visual-spatial and verbal-spatial binding in working memory.

“…This effect was evident in Experiments 1 and 2. In the study by Campo et al (2010), in contrast to our results, spatial and verbal binding occurred when the relevant dimension was verbal (i.e., changes in the location affected recognition of the letter, and changes in the letter did not affect memory of the location). These differences can be explained by the experimental conditions in the studies.…”

“…These differences can be explained by the experimental conditions in the studies. In the study by Campo et al (2010), the task required the recognition of just one item. A frame in the stimuli served as a mnemonic resource for the spatial information, and only the responses in the positive trials were analyzed.…”

Asymmetric binding in serial memory for verbal and spatial information

“…More precisely, we examined whether the number of features to be retained during the memory task influences the asymmetry. Indeed, in previous studies showing asymmetric binding, spatial information did not need to be retained (see, e.g., Campo et al, 2010;Jiang et al, 2000). In another study, Maybery et al (2009) showed asymmetric binding with letters as the independent feature when participants had to retain one feature, but symmetric binding when participants had to retain both the verbal and spatial features.…”

“…Previous results, therefore, have suggested that binding in visual memory is asymmetric: Object features are bound to their locations, whereas locations-or the spatial configuration of the display as a whole (see Jiang et al, 2000)-can be retained independently (see Campo et al, 2010). This type of asymmetry has not been observed consistently in the literature, however.…”

“…That memory representations seem to be bound conveys the idea that the features of an object are integrated in such a way that they are all equally useful for encoding and retrieving the object that they make up. The existing evidence, however, suggests that all features of an object are not equally important (see, e.g., Campo et al, 2010;Jiang, Olson, & Chun, 2000). The objective of the present study was to examine the relative importances of the verbal and spatial features of visual objects retained in serial memory.…”