Dynamics of working memory process revealed by independent component analysis in an fMRI study

Human memory is prone to errors in many everyday activities but also when cultivating hobbies such as traveling and/or learning a new language. For instance, while visiting foreign countries, people erroneously recall foreign language words that are meaningless to them. Our research simulated such errors in a modified Deese-Roediger-McDermott paradigm for short-term memory with phonologically related stimuli aimed at uncovering behavioral and neuronal indices of false memory formation with regard to time-of-day, a variable known to influence memory. Fifty-eight participants were tested in a magnetic resonance (MR) scanner twice. The results of an Independent Component Analysis revealed encoding-related activity of the medial visual network preceding correct recognition of positive probes and correct rejection of lure probes. The engagement of this network preceding false alarms was not observed. We also explored if diurnal rhythmicity influences working memory processes. Diurnal differences were seen in the default mode network and the medial visual network with lower deactivation in the evening hours. The GLM results showed greater activation of the right lingual gyrus, part of the visual cortex and the left cerebellum in the evening. The study offers new insight into the mechanisms associated with false memories, suggesting that deficient engagement of the medial visual network during the memorization phase of a task results in short-term memory distortions. The results shed new light on the dynamics of working memory processes by taking into account the effect of time-of-day on memory performance.

Word and pseudoword superiority effects: Evidence from a shallow orthography language

The word superiority effect (WSE) denotes better recognition of a letter embedded in a word rather than in a pseudoword. Along with WSE, also a pseudoword superiority effect (PSE) has been described: It is easier to recognise a letter in a legal pseudoword than in an unpronounceable nonword. At the current state of the art, both WSE and PSE have been mainly tested with English speakers. This study uses the Reicher-Wheeler paradigm with native speakers of Italian (a shallow orthography language). Different from English and French, we found WSE for reaction times (RTs) only, whereas PSE was significant for both accuracy and RTs. This finding indicates that in the Reicher-Wheeler task, readers of a shallow orthography language can effectively rely on both the lexical and the sublexical routes. As to the effect of letter position, a clear advantage for the first-letter position emerged, a finding suggesting a fine-grained processing of the letter strings with coding of letter position and indicating the role of visual acuity and crowding factors.