Word Frequency Is Associated With Cognitive Effort During Verbal Working Memory: A Functional Near Infrared Spectroscopy (fNIRS) Study.

PURPOSE: Psycholinguistic models traditionally view verbal working memory capacity as independent from linguistic features; connectionist models suggest otherwise. Moreover, lexical processing studies show high frequency words differ in cognitive effort from low frequency words, although these effects during concurrent processing of words in working memory are unknown. This novel study examines potential differences in cognitive effort, as measured by differences in HbO2 and Hb, for high frequency versus low frequency words during a working memory paradigm. METHODS: A total of 21 neurologically typical participants (age 18-23) completed an auditory, n-back, working memory task comparing performance with high- as compared to low- frequency words. Hemodynamic changes in the prefrontal cortex were recorded with a continuous-wave functional near-infrared spectroscopy (fNIRS) device. Behavioral data (accuracy, reaction time) were recorded using E-prime. RESULTS: Differences in word frequency were evident at both behavioral and neurological levels. Participants were more accurate, albeit slower in identifying the target two back in a sequence for low- as compared to high-frequency words. Patterns of hemodynamic changes were also significantly different between HF and LF conditions. CONCLUSION: The results from this study indicate that the behavioral and neurological signatures inherent in holding high- versus low-frequency words in working memory differs significantly. Specifically, the findings from this study indicated that words differing in frequency place different demands on cognitive processing load in memory updating tasks.

Attention does more than modulate suppressive interactions: attending to multiple items.

Directing attention to a visual item enhances its representations, making it more likely to guide behavior (Corbetta et al. 1991). Attention is thought to produce this enhancement by biasing suppressive interactions among multiple items in visual cortex in favor of the attended item (e.g., Desimone and Duncan 1995; Reynolds and Heeger 2009). We ask whether target enhancement and modulation of suppressive interactions are in fact inextricably linked or whether they can be decoupled. In particular, we ask whether simultaneously directing attention to multiple items may be one means of dissociating the influence of attention-related enhancement from the effects of inter-item suppression. When multiple items are attended, suppressive interactions in visual cortex limit the effectiveness with which attention may act on their representations, presumably because "biasing" the interactions in favor of a single item is no longer possible (Scalf and Beck 2010). In this experiment, we directly investigate whether applying attention to multiple competing stimulus items has any influence on either their evoked signal or their suppressive interactions. Both BOLD signal evoked by the items in V4 and behavioral responses to those items were significantly compromised by simultaneous presentation relative to simultaneous presentation, indicating that when the items appeared at the same time, they interacted in a mutually suppressive manner that compromised their ability to guide behavior. Attention significantly enhanced signal in V4. The attentional status of the items, however, had no influence on the suppressive effects of simultaneous presentation. To our knowledge, these data are the first to explicitly decouple the effects of top-down attention from those of inter-item suppression.